Interferometric near-infrared spectroscopy system

Abstract

An interferometric near-infrared spectroscopy (iNIRS) system comprising: an emission mechanism comprising a light source configured to provide a wavelength-swept emission of light; and an optical detection mechanism comprising an interferometric optical detector, wherein the iNIRS system comprises a plurality of optical channels arranged to define: (i) a first optical channel path arranged to extend between the light source and the object to deliver first sample light from the light source to the object and (ii) between the object and the detector to deliver first sample light received from the object to the detector; (i) a second optical channel path arranged to extend between the light source and the object to deliver second sample light from the light source to the object and (ii) between the object and the detector to deliver second sample light received from the object to the detector; and a reference optical channel path arranged to extend between the light source and the detector to deliver reference light from the light source to the detector along the reference channel.

Description

[Technical Field]

[0001] The present disclosure relates to the field of interferometric near-infrared spectroscopy ("iNIRS") systems, which may be provided, for example, for neuroimaging and analysis. [Background technology]

[0002] Near-infrared spectroscopy ("NIRS") is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (e.g., between 700 nm and 2500 nm). NIRS systems can be used to provide noninvasive monitoring of the scattering and absorption properties of a medium. Because radiation at NIRS wavelengths is less absorbed by human skin (and by bone) than visible light, NIRS radiation can penetrate both the skin and the skull and into brain tissue. NIRS can be used as a technique for noninvasive imaging of human brain tissue by monitoring the scattering and absorption properties of NIRS radiation within brain tissue.

[0003] When multiple wavelengths are used, NIRS methods can be extended to monitor oxygenation, but blood flow monitoring is necessary to infer metabolic information. Diffuse correlation spectroscopy (DCS) can be used to noninvasively monitor blood flow in the brain by measuring the temporal fluctuations of light re-emitted from a sample. Furthermore, DCS can extract other brain indices, including intracranial pressure (ICP). However, to extract flow, existing DCS methods require additional devices and heavy averaging, making the final method bulky, unwieldy, and slow. Furthermore, to quantify blood flow, DCS requires optical characteristics that are typically assumed or realized from a separate NIRS instrument. Finally, because DCS and NIRS rely only on light intensity, they eliminate half of the information about scattered light, which is encoded in optical phase. As a result, measurements are affected by additional assumptions made by ignoring phase information.

[0004] It is therefore desirable to provide an improved technique for neuromonitoring and analysis that combines NIRS and DCS into a single modality to rapidly provide optical and dynamic properties of biological tissues. Summary of the Invention [Means for solving the problem]

[0005] Aspects of the disclosure are set out in independent claims, and optional features are set out in dependent claims. Aspects of the disclosure may be provided in conjunction with one another, and features of one aspect may be applied to other aspects.

[0006] In one aspect, an interferometric near-infrared spectroscopy (iNIRS) system is provided, comprising: a light emission mechanism comprising a light source configured to provide a wavelength-swept emission of light; and a light detection mechanism comprising an interferometric photodetector. The iNIRS system comprises a plurality of light channels arranged to define: (i) a first light channel path arranged to extend between the light source and the object to deliver first sample light from the light source to the object and (ii) between the object and the detector to deliver first sample light received from the object to the detector; (i) a second light channel path arranged to extend between the light source and the object to deliver second sample light from the light source to the object and (ii) between the object and the detector to deliver second sample light received from the object to the detector; and a reference light channel path arranged to extend between the light source and the detector to deliver reference light from the light source to the detector along the reference channel. The detector is arranged to combine the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light, and to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light, the first optical channel path having a different length relative to the second optical channel path to prevent spectral overlap between the first beat frequencies and the second beat frequencies.

[0007] Embodiments may enable the detector to provide a single interferogram including two separate beat frequency distributions. The two beat frequency distributions may be separated and used to provide two separate time-of-flight distributions for the sample light photons. Digital processing may be performed on both of these distributions to provide imaging of the object. Embodiments may enable more data to be acquired for each measurement cycle. Also, embodiments may enable more data to be acquired without requiring additional signal processing circuitry. For example, more sample light photon time-of-flight distributions may be acquired from each single digitizer channel of the analog-to-digital converter.

[0008] An iNIRS system is arranged so that there are two or more optical paths that a photon of sample light can take through an optical channel of the iNIRS system. That is, the system is arranged so that a sample light photon emitted from a light source and received at a detector travels two or more different routes, for example, through two or more different portions of the optical channel (regardless of the path the sample light photon took through the object being imaged). For example, an iNIRS system may include at least one of (i) two different sample delivery channels connecting the light source to the object being imaged and (ii) two different sample receiving channels connecting the object being imaged to the detector. The difference in optical channel path length may be provided by making one of the sample delivery channels a different length relative to the other sample delivery channel and / or by making one of the sample receiving channels a different length relative to the other sample receiving channel. For example, an iNIRS system may include two sample delivery channels and two sample receiving channels, one sample delivery channel longer than the other sample delivery channel and one sample receiving channel longer than the other sample receiving channel. Each different light channel path may comprise a different combination of sample delivery and sample receiving channels through which light may travel between the light source and the detector.

[0009] One aspect of the present disclosure may provide an interferometric near-infrared spectroscopy (iNIRS) system comprising: a light source configured to provide a wavelength-swept emission of light; a light emission mechanism comprising: a light source configured to provide a wavelength-swept emission of light; a sample delivery channel connected to the light source and arranged to be connected to an object to be imaged to direct light from the light source toward the object; and a reference channel connected to the light source to receive light from the light source; a first sample receiving channel arranged to be connected to the object to receive first sample light from the object; and a second sample receiving channel arranged to be connected to the object to receive second sample light from the object, wherein each of the first sample light and the second sample light comprises light emitted from the light source; and a light detection mechanism comprising: an interferometric photodetector connected to (i) the first sample receiving channel to receive the first sample light, (ii) the second sample receiving channel to receive the second sample light, and (iii) the reference channel to receive the reference light. The optical detector is arranged to combine the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light, and to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light, wherein the first sample receive channel has a different length relative to the second sample receive channel to prevent spectral overlap between the first beat frequency and the second beat frequency.

[0010] Another aspect of the present disclosure may provide an interferometric near-infrared spectroscopy (iNIRS) system comprising: a light source configured to provide a wavelength-swept emission of light; a light emission mechanism comprising: a first sample delivery channel connected to the light source and arranged to be connected to an object to direct light from the light source toward the object; a second sample delivery channel connected to the light source and arranged to be connected to the object to direct light from the light source toward the object; and a reference channel connected to the light source to receive light from the light source; a sample receiving channel arranged to be connected to the object to receive first sample light and second sample light from the object, wherein the first sample light includes light emitted from the light source that has traveled along the first sample delivery channel and the second sample light includes light emitted from the light source that has traveled along the second sample delivery channel; and a light detection mechanism comprising: an interferometric photodetector connected to the sample receiving channel that receives the first sample light and the second sample light and (ii) the reference channel that receives the reference light. The optical detector is arranged to combine the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light, and to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light, wherein the first sample delivery channel has a different length relative to the second sample delivery channel to prevent spectral overlap between the first beat frequency and the second beat frequency.

[0011] Such examples may provide an iNIRS system in which two (or more) optical channel paths are defined (whether by using two or more sample delivery channels and / or two or more sample receiving channels), the two different optical channel paths having different lengths so as to avoid spectral overlap between the first beat frequency and the second beat frequency.

[0012] For iNIRS systems of the present disclosure, a portion of the first optical channel path may share a common optical channel with a portion of the second optical channel path, which may (i) connect the light source to the subject or (ii) connect the subject to the detector.

