Interference-type near-infrared spectroscopy system and method

Abstract

One aspect of the present disclosure provides an interferometric near-infrared spectroscopy (iNIRS) system, the system comprising: a first light source configured to wavelength sweep in a first wavelength range and emit light passing through a plurality of different wavelengths; a second light source configured to wavelength sweep in a second wavelength range different from the first wavelength range and emit light passing through a plurality of different wavelengths; a common sample delivery channel coupled to each of these light sources for receiving the light from the first light source and the second light source and delivering the light towards a subject; one or more reference channels for receiving reference light from the first light source and / or the second light source; a light emitting device comprising the above; and a light detecting device comprising an interferometric light detector, the interferometric light detector being coupled to one or more reference channels for receiving reference light from the first light source and the second light source, the light detecting device being arranged to be coupled to the subject so as to receive sample light including the light transmitted by the interferometric light detector along the common sample delivery channel from the first light source and the second light source, the interferometric light detector being arranged to combine the sample light and the reference light to provide a combined optical signal including one or more components of the beat frequency between the sample light and the reference light, and the iNIRS system being configured to process the combined optical signal to provide imaging and analysis of the subject.

Description

Technical Field

[0001] The present disclosure relates to the fields of imaging and analysis. The present disclosure relates, in particular, to an interferometric near-infrared spectroscopy ( "iNIRS") system and method for performing neuroimaging and analysis.

Background Art

[0002] Near-infrared spectroscopy ( "NIRS") is a spectroscopy that uses the near-infrared region of the electromagnetic spectrum (e.g., between 780 nm and 2500 nm). NIRS systems can be used to provide non-invasive monitoring of the scattering and absorption characteristics of a medium. Since radiation at NIRS wavelengths is not as readily absorbed by human skin (and bone) as visible light, NIRS radiation can penetrate the skin and skull and enter the brain tissue. NIRS can be used as a method for non-invasively imaging the human brain tissue by monitoring the scattering and absorption characteristics of NIRS radiation within the brain tissue.

[0003] It is desirable to provide improved techniques for imaging and analysis.

Summary of the Invention

[0004] Aspects of the present disclosure are set forth in the independent claims, and optional features are set forth in the dependent claims. Aspects of the present disclosure may be provided in combination, and features of one aspect may also apply to other aspects.

[0005] In one aspect, a first light source configured to emit light that is wavelength-swept in a first wavelength range (e.g., above the absorption wavelength such as for oxygen measurement etc.) and passes through a plurality of different wavelengths, a second light source configured to emit light that is wavelength-swept in a second wavelength range different from the first wavelength range (e.g., below the absorption wavelength such as for oxygen measurement etc.) and passes through a plurality of different wavelengths, a common sample delivery channel coupled to each of these light sources to receive the light from the first light source and the second light source and deliver the light toward a subject (e.g., toward the subject's scalp), one or more reference channels that receive reference light from the first light source and / or the second light source, a light emitting device comprising the same, a light detecting device comprising an interferometric photodetector, are provided. The interferometric photodetector is coupled to one or more reference channels that receive reference light from the first light source and the second light source. The light detecting device is arranged to be coupled to a subject (e.g., the subject's scalp) so as to receive sample light including light (e.g., delivered to the subject's brain tissue etc.) transmitted along the common sample delivery channel from the first light source and the second light source. The interferometric photodetector is arranged to combine the sample light and the reference light to provide a combined optical signal including one or more components of the beat frequency between the sample light and the reference light. The iNIRS system is configured to process the combined optical signal to provide (e.g., for imaging and analysis of the subject's brain).

[0006] Embodiments may allow for a single light emitting device to emit light in two separate wavelength ranges, and the light from each light source is emitted via at least one common optical channel (e.g., the light from both light sources is emitted along the same optical channel). Embodiments may allow for a single light detecting device to receive sample light and reference light from two separate light sources via one or more common optical channels. Using light in a plurality of wavelength ranges on both sides of the absorption wavelength such as for oxygen measurement etc. may allow for determining the blood oxygen concentration in the subject's brain tissue.

[0007] Each light source may be arranged to emit a series of pulses, where each pulse comprises at least one sweep over a plurality of different wavelengths. Each light source may be configured to sweep linearly through a plurality of different wavelengths. The light from each light source may be transmitted along at least one common optical path, e.g., one optical channel, when transmitted from the light source to the subject's scalp. That is, the common sample delivery channel may comprise a channel along the subject's scalp through which both (i) the light from the first light source and (ii) the light from the second light source can be transmitted when sent towards the subject's scalp, e.g., the channel may be common to the light from both light sources (e.g., used by this light). The iNIRS system may comprise a plurality of interferometric photodetectors. Each detector may be coupled to one or more reference channels that receive reference light from the first and second light sources. Each photodetector may be arranged to receive sample light from the subject's brain tissue.

[0008] The light emitting device may comprise an optical coupler arranged to couple the light from each of the first and second light sources on a common optical channel (e.g., such that the light from both light sources is transmitted along the same common optical channel). The common optical channel may be coupled to the common sample delivery channel or the common optical channel may be the common sample delivery channel. For example, the light emitted from each light source may be transmitted along the same section of the optical channel when transmitted towards the subject's scalp. The optical coupler may comprise a wavelength division multiplexing device. The light emitting device may comprise an optical splitter arranged to split the light from the first and / or second light sources between the common sample delivery channel and one or more reference channels.

[0009] The light-emitting device may include a first optical splitter arranged to split the light from the first light source into a first sample delivery channel and a first reference delivery channel, a second optical splitter arranged to split the light from the second light source into a second sample delivery channel and a second reference delivery channel, and a sample common optical coupler arranged to combine the light from the first sample delivery channel and the light from the second sample delivery channel on a common sample delivery channel. The light-emitting device may further include a reference common optical coupler arranged to combine the light from the first reference delivery channel and the light from the second reference delivery channel on a common reference delivery channel. The photodetector may be coupled to the common reference channel to receive the reference light from the common reference channel. The length of the first reference delivery channel may be different from the length of the second reference delivery channel. The light-emitting device may be arranged to combine the light from the first light source and the light from the second light source, and optionally, a common optical coupler arranged to combine the first light source and the second light source with a common optical channel, and a common optical splitter coupled to the common optical coupler and arranged to split the light received from the common optical coupler into a common sample delivery channel and a common reference channel, and optionally, a common optical splitter arranged to combine the common optical channel with the common sample delivery channel and the common reference channel.

[0010] The photodetector may be configured to (i) combine the sample light from the first light source with the reference light from the first light source and (ii) combine the sample light from the second light source with the reference light from the second light source. The iNIRS system may include a control device configured to obtain an indication of the scattering coefficient and / or absorption coefficient of the sample light from the first light source and the sample light from the second light source. For example, the control device may be configured to obtain an indication of neural activity based on the processed combined optical signal. The control device may be configured to obtain an indication of blood oxygen concentration based on the absorption coefficients for the sample light from the first light source and the sample light from the second light source. The control device may be configured to obtain an indication of blood oxygen concentration based on blood absorption data indicating the relative absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin at the wavelengths of light in the first wavelength range and the second wavelength range. The control device may be configured to obtain an indication of the optical path lengths of the sample light from the first light source and the second light source based on the beat frequency present in the combined optical signal associated with those sample lights.

[0011] The control device may be configured to obtain an indication of the depth-resolved scattering coefficient and / or absorption coefficient of the subject's brain tissue based on the obtained scattering coefficients and absorption coefficients associated with different optical path lengths. The control device may be configured to obtain an indication of the depth-resolved blood oxygen concentration of the subject's brain tissue based on the obtained depth-resolved absorption coefficient. The control device may be configured to obtain an indication of the subject's blood flow index for each of the first wavelength range and the second wavelength range. The control device may be configured to obtain an indication of the total tissue oxygenation metabolism of the subject based on the obtained blood flow index of the subject and the obtained blood oxygenation concentration of the subject.

[0012] The light emitting device may be configured to time-division multiplex the light emissions from the first light source and the second light source. The system may be configured to time-division multiplex the operations of the first light source and the second light source such that the operation of the first light source is temporally arranged alternately with the operation of the second light source. The light emitting device may be configured to wavelength-division multiplex the light emissions from the first light source and the second light source. The optical path length of the reference light from the first light source transmitted to the photodetector may be different from the optical path length of the reference light from the second light source transmitted to the photodetector such that the beat frequency associated with the first light source is separable from the beat frequency associated with the second light source. The difference between the optical path length of the reference light from the first light source and the optical path length of the reference light from the second light source may be selected such that there is no or minimal spectral overlap between (i) the beat frequency for the sample light and the reference light from the first light source and (ii) the beat frequency for the sample light and the reference light from the second light source. The difference between (i) the expected optical path length of the sample light from the first light source transmitted to the photodetector and (ii) the optical path length of the reference light from the first light source transmitted to the photodetector may be different from the difference between (iii) the expected optical path length of the sample light from the second light source transmitted to the photodetector and (iv) the optical path length of the reference light from the second light source transmitted to the photodetector in order to suppress spectral overlap between the beat frequency associated with the first light source and the beat frequency associated with the second light source. The system may be arranged to provide a wavelength-dependent delay in one of the common sample channel and the common reference channel.

[0013] The light emitting device may include a wavelength division multiplexing device, and the light detection device includes a wavelength division demultiplexing device. The light emitting device may be configured to wavelength multiplex and emit both the light from the first light source and the light from the second light source. The light detection device may be configured to wavelength demultiplex the combined optical signals such that the combined optical signals associated with the first light source are processed separately from the combined optical signals associated with the second light source. The photodetector may include a detection optical splitter arranged to split (i) the light from the first light source to the first detection channel and (ii) the light from the second light source to the second detection channel. The detection optical splitter may be arranged to provide (i) a first combined optical signal including one or more components of the beat frequency between the sample light and the reference light from the first light source to the first detection channel and (ii) a second combined optical signal including one or more components of the beat frequency between the sample light and the reference light from the second light source to the second detection channel. The light detection device may include a signal processing circuit configured to process the first combined optical signal and the second combined optical signal separately.

[0014] Each light source may include an associated optical amplifier to enhance the output of the light emitted from the light source. The iNIRS system may include a plurality of optical delivery channels and an optical switch configured to selectively send the light from the first light source and the second light source to each of the plurality of optical delivery channels. The light emitting device may include at least one common optical channel coupled (e.g., directly or indirectly) to each of the first light source and the second light source and configured to receive the light from the first light source and the second light source. The light delivered from both light sources to the subject's scalp may be transmitted along this same one channel. Similarly, the reference light from both light sources may be transmitted along at least one common optical channel to one or more detectors.

[0015] In one aspect, operating a first light source to emit light that is wavelength swept in a first wavelength range (e.g., above an absorption wavelength such as for oxygen measurement) and passes through a plurality of different wavelengths, operating a second light source to emit light that is wavelength swept in a second wavelength range different from the first wavelength range (e.g., below an absorption wavelength such as for oxygen measurement) and passes through a plurality of wavelengths, sending the light from each of the first light source and the second light source to a common sample delivery channel and sending the light towards a subject (e.g., towards the subject's scalp), sending reference light from the first light source and / or the second light source to one or more reference channels, and in an interferometric photodetector, combining reference light received from one or more reference channels with sample light received from the subject (e.g., from the subject's brain tissue) that is delivered through the common sample delivery channel towards the subject and includes light from the first light source and / or the second light source to provide a combined optical signal that includes one or more components of the beat frequency between the sample light and the reference light, and processing the combined optical signal to provide (e.g., for imaging and analysis of the subject's brain) an interferometric near-infrared spectroscopy (iNIRS) method (e.g., for neuroimaging and analysis) is provided.

[0016] Aspects of the present disclosure include one or more computer program products including computer program instructions for programming a processor to control the operation of an interferometric near-infrared spectroscopy system to perform any of the methods disclosed herein.

[0017] Embodiments may provide an iNIRS system and method for neuroimaging and analysis of a subject's brain tissue. The iNIRS system and method of the present disclosure are directed to a technique for neuroimaging and analysis that is fundamentally different from the fNIRS technology described above. Embodiments may provide an improved technique for performing iNIRS neuroimaging and analysis. As disclosed herein, the iNIRS system of the present disclosure includes two light sources and one or more photodetectors. Also, the iNIRS system of the present disclosure may include a control device arranged to receive an output signal from the one or more photodetectors.

[0018] Each light source may include a light generating element arranged to generate light (e.g., near-infrared light). For example, each light generating element may include a laser. Each light source may include an optical device coupled to the light generating element. The optical device of each light source may be configured to deliver the light generated by the light generating element to one or more different locations. The optical device of each light source may be arranged to direct a portion of the light from the light generating element towards a region where the light is sampled. The optical device of each light source may be arranged to send a portion of the light to each light detector. The optical device of each light source may include a plurality of light delivery channels. The plurality of light delivery channels may include one or more sample delivery channels and / or one or more reference delivery channels. Each light delivery channel may include an optical channel such as an optical fiber. Each light delivery channel may be configured to transmit light (e.g., from the light generating element towards the subject's scalp or the light detector) along its length. The optical device of each light source may include an optical splitter that splits the light into each of the different delivery optical channels.

