Interference near infrared spectroscopy system and method

Abstract

Aspects of the present disclosure provide an interferometric near infrared spectroscopy iNIRS system, the system comprising: a light emitting arrangement comprising: a first light source for providing wavelength-scanned light emission by a plurality of different wavelengths in a first wavelength range; a second light source for providing wavelength-scanned light emission through a plurality of different wavelengths in a second wavelength range different from the first wavelength range; a common sample delivery channel coupled to each of the first light source and the second light source to receive light from the first light source and the second light source and deliver the light to an object; the one or more reference channels are used for receiving reference light from the first light source and / or the second light source; a light detection arrangement comprising an interference optical detector; wherein the optical detector is coupled to one or more reference channels for receiving reference light from the first light source and the second light source; wherein the light detection arrangement is arranged to be coupled to an object such that the optical detector receives sample light from the first light source and the second light source, the sample light comprising light propagating along a common sample delivery channel; wherein the optical detector is arranged to combine the sample light with the reference light to provide a combined light signal comprising one or more components of a beat frequency between the sample light and the reference light; and wherein the iNIRS system is used to process the combined light signal to provide imaging and analysis of the object.

Description

Technical Field

[0001] The present disclosure relates to the field of imaging and analysis. In particular, the present disclosure relates to interferometric near infrared spectroscopy (iNIRS) systems and methods for imaging and analysis. Background Art

[0002] Near infrared spectroscopy (NIRS) is a spectroscopic method that uses the near infrared region of the electromagnetic spectrum (e.g., between 780 and 2500 nm). NIRS systems can be used to provide non-invasive monitoring of the scattering and absorption properties of a medium. Radiation at NIRS wavelengths is less easily absorbed by human skin (and bone) than visible light, so NIRS radiation can penetrate the skin and skull and penetrate into brain tissue. NIRS can be used as a technique for non-invasive imaging of human brain tissue by monitoring the scattering and absorption properties of NIRS radiation within the brain tissue.

[0003] It would be desirable to provide improved techniques for imaging and analysis. Summary of the invention

[0004] Various aspects of the disclosure are listed in the independent claims, and optional features are listed in the dependent claims. Various aspects of the disclosure may be provided in combination with each other, and features of one aspect may be applied to other aspects.

[0005] In one aspect, an interferometric near infrared spectroscopy (iNIRS) system (e.g., for neuroimaging and analysis) is provided, comprising: a light emitting arrangement, comprising: a first light source for providing wavelength-scanned light emission at a plurality of different wavelengths in a first wavelength range (e.g., above an absorption wavelength such as oximetry); a second light source for providing wavelength-scanned light emission at a plurality of different wavelengths in a second wavelength range different from the first wavelength range (e.g., below an absorption wavelength such as oximetry); a common sample delivery channel coupled to each of the first and second light sources to receive light from the first and second light sources and deliver the light to a subject (e.g., toward their scalp); and one or more reference channels for receiving reference light from the first and / or second light sources; a light detection arrangement, comprising an interferometric optical detector. The optical detector is coupled to the one or more reference channels for receiving reference light from the first and second light sources. The light detection arrangement is arranged to be coupled to the subject (e.g., to their scalp) so that the optical detector receives sample light from the first and second light sources, the sample light comprising light propagating along the common sample delivery channel (e.g., delivered to the subject, such as to their brain tissue). The optical detector is arranged to combine the sample light with the reference light to provide a combined light signal, the combined light signal including one or more components of a beat frequency between the sample light and the reference light. The iNIRS system is used to process the combined light signal to provide imaging and analysis (e.g., of a subject's brain).

[0006] Embodiments may enable a single light emitting arrangement to provide light emission in two independent wavelength ranges, wherein light from each light source is emitted via at least one common optical channel (e.g., wherein light from two light sources is emitted along the same optical channel). Embodiments may enable a single light detecting arrangement to receive sample light and reference light from two independent light sources via one or more common optical channels. Using light in a wavelength range on either side of an absorption wavelength such as oximetry may enable determination of blood oxygen concentration of brain tissue of a subject.

[0007] Each light source can be arranged to emit a series of pulses, each pulse comprising at least one scan through a plurality of different wavelengths. Each light source can be used to linearly scan a plurality of different wavelengths. When the light from each light source propagates from the light source to the scalp of the subject, it can propagate along at least one common optical path (e.g., a single optical channel). In other words, the common sample delivery channel can include a channel along which (i) the light from the first light source and (ii) the light from the second light source can both propagate when directed to the scalp of the subject, i.e., the channel is common (used) by the light of the two light sources. The iNIRS system can include a plurality of interferometric optical detectors. Each detector can be coupled to one or more reference channels for receiving reference light from the first light source and the second light source. Each optical detector can be arranged to receive sample light from the brain tissue of the subject.

[0008] The light emitting arrangement may include a light combiner arranged to combine light from each of the first light source and the second light source onto a common light channel (e.g., such that light from the two light sources will propagate along the same common light channel). The common light channel may be coupled to a common sample delivery channel, or the common light channel may be a common sample delivery channel. For example, light emitted from each light source may propagate along the same section of the light channel when propagating toward the scalp of the subject. The light combiner may include a wavelength division multiplexer. The light emitting arrangement may include an optical splitter arranged to split light from the first light source and / or the second light source between the common sample delivery channel and one or more reference channels.

[0009] The light emitting arrangement may include: a first optical splitter arranged to split light from a first light source to a first sample delivery channel and a first reference delivery channel; a second optical splitter arranged to split light from a second light source to a second sample delivery channel and a second reference delivery channel; and a sample common light combiner arranged to combine light from the first sample delivery channel and light from the second sample delivery channel to a common sample delivery channel. The light emitting arrangement may also include a reference common light combiner arranged to combine light from the first reference delivery channel and light from the second reference delivery channel to a common reference delivery channel. An optical detector may be coupled to a common reference channel for receiving reference light from the common reference channel. The length of the first reference delivery channel may be different from that of the second reference delivery channel. The light emitting arrangement may comprise: a common light combiner arranged to combine light from a first light source and a second light source, optionally wherein the common light combiner is arranged to couple the first light source and the second light source to a common light channel; and a common light splitter coupled to the common light combiner and arranged to split light received from the common light combiner onto a common sample delivery channel and a common reference channel, optionally wherein the common light splitter is arranged to couple the common light channel to a common sample delivery channel and a common reference channel.

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

[0011] The controller may be configured to determine an indication of a depth resolved scattering coefficient and / or absorption coefficient of brain tissue of the subject based on the determined scattering coefficient and absorption coefficient associated with different optical path lengths. The controller may be configured to determine an indication of a depth resolved blood oxygen concentration of brain tissue of the subject based on the determined depth resolved absorption coefficient. The controller may be configured to determine an indication of a blood flow index of the subject for each of the first wavelength range and the second wavelength range. The controller may be configured to determine an indication of a total tissue oxygenation metabolism of the subject based on the determined blood flow index and blood oxygenation concentration of the subject.

[0012] The light emitting arrangement can be used to provide time division multiplexing for the emission of light from the first light source and the second light source. The system can be used to provide time division multiplexing for the operation of the first light source and the second light source, so that the operation of the first light source is temporally interleaved with the operation of the second light source. The light emitting arrangement can be used to provide wavelength division multiplexing for the emission of light from the first light source and the second light source. The optical path length of the reference light propagating from the first light source to the optical detector can be different from the optical path length of the reference light propagating from the second light source to the optical detector, so that the beat frequency associated with the first light source can be separated from the beat frequency associated with the second light source. The difference in the optical path length of the reference light from the first light source and the second light source can be selected so that there is no spectral overlap or the spectral overlap is minimized between: (i) the beat frequency of the sample light and the reference light from the first light source, and (ii) the beat frequency of 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 to the optical detector and (ii) the optical path length of the reference light from the first light source to the optical detector may be different from the difference between (iii) the expected optical path length of the sample light from the second light source to the optical detector and (iv) the optical path length of the reference light from the second light source to the optical detector to suppress spectral overlap between beat frequencies associated with the first light source and 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 arrangement may include a wavelength division multiplexer, and the light detecting arrangement includes a wavelength division multiplexer. The light emitting arrangement may be used to provide emission of light from a first light source and light from a second light source, wherein the emission is wavelength multiplexed. The light detecting arrangement may be used to wavelength demultiplex a combined light signal, such that a combined light signal associated with the first light source and a combined light signal associated with the second light source are processed separately. The optical detector may include a detection light splitter, which is arranged to split: (i) light from the first light source onto a first detection channel, and (ii) light from the second light source onto a second detection channel. The detection light splitter may be arranged to provide: (i) a first combined light signal to the first detection channel, the first combined light signal including one or more components of a beat frequency between a sample light and a reference light from the first light source, and (ii) a second combined light signal to the second detection channel, the second combined light signal including one or more components of a beat frequency between a sample light and a reference light from the second light source. The light detecting arrangement may include a signal processing circuit for processing the first combined light signal and the second combined light signal, respectively.

[0014] Each light source may have an associated optical amplifier to increase the output power of light emitted from the light source. The iNIRS system may include a plurality of light delivery channels and an optical switch for selectively directing light from the first light source and the second light source to each of the plurality of light delivery channels. The light emitting arrangement may include at least one common optical channel comprising a single channel coupled (e.g., directly or indirectly) to each of the first light source and the second light source to receive light therefrom. The light delivered to the scalp of the subject from the two light sources may propagate along the same single channel. Similarly, reference light from the two light sources may propagate along at least one common optical channel to one or more detectors.

[0015] In one aspect, an interferometric near-infrared spectroscopy (iNIRS) method (e.g., for neural imaging and analysis) is provided, comprising: operating a first light source to provide wavelength-swept light emissions through a plurality of different wavelengths in a first wavelength range (e.g., above an absorption wavelength such as oximetry); operating a second light source to provide wavelength-swept light emissions through a plurality of different wavelengths in a second wavelength range different from the first wavelength range (e.g., below an absorption wavelength such as oximetry); directing light from each of the first and second light sources to a common sample delivery channel and toward a subject (e.g., toward their scalp); directing reference light from the first and / or second light sources to one or more reference channels; combining reference light received from the one or more reference channels with sample light received from the subject (e.g., from their brain tissue) at an interferometric optical detector to provide a combined light signal, the sample light comprising light delivered to the subject (e.g., to their brain tissue) through the common sample delivery channel, the combined light signal comprising one or more components of a beat frequency between the sample light and the reference light; and processing the combined light signal to provide imaging and analysis (e.g., of the subject's brain).

[0016] Aspects of the present disclosure include one or more computer program products comprising 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 iNIRS systems and methods for neuroimaging and analysis of brain tissue of a subject. Compared to the above-mentioned fNIRS technology, the iNIRS system and method of the present disclosure involve a completely different method for performing neuroimaging and analysis. Embodiments may provide improved methods for performing iNIRS neuroimaging and analysis. As disclosed herein, the iNIRS system of the present disclosure includes two light sources and one or more light detectors. The iNIRS system of the present disclosure may also include a controller arranged to receive output signals from one or more light detectors.

[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 arrangement coupled to the light generating element. The optical arrangement of each light source may be used to deliver the generated light from the light generating element to each of one or more different locations. The optical arrangement of each light source may be arranged to direct some of the light from the light generating element toward the area to be sampled. The optical arrangement of each light source may be arranged to direct some of the light to each light detector. The optical arrangement 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 used to transmit light along the length of the channel (e.g., from the light generating element to the scalp of the subject or the light detector). The optical arrangement of each light source may include an optical splitter for splitting light to each of the different delivery light channels.

[0019] The iNIRS system can be arranged so that when mounted on the head of a subject (e.g., for providing neuroimaging and analysis of the subject's brain tissue), the optical arrangement of each light source is used to direct some light toward the subject's scalp. For example, the optical arrangement of each light source may include a sample delivery channel (e.g., operable to direct sample light toward the subject's scalp). The iNIRS system can be arranged so that when in use, the optical arrangement of each light source can direct some light directly to a light detector (e.g., for combination with sample light from the subject's brain tissue). For example, the optical arrangement of each light source may include a reference delivery channel (e.g., operable to direct reference light to one or more of the light detectors). The optical arrangement of each light source can be used to deliver light from a light generating element to each light channel. The optical arrangement of each light source can be used to deliver: (i) light to a sample light delivery channel (sample light), and (ii) light to a reference delivery channel (reference light). For example, the optical arrangement of each light source may include an optical splitter for splitting light received from a light generating element into each of the different channels.