[0013] The multiple optical channels may include a sample delivery channel connected to the light source and arranged to be connected to the object to direct first and second sample light from the light source toward the object, a first sample receiving channel arranged to be connected to the object to receive the first sample light from the object, and a second sample receiving channel arranged to be connected to the object to receive the second sample light from the object. For example, the iNIRS system may have two separate sample receiving optical channels. The first optical channel path may include the sample delivery channel and the first sample receiving channel (e.g., may be provided by the sample delivery channel and the first sample receiving channel). The second optical channel path may include the sample delivery channel and the second sample receiving channel (e.g., may be provided by the sample delivery channel and the second sample receiving channel). The first sample receiving channel may have a different length than the second sample receiving channel, thereby providing a length difference between the first optical channel path and the second optical channel path. For example, the optical channel path length difference may be provided using sample receiving channels of different lengths. A reference channel may connect the light source to the detector. For example, the detector may be connected to each of (i) a first sample receiving channel that receives the first sample light, (ii) a second sample receiving channel that receives the second sample light, and (iii) a reference channel that receives the reference light.

[0014] The iNIRS system may include an analog-to-digital converter (ADC) configured to acquire sample data including a representation of the first and second beat frequencies detected by the photodetector. The sample data may include interferogram data. For example, the sample data may include data indicative of an interferogram acquired by an interferometer of the detector. That is, a first portion of the sample data may represent a portion of the interferogram including the first beat frequency, and a second portion of the sample data may represent a portion of the interferogram including the second beat frequency. The iNIRS system may be configured to use a single ADC channel to acquire sample data for both the first and second beat frequencies. In other words, the ADC may be configured to acquire digital signals indicative of two simultaneously acquired beat frequency distributions (of the first and second beat frequencies). The digital signals may be filtered and separated, for example, using an FFT, to provide two separated distributions (acquired simultaneously using the same detector). The system may include a controller configured to process the sample data to obtain (i) first sample data including an indication of a first beat frequency detected by the photodetector, and (ii) second sample data including an indication of a second beat frequency detected by the photodetector. For example, the controller may be capable of separating data associated with the first sample light from data associated with the second sample light. Processing the sample data may include separating the first sample data from the second sample data based on the indication of the beat frequency.

[0015] The controller may be configured to process the sample data such that (i) the first sample data includes a detected beat frequency below a threshold frequency and (ii) the second sample data includes a detected beat frequency above the threshold frequency. The controller may be configured to (i) obtain first time-of-flight data for the first sample light based on the first sample data, and (ii) obtain second time-of-flight data for the second sample light based on the second sample data. For example, the controller may first obtain time-of-flight data (e.g., for an interferogram) and then separate the first sample data and the second sample data based on their respective times of flight. The controller may be configured to average the first time-of-flight data and the second time-of-flight data to provide combined time-of-flight data. The controller may be configured to align the first time-of-flight data with the second time-of-flight data based on a time offset associated with a difference in length between the first and second optical channel paths (e.g., a difference in length between the first and second sample receiving channels and / or the first and second sample delivery channels). Aligning the first time-of-flight data with the second time-of-flight data may include at least one of: (i) applying a fixed time offset associated with a difference in the duration it takes light to travel along the first and second optical channel paths (e.g., due to a difference in length of the sample receiving channel and / or the sample delivery channel); and (ii) applying a time offset based on aligning one or more features in the first time-of-flight data with corresponding features in the second time-of-flight data. For example, the features may include a peak value (e.g., a time-of-flight at which a maximum intensity amplitude occurs), a minimum / maximum value (e.g., a lowest or highest time-of-flight in a time-of-flight distribution), and / or an average value (e.g., an average of all registered time-of-flight values, e.g., a mean value).

[0016] The difference in length between the first and second optical channel paths (e.g., between the first and second sample receiving channels and / or between the first and second sample delivery channels) may be at least as great as the distance corresponding to the expected time width (e.g., spectral width) for the time-of-flight distribution (DTOF) associated with the first sample light. The iNIRS system may include multiple optical channels arranged to define three or more optical channel paths arranged to extend (i) between the light source and the subject and (ii) between the subject and the detector, each of the optical channel paths having a different length from one another to prevent spectral overlap between the beat frequencies associated with each of the optical channel paths. For example, there may be three different sample receiving channels and / or sample delivery channels, each having a different length relative to the others. The number of different optical channel paths (e.g., different combinations of sample delivery and sample receiving channels through which light may travel between the light source and the detector) may be selected based on the digitization bandwidth for a single ADC channel. For example, the number (and organization) of different optical channel paths may be selected to maximize utilization of the full digitized bandwidth while preventing spectral overlap between the beat frequencies associated with each respective optical channel path.

[0017] The light detection mechanism may include a beam combining element that combines light from the different sample receiving channels into a single channel. The detector may be connected to the single channel to receive the sample light from the single channel. The light source may be a first light source, and the light emission mechanism may include a second light source. The interferometric light detector may be positioned to receive the first sample light from the second light source, the second sample light from the second light source, and the second reference light from the second light source.

[0018] The light detection mechanism may be a first light detection mechanism, and the iNIRS system may include a second light detection mechanism, which may include a second detector. The multiple light channels may be arranged to define: (i) a third light channel path arranged to extend between the light source and the object to deliver third sample light from the light source to the object and (ii) extend between the object and the second detector to deliver third sample light received from the object to the second detector; (i) a fourth light channel path arranged to extend between the light source and the object to deliver fourth sample light from the light source to the object and (ii) extend between the object and the second detector to deliver fourth sample light received from the object to the second detector; and a second reference light channel path arranged to extend between the light source and the second detector to deliver reference light from the light source to the second detector along a second reference channel. For example, the second optical detection mechanism may include a third sample receiving channel arranged to be connected to the object to receive the third sample light from the object, a fourth sample receiving channel arranged to be connected to the object to receive the fourth sample light from the object (each of the third sample light and the fourth sample light includes light emitted from a light source), and a second interferometric optical detector connected to (i) the third sample receiving channel to receive the third sample light, (ii) the fourth sample receiving channel to receive the fourth sample light, and (iii) a reference channel to receive the reference light. The second detector may be arranged to combine the reference light with the third sample light to provide optical signals at a plurality of third beat frequencies between the third sample light and the reference light, and to combine the reference light with the fourth sample light to provide optical signals at a plurality of fourth beat frequencies between the fourth sample light and the reference light. The third optical channel path may have a different length from the fourth optical channel path to prevent spectral overlap between the third beat frequency and the fourth beat frequency (e.g., the third sample receiving channel may have a different length from the fourth sample receiving channel). The iNIRS system may be configured to average data obtained from each of the first through fourth detected beat frequencies (e.g., associated with each of the first through fourth sample lights).

[0019] The plurality of optical channels may include a first sample delivery channel connected to the light source and arranged to be connected to the object to direct a first sample light from the light source toward the object, a second sample delivery channel connected to the light source and arranged to be connected to the object to direct a second sample light from the light source toward the object, and a sample receiving channel arranged to be connected to the object to receive the first sample light and the second sample light from the object. The first optical channel path may include the first sample delivery channel and the sample receiving channel. The second optical channel path may include the second sample delivery channel and the sample receiving channel. The first sample delivery channel may have a different length relative to the second sample delivery channel to provide a length difference between the first optical channel path and the second optical channel path.

[0020] The plurality of light channels may comprise a first sample delivery channel connected to the light source and arranged to be connected to the object to direct light from the first light source towards the object; a second sample delivery channel connected to the light source and arranged to be connected to the object to direct light from a second light source towards the object; a first sample receiving channel arranged to be connected to the object to receive from the object the first sample light from the first sample delivery channel and the first sample light from the second sample delivery channel; and a second sample receiving channel arranged to be connected to the object to receive from the object the second sample light from the first sample delivery channel and the second sample light from the second sample delivery channel. To prevent spectral overlap between (i) a first beat frequency for the first sample light from the first sample delivery channel, (ii) a first beat frequency for the first sample light from the second sample delivery channel, (iii) a second beat frequency for the second sample light from the first sample delivery channel, and (iv) a second beat frequency for the second sample light from the second sample delivery channel, the first sample delivery channel may have a different length than the second sample delivery channel, and the first sample receiving channel may have a different length than the second sample receiving channel.