[0019] The iNIRS system may be arranged such that when installed on the head of a subject (e.g., to provide neuro-imaging and analysis of the subject's brain tissue), the optical device of each light source is configured to send a portion of the light towards the subject's scalp. For example, the optical device of each light source may comprise a sample delivery channel (e.g., which can be used to send sample light towards the subject's scalp). The iNIRS system may be arranged such that when in use, the optical device of each light source is arranged to send a portion of the light directly to a photodetector (e.g., to combine with sample light from the subject's brain tissue). For example, the optical device of each light source may comprise a reference delivery channel (e.g., which can be used to send reference light to one or more photodetectors). The optical device of each light source may be configured to deliver light from a light generation element to each optical channel. The optical device of each light source may be configured to deliver both (i) light to the sample light delivery channel ("sample light") and (ii) light to the reference delivery channel ("reference light"). For example, the optical device of each light source may comprise an optical splitter configured to split the light received from the light generation element into respective different channels.

[0020] When installed and used in a subject's brain tissue, the iNIRS system may be arranged such that sample light is sent towards the subject's scalp and brain tissue (e.g., through a sample delivery channel), and reference light may be sent towards each photodetector (e.g., through a reference delivery channel). Each light source may be arranged to emit wavelength-swept light (e.g., each light source may be arranged to output light at a plurality of different wavelengths over a selected period). For example, each light source may comprise a modification element that controls the operation of the light generation element to output light at a plurality of different wavelengths. Each light source may be arranged to sweep the wavelength of the light it outputs (e.g., the wavelength increases or decreases). Each light source may be arranged to emit chirped light where each chirp (or "pulse") comprises one wavelength sweep. Each light source may be arranged to output continuous chirps comprising the same wavelength sweep, such that, for example, the wavelength of the light output from the light source changes according to a repeating pattern.

[0021] Each photodetector may provide an interferometric photodetector. Each photodetector may include an optical device. The optical device of the photodetector is configured to send the detected light (e.g., from the subject's scalp) to the photodetector. The optical device of the photodetector may include a plurality of light receiving channels. The plurality of light receiving channels may include one or more sample light receiving channels and / or one or more reference light receiving channels. Each light receiving channel may include an optical channel such as an optical fiber.

[0022] When the iNIRS system is placed on the subject's head (e.g., to provide neuroimaging and analysis of the subject's brain tissue), it may be arranged such that the optical device of the photodetector is configured to receive the light emitted from the light source (e.g., transmitted through the subject's brain tissue from the light source). For example, the optical device of the photodetector may include a sample light receiving channel (e.g., usable to receive sample light from each light source that has passed through the subject's brain tissue). When used, the iNIRS system may be arranged such that the optical device of the photodetector can receive a portion of the light from each light source transmitted directly from the light source (e.g., transmitted along an optical channel). For example, the optical device of the photodetector may include a reference light receiving channel (e.g., usable to receive reference light from one or more light sources). Each photodetector may be coupled to each light source such that the reference delivery channel of the light source is coupled to the reference light receiving channel of the photodetector (e.g., such that the reference light is transmitted from the light generating element to the photodetector via the reference delivery channel and the reference light receiving channel).

[0023] The optical device of the photodetector may be configured to deliver both (i) the light from the sample light receiving channel ("sample light") and (ii) the light from the reference light receiving channel ("reference light") to the photodetector. For example, when used, the detector is arranged to receive both (i) the sample light that has passed through the subject's brain tissue from each light source and (ii) the reference light transmitted to the photodetector along one or more reference channels from each light source.

[0024] The photodetector may be arranged to combine the reference light and the sample light in order to provide a combined optical signal. For example, the photodetector may include an optical coupler (e.g., that combines the light of the reference light receiving channel and the light of the sample light receiving channel). The combined optical signal may include, for example, a plurality of components of a beat frequency that is a frequency corresponding to the wavelength difference between the sample light and the reference light. Each photodetector is configured to convert the received combined optical signal into one or more electrical signals indicative of the combined optical signal. For example, the detector may include one or more photodiodes. Each photodiode may output an electrical signal (e.g., a current) indicative of the combined optical signal. The detector may include a balanced photodetector (e.g., that may include two photodiodes that can be 180° out of phase with each other, and the output thereof may combine the current outputs of the two photodiodes). The detector may optionally include a current-voltage conversion circuit and / or one or more amplifiers that amplify the electrical signal.

[0025] The iNIRS system may include at least one analog-to-digital converter arranged to convert an electrical signal (e.g., a combined optical signal) representing the sample light into one or more digital signals. The control device is arranged to process the digital signals in order to determine one or more characteristics of the subject's brain tissue. The control device may be configured to determine the optical characteristics (e.g., with respect to absorption and / or scattering) of the subject's brain tissue. The control device may be configured to determine one or more dynamic characteristics of the subject's brain tissue (e.g., characteristics that change over time in the subject's brain tissue). For example, the control device may be configured to detect the presence of movement (e.g., due to movement such as blood flow in the brain tissue) within the subject's brain tissue.

[0026] The control device may be configured to process digital signals so that photons of the sample light transmitted from each light source through the subject's brain tissue to the photodetector acquire flight time information. The control device may be configured to identify the penetration depth (and optionally the expected trajectory of the photons through the brain tissue) associated with different flight times of the photons of the sample light. The control device may be configured to acquire a chronological distribution of a series of flight times of the photons of the sample light reaching each photodetector. The control device may be configured to process a chronological series to identify a change over time of the distribution of flight times, such as identification of attenuation and / or attenuation rate between the distributions of successful flight times. The control device may be configured to provide depth-resolved processing, for example, by filtering the flight time data to focus only on photons within a selected flight time range (e.g., to identify changes in the optical properties of the brain tissue with respect to the penetration depth associated with the flight time range). The control device may be configured to process the data received from the photodetector to provide flight time information along with depth-resolved autocorrelation for the subject's brain tissue.

[0027] The control device may be configured to process the received light data indicating the sample light received by the photodetector and output a control signal based on the received light data. The control signal may provide an indication of the distribution of the time of flight (for example, the control device may be configured to output the distribution of the time of flight). The control signal may provide an indication of one or more characteristics such as the optical characteristics of the brain tissue determined based on the distribution of the time of flight (for example, the scattering coefficient and / or absorption coefficient, and / or how / if these coefficients have changed). The control signal may provide an indication of the blood flow in the subject's brain tissue. The control signal may provide a depth-resolved indication of one or more characteristics of the subject's brain tissue (for example, related to a specific region such as a selected depth range within the subject's brain tissue). The control signal may include an indication of one or more characteristics of the subject's brain tissue, such as intracranial pressure, blood flow index, arterial elasticity, cerebral oxygen consumption, etc. The medical characteristics may be related to a specific region / depth within the subject's brain tissue. The control signal may include an activation command for the brain-computer interface, for example, to control the operation of the device based on the activation command. The control signal may include an image for display, and the image represents a part of the subject's brain tissue (determined based on the received sample light).

[0028] Hereinafter, some examples of the present disclosure will be described with reference to the drawings by way of example only.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0030] In the drawings, like reference numerals are used to indicate like elements.

[0031] Embodiments of the present disclosure are directed to systems and methods for non-invasively obtaining an indication of blood oxygenation in a subject's brain tissue. An interferometric near-infrared spectroscopy (「iNIRS」) system including a first light source and a second light source is used. One light source emits light at a wavelength above the absorption wavelength for oxygen measurement etc., and the other light source emits light at a wavelength below the absorption wavelength for oxygen measurement etc. Each light source performs wavelength-swept emission. The iNIRS system also includes one or more photodetectors, and each photodetector is configured to receive sample light and reference light from both of the two light sources. Each photodetector combines the sample light and the reference light from each of the two light sources by an interference method to provide a combined optical signal including components of one or more beat frequencies between the sample light and the reference light. The scattering coefficient and / or the absorption coefficient may be determined based on the combined optical signal. The blood oxygenation level of the subject's brain tissue may be determined based on the absorption difference between the lights from the two different light sources. The depth-resolved blood oxygenation level may be determined by monitoring the coefficients (and the flight times / penetration depths of different photons) for photons associated with different beat frequencies.

[0032] Interferometric near-infrared spectroscopy (「iNIRS」) FIG. 1 shows a schematic diagram of an interference-type near-infrared spectroscopy ( "iNIRS") system 10. The iNIRS system 10 includes a light source 20, a plurality of photodetectors 30, and a control device 40. The inset A in FIG. 1 shows a more detailed view of one of the photodetectors 30.

[0033] The iNIRS system 10 includes a light source modifier 22 and an optical splitter 24. The iNIRS system 10 includes a sample delivery channel 25 and a reference delivery channel 26. The iNIRS system 10 is shown to be coupled to the head 2 of a subject. The iNIRS system 10 includes a sample delivery probe 25a and a plurality of sample receiving probes 35a. In each photodetector 30, there are an associated sample receiving probe 35a, a sample receiving channel 35, a reference delivery channel connection 28, and a reference receiving channel 36.

[0034] The light source modifier 22 may include a source for supplying a variable electrical control signal (e.g., a device for supplying a variable current or voltage). The light source modifier 22 is coupled to the light source 20. The light source modifier 22 may be electrically connected to the light source 20 to supply a variable current / voltage to the light source 20.

[0035] The light source 20 may include a laser. For example, the laser may be a distributed feedback laser ( "DFB") or a MEMS vertical cavity surface emitting laser ( "MEMS-VCSEL"). The light source 20 is coupled to the optical splitter 24. The optical splitter 24 has an input for receiving light from the light source 20. The optical splitter 24 has two outputs for transmitting the light from the light source 20 to two separate channels. The sample delivery channel 25, like the reference delivery channel 26, is coupled to the optical splitter 24 (to receive light from the optical splitter 24). The sample delivery channel 25 couples the optical splitter 24 to the sample delivery probe 25a. The sample delivery probe 25a is disposed at a location on the scalp of the subject.

[0036] Suitable other types of lasers include distributed Bragg reflector lasers (“DBR”), Fourier domain mode locked lasers (“FDML”), and vertical cavity surface emitting lasers (“VCSEL”). Further, or alternatively, pulsed supercontinuum lasers may be used in combination with pulse stretching mechanisms such as diffraction gratings, GRISM pulse stretchers, and lengths of dispersive optical fiber. For example, such an apparatus may be configured to temporally separate wavelengths within a pulse such that frequency chirped pulses are created (e.g., to ultimately provide an interferogram when comparing a sample pulse and a reference pulse).

[0037] The reference delivery channel 26 couples the optical splitter 24 to each of the photodetectors 30. At each detector, the reference delivery connection 28 couples the reference delivery channel 26 to a reference light receiving channel 36 for the detector. Each reference light receiving channel 36 is coupled to the photodetector 30 for the channel. Each photodetector 30 is connected to the light source 20 to directly receive reference light from the light source 20 (via one or more reference channels). Each sample light receiving probe 35a is placed on the subject's scalp. Each sample light receiving probe 35a is coupled to a sample light receiving channel 35. Each sample light receiving channel 35 is coupled to the photodetector 30 for the channel. Each photodetector 30 is connected to indirectly receive sample light from the light source 20 (via the sample delivery channel and the sample light receiving channel, and through the subject's brain tissue between those channels).

[0038] A plurality of different photodetectors 30 exist. Each detector may comprise an interferometer such as a Mach-Zehnder interferometer. Each of the different photodetectors 30 is coupled to the same light source 20 (each via one or more reference channels). The photodetectors 30 are spatially separated from the light source 20. Also, the photodetectors 30 may be spatially separated from each other, or may be arranged on a region that is sufficiently similar to tissue such that received signals can be collectively averaged. For the reference light to reach the photodetectors 30 from the light source 20, the reference light is transmitted directly along one or more reference channels. For the sample light to reach the photodetectors 30 from the light source 20, the sample light is transmitted indirectly through the subject's brain tissue. The sample light is delivered to the subject's scalp via one or more delivery channels. And the sample light may pass through the subject's brain tissue and may be transmitted and received by the photodetectors 30 via one or more sample light receiving channels 35. Thus, the subject's brain tissue may be illuminated using different optical channels for detecting light from the subject's brain tissue.

[0039] The control device 40 may comprise any suitable components having a data receiving function and a processing function. For example, the control device 40 may comprise at least one application specific integrated circuit ("ASIC"). Other examples of the control device 40 include a field programmable gate array ("FPGA"), and / or a data acquisition module ("DAQ"). The control device 40 is coupled to each of the detectors. The control device 40 may be connected to each detector via a wired connection (to receive an electrical signal indicative of the detection from the detector), and / or the connection may be wireless (to receive transmitted data indicative of the detection from the detector). The control device 40 is coupled to the light source modulator 22. This connection may be wired or wireless.

[0040] The iNIRS system 10 may be at least partially housed within a garment for the head 2 of a subject. For example, the iNIRS system 10 may be provided within a brimmed hat / hatless hat worn by the subject on their head 2. The head garment may be arranged to hold the light source 20 and the detector in a fixed arrangement with respect to the subject's scalp. Some or all of the components may be provided with the head garment. For example, the head garment may include a plurality of receptacles for housing the light source 20 and the photodetector 30. The channel connecting the light source and the photodetector 30 may be provided as part of the head garment (e.g., may be passed through a corresponding channel receptacle of the head garment). The control device 40 may be separate from the head garment (and, for example, may be connected wirelessly), or may be provided as part of the head garment (e.g., by an ASIC in the head garment that may be wired to the detector and / or the light source modifier 22). For example, the garment may be configured to house the light source, the detection channel, the probe, and other components of the system that are arranged somewhere together.