[0020] The iNIRS system can be arranged so that in use, when mounted on the brain tissue of the subject, the sample light can be directed toward the scalp and brain tissue of the subject (e.g., through the sample delivery channel), and the reference light can be directed toward each light detector (e.g., through the reference delivery channel). Each light source can be arranged to provide wavelength-scanned light emission (e.g., each light source can be arranged to output light of each of a plurality of different wavelengths over a selected time period). For example, each light source can include an adjustment element for controlling the operation of the light generating element to output light of each of a plurality of different wavelengths. Each light source can be arranged to scan the wavelength of the light output by the light source (e.g., increase or decrease the wavelength). Each light source can be arranged to provide chirped light emission, wherein each chirp (or pulse) comprises a wavelength scan. Each light source can be arranged to output continuous chirps having the same wavelength scan, for example, such that the wavelength of the light output from the light source varies according to a repeating pattern.

[0021] Each photodetector may provide an interferometric optical detector. Each photodetector may include an optical arrangement. The optical arrangement of the photodetector is used to guide the light to be detected (e.g., from the scalp of the subject) into the photodetector. The optical arrangement 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] The iNIRS system can be arranged such that when mounted on the head of a subject (e.g., for providing neuroimaging and analysis of brain tissue of the subject), the optical arrangement of the light detectors is used to receive light emitted from the light sources (e.g., that has passed from the light sources through the brain tissue of the subject). For example, the optical arrangement of the light detectors can include a sample receiving channel (e.g., operable to receive sample light from each light source that has passed through the brain tissue of the subject). The iNIRS system can be arranged such that, in use, the optical arrangement of the light detectors can receive some of the light from each light source that has propagated directly from the light source (e.g., has propagated along the light channel). For example, the optical arrangement of the light detectors can include a reference receiving channel (e.g., operable to receive reference light from one or more light sources). Each light detector can be coupled to each light source such that a reference delivery channel of the light source is coupled to a reference receiving channel of the light detector (e.g., such that reference light can propagate from the light generating element to the light detector via the reference delivery channel and the reference receiving channel).

[0023] The optical arrangement of the light detector can be used to deliver to the light detector: (i) light from a sample light receiving channel (sample light), and (ii) light from a reference receiving channel (reference light). For example, in use, the detector is arranged to receive: (i) sample light from each light source that has passed through the brain tissue of the subject, and (ii) reference light from each light source that has propagated along one or more reference channels to the light detector.

[0024] The photodetector may be arranged to combine the reference light with the sample light to provide a combined light signal. For example, the photodetector may include an optical combiner (e.g., for combining light on a reference receiving channel with light on a sample receiving channel). The combined light signal may include multiple components of a beat frequency (e.g., a frequency corresponding to the wavelength difference between the sample light and the reference light). Each photodetector is used to convert the received combined light signal into one or more electrical signals indicating the combined light signal. For example, the detector may include one or more photodiodes. Each photodiode may output an electrical signal (e.g., a current) indicating the combined light signal. The detector may include a balanced photodetector (e.g., including two photodiodes, the two photodiodes may be 180° out of phase, and the output of the balanced photodetector may be a combination of the current outputs of the two photodiodes). The detector may optionally include a current to voltage conversion circuit and / or one or more amplifiers for amplifying the electrical signal.

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

[0026] The controller can be used to process the digital signals to obtain time-of-flight information for the photons of sample light that propagate from each light source through the brain tissue of the subject to the light detector. The controller can be used to identify the penetration depths associated with the different flight times of the sample light photons (and optionally, the expected trajectories of the photons through the brain tissue). The controller can be used to obtain a time-ordered sequence of the flight time distributions of the sample light photons that arrive at each light detector. The controller can be used to process the time-ordered sequence to identify changes in the flight time distributions over time, such as identifying attenuation and / or decay rates between successful flight time distributions. The controller can be used, for example, to provide depth-resolved processing 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 at (one or more) penetration depths associated with the flight time range). The controller can be used to process the data received from the light detector to provide depth-resolved autocorrelated time-of-flight information of the brain tissue of the subject.

[0027] The controller can be used to process received data indicating sample light received at the light detector, and output a control signal based on the received data. The control signal can provide an indication of a time-of-flight distribution (e.g., the controller can be used to output a time-of-flight distribution). The control signal can provide an indication of one or more characteristics determined based on the time-of-flight distribution, such as an indication of the optical properties of brain tissue (e.g., scattering coefficient and / or absorption coefficient, and / or how these optical properties have changed / are changing). The control signal can provide an indication of blood flow within the brain tissue of the subject. The control signal can provide a depth-resolved indication of one or more characteristics of the brain tissue of the subject (e.g., related to a specific area within the brain tissue of the subject, such as within a selected penetration depth range). The control signal can include one or more characteristics of the brain tissue of the subject, such as an indication of intracranial pressure, blood flow index, arterial elasticity, brain oxygen metabolic rate. Medical characteristics can be associated with a specific area / depth within the brain tissue of the subject. The control signal can include an actuation command for a brain-computer interface, for example, to control the operation of the device based on the actuation command. The control signal can include an image for display, wherein the image represents a portion of the brain tissue of the subject (determined based on the received sample light). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Some examples of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0029] Figure 1 A schematic diagram of the iNIRS system is shown.

[0030] Figure 2a and Figure 2b A schematic diagram of an arrangement for delivering light to a sample delivery channel and a reference delivery channel is shown.

[0031] Figure 3a , Figure 3b , Figure 3c and Figure 3d A schematic diagram of an arrangement for receiving light at a detector from a sample receiving channel and a reference receiving channel is shown.

[0032] Figure 4 An example delay arrangement for a common optical channel is shown.

[0033] In the drawings, the same reference numerals are used to denote the same elements. DETAILED DESCRIPTION

[0034] Embodiments of the present disclosure relate to systems and methods for non-invasively determining an indication of blood oxygenation within a subject's brain tissue. An interferometric near infrared spectroscopy (iNIRS) system is used, the system comprising a first light source and a second light source. One of the light sources emits light at a wavelength higher than an isoabsorption wavelength for oximetry, and the other of the light sources emits light at a wavelength lower than an isoabsorption wavelength for oximetry. Each light source will provide a wavelength scanning emission. The iNIRS system also includes one or more photodetectors, wherein each photodetector is arranged to receive sample light and reference light from the two light sources. Each photodetector interferometrically combines the sample light and the reference light from each of the two light sources to provide a combined light signal including a component of one or more beat frequencies between the sample light and the reference light. A scattering coefficient and / or an absorption coefficient can be determined based on the combined light signal. The blood oxygenation level of the subject's brain tissue can be determined based on the absorption difference between the light from the two different light sources. The depth-resolved blood oxygenation level can be determined by monitoring the coefficients of photons associated with different beat frequencies (and therefore different photon flight times / penetration depths).

[0035] Interferometric Near-Infrared Spectroscopy (iNIRS)

[0036] Figure 1 A schematic diagram of an interferometric near infrared spectroscopy (iNIRS) system 10 is shown. The iNIRS system 10 includes a light source 20, a plurality of light detectors 30, and a controller 40. Figure 1 Inset A of FIG. 4 shows a more detailed view of one of the light detectors 30 .

[0037] The iNIRS system 10 includes a light source modulator 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 coupled to a subject's head 2. The iNIRS system 10 includes a sample delivery probe 25a and a plurality of sample receiving probes 35a. Each light detector 30 has an associated sample receiving probe 35a, a sample receiving channel 35, a reference delivery channel connection 28, and a reference receiving channel 36.

[0038] The light source regulator 22 may include a source for providing a variable electrical control signal (eg, a variable current or voltage provider). The light source regulator 22 is coupled to the light source 20. The light source regulator 22 may be electrically connected to the light source 20 to provide a variable current / voltage to the light source 20.

[0039] 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 an optical splitter 24. The optical splitter 24 has an input end for receiving light from the light source 20. The optical splitter 24 has two output ends for transmitting the light from the light source 20 to two independent channels. A sample delivery channel 25 is coupled to the optical splitter 24 (to receive light from the optical splitter 24), and a 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 a sample delivery probe 25a. The sample delivery probe 25a is to be placed at a position on the scalp of the subject.

[0040] Other types of suitable lasers include distributed Bragg reflector lasers (DBR), Fourier domain mode locking lasers (FDML), vertical cavity surface-emitting lasers (VCSEL). Additionally or alternatively, a pulsed supercontinuum laser can be used in combination with a pulse stretching mechanism (e.g., a grating or GRISM pulse stretcher or a length of dispersive fiber). For example, such an arrangement can be used to temporally separate the wavelengths in the pulses so that frequency chirped pulses are produced (e.g., for ultimately providing an interference pattern when comparing a sample pulse to a reference pulse).

[0041] The reference delivery channel 26 couples the optical splitter 24 to each of the photodetectors 30. For each detector, a reference delivery connection 28 couples the reference delivery channel 26 to a reference receiving channel 36 of that detector. Each reference receiving channel 36 is coupled to a photodetector 30 of that reference receiving 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 receiving probe 35a is placed on the scalp of the subject. Each sample receiving probe 35a is coupled to a sample receiving channel 35. Each sample receiving channel 35 is coupled to a photodetector 30 of that sample receiving channel. Each photodetector 30 is connected to receive sample light from the light source 20 (via a sample delivery channel and a sample receiving channel, and via brain tissue of the subject between the sample delivery channel and the sample receiving channel).

[0042] There are a plurality of different photodetectors 30. Each detector may include an interferometer, such as a Mach-Zehnder interferometer. Each of the different photodetectors 30 is coupled to the same light source 20 (via one or more reference channels). The photodetectors 30 are spatially separated from the light source 20. The photodetectors 30 may also be spatially separated from each other, or they may be co-located on sufficiently similar tissue regions so that the received signals can be averaged together. In order for reference light to reach the photodetectors 30 from the light source 20, the reference light will propagate directly along one or more reference channels. In order for sample light to reach the photodetectors 30 from the light source 20, the sample light will propagate indirectly via the subject's brain tissue. The sample light is delivered to the subject's scalp via one or more delivery channels. The sample light may then pass through the subject's brain tissue, be received via one or more sample receiving channels 35, and be transmitted to the photodetectors 30. Thus, illumination of the subject's brain tissue may use a different light channel than detection of light from the subject's brain tissue.

[0043] The controller 40 may include any suitable component having data receiving and processing functions. For example, the controller 40 may include at least one application specific integrated circuit (ASIC). Other examples of the controller 40 may include a field programmable gate array (FPGA) and / or a data acquisition module (DAQ). The controller 40 is coupled to each detector. The controller 40 may be connected to each detector via a wired connection (for receiving an electrical signal indicating detection from the detector), and / or the connection may be wireless (for receiving transmission data indicating detection from the detector). The controller 40 is coupled to the light source regulator 22. The connection may be wired or wireless.

[0044] The iNIRS system 10 can be at least partially mounted in a garment on the subject's head 2. For example, the iNIRS system 10 can be disposed in a hat / cap worn by the subject on his head 2. The head garment can be arranged to hold the light source 20 and the detector in a fixed arrangement relative to the subject's scalp. Some or all of the above components can be provided with the head garment. For example, the head garment can include a plurality of housing portions for housing the light source 20 and the light detector 30. The channels connecting the light source and the light detector 30 can be provided as part of the head garment (e.g., they can be wired through corresponding channel housing portions of the head garment). The controller 40 can be separate from the head garment (e.g., wirelessly connected), or the controller 40 can also be provided as part of the head garment (e.g., provided by an ASIC in the head garment, which can be wired to the detector and / or light source modulator 22). For example, the garment can be used to house the source channel and the detection channel and the probe, while the other components of the system are located elsewhere.

[0045] 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 a fiber-optic splitter. The iNIRS system 10 may include lenses, reflection and / or refraction devices for beam steering, as appropriate. For example, the sample delivery probe 25a may include one or more lenses for spreading sample light from the sample delivery channel 25 onto the brain tissue space of the subject. As another example, one or more of the sample receiving probes 35a may include a lens for focusing the received light into the sample receiving channel 35 connected to the sample receiving probe 35a. As another example, the probe may be a bare fiber that has been cut and / or polished.

[0046] The iNIRS system 10 is arranged to provide a plurality of source-detector pairs for each light source 20. In other words, the iNIRS system 10 is arranged so that each light detector 30 can receive two forms of light: (i) reference light, and (ii) sample light. Each detector is arranged to receive reference light directly from the light source 20 (the reference light will, for example, propagate along one or more pathways from the light source 20 to the light detector 30 without passing through the subject's brain tissue). Each detector is also arranged to receive sample light indirectly from the light source 20 (the sample light will have been directed toward the subject's scalp tissue, and a portion of the sample light may have passed through the subject's brain tissue on the way to the detector, for example, the sample light will not have only passed through the optical pathway between the light source 20 and the light detector 30).