[0021] Embodiments may provide an iNIRS system for neuroimaging and analysis of a subject's brain tissue. For example, the object being imaged may be the subject's brain. Here, an image of the subject's brain is formed noninvasively by simultaneously measuring multiple locations. The multiple measurements are achieved by coupling first and second light source channels to first and second receiver channels in a spatial pattern.

[0022] Each light source may comprise a light-generating element arranged to generate light (e.g., near-infrared light) and an optical mechanism for directing the light. For example, each light-generating element may comprise a laser. The optical mechanism may be arranged to direct a portion of the light from the light-generating element toward the area to be sampled. Each light-delivery channel and / or light-receiving channel may comprise an optical channel, such as an optical fiber. Each optical channel may be configured to transmit light along its length (e.g., from the light-generating element toward the object being imaged and / or from the object toward the photodetector). Each light source's optical mechanism may comprise an optical splitter that separates the light into each of the different delivery optical channels. The iNIRS system may be arranged such that, when placed on a subject's head (e.g., to provide neuroimaging and analysis of the subject's brain tissue), each light source's optical mechanism is configured to direct a portion of the light toward the subject's scalp (e.g., through one or more sample delivery channels). For example, the light mechanism of each light source may comprise a light splitter configured to separate the light received from the light generating element into each of the different channels (e.g., into a reference channel and one or more sample delivery channels).

[0023] The iNIRS system may be configured such that, in use when placed on a subject's head, sample light may be directed (e.g., through a sample delivery channel) to the subject's scalp and brain tissue, and reference light may be directed (e.g., through a reference delivery channel) to each photodetector. Each light source may be configured to provide a (e.g., wavelength-swept) emission of light (e.g., each light source may be configured to output light at each of a plurality of different wavelengths for a selected period of time). For example, each light source may include a modifying element that controls operation of the light-generating element to output light at each of a plurality of different wavelengths. Each light source may be configured to sweep the wavelength of the light output by that light source (e.g., increase or decrease the wavelength). Each light source may be configured to provide a chirp emission of light, with each chirp (or "pulse") comprising one wavelength sweep. Each light source may be configured, for example, to output successive chirps with the same wavelength sweep, such that the wavelength of the light output from the light source varies according to a repeating pattern.

[0024] Each photodetector may provide an interferometric photodetector. Each photodetector may include an optical mechanism. The optical mechanism of the photodetector is configured to direct detected light (e.g., from the subject's scalp) to the photodetector. The optical mechanism of the photodetector may include one or more optical receiving channels. The iNIRS system may be arranged such that, when placed on the subject's head (e.g., to provide neuroimaging and analysis of the subject's brain tissue), the optical mechanism of the photodetector is configured to receive light emitted from the light source (e.g., that has traveled from the light source through the subject's brain tissue). The photodetector may include an optical combiner (e.g., to combine light on a reference receiving channel with light on one or more sample receiving channels). Each photodetector is configured to convert a received combined optical signal into one or more electrical signals indicative of the combined optical signal (e.g., to provide interferogram data). For example, the detector may include one or more photodiodes. Each photodiode may output an electrical signal (e.g., a current) indicative of the combined optical signal. The detector may comprise a balanced photodetector (e.g., the balanced photodetector may comprise two photodiodes that may be 180° out of phase with each other, and the output of the balanced photodetector may be a combination of the two photodiode current outputs). The detector may optionally comprise a current-to-voltage conversion circuit and / or one or more amplifiers that amplify the electrical signal. The amplifier may be used with a specified gain to scale the voltage signal to achieve an optimal dynamic range of the signal received from the brain, i.e., the intense early-arriving photons and the late-arriving photons.

[0025] The iNIRS system may include at least one analog-to-digital converter arranged to convert an electrical signal indicative of the sampled light (e.g., the combined optical signal) into one or more digital signals. The controller is arranged to process the digital signals to determine one or more properties related to the subject's brain tissue. The controller may be configured to determine optical properties of the subject's brain tissue (e.g., related to absorption and / or scattering). The controller may be configured to determine one or more dynamic properties of the subject's brain tissue (e.g., properties of the subject's brain tissue that change over time). For example, the controller may be configured to detect the presence of movement within the subject's brain tissue (e.g., due to movement, e.g., flow, of blood within the brain tissue).

[0026] The controller may be configured to process the digital signals to obtain time-of-flight information for photons of the first and second sample lights traveling from each light source through the subject's brain tissue to the photodetector. The controller may be configured to identify penetration depths (optionally, expected trajectories for the photons through the brain tissue) associated with different times-of-flight for the sample light photons. The controller may be configured to obtain time-of-flight distributions of a time-ordered series for the sample light photons reaching each photodetector. The controller may be configured to process the time-ordered series to identify changes in the time-of-flight distributions over time, e.g., to identify attenuation and / or decay rates between the resulting time-of-flight distributions. The controller may be configured to provide depth-resolving processing, e.g., by filtering the time-of-flight data to focus only on photons within a selected time-of-flight range (e.g., to identify changes in the optical properties of the brain tissue for the penetration depth associated with that time-of-flight range). The controller may be configured to process the data received from the photodetector to provide time-of-flight information including depth-resolved autocorrelation for the subject's brain tissue.

[0027] The controller may be configured to process received data indicative of the sampled light received at the photodetector and output a control signal based on the received data. The control signal may provide an indication of the time-of-flight distribution (e.g., the controller may be configured to output the time-of-flight distribution). The control signal may provide an indication of one or more properties determined based on the time-of-flight distribution, such as optical properties related to brain tissue (e.g., scattering coefficient and / or absorption coefficient, and / or how the scattering coefficient and / or absorption coefficient has / is changing). The control signal may provide an indication of blood flow within the subject's brain tissue. The control signal may provide a depth-resolved indication of one or more properties related to the subject's brain tissue (e.g., tied to a particular region within the subject's brain tissue, such as a selected penetration depth range). The control signal may comprise an indication of one or more properties related to the subject's brain tissue, such as intracranial pressure, blood flow index, arterial elasticity, cerebral metabolic rate of oxygen consumption, etc. Medical properties may be associated with a particular region / depth within the subject's brain tissue. The control signal may comprise an actuation command to a brain-computer interface, for example, to control operation of a device based on the actuation command. The control signal may comprise an image for display, where the image shows a portion of the subject's brain tissue (as determined based on the received sample light). [Brief explanation of the drawings]

[0028] Some examples of the present disclosure will now be described, by way of example only, with reference to the figures. [Figure 1] FIG. 1 shows a schematic diagram of an exemplary iNIRS system. [Figure 2] FIG. 2 shows a graph showing time-of-flight data for incident photons. [Figure 3a] FIG. 3a shows a schematic diagram of an exemplary iNIRS system. [Figure 3b] FIG. 3b shows a schematic diagram of an exemplary iNIRS system. [Figure 3c] FIG. 3c shows a schematic diagram of an exemplary iNIRS system. [Figure 3d] FIG. 3d shows a schematic diagram of an exemplary iNIRS system. [Figure 3e] FIG. 3e shows a schematic diagram of an exemplary iNIRS system.