[0041] Some or all of the channels of the iNIRS system 10 may be provided by optical fibers. The optical splitter of the present disclosure may include an optical fiber splitter. The iNIRS system 10 may optionally include a lens, a reflection device for beam steering, and / or a refraction device. For example, the sample delivery probe 25a may include one or more lenses that spatially distribute the sample light from the sample delivery channel 25 towards the subject's brain tissue. As another example, one or more of the sample light receiving probes 35a may include a lens that collects the received light into the sample light receiving channel 35 connected to the sample light receiving probe 35a. As another example, the probe may be a cut and / or polished bare fiber.

[0042] The iNIRS system 10 is configured to provide a plurality of light source-detector pairs for each light source 20. That is, the iNIRS system 10 is arranged such that each photodetector 30 can receive two forms of light, namely, (i) reference light and (ii) sample light. Each detector is configured to receive the reference light directly from the light source 20 (the reference light is transmitted from the light source 20 to the photodetector 30 along one or more channels, for example, without passing through the subject's brain tissue). Also, each detector is arranged to receive the sample indirectly from the light source 20 (the sample light is sent towards the subject's scalp tissue, but a part of the sample light may be transmitted through the subject's brain tissue on the way to the detector, for example, the sample light does not transmit only through the optical channel between the light source 20 and the photodetector 30).

[0043] The detector 30 is arranged on the subject's scalp and is arranged to provide imaging of a selected region of the subject's brain. At least a part of the detector 30 is arranged to be spatially separated from the light source 20. One or more (for example, each) of the photodetectors 30 may be arranged to be sufficiently separated from the light source 20 such that at least a part of the photons of the sample light from the light source 20 received by the photodetector 30 penetrate into the subject's brain tissue. For example, the spacing between the light source and the detector may be selected such that the photodetector 30 receives photons of the sample light that have experienced many scattering events (for example, when transmitted through the subject's head 2, scattered a large number of times between the light source and the detector). That is, the spacing between the light source and the detector may be selected such that the photodetector 30 receives photons that penetrate deeply into the subject's brain tissue. Such photons may have a longer flight time from the light source to the detector compared to photons that penetrate more shallowly and experience fewer scattering events.

[0044] Detector 30 may be arranged spatially close to each other on the subject's scalp. The arrangement of detector 30 may be selected such that the detectors image similar regions of the subject's brain. For example, detector 30 may be arranged on the subject's scalp within a threshold distance from each other so that it can average the data it acquires (e.g., so as to provide an average value for the same volume of the subject's brain). That is, detector 30 may be arranged to spatially survey the same volume of tissue in the subject's brain. For example, the detectors may be arranged within one attenuation length (e.g., within the sum of the absorption coefficient and the scattering coefficient) with respect to each other's tissue.

[0045] Light source 20 is arranged to generate light and direct this light towards the subject's scalp and (via the reference channel) towards photodetector 30. Optical splitter 24 receives the light generated by light source 20 and is arranged to split this light into two channels, namely, (i) towards the subject's scalp using sample delivery channel 25 and sample delivery probe 25a, and (ii) towards photodetector 30 using reference delivery channel 26 and reference light receiving channel 36. The splitter may be configured such that most of the light is sent towards the subject's scalp. For example, the splitter may be a 90:10 splitter, or a 99:1 splitter. Sample delivery channel 25 receives the sample light from the splitter and is arranged to deliver this sample light towards the subject's scalp (via sample delivery probe 25a). Reference delivery channel 26 receives the reference light from the splitter and is arranged to deliver this reference light to the detector (via reference light receiving channel 36).

[0046] Each reference delivery connection unit 28 is arranged to deliver a part of the reference light transmitted along the reference delivery channel 26 to one of the reference light receiving channels 36. Each reference light receiving channel 36 is arranged to deliver the reference light to the channel-specific photodetector 30. The sample light receiving probe 35a is arranged to receive sample light from the subject's brain tissue. The sample light receiving probe 35a may collect the received sample light into the sample light receiving channel 35. The sample light receiving channel 35 is arranged to deliver the received sample light to the channel-specific photodetector 30. The sample light receiving probes 35a may be arranged extremely close to each other on the subject's scalp.

[0047] Each detector is arranged to receive two inputs, namely, (i) directly the reference light from the light source 20, and (ii) indirectly the sample light from the light source 20 (e.g., transmitted through the subject's brain tissue and through the skin and skull of the subject's scalp). For example, each detector may comprise two or more input ports. The first input port of the detector may be coupled to the reference delivery channel 26 for that detector. The second input port of the detector may be coupled to the sample delivery channel 25 for that detector. The detector is arranged to combine (as an interferometer) the reference light and the sample light. The detector and the control device 40 are arranged to determine one or more characteristics of the subject's brain tissue based on this combined reference light and sample light (as will be described in more detail below).

[0048] The light source 20 is configured to emit wavelength-swept light. Therefore, the light source 20 may be configured to emit a series of optical pulses. In each pulse, the wavelength of the light may be "swept" over a wavelength range. For example, the sweep may be in the form of a chirped pulse. The light is emitted at a plurality of different wavelengths within one pulse. For example, the wavelength may continuously increase or decrease within one pulse (the rate of change of the wavelength may be constant or variable). A series of chirped pulses may be continuous (e.g., the time interval between pulses is zero). The light source 20 may be configured to continuously emit a series of pulses in which each pulse is wavelength-swept. However, it will be understood that the light source 20 does not need to provide a continuous sweep. For example, the light source may be adjusted stepwise rather than continuously, and as a result, the light source 20 emits light of different wavelengths at different time intervals (e.g., individual time intervals for emission at each of a plurality of wavelengths). The light source 20 may sweep in one direction (e.g., only increase or only decrease during one wavelength sweep), or may sweep in both directions (e.g., increase and decrease during one wavelength sweep).

[0049] The control device 40 may be configured to selectively control the wavelength sweep of the light source 20. The light source modifier 22 may be arranged to control the wavelength emission of the light from the light source 20. For example, the light source modifier 22 may be arranged to apply a selected current (or voltage) to the light source 20 to select the wavelength emission from the light source 20. The wavelength sweep of the light source 20 may be controlled by using the light source modifier 22 to apply a corresponding electrical signal to the light source 20. The control device 40 may be arranged to control the application of current / voltage to the light source 20 by using the light source modifier 22 to provide a selected pattern for the wavelength of the light emitted by the light source 20.

[0050] The light source 20 may be controlled to wavelength sweep according to a selected pattern for scanning. For example, the light source 20 may sweep over a selected wavelength range of light, and / or the light source 20 may sweep over the wavelength of light according to a selected sweep profile (e.g., linear increase, sine curve, triangle, etc.). For example, the light source 20 may sweep according to a selected sweep speed, or a selected total sweep time. The light source 20 is configured to wavelength sweep the light such that, during one wavelength sweep, light is sent through the sample delivery channel towards the subject's brain tissue (and also to the detector via the reference channel) at each of a plurality of different wavelengths. The wavelength of the light emitted by the light source 20 changes with time. Accordingly, an indication of the time at which the light was emitted from the light source 20 may be determined based on the wavelength of the light.

[0051] The light source 20 may be configured to sweep over a selected wavelength range. For example, the light source 20 may be configured to sweep at an optical frequency exceeding a region of 50 GHz. For example, this may involve causing the light source 20 to emit light modulated at a plurality of different wavelengths, for example, when centered at 830 nm, between 829.94 nm and 830.06 nm, or when centered at 1310 nm, between 1309.857 nm and 1310.143 nm. The light source 20 may be configured to sweep over a wavelength range of at least 0.025 nm, at least 0.05 nm, at least 0.075 nm, at least 0.1 nm, at least 0.11 nm, etc. (e.g., around the centered wavelength). The light source 20 may have a high output and a long coherence time, and can adjust a wide range of wavelengths without mode hopping. The light source 20 may have a relatively narrow linewidth and a longer coherence length, for example, because the light source 20 is not swept over a particularly large bandwidth.

[0052] The light source of the present disclosure may be configured to emit highly coherent light, which is, for example, substantially coherent light. It will be understood that the light source cannot emit completely coherent light and wavelength-swept light because light of different wavelengths changes phase at different speeds. The light source of the present disclosure may be controlled to sweep over a relatively narrow wavelength range compared to its absolute wavelength. That is, the difference between the maximum wavelength and the minimum wavelength for one wavelength sweep is relatively small compared to these wavelengths. Each light source may be configured to emit light (e.g., an electric field) whose phase does not change significantly over time.

[0053] The iNIRS system of the present disclosure receives sample light and reference light both originating from the same light source. The light source of the present disclosure is configured to emit wavelength-swept sufficiently coherent light such that the sample light and the reference light received by the photodetector are in a relatively similar phase to each other. Thus, the combination of the sample light and the reference light causes substantially constructive interference between the two waves (e.g., two streams of light waves have a sufficiently similar phase such that the resulting combined optical signal includes a constructive combination of the two light waves). That is, the coherence length of the light source may not need to decrease due to multiple scatterings in the tissue until the contrast of the coherence or interference fringes falls below the noise level in the measurement.

[0054] For example, each light source of the present disclosure may include a laser. The laser may be selected, for example, based on its coherence length in order to enable constructive interference to occur between the sample light and the reference light as described above. That is, the iNIRS system is arranged such that the expected maximum delay in the flight time of the photons of the sample light (transmitted through the subject's brain tissue and received by the photodetector) with respect to the photons of the reference light (transmitted along one or more reference channels and received by the photodetector) is within the coherence period of the laser (for example, the difference in the optical path lengths between the sample light and the reference light is within the coherence length of the laser). During this coherence period, the phase of the light emitted by the laser remains substantially stable even though the wavelength of the emitted light changes. Therefore, in the optical signal coupled at the photodetector, the loss of amplitude may not be present (for example, the interference occurring at the detector may be substantially completely constructive).

[0055] For example, the iNIRS system may be configured to have a coherence length, or coherence distance, of approximately 50 m in air, and for example, a light source having a coherence length between 50 m and 100 m (a coherence period between 166 ns and 333 ns) may be selected. This specific range is not intended to be limiting, but rather it will be understood to exemplify an approximate range for the light source. The light source may be selected to have a coherence length that is at least twice the expected maximum difference in the optical path lengths, and for example, the coherence length may be three or four times or more. By having a light source with a coherence length much larger than the optical path length, the measurement accuracy of the photons of the sample light that have experienced many scattering interactions in the subject's brain tissue may be improved.

[0056] The iNIRS system 10 is configured such that the path lengths between the light source and the detector for the reference light and the sample light are different. That is, the iNIRS system 10 is configured such that the average optical path length, or the expected optical path length, of the light transmitted from the light source 20 through the subject's brain tissue to each detector is different from the optical path length of the light transmitted from the light source 20 through the reference channel to the detector.

[0057] As understood in the context of the present disclosure, photons of the sample light sent towards the subject's brain tissue may be transmitted to the photodetector 30 via virtually innumerable different paths from the light source 20. The photons of the sample light may experience many scattering events and, therefore, may follow a very intricate path between the sample delivery probe 25a and the sample light receiving probe 35a. The iNIRS system 10 is configured to provide neuroimaging and analysis at least partially based on activities within the subject's brain tissue. Thus, photons that do not penetrate into the brain tissue (e.g., scatter at a shallow depth such as the skin, skull, meninges, etc.) may carry little or no information regarding the blood oxygenation level in the subject's brain. The reference path may be selected such that the path length between the light source and the detector is shorter than the path length of the photons of the sample light that do not carry such information. Compared to the path length of the photons of the sample light that do not carry this information, photons that penetrate deeper into the subject's brain tissue (and, as a result, potentially carry useful information) typically traverse a longer path length from the light source 20 to the photodetector 30. The flight time of the photons of the sample light from the light source 20 to the photodetector 30 of course increases as the path length traveled increases. Thus, photons that transmit through a longer path and penetrate deeper into the subject's brain tissue take more time to reach the photodetector 30. The longer the flight time of the photons of the sample light, the higher the likelihood that the photons have penetrated deeper into the subject's brain tissue.

[0058] The iNIRS system 10 is configured such that the shortest flight time of the photons of the light transmitted from the light source 20 to the photodetector 30 is the same as the shortest flight time of the photons of the reference light transmitted along the reference channel. The flight time of the photons of the sample light is longer than the flight time of this reference light. The photons of the sample light that penetrate deepest into the subject's brain tissue are likely to have the longest flight time to the photodetector 30.

[0059] The iNIRS system 10 is configured to determine the distribution of the flight times of photons of the sample light (the "DTOF"). For this purpose, a time point spread function (the "TPSF") that is similar to the DTOF but includes an instrument response function (the "IRF") that can be removed later by filtering (e.g., by deconvolution and / or subtraction) using post-processing may be determined. Each of the determined DTOFs may provide a distribution indicating the flight times of all the photons of the sample light incident on the photodetector 30 at a given instant. The DTOF may include an ensemble average representing many of the incident photons (in each of a plurality of different TOF bins). The intensity of each TOF bin provides an indication of the number of photons incident at that TOF. The phase of the TOF bin (obtained, for example, using Fourier analysis) may represent the average phase of all the photons arriving at that TOF bin. As will be described in more detail below, a number of characteristics of the subject's brain tissue may be determined based on the DTOF data acquired for the subject's brain tissue. To acquire such data, the iNIRS system 10 is configured to acquire an interferogram for the combined reference light and sample light received at a given light source 20.