[0047] The detectors 30 are arranged to be placed on the scalp of the subject to provide imaging of a selected region of the subject's brain. At least some of the detectors 30 are arranged to be spatially separated from the light source 20. One or more (e.g., each) of the light detectors 30 can be arranged to be sufficiently spaced apart from the light source 20 so that at least some of the photons of the sample light from the light source 20 received at the light detector 30 will have penetrated into the brain tissue of the subject. For example, the source-detector spacing can be selected so that the light detector 30 is arranged to receive sample light photons that have undergone multiple scattering events (e.g., have been scattered multiple times between the source and the detector as they pass through the subject's head 2). In other words, the source-detector spacing can be selected so that the light detector 30 receives deep penetrating photons from the subject's brain tissue. Such photons can have a longer flight time from the source to the detector than photons that penetrate more shallowly and experience fewer scattering events.

[0048] Detectors 30 may be arranged to be spatially close to each other on the subject's scalp. The arrangement of detectors 30 may be selected so that the detectors image similar areas of the subject's brain. For example, detectors 30 may be located within a threshold distance of each other on the subject's scalp so that the data they acquire may be averaged (e.g., to provide an average value for the same volume of the subject's brain). That is, detectors 30 may be arranged to spatially probe the same volume of tissue within the subject's brain. For example, the detectors may be arranged to be within an attenuation length of each other's tissue (e.g., within the sum of the absorption coefficient and the scattering coefficient).

[0049] The light source 20 is arranged to generate light and direct the light (via a reference channel) toward the subject's scalp and the light detector 30. The optical splitter 24 is arranged to receive the light generated by the light source 20 and split the light into two channels: (i) toward the subject's scalp using a sample delivery channel 25 and a sample delivery probe 25a, and (ii) to the light detector 30 using a reference delivery channel 26 and a reference receiving channel 36. The splitter is used so that most of the light is directed toward the subject's scalp. For example, the splitter can be a 90:10 splitter or a 99:1 splitter. The sample delivery channel 25 is arranged to receive sample light from the splitter and deliver the sample light (via a sample delivery probe 25a) to the subject's scalp. The reference delivery channel 26 is arranged to receive reference light from the splitter and deliver the sample light (via a reference receiving channel 36) to the detector.

[0050] Each reference delivery connection 28 is arranged to deliver some reference light propagating along the reference delivery channel 26 to one of the reference receiving channels 36. Each reference receiving channel 36 is arranged to deliver reference light to a light detector 30 for the reference light. The sample receiving probe 35a is arranged to receive sample light from the brain tissue of the subject. The sample receiving probe 35a can focus the received sample light onto the sample receiving channel 35. The sample receiving channel 35 is arranged to deliver the received sample light to the light detector 30 for the sample light. The sample receiving probes 35a can be arranged on the scalp of the subject close to each other.

[0051] Each detector is arranged to receive two inputs: (i) reference light directly from the light source 20, and (ii) sample light indirectly from the light source 20 (e.g., having passed through the subject's brain tissue and through the subject's scalp skin and skull). For example, each detector may include two or more input ports. A first input port of the detector may be coupled to a reference delivery channel 26 of the detector. A second input port of the detector may be coupled to a sample delivery channel 25 of the detector. The detector (as an interferometer) is arranged to combine the reference light with the sample light. The detector and controller 40 are arranged to determine one or more characteristics of the subject's brain tissue based on the combination of the reference light and the sample light (described in more detail below).

[0052] The light source 20 is used to provide wavelength-scanned light emission. To this end, the light source 20 can be used to generate a series of light pulses for emission. During each pulse, the wavelength of the light can be "scanned" within a certain wavelength range. For example, the scan can be in the form of a chirped pulse. The light will be emitted at multiple different wavelengths during one pulse. For example, the wavelength can increase or decrease continuously during one pulse (the rate of change of the wavelength can be constant or variable). A series of chirped pulses can be continuous (for example, the time interval between pulses is zero). The light source 20 can be used to continuously emit a series of pulses, each of which has a wavelength scan. However, it should be understood that the light source 20 does not need to provide continuous scanning. For example, the light source can be tuned in steps rather than continuously, so that the light source 20 emits light of different wavelengths at different time intervals (for example, each of the multiple wavelengths is emitted at discrete time intervals). The light source 20 can scan unidirectionally (for example, only increase or decrease the wavelength during a wavelength scan) or bidirectionally (for example, increase and decrease the wavelength during a wavelength scan).

[0053] The controller 40 may be used to selectively control the wavelength scanning of the light source 20. The light source modifier 22 is arranged to control the wavelength emission of 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 scanning 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 controller 40 may be arranged to control the application of current / voltage to the light source 20 using the light source modifier 22 to provide a selected pattern for the wavelength of light emitted by the light source 20.

[0054] The light source 20 can be controlled to perform wavelength scanning according to a selected mode of scanning. For example, the light source 20 can scan a selected range of light wavelengths and / or the light source 20 can scan the light wavelength according to a selected sweep profile (e.g., linear increasing, sinusoid, triangular, etc.). For example, the light source 20 can scan according to a selected sweep rate or a selected total sweep time. The light source 20 is used to perform wavelength scanning of light, so that during one wavelength scan, the light will be directed to the brain tissue of the subject through the sample delivery channel (and directed 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 will vary with time. In this way, an indication of the time when light was emitted from the light source 20 can be determined based on the wavelength of the light.

[0055] The light source 20 can be used to scan through a selected wavelength range. For example, the light source 20 can be used to scan with an optical frequency within the range of 50 GHz. For example, this can enable the light source 20 to emit modulated light of multiple different wavelengths, such as between 829.94 nm and 830.06 nm when centered at 830 nm, or between 1309.857 nm and 1310.143 nm when centered at 1310 nm. The light source 20 can be used to scan a wavelength range (e.g., approximately around the wavelength of its center) of at least 0.025 nm (e.g., at least 0.05 nm, such as at least 0.075 nm, such as at least 0.1 nm, such as at least 0.11 nm). The light source 20 can have high output power, long coherence time, and wide range mode-hop-free wavelength tuning. The light source 20 can have a relatively narrow linewidth and a long coherence length, for example, because the light source 20 does not scan a particularly large bandwidth.

[0056] The light sources disclosed herein can be used to provide highly coherent light, for example, sufficiently coherent light, for emission. It should be understood that a light source cannot both emit fully coherent light and provide wavelength-scanned light emission, for example, because light of different wavelengths will change phase at different rates. The light sources disclosed herein can be controlled to scan a relatively narrow wavelength range compared to the absolute wavelength of the light source. In other words, the difference between the maximum wavelength and the minimum wavelength of a wavelength scan will be relatively small compared to the absolute wavelength. Each light source can be used to emit light (i.e., an electric field) whose phase does not vary much over time.

[0057] The iNIRS system of the present disclosure will receive sample light and reference light originating from the same light source. The light source of the present disclosure is used to provide wavelength-scanned sufficiently coherent light emission so that the sample light and reference light received at the optical detector will have relatively similar phases. Therefore, the combination of the sample light and the reference light will produce sufficient constructive interference between the two waves (e.g., the two light wave streams will have sufficiently similar phases so that the resulting combined light signal will contain a constructive combination of the two light waves). In other words, the coherence length of the light source can be such that multiple scattering in the tissue does not reduce the coherence or fringe contrast below the noise floor of the measurement.

[0058] For example, each light source of the present disclosure may include a laser. The laser may be selected based on the coherence length of the laser, for example, to enable the above-mentioned constructive interference to occur between the sample light and the reference light. In other words, the iNIRS system may be arranged so that the maximum expected flight delay time of the sample photons (received at the optical detector having passed through the brain tissue of the subject) relative to the reference light photons (received at the optical detector having propagated along one or more reference channels) is within the coherence time period of the laser (e.g., the optical path length difference between the sample light and the reference light is within the coherence length of the laser). During this coherence time period, the phase of the light emitted by the laser is approximately stable (although the wavelength of the emitted light changes). Therefore, the combined light signal at the optical detector may have no amplitude loss (e.g., the interference occurring at the detector may be fully constructive).

[0059] For example, an iNIRS system can be configured to have a coherence length or range of approximately 50 m in air, e.g., a light source having a coherence length between 50 m and 100 m (coherence time period between 166 ns and 333 ns) can be selected. It should be understood that this particular range is not intended to be limiting, but rather to illustrate an approximate range of light sources. A light source can be selected such that the coherence length of the light source is two or more times greater than the maximum expected optical path length difference, e.g., the coherence length can be three or four times or more. A light source having a coherence length much greater than the optical path length can improve the accuracy of measuring sample photons that have undergone a large number of scattering interactions within the subject's brain tissue.

[0060] The iNIRS system 10 is arranged so that the source-detector path lengths of the reference light and the sample light are different. In other words, the iNIRS system 10 is arranged so that the average or expected optical path length of light propagating from the light source 20 via the subject's brain tissue to each detector will be different from the optical path length of light propagating from the light source 20 via the reference channel to the above detectors.

[0061] As will be understood in the context of the present disclosure, photons of sample light directed toward the subject's brain tissue may propagate from the light source 20 to the light detector 30 via a virtually unlimited number of different paths. The photons of sample light may experience a large number of scattering events, and therefore the path between the sample delivery probe 25a and the sample receiving probe 35a is very tortuous. The iNIRS system 10 is arranged to provide neuroimaging and analysis based at least in part on activity in the subject's brain tissue. Therefore, photons that do not penetrate brain tissue (e.g., scattered at shallow depths, such as skin, skull, membranes) may carry little or no information about the blood oxygenation level in the subject's brain. The reference paths may be selected so that their source-detector path lengths are shorter than such null informaiton sample light photon path lengths. Photons that penetrate deeper into the subject's brain tissue (and therefore may carry potentially useful information) will typically travel a longer path length from the light source 20 to the light detector 30 than the null informaiton sample light photon path length. The flight time of the sample photons from the light source 20 to the light detector 30 will increase as the path length increases. Therefore, photons that have traveled a longer path and penetrated deeper into the subject's brain tissue will take even longer to reach the light detector 30. The longer the time of flight of the sample light photon, the deeper the photon is likely to penetrate into the subject's brain tissue.

[0062] The iNIRS system 10 is arranged so that the shortest flight time of a photon of light traveling from the light source 20 to the light detector 30 will be the time for a photon of reference light to travel along the reference channel. The sample light photons will have a longer flight time than the reference light. The sample light photons that penetrate the deepest into the subject's brain tissue are likely to be those photons with the longest flight time to the light detector 30.

[0063] The iNIRS system 10 is arranged to determine the distribution for time of flight (DTOF) of sample light photons. To this end, a temporal point spread function (TPSF) can be determined, which is similar to the DTOF, but the TPSF includes an instrument response function (IRF), which can then be filtered out (e.g., deconvolved and / or subtracted) using post-processing. Each determined DTOF can provide a distribution of the flight time of all sample light photons incident on the light detector 30 at a given time point. The DTOF can contain a collective average representing a large number of incident photons (in each TOF bin in a plurality of different TOF bins). The intensity of each TOF bin will provide an indication of the number of incident photons at the TOF. The phase of the TOF bin (e.g., obtained using Fourier analysis) can represent the average phase of all photons arriving at the TOF bin. As described in more detail below, multiple characteristics of the brain tissue of the object can be determined based on the DTOF data obtained for the brain tissue of the object. To obtain such data, the iNIRS system 10 is used to obtain an interference pattern of the combination of reference light and sample light as received at a given light source 20 .

[0064] The iNIRS system 10 is arranged so that each light detector 30 receives sample light and reference light, and combines the sample light and the reference light using a light combiner. For example, each detector may provide an interferometer component (combined with a sample light channel and a reference light channel) for combining the reference light and the sample light to obtain an interference pattern (interference pattern).

[0065] The light source 20 is used to emit sufficiently coherent light. The resulting interference pattern of the light from the light source 20 (as obtained at each detector) may include a combined signal having a beat frequency (or intermediate frequency / difference frequency) component corresponding to the wavelength difference between: (i) the wavelength of the sample light photon received by the light detector 30 at a given time point, and (ii) the wavelength of the reference light photon received by the light detector 30 at that time point. Due to the limitations of the inherent line width of the laser and the optical frequency scanning rate, the reference light within a single sampling interval should be of substantially narrow and uniform wavelength, because the received reference light photons will be transmitted from the light source 20 to the light detector 30 (through the reference channel) at the same distance. The sample light will include photons of different wavelengths, where the wavelength of each sample light will correspond to the flight time of the photon and its unique path in the tissue (due to the wavelength scanning of the light source 20). Therefore, the resulting interference pattern will contain multiple different beat frequencies (due to different differences in wavelength). In the case where the sample path is longer than the reference path, a higher beat frequency may correspond to a photon with a higher flight time (a photon that penetrates deeper).