[0029] In the various drawings, like reference numbers are used to indicate like elements. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present disclosure relates to an iNIRS system for an imaged object. In this regard, the system is arranged so that light is directed toward the object along one or more sample-delivery optical channels, and a portion of that light is received from the object and directed toward a photodetector along one or more sample-receiving optical channels. These optical channels are arranged so that there are at least two different optical paths between the light source and the object and / or at least two different optical paths between the object and the detector. The channels are arranged so that these optical paths have different lengths. Thus, light may travel along optical channels of different lengths as it travels from the light source (through the imaged object) to the detector, depending on which channel the light travels through. This difference in optical channel length is sufficient so that when the received light is combined with the reference light at the detector, there is minimal or no spectral overlap between the resulting beat frequencies associated with a first optical path length through the optical channel and a second optical path length through the optical channel. Thus, two different time-of-flight distributions may be obtained through one digitizer channel.

[0031] An example of an interferometric near-infrared spectroscopy ("iNIRS") system will now be described with reference to FIG.

[0032] FIG. 1 shows a schematic diagram of an interferometric near-infrared spectroscopy ("iNIRS") system 10. The iNIRS system 10 includes a light source 20, at least one detector 30, and a controller 40. The system 10 may include multiple detectors 30, although only two are shown in FIG. 1. Inset A shows a more detailed view of the light detector 30 shown within dashed box A in FIG. 1.

[0033] The iNIRS system 10 may include a light source modifier 22 and a light splitter 24. The iNIRS system 10 includes a sample delivery channel 25 and a reference delivery channel 26. The iNIRS system 10 is shown connected to the object to be imaged, which in this example may be a subject's head 2 (e.g., to provide neuroimaging). The iNIRS system 10 includes a sample delivery probe 25′ and a plurality of sample receiving probes. In examples where the object is the subject's head 2, the probes may be for connecting the optical channels to the subject's scalp.

[0034] Two photodetectors 30 are shown in FIG. 1 . Each photodetector 30 has an associated reference receiving channel 36. The reference receiving channel 36 is for receiving reference light from the light source 20 (e.g., from the reference delivery channel 26). One of the photodetectors 30 shown in FIG. 1 is connected to the subject's scalp 2 via two optical channels, a first sample receiving channel 351 and a second receiving channel 352 (having a first sample receiving probe 351′ and a second sample receiving probe 352′, respectively). The other photodetector 30 shown is connected to the subject's scalp 2 via one optical channel, a sample receiving channel 35 (having an associated sample receiving probe 35′). As will be appreciated, multiple different sample receiving channels may be provided distributed around different regions of the subject's scalp (e.g., to image different regions of the subject's brain tissue). Additionally or alternatively, the sample receiving channels may be co-located on the subject's scalp, for example, so that acquired data for the subject may be averaged for the overlapping regions that each channel is imaging. In other examples, the second sample receiving probe 35', sample receiving channel 35, and detector 30 need not be provided; instead, only the first probe / receiving channel / detector is provided.

[0035] The light source modifier 22 may comprise a source that provides a variable electrical control signal (e.g., a variable current or voltage provider). The light source modifier 22 is connected to the light source 20. The light source modifier 22 may be electrically connected to the light source 20 to provide a variable current / voltage to the light source 20.

[0036] The light source 20 may comprise 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 connected to an optical splitter 24. The optical splitter 24 has an input that receives light from the light source 20. The optical splitter 24 has two outputs that transmit light from the light source 20 into two separate channels. A sample delivery channel 25 is connected to the optical splitter 24 (to receive light from the optical splitter 24), as is a reference delivery channel 26. The sample delivery channel 25 connects the optical splitter 24 to a sample delivery probe 25'. The sample delivery probe 25' is placed at a location on the subject's scalp.

[0037] Other types of suitable lasers include distributed Bragg reflector lasers ("DBRs"), Fourier-domain mode-locked lasers ("FDMLs"), and vertical-cavity surface-emitting lasers ("VCSELs"). Additionally or alternatively, pulsed supercontinuum lasers may be used in combination with a pulse-stretching mechanism such as a grating, a GRISM pulse stretcher, or a length of dispersive optical fiber. For example, the mechanism may be configured to temporally separate wavelengths in the pulses such that frequency-chirped pulses are created (e.g., to ultimately provide an interferogram when the sample and reference pulses are compared). Additionally or alternatively, wavelength sweeping may be provided using a high-coherence laser, such as an external-cavity diode laser (ECDL), a DBR laser, a feedback-stabilized laser, or a line-locked laser, by passing the output through an electro-optic IQ modulator. The IQ modulator may be driven by an electronic signal, thereby shifting the wavelength of the light without having to directly modulate the light source (e.g., a laser). This may provide SNR advantages and may result in higher coherence light than if the laser were directly modulated, and this setup may be combined with an optical amplifier to achieve a so-called master oscillator power amplifier (MOPA) configuration.

[0038] The reference delivery channel 26 connects the optical splitter 24 to each of the photodetectors 30. For each detector 30, a reference delivery connection 28 may be provided to connect the reference delivery channel 26 to a reference receiving channel 36 for that detector 30. Each reference receiving channel 36 is connected to the photodetector 30 of the respective reference receiving channel 36. In other words, each photodetector 30 may be connected to the light source 20 to receive reference light directly from the light source 20 (via one or more reference channels). Each sample receiving probe may be placed on the subject's scalp. Each sample receiving probe may be connected to an associated sample receiving channel. Each sample receiving channel is connected to the photodetector 30 of that respective sample receiving channel. In other words, each photodetector 30 is connected to receive sample light indirectly from the light source 20 (e.g., to receive light that has traveled through the sample delivery channel, through a portion of the subject's head, and into the receiving channel associated with that detector 30).

[0039] There may be multiple different photodetectors 30. Each detector 30 may provide an interferometer, such as a Mach-Zehnder interferometer, when receiving sample light and reference light from the light source. Each of the different photodetectors 30 may be connected to the same light source 20 (each via one or more reference channels). The photodetectors 30 may be spatially separated from the light source 20. The photodetectors 30 may also be spatially separated from one another, or the photodetectors 30 may be co-located in a tissue region similar enough that the received signals can be averaged together. As the reference light travels from the light source 20 to the photodetector 30, the reference light travels directly along one or more reference channels. As the sample light travels from the light source 20 to the photodetector 30, the sample light travels indirectly through the subject's brain tissue. The sample light is directed to the subject's scalp via one or more sample delivery channels 25'. The sample light may then pass through the subject's brain tissue, travel into a receiving channel, and travel into the photodetector. Thus, illumination of the subject's brain tissue may occur using a different optical channel relative to detection of light from the subject's brain tissue.

[0040] The controller 40 may include any suitable component having data receiving and processing capabilities. 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 connected to each of the detectors. The controller 40 may be connected to each detector 30 via a wired connection (to receive electrical signals indicative of detection from each detector 30) and / or the connection may be wireless (to receive transmitted data indicative of detection from each detector 30). The controller 40 is connected to the light source modifier 22. The connection may be wired or wireless.

[0041] The iNIRS system 10 may be housed, at least in part, within a covering for the subject's head 2. For example, the iNIRS system 10 may be provided in a hat / cap worn by the subject on the subject's head 2. The iNIRS system 10 may be arranged to hold the light source 20 and the detector in a fixed mechanism against the subject's scalp. Some or all of the components of the head covering may be provided within the head covering. For example, the head covering may include multiple housings for housing the light source 20 and the photodetector 30. Channels connecting the light source and the photodetector 30 may be provided as part of the head covering (e.g., the channels may be routed through corresponding channel housings in the head covering). The controller 40 may be separate from the head covering (e.g., wirelessly connected), or the controller 40 may also be provided as part of the head covering (e.g., by an ASIC within the head covering that may be wired to the detector and / or light source modifier 22). For example, the covering may be configured to house the light source channels, the detection channels, and the probe, with the other components of the system located elsewhere.