[0060] The iNIRS system 10 is configured such that each photodetector 30 receives the sample light and the reference light and combines the two using an optical coupler. For example, each detector may provide an interferometer assembly configured to combine the reference light and the sample light (using both a sample light channel and a reference light channel) to obtain an interference pattern (an interferogram).

[0061] The light source 20 is configured to emit substantially coherent light. The interference pattern resulting from the light from the light source 20 (acquired at each detector) may comprise a combined signal having a component at a beat (or intermediate / difference) frequency corresponding to the wavelength difference between (i) the wavelength of the photons of the sample light received at the photodetector 30 in a given temporal instance, and (ii) the wavelength of the photons of the reference light received at the photodetector 30 in that given temporal instance. The reference light at one sampling interval should be at a fairly narrow and uniform wavelength limited by either the laser's inherent linewidth or the optical frequency sweep rate, because the photons of the received reference light travel the same distance from the light source 20 to the photodetector 30 (through the reference channel). The sample light comprises photons of different wavelengths, and each wavelength of the sample light corresponds to the flight time of that photon (due to the wavelength sweep of the light source 20) and the path specific to that photon through the tissue. Therefore, the resulting interferogram contains a plurality of different beat frequencies (due to the different differences in wavelength). Higher beat frequencies may correspond to photons with a greater flight time (more deeply penetrating photons) when the sample path is longer than the reference path.

[0062] Each optical detector 30 comprises an optical coupler arranged to couple light and provide the coupled light (which may include one or more components corresponding to the beat frequency) to a signal processing circuit. Each detector may comprise a square-law detector. For example, each detector may be configured to create an interference pattern based on the optical frequency difference between an incident sample electric field and a reference electric field. For example, the intensity of the detected output is proportional to the square of the incident electric field, and the incident electric field is the sum of the sample electric field and the reference electric field. The intensity of the detected output (in the form of photocurrent) is equal to the square of the sum of the incident sample electric field and the reference electric field. Such detectors may comprise photodiodes, avalanche photodiodes, and / or high-speed line scan cameras, streak cameras, high-speed CCD or high-speed CMOS sensors. The detector may be a high-bandwidth detector. For example, the detector may be configured to resolve interference fringes at 100 MHz or higher, up to 1 GHz. The detector may comprise one speckle detector. For example, the optical fiber used in the detector may be single-mode. When a multimode detector is used, the detector may comprise an array of square-law detectors, such as a photodiode array, a focal plane array, a high-speed line scan camera, a high-speed CCD array, etc. Also, the detector may comprise a balanced detector array. For example, the balanced detector array may be configured such that the reference light and the scattered light are coupled and split (e.g., evenly) for a pair of phase-shifted detectors, such as a fiber coupler or a beam splitter cube with 4 ports (2 inputs and 2 outputs with a 50:50 ratio). The balanced detector may increase the signal-to-noise of the detected signal by removing the incoherent part of the signal. Also, the balanced optical detector may suppress common noise such as laser intensity noise by fully utilizing all the light transmitted through the interferometer.

[0063] That is, each photodetector 30 may include an optical coupler configured to couple the sample light and the reference light to provide a combined optical signal. The iNIRS system 10 is configured to process the combined optical signal to obtain an indication of the intensity of the light incident on the photodetector 30 at a given instant (e.g., using optical heterodyne detection and / or balanced detection). The iNIRS system 10 is configured to obtain such a plurality of indications, e.g., the photodetector 30 may be configured to repeatedly obtain an indication of the intensity of the light incident on the photodetector 30. That is, the iNIRS system 10 is configured to measure the phase or frequency shift between the photons of the light at the two inputs (reference and sample) of the detector and consider such a difference to be due to the characteristics of the brain tissue intervening in the sample light.

[0064] The acquired interferogram may be Fourier analyzed (e.g., using FFT or IFT) to obtain an indication of the DTOF for the photons of the sample light incident on the photodetector 30, respectively. When a square-law detector is used, the intensity at the detector may be proportional to the square of the sum of the electric field intensities. By multiplying the rate of change of the optical frequency by the time delay, the frequency of the interference fringes present in each interferogram may be generated. That is, the Fourier transform of an interferogram containing a plurality of beat frequencies may be used to indicate the flight time of the photons associated with those beat frequencies present in the interferogram.

[0065] To obtain this data on the DTOF for the photons of the sample light, the photodetector 30 is arranged to couple two optical inputs (sample and reference) to the combined light beam. The photodetector 30 is arranged to convert the combined light beam into an electrical signal representing the combined optical signal. The iNIRS system 10 includes at least one digitizer arranged to receive the electrical signals indicative of the combined optical signal and convert those electrical signals into digital data representing the combined optical signal. This digital data may be processed to obtain one or more different characteristics of the subject's brain tissue for neuroimaging and analysis.

[0066] An example of an apparatus for converting a received optical signal into digital data is shown in the insert view A of FIG. 1. The insert view A shows the arrangement of components that can be used as the photodetector 30 of the present disclosure. Also, as shown in the iNIRS system 10 of FIG. 1, the detector 30 receives two inputs, namely, (i) reference light transmitted along the reference delivery channel 26 and the reference light reception channel 36, and (ii) sample light received via the sample light reception probe 35a and delivered to the detector via the sample light reception channel 35.

[0067] As shown, the detector may include an optical branching coupler 301, a first optical channel 302a, a second optical channel 302b, a balanced photodetector 303, a transimpedance amplifier 304, an amplifier 305, and an analog-to-digital converter ("ADC") 306. The ADC 306 is arranged to provide a digital signal output 307.

[0068] The optical branching coupler 301 is coupled to both the reference light receiving channel 36 and the sample light receiving channel 35. The optical branching coupler 301 is arranged to receive both the sample light and the reference light and combine these two to provide a combined optical signal. The optical branching coupler 301 is arranged to split this combined optical signal into two separate channels, namely the first optical channel 302a and the second optical channel 302b. For example, this may be a 50:50 (or thereabouts) split. The first optical channel 302a and the second optical channel 302b are coupled to the balanced photodetector 303. Each optical channel sends light towards the associated photodiode. The balanced detector is arranged to provide an output based on the difference between the outputs from the two photodetectors. The two photodetectors are typically provided such that the beat signals on each photodiode are 180° out of phase with each other and the coherent AC terms are combined positively with each other. The balanced photodetector 303 is arranged to output a current corresponding to the difference between the output currents of the two photodetectors. The balanced photodetector 303 may remove unwanted DC terms such as the gentle fluctuations originating from the light source 20 and other common mode effects such as noise from this signal.

[0069] The photodetector 30 is configured to convert the current output from the balanced photodetector 303 into a corresponding voltage using a current-voltage converter. As shown in the insertion diagram A of FIG. 1, the converter may include a transimpedance amplifier 304. Then, the voltage output from the transimpedance amplifier 304 is amplified using an amplifier 305. The amplifier may be used to expand the output signal to the full range of the ADC and further limit the electronic frequency of the circuit to maximize the SNR. Then, this amplified voltage is supplied to the ADC 306 for digitization. The ADC 306 includes a digitizer having a sufficient bandwidth so that it can digitize the entire signal bandwidth including the time-of-flight information without attenuation. For example, the bandwidth of the digitizer may be at least approximately the same as the bandwidth of the combined optical signals. For example, the digitizer may be selected to have a sufficiently high sampling rate such that the bandwidth of the signal being processed satisfies the Nyquist criterion. The digitizer may be provided as part of each photodetector 30, or the digitizer may be part of the control device 40, and the control device 40 may be coupled to each of the photodetectors 30 to receive the electrical signals from the photodetectors 30 to be digitized. For each of the combined optical signals, a digital signal output 307 is provided that gives a digital representation of the combined optical signal (and the sample light incident on the photodetector 30 at the moment the combined optical signal is generated and measured).

[0070] The iNIRS system 10 is configured to obtain a plurality of digital signal outputs 307 indicative of sample light incident on the photodetectors 30. In particular, each photodetector 30 is configured to repeatedly combine optical signals (sample and reference) in order to provide a digital signal output 307 representative of each of the combined optical signals. For example, at each photodetector 30, a time-series digital signal output 307 may be obtained, and each subsequent digital signal output 307 is for after the time when the combined optical signal is obtained and measured (and the digital signal output 307 represents that the combined optical signal is obtained and measured). As described above, each of these signals may indicate the DTOF of the sample light at that time at the detector.

[0071] That is, the iNIRS system 10 is configured to obtain a plurality of time-ordered DTOFs for each of the plurality of different photodetectors 30. The digitizer may provide a digital output indicative of different measurements, and this digital output may optionally be processed in many ways to provide DTOF data. Examples of such steps are described hereinafter.

[0072] The control device 40 may be configured to receive raw digital interferogram data (e.g., data representing an interferogram obtained by converting a combined optical signal into digital data). The raw interferogram may be divided into individual sweeps for the wavelength-swept radiation from the light source 20. For example, the sweep speed of the light source 20 and the time at which the first sweep is initiated may be used to determine the sweep period. And the data may be divided into a plurality of groups, each group representing an individual sweep. At this stage, the Hilbert transform may optionally be performed on the data. Windowing may be performed (e.g., using a Hann window or a Blackman-Harris window) to reduce the sidelobes of the data. Either inverse or normal Fourier analysis may be performed on the data. For example, an inverse Fourier transform may be performed. Fourier analysis may be performed for each wavelength sweep of the light source 20. The resulting data may be in the form of a series of time point spread functions ("TPSF"), each TPSF corresponding to the associated wavelength sweep. The TPSF data may remove the instrument response function ("IRF") to provide DTOF data.

[0073] That is, the iNIRS system 10 may be configured to determine the distribution of a series of time-ordered flight times of photons of the sample light incident on each of a plurality of different detectors. This DTOF data may be processed to provide information related to many different physical characteristics of the subject's brain tissue. The DTOF data may be used to determine the optical characteristics of the medium through which the sample light is transmitted. Each TOF bin in the DTOF may represent a selected volume in the subject's brain, and each DTOF represents the total volume of tissue investigated by the photons (e.g., each DTOF may represent a weighted average of the characteristics of the brain tissue and other tissues through which the photons are transmitted, such as the scalp and skull). Examples of optical characteristics include the scattering characteristics and absorption characteristics of the subject's brain tissue. The DTOF data may be used to determine dynamic characteristics of the subject's brain tissue, such as how certain characteristics change over time. This includes how optical characteristics and characteristics indicating movement within the subject's brain tissue (e.g., due to blood flow) evolve over time. The iNIRS system 10 may be configured to perform a Fourier transform (e.g., FFT) on the TOF distribution obtained to acquire gamma data, and may acquire a dynamic signal from the temporal changes within the gamma signal.

[0074] A series of DTOFs in time order may correspond to the surface of the data in a three-dimensional volume. The surface may represent the DTOF for each subsequent (time-ordered) DTOF, and thus the surface indicates each individual DTOF and the temporal evolution of the DTOF. This surface may provide a large amount of data from which the characteristics of the subject's brain tissue can be determined. Analysis of the temporal variation over time (e.g., decay of the DTOF value) in the DTOF value may provide an indication of one or more dynamic characteristics of the subject's brain tissue. That is, the analysis of decay is used to identify that one or more characteristics change within the subject's brain tissue and, optionally, (e.g., using the decay rate) to identify the rate at which these characteristics change. The order of decay of the DTOF (e.g., decay with t, t 2 etc.) may be used to determine one or more characteristics of the type of movement (e.g., diffusion or flow).

[0075] The control device 40 may store data associating the flight time of photons of the sample light with an indication of the average path trajectory of the photons. This data may include an indication of the depth of penetration of the photons into the subject's brain tissue and / or an indication of the region of the subject's brain tissue through which the photons travel when transmitted from the light source 20 to the photodetector 30. The control device 40 may be configured to process the DTOF data by dividing this data into selected flight time bins. Within each TOF bin, the data may provide depth-resolved evolution data for the subject's brain tissue. That is, the TOF may be related to a specific depth of penetration or region, and each TOF bin may contain data indicating characteristics related to a specific depth of penetration or region. The evolution of the data within each TOF bin may provide an indication of how one or more characteristics of the subject's brain tissue evolve. For example, when the evolution suggests a change in movement (e.g., blood flow), the movement may be specified as well as the region in which the movement occurs. Therefore, the TOF-resolved attenuation gradient may be used to specify how the curve decays over time for a specific TOF (e.g., for a specific depth of penetration / region).

[0076] That is, the iNIRS system 10 is configured to perform an autocorrelation in which the DTOF for successive wavelength sweeps is combined in order to estimate the temporal variation of the light irradiation field at the photodetector 30. The variation may be specified by the associated attenuation over time in the DTOF. Also, the variation may be depth-resolved by specifying the associated TOF (and associated depth of penetration / region) in which the variation occurs.