[0066] Each photodetector 30 includes an optical combiner for combining light and providing the combined light (which may include one or more components corresponding to the beat frequency) to a signal processing circuit. Each detector may include a square-law detector. For example, each detector may be used to create an interference pattern based on the optical frequency difference between the incident sample and reference optical fields, for example, the detected intensity or power is proportional to the square of the incident electric field, and the incident electric field is the sum of the sample and reference optical fields. Therefore, the detected intensity or power (in the form of photocurrent) is equal to the square of the sum of the incident sample and reference optical fields. These detectors may include photodiodes, avalanche photodiodes and / or fast line scan cameras, streak cameras, and fast CCD or CMOS sensors. The detector may be a high-bandwidth detector. For example, the detector may be used to resolve interference fringes at frequencies of 100 MHz or higher, such as up to 1 GHz. The detector may include a single spot detector. For example, the optical fiber used in the detector may be single-mode. If a multimode detector is used, the detector may include a square-law detector array, such as a photodiode array, a focal plane array, a fast line scan camera, or a fast CCD array. The detector may also include a balanced detector array. For example, a balanced detector array can be used to combine and (e.g., evenly) split the reference and scattered light to a pair of out-of-phase detectors, such as using a 4-port (2-in, 2-out, 50:50 ratio) fiber coupler or beam splitter cube. Balanced detectors can enhance the signal-to-noise ratio of the detected signal by rejecting incoherent portions of the signal. Balanced photodetectors can also make full use of all the light transmitted through the interferometer and suppress common noise, such as laser intensity noise.

[0067] In other words, each light detector 30 may include a light combiner for combining sample light and reference light to provide a combined light signal. The iNIRS system 10 is arranged to process the combined light signal to obtain an indication of the intensity of light incident on the light detector 30 at a given point in time (e.g., by using optical off-frequency mixing and / or balanced detection). The iNIRS system 10 is arranged to obtain a plurality of such indications, for example, the light detector 30 may be arranged to repeatedly obtain an indication of the intensity of light incident on the light detector 30. In other words, the iNIRS system 10 is arranged to measure the phase or frequency shift between the photons of light in the two inputs (reference and sample) of the detector, and attribute this difference to the characteristics of the intervening brain tissue with respect to the sample light.

[0068] Each obtained interference pattern can be Fourier analyzed (e.g., using FFT or IFT) to obtain an indication of the DTOF of the sample light photons incident on the light detector 30. When a square-law detector is used, the intensity on the detector can be proportional to the square of the total electric field intensity. The rate of change of the optical frequency multiplied by the time delay can cause the frequency of the interference fringes present in each interference pattern. In other words, a Fourier transform interference pattern containing multiple beat frequencies can be used to indicate the photon flight time associated with those beat frequencies present in the interference pattern.

[0069] In order to obtain DTOF data of sample light photons, the light detector 30 is arranged to combine the two light inputs (sample light and reference light) into a combined light beam. The light detector 30 is arranged to convert the combined light beam into an electrical signal representing the combined light signal. The iNIRS system 10 includes at least one digitizer, which is arranged to receive electrical signals indicating the combined light signal and convert these electrical signals into digital data representing the combined light signal. These digital data can be processed to obtain one or more different characteristics of the subject's brain tissue for neural imaging and analysis.

[0070] An example of an arrangement for converting a received optical signal into digital data is as follows Figure 1 As shown in the illustration A of FIG. Illustration A shows an arrangement of components that can be used as the light detector 30 of the present disclosure. Figure 1 As shown in the iNIRS system 10 , the detector 30 receives two inputs: (i) reference light that has propagated along the reference delivery channel 26 and the reference receiving channel 36 , and (ii) sample light that has been received by the sample receiving probe 35 a and delivered to the detector via the sample receiving channel 35 .

[0071] As shown, the detector may include an optical combiner and splitter 301, a first optical channel 302a and 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.

[0072] The optical combiner and splitter 301 is coupled to the reference receiving channel 36 and the sample receiving channel 35. The optical combiner and splitter 301 is arranged to receive the sample light and the reference light, and combine the sample light and the reference light to provide a combined optical signal. The optical combiner and splitter 301 is arranged to split the combined optical signal into two independent channels: a first optical channel 302a and a second optical channel 302b. For example, this can be a 50:50 split (or approximately so). The first optical channel 302a and the second optical channel 302b are coupled to a balanced photodetector 303. Each optical channel guides light to an associated photodiode. The balanced detector is arranged to provide an output based on the difference between the outputs from the two photodetectors. Two photodetectors will typically be provided so that the beat signals on each photodiode are 180° out of phase with each other, and therefore the coherent AC terms will be forward combined 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. Balanced photodetector 303 may remove any unwanted DC terms from the signal, such as slow fluctuations from light source 20 or other common mode effects, such as noise.

[0073] The photodetector 30 is used to convert the current output by the balanced photodetector 303 into a corresponding voltage using a current-to-voltage converter. Figure 1As shown in the illustration A of , the converter may include a transimpedance amplifier 304. The voltage output by the transimpedance amplifier 304 is then amplified using an amplifier 305. The amplifier may be used to scale the output signal to the full range of the ADC and limit the electronic frequency of the circuit to further maximize the SNR. The amplified voltage is then provided to the ADC 306 for digitization. The ADC 306 includes a digitizer with sufficient bandwidth so that the full signal bandwidth containing the time-of-flight information can be digitized without attenuation. For example, the bandwidth of the digitizer may be at least the same as the bandwidth of the combined optical signal. For example, the sampling rate of the digitizer may be selected to be high enough to meet the Nyquist criterion for processing the signal bandwidth. The digitizer may be provided as part of each optical detector 30, or the digitizer may be part of the controller 40, and the controller 40 may be coupled to each optical detector 30 to receive the electrical signal to be digitized from the optical detector. For each combined optical signal, a digital signal output 307 is provided, which gives a digital representation of the combined optical signal (and therefore also a digital representation of the sample light incident on the optical detector 30 when generating and measuring the combined optical signal).

[0074] The iNIRS system 10 is used to obtain a plurality of digital signal outputs 307 indicating sample light incident on the light detectors 30. Specifically, each light detector 30 is used to repeatedly combine light signals (sample light and reference light) to provide a digital signal output 307 representing each combined light signal. For example, for each light detector 30, a time series of digital signal outputs 307 can be obtained, wherein each subsequent digital signal output 307 corresponds to a subsequent time point at which the combined light signal is obtained and measured (and the digital signal output 307 represents the obtained and measured combined light signal). As described above, each of these signals can indicate the sample light DTOF at that time point of that detector.

[0075] In other words, the iNIRS system 10 is used to obtain multiple time-sequenced DTOFs for each of the multiple different photodetectors 30. The digitizer can provide digital outputs indicative of the different measurements, and these digital outputs can optionally be processed in a variety of ways to provide DTOF data. Examples of these steps will now be described.

[0076] The controller 40 can be used 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 can be divided into individual scans of a wavelength scan emission from the light source 20. For example, the scan rate of the light source 20 and the time when the first scan begins can be used to determine the scan period. The data can then be divided into groups, each of which represents a single scan. An optional Hilbert transform can be performed on the data at this stage. The data can be windowed (e.g., using a Hanning window or a Blackman-Harris window) to reduce side lobes in the data. Fourier analysis can be performed on the data, which can be inverse or forward. For example, an inverse Fourier transform can be performed. Fourier analysis can be performed for each wavelength scan of the light source 20. The resulting data can be in the form of a series of time point spread functions (TPSFs), each TPSF corresponding to an associated wavelength scan. The TPSF data can be processed to remove the instrument response function (IRF) therefrom to provide DTOF data.

[0077] In other words, the iNIRS system 10 can be used to determine a time-ordered sequence of the distribution of flight time (DTOF) of sample light photons incident on each of a plurality of different detectors. These DTOF data can be processed to provide information related to a plurality of different physical properties of the subject's brain tissue. The DTOF data can be used to determine the optical properties of the medium through which the sample light has passed. Each TOF bin in the DTOF can represent a selected volume within the subject's brain, and each DTOF represents the total volume of tissue detected by the photons (e.g., each DTOF can represent a weighted average of the properties of brain tissue and other tissues (such as scalp, skull, etc.) through which the photons have passed). Optical properties include scattering and absorption properties of the subject's brain tissue. The DTOF data can be used to determine the dynamic properties of the subject's brain tissue, such as changes in specific properties over time. This includes how the optical properties evolve over time, and properties indicating motion (e.g., caused by blood flow) within the subject's brain tissue. The iNIRS system 10 can be used to Fourier transform (e.g., FFT) the obtained TOF distribution to obtain gamma data, wherein the dynamic signal can be obtained from the temporal changes of the gamma signal.

[0078] The time-ordered sequence of DTOFs can be viewed as corresponding to a data surface in a 3D volume. The surface can represent the DTOF of each subsequent DTOF (ordered in time), and therefore the surface shows each individual DTOF and the evolution of the DTOF over time. The surface can provide a large amount of data from which the characteristics of the brain tissue of the object can be determined. Analysis of the temporal fluctuations of the DTOF values ​​over time (e.g., decay) can provide an indication of one or more dynamic characteristics of the brain tissue of the object. That is, decay analysis can be used to identify that one or more characteristics within the brain tissue of the object are changing, and optionally identify the rate at which these characteristics are changing (e.g., using a decay rate). The order of the decay of the DTOF (e.g., with t, t 2 Equal attenuation) can be used to determine one or more characteristics of the type of motion (e.g., diffusion or flow).

[0079] The controller 40 may store data associating the time of flight of the sample light photon with an indication of the average path trajectory of the photon. This may include an indication of the depth of penetration of the photon into the brain tissue of the object, and / or an indication of the region through which the photon passes from the light source 20 to the brain tissue of the object. The controller 40 may be used to process the data by dividing the DTOF data into selected time of flight bins. Within each TOF bin, the data may provide depth-resolved evolution data of the brain tissue of the object. That is, since TOF may be associated with a specific penetration depth or region, each TOF bin may contain data showing characteristics associated with a specific penetration depth or region. Therefore, the evolution of the data within each TOF bin may provide an indication of how one or more characteristics of the brain tissue of the object evolve. For example, when the evolution indicates a change in motion (e.g., blood flow), the motion and the region in which the motion occurs may be identified. To this end, the TOF-resolved attenuation slope may be used to identify a curve of a specific TOF (e.g., a specific penetration depth / region) decaying over time.

[0080] In other words, the iNIRS system 10 is used to perform autocorrelation, where the DTOF of consecutive wavelength scans are combined to evaluate the light field fluctuations over time at the light detector 30. The fluctuations can be identified due to the correlated decay of the DTOF over time. The fluctuations can also be depth resolved by identifying the associated TOF (and therefore the associated penetration depth / region) where the fluctuations occur.

[0081] The controller 40 can be used to process the data received from the photodetector 30 to provide time-of-flight information that is depth-resolved and autocorrelated with the subject's brain tissue. The controller 40 can be used to use this information to obtain a plurality of different characteristics of the subject's brain tissue, such as indications of intracranial pressure (ICP), blood flow index, arterial elasticity, cerebral metabolic rate of oxygen consumption (CMRO2), etc. These characteristics of the subject's brain tissue can be used for a variety of different forms of neural imaging and analysis, such as in brain-computer interfaces, for imaging brain regions to identify potential localized damage or stroke, and / or for monitoring neural responses to substances (e.g., drugs).

[0082] Blood oximetry

[0083] Now refer to Figures 2a to 3d , Figures 2a to 3d The components of the iNIRS system are shown.

[0084] Figure 2a and Figure 2b An arrangement for outputting sample light and reference light (ie, the sample light will be delivered toward the subject's brain tissue, and the reference light will be delivered along one or more reference channels directly to a detector) is shown. Figure 2a and Figure 2b The light source arrangement is arranged to output sample light and reference light from two light sources, wherein one light source emits light having a wavelength higher than the oximetry isoabsorption wavelength and the other light source emits light having a wavelength lower than the oximetry isoabsorption wavelength. Specifically, Figure 2a and Figure 2b The light source arrangement is used to deliver light from each light source onto the same single common optical channel as the light propagates from its light source toward the subject's scalp. Some light from each light source is also delivered to a reference channel that directly connects the light source to the light detector.