[0042] Some or all of the optical channels of the iNIRS system 10 may be provided by optical fiber. The optical splitter of the present disclosure may comprise an optical fiber splitter. The iNIRS system 10 may also include associated lenses, reflectors, and / or refractive devices for beam steering. For example, the sample delivery probe 25' may include one or more lenses that spatially distribute sample light from the sample delivery channel 25 toward the subject's brain tissue. As another example, one or more of the sample receiving probes may include a lens that focuses the received light into a sample receiving channel associated with the received light (as connected to that sample receiving probe). As another example, the probes may be bare fiber that has been cleaved and / or polished.

[0043] The iNIRS system 10 is configured to provide multiple light source-detector pairs for each light source 20. In other words, the iNIRS system 10 is configured so that each photodetector 30 may receive two forms of light: (i) reference light and (ii) sample light. Each detector 30 is configured to receive the reference light directly from the light source 20 (e.g., the reference light travels from the light source 20 to the photodetector 30 along one or more channels without passing through the subject's brain tissue). Each detector 30 is also configured to receive the sample light indirectly from the light source 20 (e.g., the sample light is directed toward the subject's scalp tissue, and some of the sample light may travel through the subject's brain tissue on its way to the detector 30; e.g., the sample light does not travel solely through the optical channel between the light source 20 and the photodetector 30).

[0044] The detectors 30 are positioned to rest on the subject's scalp to provide imaging of selected areas of the subject's brain. At least a portion of the detectors 30 are positioned to be spatially separated from the light source 20. One or more (e.g., each) of the light detectors 30 may be positioned sufficiently far from the light source 20 so that at least a portion of the sample light photons from the light source 20 received by the light detector 30 penetrate into the subject's brain tissue. For example, the light source-detector spacing may be selected so that the light detector 30 is positioned to receive sample light photons that have experienced multiple scattering events (e.g., scattered multiple times between the light source and the detector as they move through the subject's head 2). In other words, the light source-detector spacing may be selected so that the light detector 30 receives deeply penetrating photons from the subject's brain tissue. Such photons may have a longer time of flight from the light source to the detector compared to photons that penetrate more shallowly and experience fewer scattering events.

[0045] The detectors 30 may be positioned to be spatially close to each other on the subject's scalp. The placement of the detectors 30 may be selected so that the detectors image similar regions of the subject's brain. For example, the detectors 30 may be located within a threshold distance of each other on the subject's scalp so that data acquired by the detectors 30 may be averaged (e.g., to provide an average value for the same volume of the subject's brain). That is, the detectors 30 may be positioned to spatially probe the same volume of tissue within the subject's brain. For example, the detectors may be positioned to be within one attenuation length of each other with respect to the tissue (e.g., within the sum of the absorption and scattering coefficients).

[0046] Light source 20 is positioned to generate light and direct this light toward the subject's scalp and toward photodetector 30 (via the reference channel). Light splitter 24 is positioned to receive the light generated by light source 20 and split the light into two channels: (i) toward the subject's scalp using sample delivery channel 25 and sample delivery probe 25′, and (ii) toward photodetector 30 using reference delivery channel 26 and reference receiving channel 36. The splitter is configured to direct a majority of the light toward the subject's scalp. For example, the splitter may be a 90:10 splitter or a 99:1 splitter. Sample delivery channel 25 is positioned to receive sample light from the splitter and deliver the sample light toward the subject's scalp (via sample delivery probe 25′). Reference delivery channel 26 is positioned to receive reference light from the splitter and deliver the sample light to one or more detectors 30 (via reference receiving channel 36).

[0047] Each reference delivery connection 28 is positioned to deliver a portion of the reference light traveling along the reference delivery channel 26 to one of the reference receiving channels 36. Each of the reference receiving channels 36 is positioned to deliver the reference light to its respective photodetector 30. The sample receiving probes are positioned to receive sample light from the subject's brain tissue. Each sample receiving probe may focus the received sample light into a sample receiving channel associated with the received sample light. Each sample receiving channel may be positioned to deliver the received sample light to its respective photodetector 30. The sample receiving probes may be positioned adjacent to one another on the subject's scalp.

[0048] 1, a detector connected to the subject's scalp via only one sample receiving channel 35 (and associated sample receiving probe 35') need not be provided. This detector is shown as an example to illustrate that multiple detectors may be connected to the subject's scalp (and not all of the detectors need be connected to the subject's scalp via more than one sample receiving channel). However, for the following description, reference will be made primarily to detector 30 connected to the subject's scalp via more than one sample receiving channel.

[0049] Detector 30 is connected to light source 20 via reference receiving channel 36 (and reference delivery channel 26). Detector 30 is also connected to the subject's scalp via two separate optical channels: first sample receiving channel 351 and second sample receiving channel 352. Each of these sample receiving channels may be connected to the subject's scalp via a sample receiving probe (first sample receiving probe and second sample receiving probe, respectively). First sample receiving channel 351 has a different length relative to second sample receiving channel 352. In this regard, second sample receiving channel 352 has an additional optical channel length 352a (as shown in FIG. 1). Taking into account additional optical channel length 352a, the distance light must travel from the subject's scalp through second sample receiving channel 352 to detector 30 is shorter than the distance light must travel through first sample receiving channel 351.

[0050] The first sample receiving channel 351 may be connected to the subject's scalp (e.g., via the first sample receiving probe 351′) at a location adjacent to where the second sample receiving channel 352 is connected to the subject's scalp. Thus, the first sample receiving channel 351 may be positioned such that the first sample receiving channel 351 images a substantially similar (e.g., the same) region of the subject's brain relative to the second sample receiving channel 352. That is, on average, light entering the first sample receiving channel 351 and traveling to the detector 30 will be indicative of the same region of the subject's brain as light entering the second sample receiving channel 352 and traveling to the detector 30. The difference between the two is that light traveling to the detector 30 via the second sample receiving channel 352 travels a longer distance between the subject's scalp and the detector (due to the additional optical channel length 352a).

[0051] Detector 30 is positioned to receive three inputs: (i) direct reference light from light source 20; (ii) indirect sample light from light source 20 that has traveled through a first sample receiving channel 351 (e.g., through the subject's brain tissue, through the subject's scalp, and / or skull); and (iii) indirect sample light from light source 20 that has traveled through a second sample receiving channel 352 along a longer optical path compared to first sample receiving channel 351. For example, detector 30 may include three or more input ports. A first input port of detector 30 may be connected to the reference delivery channel 26 for that detector 30. A second input port of detector 30 may be connected to the first sample receiving channel 351 for that detector 30. A third input port of detector 30 may be connected to the second sample receiving channel 352 for that detector 30. The detectors are positioned to combine the reference light with the sample light (as an interferometer). The iNIRS system 10 (e.g., the detector 30 and the controller 40) may be configured to determine one or more characteristics of the subject's brain tissue based on this combination of the reference light and the sample light (as described in more detail below). In the context of the present disclosure, it will be understood that the combination of different lights may be provided by a single component, or this may be offset. For example, the first sample light and the second sample light may be combined into a single channel, which may then be combined with a reference light-carrying channel, or three different channels may be combined into one channel in a single component.

[0052] Hereinafter, sample light received at detector 30 from the object being imaged (e.g., the subject's brain) that has traveled along first sample receiving channel 351 will be referred to as "first sample light." Similarly, sample light received at detector 30 but that has traveled along second sample receiving channel 352 will be referred to as "second sample light." The second sample light takes longer to travel from the subject's scalp to detector 30 than the first sample light due to the additional optical channel length 352a for second sample receiving channel 352. Reference light is light that has traveled directly through one or more optical channels (reference channels) from light source 20 to detector 30 (e.g., without passing through the object being imaged).