[0077] The control device 40 may be configured to process the data received from the photodetector 30 in order to provide depth-resolved autocorrelation and time-of-flight information for the subject's brain tissue. The control device 40 may be configured to use this information to obtain indications of a plurality of different characteristics of the subject's brain tissue, such as intracranial pressure ("ICP"), blood flow index, arterial elasticity, cerebral oxygen consumption (CMRO2), and the like. These characteristics of the subject's brain tissue may be used in a plurality of different forms of neuroimaging and analysis, such as brain-computer interface, etc., to identify potential local damage or paralysis by imaging regions of the brain and / or to monitor neurological responses to substances such as drugs.

[0078] Determination of blood oxygenation Refer to FIGS. 2A to 3D, which show the components of the iNIRS system.

[0079] FIGS. 2A and 2B show an apparatus that outputs sample light and reference light (i.e., the sample light is delivered toward the subject's brain tissue and the reference light is delivered directly to the detector along one or more reference channels). The light source devices of FIGS. 2A and 2B output sample light and reference light from two light sources, where one light source emits light at a wavelength above the absorption wavelength for oxygen measurement, etc., and the other light source emits light at a wavelength below the absorption wavelength for oxygen measurement, etc. In particular, the light source devices of FIGS. 2A and 2B are configured to deliver the light from each light source to the same one common light channel when the light travels from that light source toward the subject's scalp. Also, a portion of the light from each light source is delivered to a reference channel that directly optically connects the light source to the photodetector.

[0080] FIGS. 3A and 3D show an apparatus that receives sample light and reference light (i.e., the sample light arrives from the subject's brain tissue and the reference light arrives directly from the light source). The photodetection devices of FIGS. 3A to 3D are arranged to receive sample light and reference light from two light sources, where the wavelength of the light from one light source is above the absorption wavelength for oxygen measurement, etc., and the wavelength of the light from the other light source is below the absorption wavelength for oxygen measurement, etc.

[0081] The light source device of FIGS. 2A and 2B and / or the light detection device of FIGS. 3A to 3D may be provided in the iNIRS system shown in FIG. 1 (as described above). In particular, embodiments of the present disclosure may provide an iNIRS system including the light generation device of FIGS. 2A and / or 2B and a light receiving device of any one of FIGS. 3A to 3D. Therefore, embodiments may provide an iNIRS system designed to emit and detect light of wavelengths on both sides of the absorption wavelength such as oxygen measurement to obtain the blood oxygenation concentration in the subject's brain tissue.

[0082] FIG. 2A shows a light emitting device 120. The light emitting device 120 includes a first light source 120a (above the absorption wavelength such as oxygen measurement) and a second light source 120b (below the absorption wavelength such as oxygen measurement). The light emitting device 120 includes a common optical coupler 122, a common optical channel 123, and a common optical splitter 124. Similar to the iNIRS system described above, the light emitting device 120 includes a common sample delivery channel 125 and a common reference delivery channel 126.

[0083] The common optical coupler 122 couples two light sources to a common optical channel 123. The first light source 120a may be coupled to the common optical coupler 122 via the first coupling channel 121a, and the second light source 120b may be coupled to the common optical coupler 122 via the second coupling channel 121b. The common optical channel 123 couples the common optical coupler 122 to a common optical splitter 124. The common optical channel 123 may be a single optical channel. The common optical channel 123 may extend from the common optical coupler 122 to the common optical splitter 124. The common optical splitter 124 couples a single common optical channel 123 to two separate channels, namely, a common sample delivery channel 125 and a common reference delivery channel 126. As described above, the common sample delivery channel 125 may be coupled to the scalp of a subject in one or more regions via, for example, one or more sample delivery probes. Similarly, the common reference delivery channel 126 may be coupled to one or more photodetectors via, for example, one or more reference light receiving channels.

[0084] The light emitting device 120 is configured to deliver both (i) sample light to the brain tissue of a subject (e.g., through the common sample delivery channel 125) and (ii) reference light to one or more photodetectors (e.g., through the common reference delivery channel 126). The light emitting device 120 is configured such that light from each of the two light sources is transmitted along the same optical channel. For example, the sample light from the first light source 120a and the sample light from the second light source 120b are each transmitted along at least one common optical channel. In the example shown in FIG. 2A, the sample light from the two light sources is transmitted along the same common optical channel 123 and the same common sample delivery channel 125. For example, the reference light from the first light source 120a and the reference light from the second light source 120b are each transmitted along at least one common optical channel. In the example shown in FIG. 2A, the reference light from the two light sources is transmitted along the same common optical channel 123 and the same common reference delivery channel 126.

[0085] Also, a similar light emitting device is shown in FIG. 2B.

[0086] FIG. 2B shows the light emitting device 120. Similar to FIG. 2A, the light emitting device 120 includes a first light source 120a and a second light source 120b. Similarly, the first light source 120a may be coupled to the first coupling channel 121a, and the second light source 120b may be coupled to the second coupling channel 121b.

[0087] In FIG. 2B, the light from each light source first passes through an optical splitter before the light from the two light sources is combined into the same channel. Therefore, the light emitting device 120 in FIG. 2B includes a first optical splitter 124a and a second optical splitter 124b. The first light source 120a is coupled to the first optical splitter 124a (e.g., via the first coupling channel 121a), and the second light source 120b is coupled to the second optical splitter 124b (e.g., via the second coupling channel 121b). The light emitting device 120 in FIG. 2B includes two common optical couplers, namely, a sample common optical coupler 122s and a reference common optical coupler 122r. The sample common optical coupler 122s is coupled to each of the first optical splitter 124a and the second optical splitter 124b, and also to a common sample delivery channel 125. The reference common optical coupler 122r is coupled to each of the first optical splitter 124a and the second optical splitter 124b, and also to a common reference delivery channel 126. The common sample delivery channel 125 may be coupled to the scalp of a subject in one or more regions, for example, via one or more sample delivery probes. Similarly, the common reference delivery channel 126 may be coupled to one or more photodetectors, for example, via one or more reference light receiving channels.

[0088] The first optical splitter 124a couples the first light source 120a to two separate optical channels, namely, the first sample delivery channel 123as and the first reference delivery channel 123ar, respectively. The second optical splitter 124b couples the second light source 120b to two separate optical channels, namely, the second sample delivery channel 123bs and the second reference delivery channel 123br, respectively. The first sample delivery channel 123as couples the first optical splitter 124a (and the first light source 120a) to the sample common optical coupler 122s. The first reference delivery channel 123ar couples the first optical splitter 124a (and the first light source 120a) to the reference common optical coupler 122r. The second sample delivery channel 123bs couples the second optical splitter 124b (and the second light source 120b) to the sample common optical coupler 122s. The second reference delivery channel 123br couples the second optical splitter 124b (and the second light source 120b) to the reference common optical coupler 122r. The sample common optical coupler 122s couples both the first sample delivery channel 123as and the second sample delivery channel 123bs to the common sample delivery channel 125. The reference common optical coupler 122r couples both the first reference delivery channel 123ar and the second reference delivery channel 123br to the common reference delivery channel 126.

[0089] In the light emitting device 120 of FIG. 2B, there are two common optical channels, and light from either one of the light sources is transmitted along these common optical channels. These are the common sample delivery channel 125 and the common reference delivery channel 126. Each of these common optical delivery channels is coupled to a common optical coupler to receive light from one or both of the two light sources. One or both of these common optical channels may be a single optical channel. For example, the common sample delivery channel 125 may be a single optical channel extending from the sample common optical coupler 122s towards the subject's brain tissue. For example, the common reference delivery channel 126 may be a single optical channel extending from the reference common optical coupler 122r towards one or more photodetectors.

[0090] The light-emitting device 120 is configured to deliver both (i) sample light to the brain tissue of a subject (e.g., through the common sample delivery channel 125) and (ii) reference light to one or more light detectors (e.g., through the common reference delivery channel 126). The light-emitting device 120 is configured such that light from each of the two light sources is transmitted along the same optical channel. For example, the sample light from the first light source 120a and the sample light from the second light source 120b are each transmitted along at least one common optical channel. In the example shown in FIG. 2B, the sample light from the two light sources is transmitted along the same common sample delivery channel 125. For example, the reference light from the first light source 120a and the reference light from the second light source 120b are each transmitted along at least one common optical channel. In the example shown in FIG. 2B, the reference light from the two light sources is transmitted along the same common reference delivery channel 126.

[0091] The functions of the two light-emitting devices 120 are described together as follows.

[0092] The light-emitting device 120 in each of FIGS. 2A and 2B is configured to deliver sample light from two separate light sources toward the brain tissue of the subject, and the sample light from each light source is transmitted along at least one common optical channel when transmitted from each light source toward the scalp of the subject. Similarly, the light-emitting device 120 in each of FIGS. 2A and 2B is configured to deliver reference light from two separate light sources toward one or more detectors, and the reference light from each light source is transmitted along at least one common optical channel when transmitted from each light source toward one or more detectors.

[0093] In each light-emitting device 120, each of the first light source 120a and the second light source 120b is similar to the light sources described above in relation to FIG. 1. That is, each light source is configured to emit wavelength-swept light. Since the details of the functions of the first light source 120a and the second light source 120b have already been described above, they will not be described again. The wavelength of the light emitted by the first light source is different from the wavelength of the light emitted by the second light source. The main wavelength of the first light source 120a (for example, the first laser) is different from the main wavelength of the second light source 120b (for example, the second laser).

[0094] The first light source 120a is arranged to emit light at a wavelength above the absorption wavelength for oxygen measurement or the like. The second light source 120b is arranged to emit light at a wavelength below the absorption wavelength for oxygen measurement or the like. The absorption wavelength for oxygen measurement or the like is the wavelength at which the absorption characteristics of oxygenated hemoglobin and deoxygenated hemoglobin become the same (for example, when they have the same absorption coefficient). At wavelengths above the absorption wavelength for oxygen measurement or the like and below the absorption wavelength for oxygen measurement or the like (excluding any other isosbestic wavelengths), the absorption coefficient of oxygenated hemoglobin is different from the absorption coefficient of deoxygenated hemoglobin. That is, the absorption wavelength for oxygen measurement or the like is the wavelength at which the values of the wavelength-dependent absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin are interchanged. In the oxygen measurement of hemoglobin, there are two related absorption wavelengths for oxygen measurement or the like, one is approximately 590 nm, and one is approximately 805 nm. For example, the absorption wavelength for oxygen measurement or the like used in the present disclosure may be approximately 805 nm, approximately 808 nm, etc.

[0095] The first light source 120a is configured to perform wavelength-swept emission that passes through a plurality of wavelengths greater than the absorption wavelength for oxygen measurement or the like (for example, greater than 808 nm). As described above in relation to FIG. 1, the first light source 120a is a laser configured to emit light at a selected wavelength, and the light-emitting device 120 may include a light source modifier configured to change the wavelength of the light emitted around the selected wavelength (for example, for wavelength-sweeping over wavelengths around the selected wavelength at which this laser emits light). For example, the first light source 120a may be configured to emit light at a selected wavelength of approximately 830 nm, 850 nm, or 900 nm. Preferably, the first light source 120a may be configured to emit light at a wavelength of 852 nm. The light-emitting device 120 is configured to perform wavelength-sweeping over 852 nm and a plurality of wavelengths around it with respect to the first light source 120a.

[0096] The second light source 120b is configured to emit light with wavelength-sweeping over a plurality of wavelengths below the absorption wavelength for oxygen measurement or the like (for example, below 808 nm). For example, the second light source 120b may include a laser configured to emit light at a selected wavelength of approximately 690 nm, 760 nm, or 785 nm. Preferably, the second light source 120b may be configured to emit light at a wavelength of 780 nm. The light-emitting device 120 is configured to perform wavelength-sweeping over 780 nm and a plurality of wavelengths around it with respect to the second light source 120b. For example, the first light source and the second light source may be used at wavelengths, in the range from 760 nm to 880 nm, where one of the light sources is above the absorption wavelength for oxygen measurement or the like and the other light source is below the absorption wavelength for oxygen measurement or the like. For example, the first light source 120a may emit light at approximately 830 nm or 850 nm (for example, at 830 nm or 850 nm), and the second light source 120b may emit light at approximately 780 nm (for example, at 780 nm).

[0097] As described above, the light emitting device 120 is arranged to be wavelength-swept and radiated at wavelengths above the absorption wavelength for oxygen measurement etc. and wavelengths below the absorption wavelength for oxygen measurement etc. Further, the light emitting device 120 is arranged to combine the light from both light sources on one or more common optical channels. Each optical channel may comprise an optical fiber cable.

[0098] As previously described in connection with FIG. 1, the optical coupler of the present disclosure is arranged to combine two separate optical input streams on one optical channel. For example, each optical coupler may be configured to receive light input from two separate channels, for example, two separate optical fiber cables, and combine these two input optical streams on one optical channel (as an output). An optical splitter is arranged to separate one input stream from one optical channel into two separate optical channels. For example, each optical splitter may be configured to receive light input from one channel, for example, one common optical fiber cable, and split the input optical stream into two separate optical channels (for example, as two outputs). Each optical coupler may be a wavelength coupler, for example, a wavelength division multiplexing device (WDM). Each optical separator may, conversely, be a wavelength separator. For example, a wavelength coupler / separator (for example, a WDM) may comprise, as relevant, one or more diffraction gratings and / or a prism arranged to split and / or combine light. Further, or alternatively, the coupler and / or separator may be realized using separate components (for example, in free space). A fiber coupler may be used instead of, or in addition to, a WDM, and / or may be used for optical coupling / splitting without the WDM being used for multiplexing and / or demultiplexing.