[0085] Figures 3a to 3d An arrangement for receiving sample light and reference light (ie the sample light comes from the subject's brain tissue and the reference light comes directly from the light source) is shown. Figures 3a to 3d The light detection arrangement is arranged to receive sample light and reference light from two light sources, wherein the wavelength of light from one light source is higher than the oximetry isoabsorption wavelength and the wavelength of light from the other light source is lower than the oximetry isoabsorption wavelength.

[0086] Figure 2a and Figure 2b Light source arrangement and / or Figure 3a to Figure 3d The light detection arrangement in can be set in Figure 1In the iNIRS system shown in (and described above). In particular, embodiments of the present disclosure may provide a Figure 2a and / or the light generating arrangement of 2b and from Figures 3a to 3d Thus, embodiments may provide an iNIRS system designed to emit and detect light at wavelengths on either side of an oximetry absorption wavelength for determining the blood oxygenation concentration of a subject's brain tissue.

[0087] Figure 2a A light emitting arrangement 120 is shown. The light emitting arrangement 120 includes a first light source 120a (above the oximetry isoabsorption wavelength) and a second light source 120b (below the oximetry isoabsorption wavelength). The light emitting arrangement 120 includes a common light combiner 122, a common light channel 123, and a common light splitter 124. As with the iNIRS system described above, the light emitting arrangement 120 includes a common sample delivery channel 125 and a common reference delivery channel 126.

[0088] The common optical combiner 122 couples two light sources to a common optical channel 123. The first light source 120a can be coupled to the common optical combiner 122 via a first coupling channel 121a, and the second light source 120b can be coupled to the common optical combiner 122 via a second coupling channel 121b. The common optical channel 123 couples the common optical combiner 122 to a common optical splitter 124. The common optical channel 123 can be a single optical channel. The common optical channel 123 can extend from the common optical combiner 122 to the common optical splitter 124. The common optical splitter 124 couples the single common optical channel 123 to two independent channels: a common sample delivery channel 125 and a common reference delivery channel 126. As described above, the common sample delivery channel 125 can be coupled to one or more areas of the subject's scalp, for example, via one or more sample delivery probes. Similarly, the common reference delivery channel 126 can be coupled to one or more of the optical detectors, for example, via one or more reference receiving channels.

[0089] The light emitting arrangement 120 is used to deliver: (i) sample light (e.g., via a common sample delivery channel 125) to the subject's brain tissue, and (ii) reference light (e.g., via a common reference delivery channel 126) to one or more light detectors. The light emitting arrangement 120 is used so that light from each of the two light sources will propagate along the same light channel. For example, sample light from the first light source 120a and sample light from the second light source 120b will each propagate along at least one common light channel. Figure 2aIn the example shown, the sample light from the two light sources will propagate 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 will each propagate along at least one common optical channel. Figure 2a In the example shown, the reference light from both light sources will propagate along the same common optical channel 123 and the same common reference delivery channel 126 .

[0090] Figure 2b A similar lighting arrangement is also shown in .

[0091] Figure 2b A light emitting arrangement 120 is shown. Figure 2a Similarly, the light emitting arrangement 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.

[0092] exist Figure 2b In the optical splitter, 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 optical channel. Figure 2b The light emitting arrangement 120 comprises a first optical splitter 124a and a second optical splitter 124b. The first light source 120a is coupled to the first optical splitter 124a (eg, via the first coupling channel 121a), and the second light source 120b is coupled to the second optical splitter 124b (eg, via the second coupling channel 121b). Figure 2b The light emitting arrangement 120 includes two common light combiners: a sample common light combiner 122s and a reference common light combiner 122r. The sample common light combiner 122s is coupled to each of the first optical splitter 124a and the second optical splitter 124b, and is also coupled to a common sample delivery channel 125. The reference common light combiner 122r is coupled to each of the first optical splitter 124a and the second optical splitter 124b, and is also coupled to a common reference delivery channel 126. The common sample delivery channel 125 can be coupled to one or more regions of the scalp of the subject, for example via one or more sample delivery probes. Similarly, the common reference delivery channel 126 can be coupled to one or more of the light detectors, for example via one or more reference receiving channels.

[0093] The first optical splitter 124a couples the first light source 120a to each of the following two independent optical channels: a first sample delivery channel 123as and a first reference delivery channel 123ar. The second optical splitter 124b couples the second light source 120b to each of the following two independent optical channels: a second sample delivery channel 123bs and a second reference delivery channel 123br. The first sample delivery channel 123as couples the first optical splitter 124a (and therefore the first light source 120a) to the sample common light combiner 122s. The first reference delivery channel 123ar couples the first optical splitter 124a (and therefore the first light source 120a) to the reference common light combiner 122r. The second sample delivery channel 123bs couples the second optical splitter 124b (and therefore the second light source 120b) to the sample common light combiner 122s. The second reference delivery channel 123br couples the second optical splitter 124b (and thus the second light source 120b) to the reference common light combiner 122r. The sample common light combiner 122s couples the first sample delivery channel 123as and the second sample delivery channel 123bs to a common sample delivery channel 125. The reference common light combiner 122r couples the first reference delivery channel 123ar and the second reference delivery channel 123br to a common reference delivery channel 126.

[0094] exist Figure 2b There are two common light channels in the light emitting arrangement 120, wherein light from any light source will propagate along the above-mentioned common light channels. These common light channels are a common sample delivery channel 125 and a common reference delivery channel 126. Each of these common light delivery channels is coupled to a common light combiner to receive light from one or both of the two light sources. One or both of these common light channels can be a single light channel. For example, the common sample delivery channel 125 can be a single light channel extending from the sample common light combiner 122s to the brain tissue of the subject. For example, the common reference delivery channel 126 can be a single light channel extending from the reference common light combiner 122r to one or more optical detectors.

[0095] The light emitting arrangement 120 is used to deliver: (i) sample light (e.g., via a common sample delivery channel 125) to the subject's brain tissue, and (ii) reference light (e.g., via a common reference delivery channel 126) to one or more light detectors. The light emitting arrangement 120 is used so that light from each of the two light sources will propagate along the same light channel. For example, sample light from the first light source 120a and sample light from the second light source 120b will each propagate along at least one common light channel. Figure 2bIn the example shown, the sample light from the two light sources will propagate 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 will each propagate along at least one common light channel. Figure 2a In the example shown, reference light from two light sources propagates along the same common reference delivery channel 126 .

[0096] Next, the functionality of the two lighting arrangements 120 will be described together.

[0097] Figure 2a and Figure 2b The light emitting arrangement 120 in each of the two independent light sources is used to deliver sample light to the brain tissue of the subject from two independent light sources, wherein the sample light from each light source will propagate along at least one common light channel when propagating from either light source to the scalp of the subject. Similarly, Figure 2a and Figure 2b The light emitting arrangement 120 in each of is used to deliver reference light from two independent light sources to one or more detectors, wherein the reference light from each light source will propagate along at least one common optical channel when propagating from either light source to the one or more detectors.

[0098] For each lighting arrangement 120, each of the first light source 120a and the second light source 120b is the same as the above Figure 1 . That is, each light source is used to provide wavelength scanning light emission. These details about the functions of the first light source 120a and the second light source 120b will not be described again because they have been described above. The wavelengths of light emitted by the first light source and the second light source are different. The primary wavelengths of the first light source 120a (e.g., the first laser) and the second light source 120b (e.g., the second laser) will be different.

[0099] The first light source 120a is arranged to emit light at a wavelength higher than the oximetry isosbestic wavelength. The second light source 120b is arranged to emit light at a wavelength lower than the oximetry isosbestic wavelength. The oximetry isosbestic wavelength is a wavelength at which the absorption characteristics of oxyhemoglobin and deoxyhemoglobin are the same (e.g., they have the same absorption coefficient). At wavelengths above and below the oximetry isosbestic wavelength, the absorption coefficients of oxyhemoglobin and deoxyhemoglobin will be different (except at any other isosbestic wavelength). In other words, the oximetry isosbestic wavelength is a wavelength at which the wavelength-dependent absorption coefficient values ​​of oxyhemoglobin and deoxyhemoglobin are swapped. For oximetry of hemoglobin, there are two relevant oximetry isosbestic wavelengths: one at about 590 nm and one at about 805 nm. For example, the oximetry isosbestic wavelength used in the present disclosure can be at about 805 nm, such as at about 808 nm.

[0100] The first light source 120a is used to provide wavelength scanning emission through multiple wavelengths above the absorption wavelength of blood oximetry (e.g., greater than 808nm). Figure 1 As described, the first light source 120a can be a laser for emitting light of a selected wavelength, and the light emitting arrangement 120 can also include a light source regulator, which is used to change the wavelength of the emitted light around the selected wavelength (e.g., to provide a wavelength scan around the selected wavelength of the laser emitted light). For example, the first light source 120a can be used to emit light of a selected wavelength of about 830nm, 850nm, or 900nm. Preferably, the first light source 120a can be used to emit light of a wavelength of 852nm. The light emitting arrangement 120 is used to provide a wavelength scan for the first light source 120a by a plurality of wavelengths around 852nm and 852nm.

[0101] The second light source 120b is used to provide wavelength scanning emission through multiple wavelengths below the oximetry isoabsorption wavelength (e.g., less than 808nm). For example, the second light source 120b may include a laser for emitting light of a selected wavelength of about 690nm, 760nm, or 785nm. Preferably, the second light source 120b can be used to emit light with a wavelength of 780nm. The light emitting arrangement 120 is used to provide wavelength scanning for the second light source 120b through multiple wavelengths around 780nm and 780nm. For example, the first light source and the second light source can utilize wavelengths in the range of 760nm to 880nm, wherein one wavelength is above the oximetry isoabsorption wavelength and the other wavelength is below the oximetry isoabsorption wavelength. For example, the first light source 120a can emit light of about 830nm or 850nm (e.g., 830nm or 850nm), and the second light source 120b can emit light of about 780nm (e.g., 780nm).

[0102] As described above, the light emitting arrangement 120 is arranged to provide wavelength-scanned emission at wavelengths above the oximetry isoabsorption wavelength and below the oximetry isoabsorption wavelength. The light emitting arrangement 120 is also arranged to couple light from the two light sources onto one or more common optical channels. Each optical channel may include a fiber optic cable.

[0103] As mentioned above about Figure 1As described, the optical combiner of the present disclosure is arranged to combine two independent input light streams onto a single optical channel. For example, each optical combiner can be used to receive input light from two independent channels (e.g., two independent optical fiber cables) and combine the two input light streams onto a single optical channel (as an output). The optical splitter is arranged to split an input stream from a single optical channel into two independent optical channels. For example, each optical splitter can be used to receive input light from a single channel (e.g., a common optical fiber cable) and split the input light stream into two independent optical channels (e.g., as two outputs). Each optical combiner can be a wavelength combiner, such as a wavelength division multiplexer (WDM). Each optical separator can be an opposite wavelength separator. For example, a wavelength combiner / separator (e.g., WDM) can include one or more gratings and / or prisms, which are arranged to split and / or combine light (as the case may be). Additionally or alternatively, the combiner and / or separator can be implemented with discrete components (e.g., in free space). Fiber optic couplers may be used instead of or in addition to WDM, and / or WDM may be used for optical combining / splitting without being used for multiplexing and / or demultiplexing.

[0104] The light emitting arrangement 120 is operable to provide two active wavelength outputs from the same device. At least one common channel is used to deliver light from one or both light sources for output. The light emitting arrangement 120 can be used to output light from two light sources simultaneously. In this case, the light from the two light sources can propagate along the same at least one common optical channel at the same time. The light emitting arrangement 120 can be used to operate the two light sources staggered in time so that light is output from one light source at a time. In this case, although the light from the two light sources will propagate along the same common optical channel, only the light from one light source can propagate along the channel at any time.

[0105] The light emitting arrangement 120 can be arranged such that reference light from the first light source 120a travels a different distance than reference light from the second light source 120b (when propagating from the respective light sources to each detector). For example, the reference path from one of the light sources to the light detector can include an excess of light channels such that reference light from that light source will take longer to propagate to the detector than reference light from the other light source. The lengths of the light channels along which light from both light sources propagate for delivering sample light to brain tissue of the subject can be substantially the same (e.g., sample light from either light source can propagate the same distance to brain tissue of the subject).