[0053] The light source 20 is configured to provide wavelength-swept emission of light. In this regard, the light source 20 may be configured to generate a series of pulses of light. During each pulse, the wavelength of the light may be "swept" through a range of wavelengths. For example, the sweep may be in the form of chirped pulses. Light is emitted at multiple different wavelengths during a pulse. For example, the wavelength may increase or decrease continuously during a pulse (the rate of change of wavelength may be constant, or the rate may be variable). Successive chirped pulses may be adjacent (e.g., with a time interval between pulses of zero). The light source 20 may be configured to continuously emit a series of pulses, each pulse having a wavelength sweep. However, it will be understood that the light source 20 need not provide a continuous sweep. For example, the light source may be adjusted in steps rather than continuously, such that the light source 20 emits light at different wavelengths at different time intervals (e.g., separate time intervals for emission at each of multiple wavelengths). Light source 20 may sweep unidirectionally (e.g., only increasing or decreasing wavelength during a single wavelength sweep), or light source 20 may sweep bidirectionally (e.g., both increasing and decreasing wavelength during a single wavelength sweep). Unidirectional sweeping can be advantageous because it increases the number of detected photons per sweep.

[0054] The controller 40 may be configured to selectively control the wavelength sweep of the light source 20. The light source modifier 22 may be arranged to control the wavelength emission of 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 a wavelength emission from the light source 20. The wavelength sweep of the light source 20 may be controlled by using the light source modifier 22 to apply a corresponding electrical signal to the light source 20. The controller 40 may be arranged to control the application of a current / voltage to the light source 20 using the light source modifier 22 to provide a selected pattern of wavelengths of light emitted by the light source 20.

[0055] The light source 20 may be controlled for a wavelength sweep according to a selected pattern for the sweep. For example, the light source 20 may sweep through a selected range of wavelengths of light, and / or the light source 20 may sweep through the wavelengths of light according to a selected sweep profile (e.g., linear increase, sinusoidal, triangular, etc.). For example, the light source 20 may sweep according to a selected sweep rate or a selected total sweep time. The light source 20 is configured to perform a wavelength sweep of light such that, during a wavelength sweep, light is directed through the sample delivery channel to the subject's brain tissue (and via the reference channel to the detector) at each of a plurality of different wavelengths. The wavelength of the light emitted by the light source 20 changes over time. Thus, an indication of the time that light was emitted from the light source 20 may be determined based on the wavelength of the light.

[0056] The light source 20 may be configured to sweep through a selected wavelength range. For example, the light source 20 may be configured to sweep at an optical frequency in the 50 GHz range. For example, this may enable the light source 20 to emit modulated light at multiple different wavelengths, e.g., between 829.94 nm and 830.06 nm, centered at 830 nm, or between 1309.857 nm and 1310.143 nm, centered at 1310 nm. The light source 20 may be configured to sweep through a wavelength range of at least 0.025 nm, e.g., at least 0.05 nm, e.g., at least 0.075 nm, e.g., at least 0.1 nm, e.g., at least 0.11 nm (e.g., around a central wavelength for the light source 20). The light source 20 may have high output power, long coherence time, and wide mode-hop-free wavelength tuning. For example, because light source 20 does not sweep over a particularly large bandwidth, light source 20 may have a relatively narrow linewidth and a longer coherence length.

[0057] The light sources of the present disclosure may be configured to provide emission of high-coherence light, e.g., substantially coherent light. For example, it will be understood that a light source may not emit completely coherent light or provide wavelength-swept emission of light, because light at different wavelengths changes phase at different rates. The light sources of the present disclosure may be controlled to sweep through a relatively narrow wavelength range compared to the absolute wavelength of the light source. In other words, the difference between the maximum and minimum wavelengths for a wavelength sweep is relatively small compared to the wavelength. Each light source may be configured to emit light (i.e., an electric field) whose phase does not change significantly over time.

[0058] The iNIRS system of the present disclosure receives first sample light, second sample light, and reference light, all originating from the same light source (i.e., light source 20). The light source of the present disclosure is configured to provide a wavelength-swept emission of light that is sufficiently coherent so that the sample light and reference light as received at the photodetector 30 are in relatively similar (e.g., substantially similar) phase with each other. Thus, the combination of the sample light with the reference light produces substantially constructive interference between the two waves (e.g., the stream of sample light waves has a sufficiently similar phase to the corresponding stream of reference light waves such that the resulting combined light signal includes constructive coupling of the two light waves). In other words, the coherence length of the light source may be such that multiple scattering in tissue is below the noise floor for the measurement and does not reduce coherence or interference fringe contrast.

[0059] For example, each light source of the present disclosure may comprise a laser. The laser may be selected, for example, based on the coherence length of the laser to enable the aforementioned constructive interference between the sample light and the reference light to occur. In other words, the iNIRS system may be configured so that the maximum expected time-of-flight delay of a sample light photon (received at a photodetector after traveling through the subject's brain tissue) relative to a reference light photon (received at a photodetector after traveling along one or more reference channels), for example, relative to a second sample light (described in more detail below), is within the coherence period of the laser (e.g., the difference in optical path length between the sample light and the reference light is within the coherence length of the laser). Within this coherence period, the phase of the light emitted by the laser is approximately stable (regardless of changes in the wavelength of the emitted light). Therefore, there may be no loss in amplitude of the combined light signal at the photodetector (e.g., the interference occurring at the detector may be substantially completely constructive).

[0060] For example, an iNIRS system may be configured to have a coherence length or range of approximately 50 m in air, and a light source may be selected having a coherence length between 50 m and 100 m (coherence period between 166 ns and 333 ns). It will be understood that this particular range is not intended to be limiting; rather, the range is an example of an approximate range for the light source. The light source may be selected so that it has a coherence length that is more than two times greater than the maximum expected optical path length difference, for example, so that the coherence length may be three or four times greater or more. By having a light source with a coherence length that is much greater than the optical path length, the accuracy of measuring sample light photons that have experienced multiple scattering interactions within the subject's brain tissue may be improved.

[0061] The iNIRS system 10 is arranged so that the source-detector path lengths for 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 for light traveling from the light source 20 through the subject's brain tissue to each detector is different from the optical path length for light traveling from the light source 20 to that detector via the reference channel.

[0062] The iNIRS system 10 is arranged so that the sample light may travel along two or more different paths of the optical channel as it travels from the light source 20 to the detector 30. Thus, the sample light may be capable of traveling along different paths through the optical channel (in addition to traveling through different paths through the subject's head). The iNIRS system 10 includes at least two different routes of the optical channel along which the sample light may travel from the light source 20 to the detector 30 (in addition to traveling through the subject's brain). In the example shown in FIG. 1 , the different optical channel paths extend from the object being imaged (e.g., the subject's scalp) to the detector 30. That is, the sample light may be directed from the light source 20 to the object (along the sample delivery channel 25), and the sample light may travel through the object to the detector 30, where the route from the object to the detector 30 is along either the first sample receiving channel 351 or the second sample receiving channel 352. In other words, the iNIRS system 10 is arranged to provide two or more different source-detector optical path lengths for the sample light (regardless of the route that the sample light takes as it travels through the object being imaged).

[0063] As understood in the context of the present disclosure, photons of sample light directed toward a subject's brain tissue may travel from the light source 20 to the photodetector 30 via a virtually infinite number of different paths. The sample light photons may experience numerous scattering events and follow highly tortuous paths between the sample delivery probe 25′ and the sample receiving probe 35′. The iNIRS system 10 may be configured to provide neuroimaging and analysis based, at least in part, on activity in the subject's brain tissue. The time of flight for sample light photons from the light source 20 to the photodetector 30, of course, increases as the path length taken by the photons increases. Thus, photons that travel a longer path and penetrate deeper into the subject's brain tissue will take longer to arrive at the photodetector 30. The longer the time of flight for a sample light photon, the deeper the photon is considered to have penetrated into the subject's brain tissue.