[0099] The light-emitting device 120 can be used to provide two dynamic wavelength outputs from the same device. At least one common channel is used for the delivery of light output from one or both light sources. The light-emitting device 120 may be configured to output light from both light sources simultaneously. In that case, the light from both light sources may be transmitted simultaneously along at least one same common optical channel. The light-emitting device 120 may be configured to arrange the operation of the two light sources alternately in time so that light is output from one light source at a time. In that case, the light from both light sources is transmitted along the same common optical channel, but only the light from one light source may be transmitted along that channel at any given time.

[0100] The light-emitting device 120 may be arranged such that the reference light from the first light source 120a travels a different distance from the reference light from the second light source 120b (when transmitting from each light source to each detector). For example, the reference path from one light source to the photodetector may include an excess amount of optical channel such that the time it takes for the reference light from that light source to reach the detector is longer than the time it takes for the reference light from the other light source to reach the detector. The lengths of the optical channels through which the light from the two light sources is transmitted to direct the sample light towards the brain tissue of the subject may be substantially the same (e.g., the sample light from either light source may travel the same distance towards the brain tissue of the subject).

[0101] For example, in FIG. 2B, the distance from the first light source 120a to the common sample delivery channel 125 may be the same as, or approximately the same as, the distance from the second light source 120b to the common sample delivery channel 125. That is, the length of the first sample delivery channel 123as may be the same as the length of the second sample delivery channel 123bs (and / or when the first coupling channel and the second coupling channel are used, the combined length of the first coupling channel 121a and the first sample delivery channel 123as may be the same as the combined length of the second coupling channel 121b and the second sample delivery channel 123bs). However, the distance from the first light source 120a to the common reference delivery channel 126 may be different from the distance from the second light source 120b to the common reference delivery channel 126. That is, the length of the first reference delivery channel 123ar may be different from the length of the second reference delivery channel 123br (and / or when the first coupling channel and the second coupling channel are used, the combined length of the first coupling channel 121a and the first reference delivery channel 123ar may be different from the combined length of the second coupling channel 121b and the second reference delivery channel 123br). One of the sample channel and the reference channel may be arranged to provide a difference in the relative delay of the combined light.

[0102] The difference in the distance of the associated reference path length may be selected such that the resulting beat frequency between the sample light and the reference light from one light source is different from the resulting beat frequency between the sample light and the reference light from the other light source. That is, by the reference light for one light source transmitting a longer path, the difference in the flight time between the reference light and the sample light from that light source is different from the difference in the flight time from the other light source. Usually, the longer reference path results in a smaller difference in the flight time between the sample light and the reference light when received by the detector, thus resulting in a smaller beat frequency. The difference in the optical path lengths of the reference lights from the two light sources may be selected such that there is no or a minimum spectral overlap between (i) the beat frequency for the sample light and the reference light from the first light source 120a and (ii) the beat frequency for the sample light and the reference light from the second light source 120b. As will be described in more detail below with respect to the detector, this technique may be used such that the light from both light sources can be simultaneously emitted and detected while enabling the separately identifying of the detected signals associated with the two different light sources.

[0103] Some examples of the optical detection device will now be described with reference to FIGS. 3A to 3C, and the operation of such a detection device will be described in conjunction with the corresponding operations of different light emitting devices 120.

[0104] FIG. 3A shows an optical detection device 130. The optical detection device 130 includes a sample light receiving channel 135 and a reference light receiving channel 136. The optical detection device 130 includes a detection optical branching coupler 131, a first detection channel 133', and a second detection channel 133''. The optical detection device 130 includes at least one element that converts the received optical signal into an electrical signal, for example, a photodetector such as a photodiode. In the example of FIG. 3A, this element is a balanced photodetector 134. Also shown in FIG. 3A are a transimpedance amplifier 137 and an analog-to-digital converter 138.

[0105] The sample light receiving channel 135 is arranged to be coupled to the scalp of a subject, for example, via one or more sample light receiving probes. The reference light receiving channel 136 is arranged to be coupled to both the first light source and the second light source. For example, the reference light receiving channel 136 may be coupled to one of the reference delivery channels in FIGS. 2A and 2B. Both the sample light receiving channel 135 and the reference light receiving channel 136 are coupled to an optical splitter / combiner. The optical splitter / combiner is coupled to both the first detection channel 133' and the second detection channel 133''. The two detection channels are coupled to a balanced photodetector 134. The output of the balanced photodetector 134 is coupled to an analog-to-digital converter 138 via a transimpedance amplifier 137.

[0106] The optical detection device 130 is configured to combine sample light and reference light to provide a combined signal and analyze the combined signal to determine characteristics of the brain tissue of a subject. In the example of FIG. 3A, the detection optical splitter / combiner 131 is configured to combine the sample light from the sample light receiving channel 135 with the reference light from the reference light receiving channel 136 to provide a combined optical signal and split the combined optical signal into two separate optical channels, namely, the first detection channel 133' and the second detection channel 133''. The optical detection device 130 is arranged to provide this light on the two detection channels as an input to the balanced photodetector 134. The balanced photodetector 134, the transimpedance amplifier 137, and the analog-to-digital converter 138 are configured to process this optical input as described above.

[0107] A similar optical detection device is shown in FIG. 3B.

[0108] FIG. 3B shows the optical detection device 130. Similar to FIG. 3A, the optical detection device 130 includes a sample light receiving channel 135 and a reference light receiving channel 136. The optical detection device 130 also includes a detection optical coupler 131 and a wavelength demultiplexing device 132. The wavelength demultiplexing device 132 is arranged to demultiplex the light related to the second light source from the light related to the first light source. The wavelength demultiplexing device 132 demultiplexes the light into two channels, namely, the first light source detection channel 133a and the second light source detection channel 133b (i.e., one optical channel for the light from each light source). Each of the light source detection channels includes a related photodetector (the first photodetector 134a and the second photodetector 134b). These photodetectors may be single photodetectors (e.g., not a balanced photodetector in a single-ended manner). Each photodetector may include a related TIA (the first TIA 137a and the second TIA 137b), and the device 130 may include at least one ADC (ADC 138).

[0109] The detection optical coupler 131 is coupled to both the sample light receiving channel and the reference light receiving channel. The detection optical coupler 131 is coupled to the wavelength demultiplexing device 132 (e.g., via an optical channel). The wavelength demultiplexing device 132 is coupled to each of the first light source detection channel 133a and the second light source detection channel 133b. Each of the light source detection channels couples the wavelength demultiplexing device 132 to its respective photodiode (the first photodiode 134a or the second photodiode 134b).

[0110] The optical detection device 130 is configured to combine the sample light and the reference light to provide a combined signal and to analyze the combined signal to determine the characteristics of the subject's brain tissue. In the example of FIG. 3B, the detection optical coupler 131 is configured to combine the sample light from the sample light receiving channel 135 with the reference light from the reference light receiving channel 136 to provide a combined optical signal. The wavelength demultiplexing device 132 is configured to divide the combined optical signal into two separate optical channels such that the light associated with the first light source 120a is provided to a different channel (the first light source detection channel 133a) than the light associated with the second light source 120b (the second light source detection channel 133b). The optical signals of these two channels are processed separately, for example, to provide two digital outputs, one for each of the lights from the respective light sources.

[0111] FIG. 3C shows the optical detection device 130. Similar to FIGS. 3A and 3B, the optical detection device 130 includes a sample light receiving channel 135 and a reference light receiving channel 136. Each channel is connected to a corresponding wavelength demultiplexing device (the sample light wavelength demultiplexing device 132s and the reference light wavelength demultiplexing device 132r). The optical detection device 130 also includes a first light source branching coupler 131a and a second light source branching coupler 131b.

[0112] The sample optical wavelength demultiplexing device 132s includes an input coupled to the sample light receiving channel 135 and two outputs, namely, an output coupled to the first light source branching coupler 131a (via the first sample delivery channel 133sa) and an output coupled to the second light source branching coupler 131b (via the second sample delivery channel 133sb). The reference optical wavelength demultiplexing device 132r includes an input coupled to the reference light receiving channel 136 and two outputs, namely, an output coupled to the first light source branching coupler 131a (via the first reference delivery channel 133ra) and an output coupled to the second light source branching coupler 131b (via the second reference delivery channel 133rb). The first light source branching coupler 131a is coupled to the balanced photodetector 134a (via channels 133a' and 133a'' respectively). The second light source branching coupler 131b is coupled to the balanced photodetector 134b (via channels 133b' and 133b'' respectively). Each balanced photodetector is coupled to the ADC 138 via its respective TIA (the first TIA 137a and the second TIA 137b).

[0113] The optical detection device 130 is configured to demultiplex the light related to the first light source from the light related to the second light source for the sample light and the reference light received via the sample channel 135 and the reference channel 136 respectively. Each of the first light source branching coupler 131a and the second light source branching coupler 131b is configured to combine and split the respective sample light and reference light so as to be detected by its associated balanced photodetector. The optical signals of these two channels are processed separately, for example, to provide two digital outputs, one for each of the lights from each light source.

[0114] FIG. 3D shows the optical detection device 130. The device 130 includes a sample light receiving channel 135 and a reference light receiving channel 136. The device also includes an optical branching coupler 131, a first wavelength demultiplexing device 132a, and a second wavelength demultiplexing device 132b.

[0115] The optical branching coupler 131 is coupled to a sample delivery channel 135 (for receiving sample light from both light sources) and a reference delivery channel 136 (for receiving reference light from both light sources), respectively. The optical branching coupler 131 is coupled to a first wavelength division demultiplexer 132a via a channel 133a and a second wavelength division demultiplexer 132b via a channel 133b. The first wavelength division demultiplexer 132a has two outputs, the first of which is coupled to a first photodetector of a first balanced photodetector 134a via a channel 133aa, and the second of which is coupled to a first photodetector of a second balanced photodetector 134b via a channel 133ab. The second wavelength division demultiplexer 132b has two outputs, the first of which is coupled to a second photodetector of the first balanced photodetector 134a via a channel 133ba, and the second of which is coupled to a second photodetector of the second balanced photodetector 134b via a channel 133bb. The first balanced photodetector 134a is coupled to a first TIA 137a and an ADC channel (ADC138a), respectively. The second balanced photodetector 134b is coupled to a second TIA 137b and an ADC channel (ADC138b), respectively.

[0116] The apparatus 130 is configured to provide an optical signal related to a first light source to a first digitized stream via the first balanced photodetector 134a and an optical signal related to a second light source to a second digitized stream via the second balanced photodetector 134b.

[0117] In FIGS. 3A to 3D, examples with one or two ADC channels are shown. It should be understood that when an optical delay is introduced to avoid spectral overlap related to the beat frequency, multiple combined optical signals may be digitized simultaneously using one ADC channel. When such an optical delay is not introduced, separate ADC channels may be used to provide simultaneous digitization for light from the first and second light sources.

[0118] The functions of the photodetection apparatus 130 will be described together as follows.

[0119] Each optical detection device 130 is configured to operate in the same manner as the detector described above in relation to FIG. 1. That is, each optical detection device 130 is configured to combine the sample light and the reference light in order to provide a combined optical signal that includes one or more components of the beat frequency between the sample light and the reference light. Here, the sample light includes light from the first light source 120a (e.g., light having a wavelength above the absorption wavelength such as for oxygen measurement, etc.) that has passed through the subject's brain tissue, and / or light from the second light source 120b (e.g., light having a wavelength below the absorption wavelength such as for oxygen measurement, etc.) that has passed through the subject's brain tissue. Similarly, the reference light includes light from the first light source 120a that has been transmitted along one or more reference channels, and / or light from the second light source 120b that has been transmitted along one or more reference channels. Thus, each optical detection device 130 receives light related to two different light sources (and as a result, two different wavelength ranges, one above the absorption wavelength such as for oxygen measurement, etc. and one below the absorption wavelength such as for oxygen measurement, etc.).

[0120] The iNIRS system may also include a control device configured to process the combined optical signal related to each light source, in the same manner as the one disclosed above in relation to FIG. 1. That is, the absorption coefficient and / or the scattering coefficient may be determined, as well as depth-resolved information about the subject's brain tissue (e.g., based on the distribution of the flight times of photons passing through the subject's brain tissue), and other characteristics such as an indication of blood flow.

[0121] In particular, for the light from each light source, the control device may be configured to determine absorption characteristics, for example, an absorption coefficient related to the light emitted from that light source. The control device may determine absorption coefficients in two different wavelength ranges (e.g., for light of a larger wavelength from the first light source 120a and light of a smaller wavelength from the second light source 120b). The control device may be configured to compare the absorption coefficients in the two wavelength ranges to obtain an indication of the relative concentrations of oxygenated hemoglobin and deoxygenated hemoglobin. That is, the control device may be configured to obtain a value of the blood oxygen concentration in the subject's brain tissue. As described above, the control device may be configured to provide depth-resolved information, such as a depth-resolved blood oxygen concentration level, by analyzing data related to the flight times of different photons passing through the subject's brain tissue. The control device may be configured to obtain an indication of the absolute amount of oxygen in the blood based on the oxygen concentration.