[0106] For example, in Figure 2b, the distance from the first light source 120a to the common sample delivery channel 125 can be the same or approximately the same as the distance from the second light source 120b to the common sample delivery channel 125. That is, the first sample delivery channel 123as and the second sample delivery channel 123bs can have the same length (and / or in the case of using the first coupling channel and the second coupling channel, the combined length of the first coupling channel 121a and the first sample delivery channel 123as can 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 can be different from the distance from the second light source 120b to the common reference delivery channel 126. That is, the first reference delivery channel 123ar and the second reference delivery channel 123br can have different lengths (and / or in the case of using the first coupling channel and the second coupling channel, the combined length of the first coupling channel 121a and the first reference delivery channel 123ar can be different from the combined length of the second coupling channel 121b and the second reference delivery channel 123br). One of the sample channel or the reference channel may be arranged to provide a relative delay difference for the light to be combined.

[0107] The distance difference of the relevant reference path lengths can be selected so that the resulting beat frequency between the sample light and the reference light from one of the light sources is different from the resulting beat frequency between the sample light and the reference light from the other of the light sources. In other words, because the reference light from one of the light sources propagates along a longer path, the flight time difference between the reference light and the sample light from that light source will be different from the flight time difference from the other light source. In general, a longer reference path will result in a smaller beat frequency because the flight time difference between the sample light and the reference light received at the detector will be smaller. The difference in the optical path lengths of the reference light from the two light sources can be selected so that there is no spectral overlap or minimal spectral overlap between: (i) the beat frequency of the sample light and the reference light from the first light source 120a, and (ii) the beat frequency of the sample light and the reference light from the second light source 120b. As described in the detailed description of the detector below, this method can be used so that light from two light sources can be emitted and detected simultaneously, while enabling detection signals associated with two different light sources to be individually identified.

[0108] Now refer to Figures 3a to 3d Some example light detection arrangements are described, and then the operation of these detection devices will be described in conjunction with the corresponding operation of different light emitting arrangements 120 .

[0109] Figure 3aA light detection arrangement 130 is shown. The light detection arrangement 130 has a sample receiving channel 135 and a reference receiving channel 136. The light detection arrangement 130 has a detection light combiner and splitter 131, a first detection channel 133', a second detection channel 133". The light detection arrangement 130 comprises at least one element for converting a received light signal into an electrical signal, for example a photodetector such as a photodiode. Figure 3a An example of this is a balanced photodetector 134 . Figure 3a Also shown are a transimpedance amplifier 137 and an analog-to-digital converter 138.

[0110] The sample receiving channel 135 is arranged to be coupled to the scalp of the subject, for example via one or more sample receiving probes. The reference receiving channel 136 is arranged to be coupled to the first light source and the second light source, for example, the reference receiving channel 136 may be coupled to Figure 2a and Figure 2b The sample receiving channel 135 and the reference receiving channel 136 are both coupled to an optical combiner and an optical splitter. The optical combiner and the splitter are coupled to a first detection channel 133' and a 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.

[0111] The light detection arrangement 130 is used 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. Figure 3a In the example of , the detection light combiner and splitter 131 is used to combine the sample light from the sample receiving channel 135 with the reference light from the reference receiving channel 136 to provide a combined light signal, and to split the combined light signal into two independent light channels: a first detection channel 133' and a second detection channel 133". The light detection arrangement 130 is arranged to provide the light in the two detection channels as input to the balanced photodetector 134. The balanced photodetector 134, the transimpedance amplifier 137, and the analog-to-digital converter 138 are used to process the light input as described above.

[0112] Figure 3b A similar light detection arrangement is shown in .

[0113] Figure 3b A light detection arrangement 130 is shown. Figure 3aSimilarly, this includes a sample receiving channel 135 and a reference receiving channel 136. The optical detection arrangement 130 also includes a detection light combiner 131 and a wavelength demultiplexer 132. The wavelength demultiplexer 132 is arranged to demultiplex the light associated with the first light source and the light associated with the second light source. The wavelength demultiplexer 132 demultiplexes the light into two channels: a first light source detection channel 133a and a second light source detection channel 133b (i.e., one light channel for light from each light source). Each light source detection channel has an associated photodetector (a first photodetector 134a and a second photodetector 134b). These can be single photodetectors (e.g., single-ended, not balanced photodetectors). Each photodetector can have an associated TIA (a first TIA 137a and a second TIA 137b), and the arrangement 130 also includes at least one ADC (ADC 138).

[0114] The detection light combiner 131 is coupled to the sample light receiving channel and the reference light receiving channel. The detection light combiner 131 is coupled to the wavelength demultiplexer 132 (e.g., via an optical channel). The wavelength demultiplexer 132 is coupled to each of the first light source detection channel 133a and the second light source detection channel 133b. Each light source detection channel couples the wavelength demultiplexer 132 to a corresponding photodiode (the first photodiode 134a or the second photodiode 134b).

[0115] The light detection arrangement 130 is used 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. Figure 3b In the example of , the detection light combiner 131 is used to combine the sample light from the sample receiving channel 135 with the reference light from the reference receiving channel 136 to provide a combined light signal. The wavelength demultiplexer 132 is used to split the combined light signal into two independent light channels, so that the channel to which the light associated with the first light source 120a is provided (the first light source detection channel 133a) is different from the channel to which the light associated with the second light source 120b is provided (the second light source detection channel 133b). The light signals in the two channels will be processed separately, for example, to provide two digital outputs, one digital output corresponding to the light from each light source.

[0116] Figure 3c A light detection arrangement 130 is shown. Figure 3a and Figure 3b Again, this includes a sample receiving channel 135 and a reference receiving channel 136. Each channel is connected to a corresponding wavelength demultiplexer (sample light wavelength demultiplexer 132s and reference light wavelength demultiplexer 132r). The light detection arrangement 130 also includes a first light source combiner and splitter 131a and a second light source combiner and splitter 131b.

[0117] The sample light wavelength demultiplexer 132s has an input coupled to the sample receiving channel 135, and has two outputs: one coupled to the first light source combiner and splitter 131a (via the first sample delivery channel 133sa), and one coupled to the second light source combiner and splitter 131b (via the second sample delivery channel 133sb). The reference light wavelength demultiplexer 132r has an input coupled to the reference receiving channel 136, and has two outputs: one coupled to the first light source combiner and splitter 131a (via the first reference delivery channel 133ra), and one coupled to the second light source combiner and splitter 131b (via the second reference delivery channel 133rb). The first light source combiner and splitter 131a is coupled to a balanced photodetector 134a (via channels 133a' and 133a", respectively). The second light source combiner and splitter 131b is coupled to a balanced photodetector 134b (via channels 133b' and 133b", respectively). Each balanced photodetector is coupled to an ADC 138 via a corresponding TIA (a first TIA 137a and a second TIA 137b).

[0118] The light detection arrangement 130 is used to demultiplex the light associated with the first light source from the light associated with the second light source, as the sample light is received via the sample channel 135 and the reference light is received via the reference channel 136. The first light source combiner and splitter 131a is used to combine its corresponding sample light and reference light, and the second light source combiner and splitter 131b is used to split its corresponding sample light and reference light for detection by its associated balanced photodetector. The light signals in the two channels will be processed separately, for example to provide two digital outputs, one digital output corresponding to the light from each light source.

[0119] Figure 3d An optical detection arrangement 130 is shown. The arrangement 130 comprises a sample receiving channel 135 and a reference receiving channel 136. The arrangement further comprises an optical combiner and splitter 131, a first wavelength demultiplexer 132a, and a second wavelength demultiplexer 132b.

[0120] The optical combiner and splitter 131 is coupled to each of the sample delivery channel 135 (to receive sample light from two light sources) and the reference delivery channel 136 (to receive reference light from two light sources). The optical splitter and combiner 131 is coupled to: a first wavelength division multiplexer 132a (via channel 133a) and a second wavelength division multiplexer 132b (via channel 133b). The first wavelength division multiplexer 132a has two output ends: a first output end (via channel 133aa) is coupled to a first photodetector of a first balanced photodetector 134a, and a second output end (via channel 133ab) is coupled to a first photodetector of a second balanced photodetector 134b. The second wavelength division multiplexer 132b has two output ends: a first output end (via channel 133ba) is coupled to a second photodetector of the first balanced photodetector 134a, and a second output end (via channel 133bb) is coupled to a second photodetector of the second balanced photodetector 134b. The first balanced photodetector 134a is coupled to a corresponding first TIA 137a and an ADC channel (ADC 138a). The second balanced photodetector 134b is coupled to a corresponding second TIA 137b and an ADC channel (ADC 138b).

[0121] The arrangement 130 is used to provide optical signals associated with the first light source (via a first balanced photodetector 134a) to a first digitized stream and optical signals associated with the second light source (via a second balanced photodetector 134b) to a second digitized stream.

[0122] exist Figures 3a to 3d Examples with one or two ADC channels are shown in FIG. It will be appreciated that if an optical delay is introduced to avoid spectral overlap associated with the beat frequency, a single ADC channel can be used to simultaneously digitize the two combined optical signals. Without introducing such an optical delay, separate ADC channels can be used to simultaneously digitize the light from the first light source and the light from the second light source.

[0123] The functionality of the light detection arrangement 130 will be described together below.

[0124] Each light detection arrangement 130 is used to Figure 1. That is, each light detection arrangement 130 is used to combine sample light and reference light to provide a combined light signal that includes one or more components of the beat frequency between the sample light and the reference light. Here, the sample light will include light from the first light source 120a that has passed through the brain tissue of the subject (e.g., at a wavelength above the oximetry isoabsorption wavelength) and / or light from the second light source 120b that has passed through the brain tissue of the subject (e.g., at a wavelength below the oximetry isoabsorption wavelength). Similarly, the reference light will include light from the first light source 120a that has propagated along one or more reference channels and / or light from the second light source 120b that has propagated along one or more reference channels. Thus, each light detection arrangement 130 will receive light associated with two different light sources (and therefore also include two different wavelength ranges - one above the oximetry isoabsorption wavelength and one below the oximetry isoabsorption wavelength).

[0125] The iNIRS system may include a controller for use with the Figure 1 The combined light signal associated with each light source is processed in the same manner as disclosed herein. That is, absorption and / or scattering coefficients can be determined, and depth-resolved information of the subject's brain tissue can be determined (e.g., based on the flight time distribution of photons passing through the subject's brain tissue), as well as other characteristics, such as an indication of blood flow, etc.

[0126] In particular, for light from each light source, the controller can be used to determine an absorption characteristic associated with the light emitted from the light source, such as an absorption coefficient. The controller can determine the absorption coefficients for two different wavelength ranges (e.g., for larger wavelength light from the first light source 120a and smaller wavelength light from the second light source 120b). The controller can be used to compare the absorption coefficients for the two wavelength ranges to determine an indication of the relative concentrations of oxyhemoglobin and deoxyhemoglobin. In other words, the controller can be used to determine the blood oxygen concentration value of the brain tissue of the object. As described above, the controller can be used to provide depth-resolved information, such as depth-resolved blood oxygen concentration levels, by analyzing data associated with different photon flight times passing through the brain tissue of the object. The controller can be used to determine an indication of the absolute amount of oxygen in the blood based on the oxygen concentration.

[0127] The light emitting arrangement 120 and the light detecting arrangement 130 are operable to obtain an indication of the blood oxygen concentration of the subject's brain tissue by emitting and detecting light in two different wavelength ranges (either side of the absorption wavelength such as blood oximetry). This functionality can be provided in a single device, for example, rather than requiring separate components to measure different characteristics. In order to reduce the requirements on the equipment, the iNIRS system can be used to control the operation of the light emitting arrangement 120 and / or the light detecting arrangement 130 so that a measurement of blood oxygenation concentration can be obtained using a single detector (e.g., using a single interferometer, a single sample receiving channel 135, and a single reference receiving channel 136). Similarly, each light emitting arrangement 120 can be coupled to a plurality of different light detecting arrangements 130, which can still detect light from the light source. To this end: 1. The light emitting arrangement 120 may be used 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 the two light sources. 2. The light detection arrangement 130 may be used to wavelength demultiplex the received sample and reference lights (eg, so that the output from each photodetector represents only one of the light sources). 3. The controller (signal processing circuit in hardware / software) can be used to: (i) attribute the acquired data to the relevant light source based on a time division multiplexing scheme, (ii) attribute the data from each photodetector to the corresponding light source, and / or (iii) Assign data of different frequencies to the corresponding light sources.