[0064] The iNIRS system 10 may be arranged so that the shortest time of flight for a light photon traveling from the light source 20 to the photodetector 30 is relative to the photons of the reference light traveling along the reference channel. The sample light photons have a longer time of flight than the reference light. Sample light photons that penetrate deeper into the subject's brain tissue are considered to have a longer time of flight to the photodetector 30. The additional optical path length 352a is arranged so that the difference in optical path length between the first sample receiving channel 351 and the second sample receiving channel 352 means that the first sample light photons have a shorter time of flight than the second sample light photons.

[0065] As understood in the context of the present disclosure, the path that each individual sample light photon travels through the object being imaged (between the sample delivery channel and the sample receiving channel) is not predictable. However, if there are a large number of such sample light photons, the overall time-of-flight distribution for the sample light photons may be statistically modeled. Thus, one or more expected characteristics of the time-of-flight distribution for the sample light may be known for a given light source-detector pair. For example, the expected time difference between the shortest time-of-flight of a photon and the longest time-of-flight of a photon (e.g., spectral width) may be known for each light source-detector pair. For example, this may be based on previous observable signals for the earliest and latest arriving detectable photons. In other words, a known maximum expected spectral width for the resulting time-of-flight distribution for the sample light photons may exist for any given light source-detector pair.

[0066] In other words, the photons of the first and second sample lights each provide a photon distribution ranging from the earliest arriving sample light photon to the latest arriving sample light photon. Before the earliest photon and after the latest photon, incident photons are not resolvable above the system's noise floor. This difference in time between the first and last detected incident photon (and thus the frequency difference between the associated lowest and highest beat frequencies) provides a width or range for the distribution of incident photons. Additional channel lengths may be selected based on this time width / range for the sample light photons from the first and second lights. For example, this may be selected based on a D4σ width (e.g., in accordance with ISO 11146 for beam diameter determination).

[0067] The iNIRS system 10 may effectively provide two light source-detector pairs between the same light source 20 and detector 30. In the example of FIG. 1, this is due to two different optical paths (e.g., first sample receiving channel 351 and second sample receiving channel 352) provided between the object and detector 30. There is a known expected spectral width for the time-of-flight distribution for the first sample light photons (e.g., a known time interval spanning between the shortest and longest times-of-flight for the first sample light photons). For example, this spectral width may be anywhere in the range of 0.5 ns to 2 ns. The additional optical channel length 352a may add an additional distance in the optical channel that the second sample light photons must travel to reach the detector 30, where the additional distance corresponds at least to the expected spectral width for the first sample light photons. For example, the additional optical channel length 352a may have a distance that is at least as long as a distance corresponding to the combination of both (i) the expected spectral width for the first sample light and (ii) an additional buffer period (selected so that the unusually long first sample light photon flight times still reach the detector before any of the second sample light photons).

[0068] In other words, the additional optical channel length 352a adds an additional distance of the optical channel such that the duration it takes for a second sample light photon to travel along that additional length of the optical channel is at least as long as the expected spectral width of the first sample light photon time-of-flight distribution. The additional optical channel length 352a is positioned so that detectable photons of the first sample light may always have a shorter time-of-flight than detectable photons of the second sample light. For example, a photon of the first sample light having the longest time-of-flight through the object being imaged and detected by detector 30 will still have a shorter overall time-of-flight from light source 20 to detector 30 than a photon of the second sample light having the shortest time-of-flight through the object being imaged.

[0069] The iNIRS system 10 is arranged such that the detector 30 is configured to receive three inputs: reference light (from the reference receiving channel 36), first sample light (from the first sample receiving channel 351), and second sample light (from the second sample receiving channel 352). The detector 30 is configured to combine the three using an optical combiner. For example, the detector may provide an interferometer assembly (combined with the first sample channel, the second sample channel, and the reference channel) configured to combine the reference light and sample light to obtain an interference pattern (interferogram). The obtained interference pattern may include a contribution associated with the first sample light (and the first sample receiving channel 351) and a contribution associated with the second sample light (and the second sample receiving channel 352).

[0070] Light source 20 is configured to emit substantially coherent light. The resulting interference pattern of light from light source 20 (as acquired at each detector) may include a combined signal having a component at a beat (or mean / difference) frequency corresponding to the wavelength difference between (i) the wavelength of the photons of the sample light received at photodetector 30 at a given time instance and (ii) the wavelength of the photons of the reference light received at photodetector 30 at that time instance. Because received photons of the reference light travel the same distance from light source 20 to photodetector 30 (through the reference channel), the reference light over a single sampling interval should be of a substantially narrow and uniform wavelength, limited either by the intrinsic linewidth of the laser or the optical frequency sweep rate.

[0071] The sample light received at detector 30 (combined with the reference light) includes photons of the first sample light and photons of the second sample light. These received photons are of different wavelengths. The photons of the first sample light received at detector 30 have taken different unique paths through the object being imaged. Therefore, the photons of the first sample light received at detector 30 have different times of flight and are therefore of different wavelengths (due to the wavelength-swept emission from light source 20). Similarly, the photons of the second sample light received at detector 30 have different times of flight through the object and are therefore of different wavelengths.

[0072] The additional optical path length 352a is positioned such that the photons of the first sample light received at the detector 30 include photons within a first wavelength range and the photons of the second sample light received at the detector 30 include photons within a second wavelength range. The additional optical path length 352a may have a length selected such that there is no overlap between the first wavelength range and the second wavelength range.

[0073] Thus, the resulting interferogram acquired by detector 30 includes multiple different beat frequencies (due to the different differential wavelengths). The detected second sample light has a higher beat frequency than the detected first sample light (because the photons of the second sample light had a longer time of flight). Within the range of beat frequencies acquired for each of the first and second sample lights, a higher beat frequency may correspond to photons with a longer time of flight (e.g., photons that penetrate deeper). It should be understood that in this example, the reference light travels a shorter distance than the sample light to reach the detector. Of course, alternatives may be provided in which the sample light does not travel as far as the reference light, in which case a higher beat frequency would be associated with the shortest time of flight. However, in this example, it is assumed that the reference light does not travel as far as the sample light.

[0074] The iNIRS system 10 may be configured to acquire a digital representation of each resulting interferogram. For example, the detector 30 may include an analog-to-digital converter ("ADC") configured to acquire interferogram data from each interferogram provided by the detector 30. An example of a circuit for acquiring such interferogram data is described below in connection with inset A of FIG. 1. Each acquired interferogram may be Fourier analyzed (e.g., using an FFT or IFT) to obtain a representation of the time-of-flight distribution ("DTOF") for the sample light photons incident on the photodetector 30. Each determined DTOF may provide a distribution indicative of the time-of-flight for all sample light photons incident on the photodetector 30 at a given instant. The DTOF may include an ensemble average indicative of a large number of incident photons (in each of a plurality of different time-of-flight ("TOF") bins). The intensity for each TOF bin provides an indication of the number of incident photons in that TOF bin (e.g., for all incident photons having a time of flight within the range of time of flight covered by that TOF bin). The phase of a TOF bin (e.g., obtained using Fourier analysis) may represent the average phase for all of the photons arriving at that TOF bin.

[0075] In the example of Figure 1, detector 30 acquires an interferogram that effectively includes two separate DTOFs, one for photons of the first sample light that have traveled through the object being imaged, and one for photons of the second sample light that have traveled through the object being imaged. An example of interferogram data acquired in this manner is shown in Figure 2.