[0122] The light emitting device 120 and the light detecting device 130 may be operated to obtain an indication of the blood oxygen concentration in the subject's brain tissue by emitting and detecting light in two separate wavelength ranges (one on either side of the absorption wavelength for oxygen measurement, etc.). This function may be provided in one device, for example, rather than requiring separate components for measuring different characteristics. To reduce the requirements on the device, the iNIRS system may be configured to control the operation of the light emitting device 120 and / or the light detecting device 130 so that the blood oxygenation concentration can be measured using one detector (e.g., comprising one interferometer, one sample receiving channel 135, and one reference receiving channel 136). Similarly, each light emitting device 120 may be coupled to a plurality of different light detecting devices 130, and the light detecting device 130 may still detect the light from its light source. Therefore, 1. The light emitting device 120 may be configured to (i) time-division multiplex the sample light and the reference light, (ii) wavelength multiplex the sample light and the reference light, and / or (iii) provide different optical path lengths for the reference light from two light sources. 2. The optical detection device 130 may be configured to wavelength demultiplex the received sample light and reference light (e.g., such that the output from each photodetector represents only one of the light sources). 3. The control device (a signal processing circuit in hardware / software) may be configured to (i) consider the acquired data as being from the relevant light source based on the time-division multiplexing method, (ii) consider the data from each photodetector as being from the corresponding light source, and / or (iii) consider the data in different frequency bands as being from the corresponding light source.

[0123] For example, the iNIRS system may be configured to perform time-domain multiplexed detection. Therefore, the operations of the two light sources are temporally interleaved such that (e.g., for a selected number of wavelength sweeps) only one light source operates at a time. At this time, the output from the detector indicates either the first light source 120a or the second light source 120b depending on the time. The control device may store an instruction for the time modulation pattern of the light emitting device 120 (such as the emission start time, sweep speed, and / or an instruction for the number of sweeps for each light source until switching the operating light source, etc.). The control device may be configured to filter the output data from the optical detection device 130 such that this data is filtered according to the operation timing, and as a result, this data may be separated for each of the two light sources.

[0124] As another example, the iNIRS system may be configured to perform wavelength region multiplexed detection. Therefore, the simple light from both light sources is emitted simultaneously, and wavelength multiplexing is performed on the sample light from the two light sources. The light detection device 130 may include a sample light splitter such as a wavelength demultiplexing device configured to demultiplex on another channel based on the wavelength multiplexing method applied by the wavelength multiplexing device of the light emitting device 120 for the received light (both sample and reference). Therefore, the light detection device 130 may split the received light into two separate signal processing channels, that is, one channel for the light from each light source, and the light received from each light source may be processed separately. Accordingly, the two signal processing channels may provide independent outputs, that is, one channel for each light source, and the control device may process the output data in the two signal processing channels separately.

[0125] As a third example, the iNIRS system may be configured to provide an optical path length offset between the two light sources and the detector. Therefore, the beat frequency associated with one light source may be in a different range from the beat frequency associated with the other light source. The light detection device 130 may be configured to acquire spectral data consisting of two separate components (each component associated with a respective light source) in separable frequency ranges. The signal processing circuit and / or the control device may be configured to process the received optical signal / data output from the ADC to associate the data with the corresponding light source having two separable frequency ranges.

[0126] An example of such a delay device is shown in FIG. 4. The delay device is configured to be used in a common optical path (i.e., when light is transmitted simultaneously from both the first and second light sources). The common optical path can be made to be in the sample arm or the reference arm (or the common channel before splitting into another reference channel / sample channel).

[0127] Figure 4 shows a delay device 200 provided in a common optical channel. The delay device 200 includes an input channel 201 and an output channel 206. The input channel 201 and the output channel 206 may be the remaining portions of the common optical channel provided by the delay device 200. Further, the delay device 200 includes a wavelength demultiplexing device 202, a first channel 203, a second channel 204, and a wavelength multiplexing device 205. The wavelength demultiplexing device has an input coupled to the input channel 201 and two outputs, namely, an output coupled to the first channel 203 and an output coupled to the second channel 204. The wavelength multiplexing device has two inputs, namely, an input coupled to the first channel 203, an input coupled to the second channel 204, and an output coupled to the output channel 206. The second channel 204 includes a delay section 204d. The delay section includes an additional length of channel such that the optical path length along the first channel 203 (from the demultiplexing device 202 to the multiplexing device 205) is shorter than the optical path length along the second channel 204 (from the demultiplexing device 202 to the multiplexing device 205).

[0128] The demultiplexing device 202 is arranged to wavelength demultiplex the received light onto two separate channels. For example, the demultiplexing device 202 may be configured to demultiplex the light from the first light source onto the first channel 203 and demultiplex the light from the second light source onto the second channel 204. The multiplexing device 205 is configured to multiplex the light from the first channel 203 and the light from the second channel 204 onto a common channel (output channel 206). The delay section 204d has a length selected such that the resulting beat frequencies generated by combining the sample light and the reference light from the first light source and the second light source do not overlap spectrally, or have a minimum overlap, with each other. For example, when the light from the second light source is transmitted through the delay section 204d, the difference in the flight times of the sample light and the reference light from the second light source may be significantly different from the difference in the flight times of the sample light and the reference light from the first light source (e.g., the delay may be smaller or larger).

[0129] In FIGS. 3A through 3D, the light detection device 130 may be configured to provide an output (e.g., a digital output from an ADC), which output comprises at least one of: (i) data indicating, alternately, that the light source is the first light source 120a or the second light source 120b (e.g., this data may be separately associated with the relevant light source using information about the operating timing of the two light sources), (ii) simultaneous data for both light sources from another signal processing flow (e.g., where the data output for each signal processing flow indicates one of the light sources), and / or (iii) data that includes simultaneous data for both light sources but can be separated into two separate data streams (e.g., based on the beat frequency).

[0130] Three examples of the operation of the iNIRS system are now described with reference to the light emitting device 120 and the light detection device 130 shown in FIGS. 2A through 3D.

[0131] In a first example, the light emitting device 120 of FIG. 2A may be used in combination with the light detection device 130 of FIG. 3A.

[0132] The control device controls the operations of the first light source 120a and the second light source 120b such that their operations are arranged alternately in time. In the first period, the first light source 120a emits wavelength-swept light. This light is provided from the first light source 120a (via the common optical coupler 122) to the common optical channel 123 and is split by the common optical splitter 124 into a common sample delivery channel 125 and a common reference delivery channel 126. The reference light is transmitted along the common reference delivery channel 126 to the location where it is received by the reference light receiving channel 136. The sample light is transmitted along the common sample delivery channel 125 to the subject's brain tissue where it is scattered and received by the sample light receiving channel 135. The light detection device 130 combines the sample light and the reference light and processes this combined light. The control device processes the data acquired in this first period in order to obtain an indication of the absorption coefficient for the wavelengths relevant in the first period. This process is repeated in the second period, except for the second light source 120b that emits light. This time, the control device processes the data acquired in this second period in order to obtain an indication of the absorption coefficient for the wavelengths relevant in the second period. The control device compares the absorption coefficient related to the first period with the absorption coefficient related to the second period in order to obtain the ratio of oxygenated hemoglobin in the subject's blood to deoxygenated hemoglobin.

[0133] In a second example, the light emitting device 120 of FIG. 2B may be used in combination with the light detection device 130 of FIG. 3A.

[0134] The first light source 120a and the second light source 120b emit light simultaneously. The light from each light source is transmitted to both the common sample delivery channel 125 and the common reference delivery channel 126. The light from one light source is transmitted a longer distance to reach the common reference delivery channel 126 than the light from the other light source. The wavelength difference that occurs between the sample light and the reference light received from one light source is different from the wavelength from the other light source (because the optical path length of the reference light increases). The light detection device 130 may simultaneously acquire the absorption data instructions for both light sources, and the data for one light source is at a larger beat frequency than the data for the other light source. That is, the resulting data may include two subsets, namely, those related to the light from each light source. The control device processes this data to extract information for each light source. Then, the control device determines the absorption coefficients for the two light sources (in order to obtain blood oxygen concentration data).

[0135] In a third example, the light emitting device 120 of FIG. 2B may be used in combination with the light detection device 130 of FIG. 3C or FIG. 3D.

[0136] Similar to the second example, the first light source 120a and the second light source 120b operate simultaneously, but the reference optical path lengths can be the same. The light from each light source is wavelength multiplexed on each of the common sample delivery channel 125 and the common reference delivery channel 126. Therefore, the light from both light sources may be transmitted along these optical channels, but this light may ultimately be separated into two components using the corresponding wavelength demultiplexing method. In the light detection device 130, the sample light and the reference light are wavelength demultiplexed so that the combined optical signal is split into two components, namely, those for the light associated with each of the two light sources (e.g., as shown in FIG. 3C). Alternatively, in the light detection device 130, the sample light and the reference light are combined, and this combined optical signal is wavelength demultiplexed to be split into two components, namely, those for the light associated with each of the two light sources (e.g., as shown in FIG. 3D). The light associated with each light source is processed individually (similar to the first example), and the control device may obtain the absorption coefficient / blood oxygenation data based on the two separate outputs (associated with each light source).

[0137] Although not shown in the figures, the light emitting device of the present disclosure may utilize one or more optical amplifiers. For example, a small signal amplifier may be used. This may be based on a semiconductor gain chip (e.g., without a cavity for making a laser). The optical amplifier may be provided in the sample arm, and a small portion (e.g., 10% to 20%) of the light from the light source is provided to the amplifier for amplification, and the remainder is provided to the reference channel / detector. As another example, a high-power amplifier such as one based on a tapered amplifier design may be used. The optical amplifier may be arranged to optically amplify the light emitted from the first light source and / or the second light source (e.g., with respect to the sample light and / or the reference light).

[0138] Although not shown, the light-emitting device of the present disclosure may include a plurality of light delivery channels for delivering light from the first light source and the second light source 120b to the subject's scalp. Therefore, the light-emitting device may include an optical switch and a plurality of light delivery channels coupled to the common sample delivery channel 125. The optical switch may be used to send light from the common sample delivery channel 125 (e.g., from the first light source and / or the second light source) to each of the different sample delivery channels. The different sample delivery channels may be coupled to the subject's scalp at a plurality of different locations (e.g., the sample probes used). The optical switch may select one light delivery channel at a time, and may switch, for example, using a pattern selected when light is delivered to the subject's scalp through each of the different light delivery channels.

[0139] In the iNIRS system of the present disclosure, a plurality of light sources and / or photodetectors may be present. The iNIRS system may include a plurality of photodetection devices 130 coupled to the same light-emitting device. Each photodetector may be coupled to the same common reference delivery channel 126 (e.g., as shown in FIG. 1) of the light-emitting device to receive reference light from the first light source and the second light source (e.g., via the same common reference delivery channel 126). Thus, one light-emitting device may provide light from two light sources that is received as reference light in each of the plurality of photodetectors. The plurality of photodetectors may be dispersed around different locations on the subject's scalp (e.g., to provide information related to different regions of the subject's brain tissue). Some of the photodetectors may be grouped together on the scalp (e.g., all are arranged very close to each other in the same region of the subject's scalp). When the photodetectors are arranged very close to each other, the control device may be configured to process the combined optical signal based on data from the plurality of said detectors (e.g., based on the combined sensor outputs of those detectors). For example, the control device may average data from at least some of the different detectors to determine the characteristics of the same region of the subject's brain tissue. By comparing data from detectors in approximately the same region as the subject's scalp, the signal-to-noise ratio may be increased.

[0140] The examples described herein relate to placing an iNIRS system on a subject's scalp and performing neuro-imaging and analysis of the subject's brain using the iNIRS system. However, the iNIRS system may be used to provide imaging of any suitable subject. As described, the iNIRS system may be used to non-invasively obtain an indication of the subject's blood oxygenation level. This may be used in any suitable region of the subject's body where the blood oxygenation level is detected (e.g., on the subject's wrist or on the subject's foot). The iNIRS system may be configured to obtain the blood oxygenation level in any suitable part of the subject's body.

[0141] In the foregoing example, two light sources are used, with the first light source emitting at a wavelength above the absorption wavelength for oxygen measurement etc., and the second light source emitting at a wavelength below the absorption wavelength for oxygen measurement etc. However, this should not be considered limiting. At two different wavelengths, the absorption coefficient (and scattering coefficient) for the volume being imaged is likely to be different. This is at least partly due to the difference in the absorption characteristics between oxygenated and deoxygenated hemoglobin at different wavelengths. By using known data on these absorption characteristics, the relative contributions to the total absorption coefficient from oxygenated and deoxygenated hemoglobin respectively can be determined. From these relative contributions, the blood oxygenation level may be determined. The two different wavelengths used may be selected to be wavelengths having a distinguishable difference between the oxygenated absorption coefficient and the deoxygenated absorption coefficient. An example of such wavelengths is on both sides of the absorption wavelength for oxygen measurement etc., but this is not the only option. These wavelengths can also both be on the same side of the oxygen measurement wavelength as long as there is known data on the difference in the absorption characteristics between oxygenated and deoxygenated blood. This known data may be used by the control device to determine an indication of the blood oxygenation level based on the absorption coefficients determined for the volume with respect to the first and second light sources.