[0128] For example, the iNIRS system can be used to provide time domain multiplexing detection. To this end, the operation of the two light sources is staggered in time so that one light source is operated at a time (e.g., a selected number of wavelength scans are performed). In this case, the output from the detector will indicate the first light source 120a or the second light source 120b, depending on the time. The controller can store an indication of the time modulation mode of the light emitting arrangement 120 (e.g., an indication of the number of scans of each light source before the active light source is switched, the emission start time, the scan rate, and / or). The controller can be used to process the output data from the light detection arrangement 130 so that the data is filtered according to the operation time, so that the data of each light source in the two light sources can be isolated.

[0129] As another example, the iNIRS system can be used to provide wavelength domain multiplexing detection. To this end, wavelength multiplexing is performed on sample light from two light sources, and the sample light is emitted from the two light sources simultaneously. The light detection arrangement 130 may include a sample light splitter, such as a wavelength demultiplexer, which is used to demultiplex the received light (sample light and reference light) into independent channels based on the wavelength multiplexing scheme applied by the wavelength multiplexer of the light emitting arrangement 120. Therefore, the light detection arrangement 130 can split the received light into two independent signal processing channels: one channel for the light from each light source, so that the received light from each light source can be processed independently. Therefore, the two signal processing channels can provide independent outputs: one output for each light source, and the controller can independently process the output data of the above two signal processing channels.

[0130] As a third example, the iNIRS system can be used to provide an optical path length offset between two light sources and a detector. Thus, the beat frequency associated with one of the light sources can be in a different range than the beat frequency associated with the other light source. The light detection arrangement 130 can be used to obtain spectral data formed by two independent components (each component associated with a corresponding light source) in a separable frequency range. The signal processing circuit and / or controller can be used to process the received light signal / data output from the ADC to associate the data of the two separable frequency ranges with the corresponding light sources.

[0131] An example of such a delay arrangement is Figure 4 The delay arrangement is for a common light path (ie, where light can be delivered simultaneously from a first light source and a second light source). The common light path can be located in the sample or reference arm (or in a common channel before branching into separate reference / sample channels).

[0132] Figure 4A delay device 200 included in a common optical channel is shown. The delay device 200 has an input channel 201 and an output channel 206. The input channel 201 and the output channel 206 may be the remaining parts of the common optical channel provided with the delay device 200. The delay device 200 also includes a wavelength demultiplexer 202, a first channel 203, a second channel 204, and a wavelength multiplexer 205. The wavelength demultiplexer has an input end coupled to the input channel 201, and has two output ends: one coupled to the first channel 203 and one coupled to the second channel 204. The wavelength multiplexer has two input ends: one coupled to the first channel 203 and one coupled to the second channel 204, and has an output end coupled to the output channel 206. The second channel 204 includes a delay portion 204d. The delay portion includes an additional length of path such that the optical path length along the first path 203 (from the demultiplexer 202 to the multiplexer 205) is shorter than the optical path length along the second path 204 (from the demultiplexer 202 to the multiplexer 205).

[0133] The demultiplexer 202 is arranged to demultiplex the wavelength of light it receives into two independent channels. For example, the demultiplexer 202 can be used to demultiplex the light from the first light source into the first channel 203, and demultiplex the light from the second light source into the second channel 204. The multiplexer 205 is used to multiplex the light from the first channel 203 and the second channel 204 into a common channel (output channel 206). The delay portion 204d has a selected length so that the beat frequency spectrum overlap generated by combining the sample light and the reference light from the first light source and the second light source is minimal or there is no spectral overlap. For example, when the light from the second light source passes through the delay portion 204d, this may cause the flight time difference of the sample light and the reference light from the second light source to be significantly different from the flight time difference of the sample light and the reference light from the first light source (for example, the delay may be smaller or larger).

[0134] for Figure 3a to Figure 3d , the light detection arrangement 130 can be used to provide an output (e.g., a digital output from an ADC) that includes at least one of: (i) data that alternately indicates the first light source 120a or indicates the second light source 120b (e.g., where such data can be separated and associated with the relevant light source using operation time information of the two light sources) (ii) parallel data of the two light sources, but from independent signal processing streams (e.g., where the data output of each signal processing stream indicates one of the light sources), and / or (iii) data that includes parallel data of the two light sources, but can be separated into two independent data streams (e.g., based on a beat frequency).

[0135] Now refer to Figures 2a to 3d The light emitting arrangement 120 and light detecting arrangement 130 shown in FIG. 1 describe three examples of operating an iNIRS system.

[0136] In the first example, Figure 2a The light emitting arrangement 120 may be Figure 3a The light detection arrangement 130 is used in combination.

[0137] The controller controls the operation of the first light source 120a and the second light source 120b so that their operation is staggered in time. For the first time period, the first light source 120a will provide a wavelength scanning light emission. The light is provided to the common light channel 123 from the first light source 120a (via the common light combiner 122), and the light is branched to the common sample delivery channel 125 and the common reference delivery channel 126 by the common light splitter 124. The reference light propagates along the common reference delivery channel 126 until it is received at the reference receiving channel 136. The sample light propagates along the common sample delivery channel 125 and enters the brain tissue of the object, where it is scattered and received at the sample receiving channel 135. The light detection arrangement 130 combines the sample light and the reference light and processes the combined light. The controller processes the data obtained in the first time period to determine the indication of the absorption coefficient of the relevant wavelength during the first time period. Then repeat the process in the second time period, but the second light source 120b emits light. This time, the controller processes the data obtained in the second time period to determine the indication of the absorption coefficient of the relevant wavelength during the second time period. The controller compares any absorption coefficients associated with the first time period to any absorption coefficients associated with the second time period to determine a ratio of oxygenated hemoglobin to deoxygenated hemoglobin in the subject's blood.

[0138] In the second example, Figure 2b The light emitting arrangement 120 may be Figure 3a The light detection arrangement 130 is used in combination.

[0139] The first light source 120a and the second light source 120b emit light simultaneously. The light from each light source propagates to a common sample delivery channel 125 and a common reference delivery channel 126. The distance that the light from one light source propagates to the common reference delivery channel 126 is farther than the light from another light source. The resulting wavelength difference between the sample light and the reference light received from one light source will be different from the wavelength difference between the sample light and the reference light received from another light source (due to the increased reference light path length). The light detection arrangement 130 can simultaneously obtain an indication of the absorption data of the two light sources, where the data of one light source has a higher beat frequency than the data of the other light source. In other words, the resulting data can contain two subsets: each subset is associated with light from one light source. The controller processes the data to extract information from each light source. The controller then determines the absorption coefficients of the two light sources (for obtaining blood oxygen concentration data).

[0140] In the third example, Figure 2b The light emitting arrangement 120 may be Figure 3cor Figure 3d The light detection arrangement 130 is used in combination.

[0141] As with 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 into each of the common sample delivery channel 125 and the common reference delivery channel 126. Thus, light from both light sources can propagate along these optical channels, but ultimately the light can be split back into its two components using a corresponding wavelength demultiplexing scheme. At the optical detection arrangement 130, the sample light and the reference light are wavelength demultiplexed to separate the combined optical signal into two components: each component corresponds to light associated with one of the two light sources (e.g., Figure 3c Optionally, at the light detection arrangement 130, the sample light and the reference light are combined, and the combined light signal is then wavelength demultiplexed to separate the combined light signal into two components: each component corresponds to light associated with one of the two light sources (e.g., Figure 3d ). The light associated with each light source is processed separately (as shown in the first example), and the controller can determine the absorption coefficient / blood oxygenation data based on the two independent outputs (associated with each light source).

[0142] Although not shown in the figures, the light emitting arrangement of the present disclosure can utilize one or more optical amplifiers. For example, a small signal amplifier can be used. This can be based on a semiconductor gain chip (e.g., but without a cavity that makes it a laser). The optical amplifier can be set in the sample arm, and only a portion of the light from the light source (e.g., 10-20%) is provided to the amplifier for amplification, and the rest will be provided to the reference channel / detector. As another example, a high power amplifier can be used, such as a high power amplifier based on a tapered amplifier design. The optical amplifier can be arranged to provide optical amplification for light emitted from the first light source and / or the second light source (e.g., for sample light and / or reference light).

[0143] Although not shown, the light emitting arrangement of the present disclosure may include multiple light delivery channels for delivering light from the first light source 120b and the second light source 120b to the scalp of the subject. To this end, the light emitting arrangement may include an optical switch and multiple light delivery channels coupled to a common sample delivery channel 125. The optical switch can be operated to direct 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 can be coupled to the scalp of the subject at multiple different locations (e.g., using a sample probe). The optical switch can select one light delivery channel at a time, for example, when light is delivered to the scalp of the subject through each of the different light delivery channels, the optical switch can be switched through a selected mode.

[0144] For the iNIRS system of the present disclosure, there may be multiple light sources and / or optical detectors. The iNIRS system may include multiple light detection arrangements 130 coupled to the same light emitting arrangement. Each of the optical detectors may be coupled to the same common reference delivery channel 126 of the light emitting arrangement (e.g., Figure 1 ) 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 arrangement can provide light from two light sources that is received as reference light in each of a plurality of optical detectors. The plurality of optical detectors can be distributed around different locations on the scalp of the subject (e.g., to provide information related to different regions of the brain tissue of the subject). Some of the optical detectors can be clustered on the scalp (e.g., all located in the same region on the scalp, close to each other). Where the optical detectors are arranged close to each other, a controller can be used to process a combined light signal based on data from the plurality of detectors (e.g., based on a combination of their sensor outputs). For example, the controller can average data from at least some of the different detectors to determine characteristics of the same region of the brain tissue of the subject. By comparing data from detectors in substantially the same region of the subject's scalp, the signal-to-noise ratio can be improved.

[0145] The examples described herein relate to placing an iNIRS system on the scalp of a subject, and performing neuroimaging and analysis of the subject's brain using the iNIRS system. However, the iNIRS system can be used to provide imaging of any suitable subject. As previously described, the iNIRS system can be used to non-invasively obtain an indication of the subject's blood oxygenation level. This can be used for any suitable area of ​​the subject's body where the blood oxygenation level is to be sensed, such as at their limbs (e.g., at the wrist or in the leg). The iNIRS system can be used to obtain the blood oxygenation level of any suitable part of the subject's body.

[0146] In the above example, two light sources are used, with the first light source emitting at a wavelength above the oximetry isoabsorption wavelength and the second light source emitting at a wavelength below the oximetry isoabsorption wavelength. However, this should not be considered limiting. At two different wavelengths, the absorption (and scattering) coefficients of the imaged volume may be different. This is at least in part due to the difference in the absorption properties of oxyhemoglobin and deoxyhemoglobin at different wavelengths. By using known data on these absorption properties, the relative contribution of each of oxyhemoglobin and deoxyhemoglobin to the total absorption coefficient can be determined. Based on these relative contributions, the blood oxygenation level can be determined. The two different wavelengths used can be selected as wavelengths with a discernible difference between the oxygenated and deoxygenated absorption coefficients. An example of this is either side of the oximetry isoabsorption wavelength, but this is not the only option. As long as there is known data on the difference in the absorption properties of oxygenated and deoxygenated blood, the wavelengths can all be on the same side of the oximetry wavelength. The controller can use these known data to determine the blood oxygenation level based on the absorption coefficients determined by the volume of the first light source and the second light source.

[0147] In addition, blood oxygen level may not be the only information extracted. As will be appreciated, the total absorption coefficient of a volume will have many different contributors (with blood oxygenation being the primary contributor). However, other light sources of different wavelengths may be used to extract information related to the other contributors. For example, the additional light source may use light of different wavelengths selected based on the relevant absorption characteristics of the other substances to be sensed. For example, water (e.g., wavelength greater than 1000nm) concentration may be detected. For example, pigments such as cytochrome C oxidase may be detected. For example, an iNIRS system may include multiple light sources of different wavelengths, each wavelength being selected to be appropriate for the key absorption characteristics of the substance to be detected. The total absorption coefficient of the volume may then be decomposed to extract information related to the individual components to be analyzed (e.g., blood, water, etc.), for example to identify the relative contribution of each component to the total signal (e.g., the relative concentrations of these components).

[0148] It should be understood that in the context of the present disclosure, the examples described herein are not intended to be limiting. Rather, the examples describe certain potential methods of implementing the claimed technology. For example, an iNIRS system is described as having a series of optical cables that provide channels and probes for coupling these channels to the scalp of a subject. However, it should be understood that the probes themselves can be part of the optical channels, or no probes may be provided at all. Similarly, the arrangement of reference channels is intended only to indicate that reference light is delivered from the light source to the light detector via the optical channels (rather than via the subject's brain tissue). For example, each light source may include a reference channel for each light detector, wherein the reference channel connects the light source directly to the light detector. In this case, there may be no reference connection at all in the system. Optionally, and as Figure 1As shown, reference light can be transmitted on a common reference light channel, where some of the reference light is extracted from the common reference light channel to each optical detector. The light source can also be arranged to deliver light to one of a plurality of different locations on the subject's scalp. For example, the light source can be coupled to a plurality of different sample delivery channels, each sample delivery channel extending (e.g., from an optical splitter) toward the subject's scalp.

[0149] In the examples described herein, there are two light sources, such as two independent lasers (one for each different wavelength range). However, in other examples, such as examples of time division multiplexing of laser operation, the same light source can provide emission of light above and below isoabsorption wavelengths. In the example shown in the figure, a common reference delivery channel 126 is used, which can deliver reference light from the first light source 120a and the second light source 120b to one or more detectors. However, this need not be viewed as limiting, as in other examples, each light source can be coupled to an associated reference channel that couples the light source to the corresponding detector. Each optical detector can be arranged to receive reference light directly from each light source and sample light that propagates from each light source to the detector via the brain tissue of the subject. The reference light can propagate along a common reference channel or along independent reference channels. Each light source can be delivered via one or more other channels, such as other reference channels (e.g., such as Figure 2b shown) are coupled to a common reference channel. Figure 2a , a common optical combiner 122, a common optical channel 123, and a common optical splitter 124 are shown, but this division should not be considered limiting. For example, the functionality can be provided by an optical combiner and an optical splitter - for example, as long as the optical signal branched to the sample arm and the reference arm will contain light from either / both light sources.

[0150] It should be understood that the specific arrangement of the signal processing circuits of the detectors shown should not be considered limiting. Each light detection arrangement 130 is used to combine sample light and reference light to provide a combined light signal having a component of one or more beat frequencies, and to process those combined light signals to determine one or more characteristics of the subject's brain tissue. Any suitable signal processing and / or conversion circuitry may be used. For example, a transimpedance amplifier may not be required (e.g., depending on the photodetector / ADC, a current-to-voltage conversion may not be required, or this may be performed in a different manner). Similarly, a balanced photodetector need not be used, but a single photodetector, such as a photodiode, may be used. Similarly, the arrangement shown in the figure with an ADC need not be considered limiting. For example, multiple ADCs may be used (e.g., one for each detector output stream), or all detector output streams may be fed into a common ADC.

[0151] It will be appreciated from the above discussion that the examples shown in the accompanying drawings are merely exemplary and include features that may be generalized, removed, or replaced as described herein and in the claims. In general, with reference to the accompanying drawings, it will be appreciated that schematic functional block diagrams are used to indicate the functionality of the systems and devices described herein. In addition, processing functions may also be provided by devices supported by electronic devices. However, it should be understood that the functionality does not need to be divided in this manner and should not be construed as meaning any specific hardware structure other than the hardware described and claimed below. The functionality of one or more elements shown in the accompanying drawings may be further subdivided and / or distributed in the device of the present disclosure. In some examples, the functionality of one or more elements shown in the accompanying drawings may be integrated into a single functional unit.

[0152] As readers in the art will appreciate in the context of the present disclosure, each example described herein can be implemented in a variety of different ways. Any feature of any aspect of the present disclosure can be combined with any other aspect of the present disclosure. For example, method aspects can be combined with device aspects, and features described by the operation of specific elements of reference devices can be provided in methods that do not use those specific types of devices. In addition, unless it is explicitly stated that certain other features are necessary for its operation, each feature of each example is intended to be independent of the features described in combination therewith. Each of these independent features can of course be combined with any other feature of the example describing the feature, or combined with any other feature or combination of features of any other example described herein. In addition, without departing from the present invention, equivalents and modifications not described above may also be adopted.

[0153] Certain features of the methods described herein may be implemented in hardware, and one or more functions of the device may be implemented in method steps. It will also be understood that in the context of the present disclosure, the methods described herein do not need to be performed in the order in which the methods are described, nor in the order in which the methods are described in the accompanying drawings. Therefore, the aspects of the present disclosure described with reference to a product or device are also intended to be implemented as a method, and vice versa. The methods described herein may be implemented in a computer program, or hardware, or any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such a program may be provided as a signal or network message, and may be recorded on a computer-readable medium, such as a tangible computer-readable medium that may store a computer program in a non-temporary form. Hardware includes computers, handheld devices, programmable processors, general-purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and logic gate arrays.

[0154] Any controller of the present disclosure may be implemented with fixed logic or programmable logic such as software and / or computer program instructions executed by a processor such as a logic gate component. The controller may include a central processing unit (CPU) and its associated memory, which may be connected to a graphics processing unit (GPU) 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 any other type of digital logic, software, code, electronic instructions, flash memory, 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). Specifically, any controller of the present disclosure may be provided by an ASIC.

[0155] Other examples and variations of the present disclosure will be apparent to skilled artisans in the context of the present disclosure.

Claims

1. An interferometric near-infrared spectroscopy (iNIRS) system, comprising: Lighting arrangement, comprising: a first light source for providing wavelength-scanned light emission via a plurality of different wavelengths in a first wavelength range; a second light source for providing wavelength-scanned light emission at a plurality of different wavelengths in a second wavelength range different from the first wavelength range; a common sample delivery channel coupled to each of the first light source and the second light source to receive light from the first light source and the second light source and deliver the light to a subject; and one or more reference channels, for receiving reference light from the first light source and / or the second light source; a light detection arrangement including an interferometric optical detector; wherein the optical detector is coupled to the one or more reference channels for receiving reference light from the first light source and the second light source; wherein the light detection arrangement is arranged to be coupled to the object so that the optical detector receives sample light from the first light source and the second light source, the sample light comprising light propagating along the common sample delivery channel; wherein the optical detector is arranged to combine the sample light with the reference light to provide a combined light signal, the combined light signal comprising one or more components of a beat frequency between the sample light and the reference light; and Wherein, the iNIRS system is used to process the combined optical signal to provide imaging and analysis of the object.

2. An iNIRS system according to any one of the preceding claims, wherein: The optical detector is used to: (i) combine sample light from the first light source with reference light from the first light source, and (ii) combine sample light from the second light source with reference light from the second light source.

3. The iNIRS system according to claim 2, wherein: The iNIRS system includes a controller for determining an indication of a scattering coefficient and / or an absorption coefficient of sample light from the first light source and sample light from the second light source.

4. The iNIRS system according to claim 3, wherein: The controller is used to determine an indication of blood oxygen concentration based on the absorption coefficient of sample light from the first light source and the second light source.

5. The iNIRS system according to claim 4, wherein: The controller is to determine the indication of blood oxygen concentration based on blood absorption data indicating relative absorption coefficients of oxyhemoglobin and deoxyhemoglobin at wavelengths of light in the first wavelength range and the second wavelength range.

6. The iNIRS system according to any one of claims 2 to 5, wherein: The controller is for determining an indication of an optical path length of sample light from the first light source and the second light source based on a beat frequency present in an associated combined light signal of the first light source and the second light source.

7. The iNIRS system according to claim 6, wherein: The controller is configured to determine an indication of a depth resolved scattering coefficient and / or absorption coefficient of the object based on the determined scattering coefficients and absorption coefficients associated with different optical path lengths.

8. The iNIRS system according to claim 7, wherein: The controller is configured to determine an indication of a depth-resolved blood oxygen concentration of the subject based on the determined depth-resolved absorption coefficient.

9. The iNIRS system according to claim 8, wherein: The controller is for determining an indication of a blood flow index of the subject for each of the first wavelength range and the second wavelength range.

10. The iNIRS system according to claim 9, wherein: The controller is configured to determine an indication of the subject's total tissue oxygenation metabolism based on the determined blood flow index and the blood oxygenation concentration of the subject.

11. An iNIRS system according to any one of the preceding claims, wherein: The first wavelength range includes wavelengths above an oximetry isoabsorption wavelength, and the second wavelength range includes wavelengths below the oximetry isoabsorption wavelength.

12. An iNIRS system according to any one of the preceding claims, wherein: The system is for coupling to the subject's scalp to provide neural imaging and analysis of the subject's brain tissue.

13. An iNIRS system according to any one of the preceding claims, wherein: The iNIRS system comprises a plurality of interferometric optical detectors, wherein each detector is coupled to the one or more reference channels for receiving reference light from the first and second light sources, and wherein each optical detector is arranged for receiving sample light from the subject.

14. An iNIRS system according to any one of the preceding claims, wherein: The light emitting arrangement comprises a light combiner arranged to combine light from each of the first and second light sources onto a common light channel.

15. The iNIRS system according to claim 14, wherein: The common optical channel is coupled to the common sample delivery channel, or wherein the common optical channel is the common sample delivery channel, optionally wherein the optical combiner comprises a wavelength division multiplexer and / or a polarization beam splitter.

16. An iNIRS system according to any one of the preceding claims, wherein: The light emission arrangement comprises a light splitter arranged to split light from the first light source and / or the second light source between the common sample delivery channel and the one or more reference channels.

17. An iNIRS system according to any one of the preceding claims, wherein: The lighting arrangement comprises: a first optical splitter arranged to split light from the first light source onto a first sample delivery channel and a first reference delivery channel; a second optical splitter arranged to split light from the second light source onto a second sample delivery channel and a second reference delivery channel; and a sample common light combiner arranged to combine light from the first sample delivery channel and light from the second sample delivery channel onto the common sample delivery channel, optionally wherein the light emission arrangement further comprises a reference common light combiner arranged to combine light from the first reference delivery channel and light from the second reference delivery channel onto a common reference delivery channel, and optionally wherein the optical detector is coupled to the common reference channel for receiving reference light from the common reference channel.

18. An iNIRS system according to any one of the preceding claims, wherein: The lighting arrangement comprises: a common light combiner arranged to combine light from the first light source and the second light source, optionally wherein the common light combiner is arranged to couple the first light source and the second light source to a common light channel; and A common optical splitter is coupled to the common optical combiner and is arranged to split the light received from the common optical combiner onto the common sample delivery channel and the common reference channel, optionally wherein the common optical splitter is arranged to couple the common optical channel to the common sample delivery channel and the common reference channel.

19. An iNIRS system according to any one of the preceding claims, wherein: At least one of the following: the light emitting arrangement being for providing time division multiplexing for emission of light from the first light source and the second light source; the light emitting arrangement being for providing wavelength division multiplexing for emission of light from the first light source and the second light source; and / or The difference between (i) an expected optical path length of sample light propagating from the first light source to the optical detector and (ii) an optical path length of reference light propagating from the first light source to the optical detector is different from the difference between (iii) an expected optical path length of sample light propagating from the second light source to the optical detector and (iv) an optical path length of reference light propagating from the second light source to the optical detector to suppress spectral overlap between beat frequencies associated with the first light source and the second light source.

20. An iNIRS system according to any one of the preceding claims, wherein: The light emitting arrangement comprises a wavelength division multiplexer, and the light detecting arrangement comprises a wavelength division multiplexer; wherein the light emitting arrangement is for providing emission of light from the first light source and light from the second light source, wherein the emission is wavelength multiplexed; and The optical detection arrangement is used to wavelength demultiplex the combined optical signal so that the combined optical signal associated with the first light source and the combined optical signal associated with the second light source are processed separately.

21. An iNIRS system according to any one of the preceding claims, wherein: Each light source has an associated optical amplifier to increase the output power of light emitted from the light source.

22. The iNIRS system of any of the preceding claims, further comprising a plurality of light delivery channels and an optical switch for selectively directing light from the first light source and the second light source to each of the plurality of light delivery channels.

23. An iNIRS system according to any one of the preceding claims, wherein: The system is arranged to provide a wavelength dependent delay in one of a common sample channel and a common reference channel.

24. An interferometric near-infrared spectroscopy (iNIRS) method, comprising: operating the first light source to provide wavelength-swept light emission via a plurality of different wavelengths in a first wavelength range; operating a second light source to provide wavelength-swept light emission at a plurality of different wavelengths in a second wavelength range different from the first wavelength range; directing light from each of the first light source and the second light source into a common sample delivery channel and toward a subject; directing reference light from the first light source and / or the second light source to one or more reference channels; combining, at an interferometric optical detector, reference light received from the one or more reference channels and sample light received from the subject to provide a combined light signal, the sample light comprising light delivered to the subject through the common sample delivery channel, the combined light signal comprising one or more components of a beat frequency between the sample light and the reference light; as well as The combined light signal is processed to provide imaging and analysis of the object.

25. A computer program product comprising computer program instructions for programming a processor to control the operation of an interferometric near infrared spectroscopy system to perform the method according to claim 24.

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