[0142] Furthermore, the blood oxygenation level may not be the only information extracted. As understood, the total absorption coefficient with respect to volume has many different contributing factors (blood oxygenation being the major one). However, additional light sources at different wavelengths may be used to extract information related to other contributing factors. For example, the additional light source may use light at different wavelengths selected based on the relevant absorption characteristics for other substances to be detected. For example, the concentration of water (e.g., at wavelengths above 1000 nm) can be detected. For example, chromophores such as cytochrome c oxidase can be detected. For example, an iNIRS system may comprise a plurality of light sources at different wavelengths, each wavelength being selected to match the major absorption signature of the substance to be detected. And the total absorption coefficient with respect to volume may be decomposed, for example, to extract information related to the individual components (e.g., blood, water, etc.) being analyzed, such as to identify the relevant contribution of each component to the overall signal (e.g., the relevant concentration of those components).

[0143] In the context of the present disclosure, it will be understood that the examples described herein are not intended to be limiting. On the contrary, the examples illustrate certain possible ways of implementing the claimed technology. For example, an iNIRS system is described using a series of optical cables that provide a plurality of channels and a probe that couples those channels to a subject's scalp. However, it will be understood that the probe itself may be part of the optical channels or that no probe may be provided at all. Similarly, the placement of the reference channels is only intended to show that the reference light is delivered from the light source to the photodetector via the optical channels (rather than through the subject's brain tissue). For example, each light source may include one reference channel for each photodetector, and the reference channel directly connects the light source to the photodetector. In that case, there may be no reference connection within the system at all. Alternatively, as shown in FIG. 1, the reference light may be transmitted over a common reference optical channel, and in this case, a portion of the reference light is taken out from the common reference optical channel to each photodetector. Also, the light sources may be arranged to deliver light to one of a plurality of different locations on the subject's scalp. For example, the light sources may each be coupled to a plurality of different sample delivery channels that extend (e.g., from an optical splitter) towards the subject's scalp.

[0144] In the examples described herein, there are two light sources, for example, two separate lasers (one for each of two different wavelength ranges). However, in other examples, such as those using time-division multiplexing for laser operation, the same light source may emit both light above the isosbestic wavelength and light below the isosbestic wavelength. In the example shown in the figures, a common reference delivery channel 126 is used that can direct reference light from both the first light source 120a and the second light source 120b towards one or more detectors. However, this, as with other examples, need not be considered limiting, and each light source may be coupled to an associated reference channel that couples to the detector corresponding to the light source. Each photodetector may be arranged to directly receive reference light from each light source and to receive sample light transmitted from each light source to the detector through the subject's brain tissue. The reference light can be transmitted along a common reference channel or along individual reference channels. Each light source may be coupled to the common reference channel via one or more other channels, for example, other reference channels (such as those shown in FIG. 2B). In FIG. 2A, a common optical coupler 122, a common optical channel 123, and a common optical splitter 124 are shown, but this splitting need not be considered limiting. For example, this functionality may be provided by an optical branching coupler, for example, as long as the optical signals split into a sample arm and a reference arm include light from one / both of the light sources.

[0145] It will be understood that it is not necessary to consider the specific arrangements shown for the signal processing circuits of the detectors to be limiting. Each optical detection device 130 is configured to combine sample light and reference light to provide a combined optical signal containing components of one or more beat frequencies and to process that combined optical signal to determine one or more characteristics of the subject's brain tissue. Any suitable signal processing circuit and / or conversion circuit can be used for this purpose. For example, a transimpedance amplifier may not be necessary (e.g., the current-voltage conversion may not be necessary by the photodetector / ADC, or it may be performed in a different way). Similarly, a balanced photodetector need not be used, and instead, one photodetector such as a photodiode can be used. Similarly, a device with an ADC shown in multiple figures need not be considered limiting. For example, a number of ADCs (e.g., one for each detector's output stream) may be used, or the output streams of all detectors may be supplied to one common ADC.

[0146] From the above considerations, it will be understood that the examples shown in the multiple figures are merely illustrative and may include features that can be generalized, removed, or replaced as described herein and as claimed. Referring to the general drawings, it will be understood that schematic functional block diagrams are used to illustrate the functions of the systems and devices described herein. Additionally, the processing functions may be provided by devices supported by electronic devices. However, it will be understood that the functions need not be divided in this way and should not be construed as suggesting a particular hardware structure other than those described and claimed below. The functions of one or more elements shown in the drawings may be further subdivided and / or distributed throughout the devices of the present disclosure. In some examples, the functions of one or more elements shown in the drawings may be integrated into one functional unit.

[0147] As will be understood by those of ordinary skill in the art in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Features of aspects of the present disclosure may be combined with any of the other aspects of the present disclosure. For example, an aspect of a method may be combined with an aspect of an apparatus, and features described with reference to the operation of a particular element of an apparatus may be provided in a method that does not use that particular type of apparatus. Also, each feature of an example is intended to be separable from the features described together, unless explicitly written that several other features are essential to its operation. Each of these separable features may, of course, be combined with any of the other features of the example in which the feature is described, or with a combination of features of any of the other examples described herein. Further, equivalents and modifications not recited above may be employed without departing from the present invention.

[0148] Particular features of the methods described herein may be implemented in hardware, and one or more functions of an apparatus may be implemented in method steps. Also, in the context of the present disclosure, it will be understood that the methods described herein need not be performed in the order described, and need not necessarily be performed in the order depicted in the drawings. Thus, aspects of the present disclosure described with reference to a product or apparatus are also intended to be implemented as a method, and vice versa. The methods described herein may be implemented in a computer program, hardware, or any combination thereof. The computer program comprises software, middleware, firmware, or any combination thereof. Such a program may be provided as a signal or network message, or may be recorded on a computer-readable medium such as a tangible computer-readable medium that can store the computer program in a non-transitory form. The hardware comprises a computer, a portable device, a programmable processor, a general-purpose processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and a logic gate array.

[0149] Any control device of the present disclosure may be implemented using fixed logic such as an assembly of logic gates, or programmable logic such as software and / or instructions of a computer program executed by a processor. The control device may include a central processing unit (CPU) connected to an image processing unit (GPU) and its associated memory, and its associated memory. Other types of programmable logic include programmable processors, programmable digital logic (e.g., field programmable gate arrays (FPGAs)), tensor processing units (TPUs), erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), application-specific integrated circuits (ASICs), or other types of digital logic, software, code, electronic instructions, flash memories, optical disks, CD-ROMs, DVD ROMs, magnetic cards, or optical cards, other types of machine-readable media suitable for storing electronic instructions, or any suitable combination thereof. In particular, any control device of the present disclosure may be provided by an ASIC.

[0150] Other examples and variations of the present disclosure will be apparent to those skilled in the art within the context of the present disclosure.

Claims

1. A first light source configured to emit light that passes through multiple different wavelengths by wavelength sweeping within a first wavelength range, A second light source is configured to emit light passing through multiple different wavelengths by wavelength sweeping in a second wavelength range different from the first wavelength range, A common sample distribution channel is coupled to the first light source and the second light source, respectively, in order to receive light from the first light source and the second light source and deliver the light to the subject. A set of reference channels that receive reference light from the first light source and the second light source, A light-emitting device equipped with, A photodetector including an interferometric photodetector, A control device configured to request an instruction for the depth-resolved blood oxygen concentration of the subject, It has, The interference photodetector is coupled to one or more reference channels that receive the reference light from the first light source and the second light source, The photodetector is arranged to be coupled with the subject so that the interferometric photodetector receives sample light, including light transmitted along the common sample delivery channel from the first light source and the second light source. The interference photodetector is configured to provide coupled optical signals each containing one or more components of the beat frequency between the sample light and the reference light, by (i) coupling the sample light from the first light source with the reference light from the first light source, and (ii) coupling the sample light from the second light source with the reference light from the second light source. The above instruction is based on the absorption coefficients related to the different optical path lengths of the sample light from the first light source and the second light source, The different optical path lengths are determined based on the beat frequencies present in the coupled optical signals associated with them. An interferometric near-infrared spectroscopy (iNIRS) system characterized by the following features.

2. The control device is configured to determine the indication of blood oxygen concentration based on blood absorption data showing the relative absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin at light wavelengths in the first wavelength range and the second wavelength range. The iNIRS system according to claim 1.

3. The control device is configured to request instructions for the blood flow index of the subject for each of the first and second wavelength ranges. The iNIRS system according to claim 1 or 2.

4. The control device is configured to determine the total tissue oxygenation metabolism of the subject based on the determined blood flow index and the subject's blood oxygenation concentration. The iNIRS system according to claim 3.

5. The first wavelength range is, Wavelengths above the absorption wavelength for oxygen measurement, etc. Includes, The second wavelength range is, Wavelengths below the absorption wavelength for oxygen measurement, including, The iNIRS system according to claim 1.

6. The iNIRS system is Multiple interferometric photodetectors, Equipped with, Each of the aforementioned interferometric photodetectors is coupled to one or more of the reference channels that receive the reference light from the first light source and the second light source, and is arranged to receive the sample light from the subject. The iNIRS system according to claim 1.

7. The light-emitting device is An optical coupler is arranged to couple the light from the first light source and the second light source on a common optical channel. Equipped with, The iNIRS system according to claim 1.

8. The aforementioned common optical channel is coupled with the common sample distribution channel, or the aforementioned common optical channel is the common sample distribution channel. Optionally, the optical coupler is: Wavelength division multiplexing device and / or polarizing beam splitter, Equipped with, The iNIRS system according to claim 7.

9. The light-emitting device is An optical splitter is arranged to split the light from the first light source and / or the second light source between the common sample distribution channel and one or more of the reference channels. Equipped with, The iNIRS system according to claim 1.

10. The light-emitting device is A first optical splitter is arranged to split the light from the first light source into a first sample distribution channel and a first reference distribution channel, A second optical splitter is arranged to split the light from the second light source into a second sample distribution channel and a second reference distribution channel, A sample common optical coupler is arranged to couple light from the first sample distribution channel and light from the second sample distribution channel on the common sample distribution channel, Equipped with, Optionally, the light-emitting device is A reference common optical coupler is arranged to couple the light from the first reference distribution channel and the light from the second reference distribution channel over a common reference distribution channel. Equipped with, Optionally, the interferometric photodetector is coupled to the common reference channel to receive the reference light from the common reference channel. The iNIRS system according to claim 1.

11. The light-emitting device is A common optical coupler is arranged to combine the light from the first light source and the light from the second light source, and optionally arranged to combine the first light source and the second light source with a common optical channel. A common optical splitter coupled to the common optical coupler and configured to split the light received from the common optical coupler into the common sample distribution channel and the common reference channel, wherein the common optical channel is optionally configured to couple the common optical channel with the common sample distribution channel and the common reference channel, Equipped with, The iNIRS system according to claim 1.

12. The light-emitting device is configured to time-division multiplex the emission of light from the first light source and the second light source. The light-emitting device is configured to wavelength-division multiplex the emission of light from the first light source and the second light source, and / or (i) The difference between the expected optical path length of the sample light from the first light source transmitted to the interferometric photodetector and (ii) the optical path length of the reference light from the first light source transmitted to the interferometric photodetector is different from the difference between (iii) the expected optical path length of the sample light from the second light source transmitted to the interferometric photodetector and (iv) the optical path length of the reference light from the second light source transmitted to the interferometric photodetector, in order to suppress spectral overlap between the beat frequency associated with the first light source and the beat frequency associated with the second light source. At least one of the following: The iNIRS system according to claim 1.

13. The light-emitting device is wavelength division multiplexer, Equipped with, The aforementioned light detection device is wavelength division demultiplexer, Equipped with, The light-emitting device is configured to emit light from both the first light source and the second light source by wavelength multiplexing, The light detection device is configured to demultiplex the coupled optical signals such that the coupled optical signals associated with the first light source are processed separately from the coupled optical signals associated with the second light source. The iNIRS system according to claim 1.

14. Each of the aforementioned light sources is A related optical amplifier for increasing the output of the light emitted from the light source, Equipped with, The iNIRS system according to claim 1.

15. Multiple optical distribution channels, An optical switch configured to selectively send light from the first light source and the second light source to each of the plurality of optical distribution channels, Having, The iNIRS system according to claim 1.

16. The iNIRS system is configured to provide wavelength-dependent delay in one of the common sample channel and the common reference channel. The iNIRS system according to claim 1.

17. A step of operating a first light source configured to emit light that passes through multiple different wavelengths by wavelength sweeping within a first wavelength range, A step of operating a second light source configured to emit light passing through multiple wavelengths by wavelength sweeping in a second wavelength range different from the first wavelength range, A step of sending light from the first light source and the second light source to a common sample distribution channel and sending the light towards the subject, A step of sending reference light from the first light source and the second light source to one or more reference channels, In an interferometric photodetector, the steps include: (i) coupling sample light from a first light source with reference light from the first light source; and (ii) coupling sample light from a second light source with reference light from the second light source, wherein the reference light is received from one or more reference channels, and the sample light, which includes light delivered to the subject through a common sample distribution channel, is received from the subject, in order to provide each coupled optical signal containing one or more components of the beat frequency between the sample light and the reference light; A step of using a control device to obtain an indication of the depth-resolved blood oxygen concentration of the subject, wherein the indication is determined based on the absorption coefficients associated with different optical path lengths of the sample light from the first light source and the second light source, and the different optical path lengths are determined based on the beat frequencies present in the coupled optical signals associated therewith. including, Interferometric near-infrared spectroscopy (iNIRS) characterized by the following features.

18. Computer program instructions for programming a processor to control the operation of an interferometric near-infrared spectroscopy system in order to carry out the method described in claim 17, including, A computer program product characterized by the following features.

Images