[0076] FIG. 2 illustrates a plot 400 of amplitude versus time-of-flight for photons of sample light received at detector 30. The data illustrated in FIG. 2 may be obtained by performing an FFT on the acquired interferogram data. The amplitude may provide an indication of the total number of photons detected at each time-of-flight. Plot 400 includes first sample light data 401, which includes photons of the first sample light received in a first time-of-flight range 401a, and second sample light data 402, which includes photons of the second sample light received in a second time-of-flight range 402a. The data illustrated in FIG. 2 may have been acquired using a single digitizer channel of the ADC. As can be seen in FIG. 2, first sample light data 401 falls within a much smaller time-of-flight range than second sample light data 402. Plot 400 effectively includes two separable DTOFs: one for the first sample light and one for the second sample light.

[0077] Each DTOF follows a similar distribution, which includes an initial sharp peak followed by a gradually decreasing tail. The end of a DTOF may be defined by the point at which any signal associated with that DTOF is no longer distinguishable from background noise. In other words, the points at which a DTOF begins and ends for detected sample light are points where the number of received sample light photons is sufficiently low (or absent) that the detected amplitude at that beat frequency (i.e., time of flight) is not significantly (e.g., statistically significantly) greater than the detected amplitude associated with background noise alone (as opposed to incident sample light photons). That is, the detected amplitude at that beat frequency consistently does not exceed the noise floor for the system (e.g., on average less than one incident photon at that frequency per measurement).

[0078] The two DTOFs shown in plot 400 of FIG. 2 are separated from each other by a separation time 410. The separation time 410 is the time offset between the first DTOF (for the first sample light) and the second DTOF (for the second sample light) included in the data. In FIG. 2, this separation time 410 is shown as the time offset between the peak value of the first sample light data 401 and the peak value of the second sample light data 402. However, it should be understood that the separation time 410 may be the time offset between other suitable points in each time-of-flight distribution, such as the minimum time-of-flight for the first and second sample lights, the maximum time-of-flight for the first and second sample lights, and / or the average value for the first and second sample times-of-flight (e.g., the average time-of-flight for the first and second sample lights). In other words, the separation time 410 indicates the difference in the detected times-of-flight for the first and second sample light photons.

[0079] The separation time 410 corresponds to the additional optical channel length 352a associated with the second sample light received at the detector 30. The separation time 410 is longer than the spectral width for the first sample light data 401 (e.g., the separation time 410 is greater than the amount of time separating the beginning and end of the first time-of-flight range 401a). As can be seen in FIG. 2 , there is no spectral overlap between the first sample light data 401 and the second sample light data 402. The first sample light data 401 may be separable from the second sample light data 402. In other words, two separate DTOFs (one for the first sample light and one for the second sample light) may be extracted from the acquired interferogram. Each of the separate extractable DTOFs may not include any time-of-flight data corresponding to photons from the other sample light.

[0080] The controller 40 of the iNIRS system 10 may be configured to process interferogram data. The controller 40 may be configured to process interferogram data obtained from the detector 30 (and the ADC) to obtain DTOF data for the first sample light and DTOF data for the second sample light. As described above, this DTOF data may indicate beat frequency data. That is, the first DTOF data may correspond to the first beat frequency data, and the second DTOF data may correspond to the second beat frequency data. The controller 40 may be configured to extract the first DTOF data and the second DTOF data. This may include separating the two DTOFs included in the interferogram. The controller 40 may be configured to separate based on an indication of the time of flight. The indication of the time of flight may include an indication of a value for the beat frequency (e.g., before processing of the data to obtain DTOF data) or an indication of the time of flight (e.g., as obtained from the processed DTOF data).

[0081] The controller 40 may be configured to process the interferogram data to obtain two different DTOFs. The controller 40 may be configured to perform imaging of an object (e.g., neuroimaging of a subject's brain) based on two different DTOFs obtained from the same interferogram data. First, the controller 40 may be configured to separate the two different DTOFs from the interferogram data. This may include identifying the first DTOF data as all data points below a first threshold time-of-flight (optionally, above a lower threshold time-of-flight that is below the first threshold time-of-flight), or identifying the first DTOF data as all data points above a second threshold time-of-flight (optionally, below an upper threshold time-of-flight that is greater than the second threshold time-of-flight). The first and second threshold time-of-flights may be the same or different (the second threshold time-of-flight is greater than the first threshold time-of-flight).

[0082] In other words, the controller 40 may be configured to acquire (i) first DTOF data including time-of-flight distribution values ​​for the first sample light, and (ii) second DTOF data including time-of-flight distribution values ​​for the second sample light. The time-of-flight values ​​derived from the interferogram data may indicate that the time-of-flight for the first sample light is less than the time-of-flight for the second sample light. However, as will be appreciated, this difference in time-of-flight values ​​is caused, at least in part, by the additional optical channel length 352a that the second sample light must travel compared to the first sample light.

[0083] The controller 40 may be configured to correct for this apparent difference in time of flight between the first and second sample lights. In this regard, the controller 40 may be configured to align the first DTOF (for the first sample light) with the second DTOF (for the second sample light). The iNIRS system 10 is configured to provide imaging of an object being imaged based on time-of-flight data associated with the time of flight of photons and how the time of flight changes as the photons travel through the object being imaged (e.g., through the subject's brain). Thus, the controller 40 may be configured to process the acquired DTOF data to obtain data indicative of the different times of flight of photons traveling through the object (e.g., between the point where the sample light leaves the sample delivery channel 25 and the point where the sample light enters the first / second sample receiving channels 351, 352).

[0084] The controller 40 may be configured to align the first DTOF data with the second DTOF data. For example, the controller 40 may apply a time offset to one or both of the first and second DTOF data. The time offset may be selected to eliminate the effect of the additional optical channel length 352a in the time-of-flight data for the second DTOF. For example, the controller 40 may align the first and second DTOFs so that both contain information only about photon time-of-flight through the object (and not the channel between the light source and the object and / or the channel between the object and the detector). The controller 40 may be configured to align the first and second DTOFs by applying a fixed time offset associated with the difference in the duration it takes light to travel along the first and second sample receiving channels. The controller 40 may be configured to align the first and second DTOFs by applying a time offset based on aligning one or more features in the first time-of-flight data with corresponding features in the second time-of-flight data, for example, by alignment based on peak TOF value, average TOF value, and / or maximum or minimum TOF value for each of the two DTOFs.

[0085] Thus, the controller 40 of the iNIRS system 10 may be configured to acquire two DTOF data (e.g., first DTOF data and second DTOF data) using one light source 20 and one photodetector 30. The controller 40 may acquire the two DTOF data using, for example, only one ADC that simultaneously digitizes both DTOF distributions within the same interferogram acquired by the detector 30. Thus, the iNIRS system 10 may be configured to acquire twice as much data for each light source-detector pair. The first sample receiving channel 351 and the second sample receiving channel 352 may be positioned near each other on the object being imaged. The controller 40 may be configured to average the first DTOF data and the second DTOF data for the object. For example, the iNIRS system 10 may be configured to continuously acquire successive interferograms (and therefore interferogram data). For each item of interferogram data, the controller 40 may be configured to acquire first DTOF data and second DTOF data. The controller 40 may be configured to provide imaging of the object (e.g., neuroimaging of the subject's brain) based on the time evolution of the DTOF data (e.g., based on how the time-of-flight distribution evolves over time). In this regard, the first DTOF data and the second DTOF data in each item of interferogram data may be combined to provide average DTOF data, and the imaging of the object may be based on the time evolution of successive items of average DTOF data.

[0086] An example of a mechanism for converting received light signals to digital data is shown in inset A of Figure 1. Inset A shows an arrangement of components that may be used as part of the light detector 30 of the present disclosure. As shown in the iNIRS system 10 of Figure 1, the detector 30 is positioned to receive three inputs: (i) reference light traveling along the reference delivery channel 26 and the reference receiving channel 36, (ii) first sample light received through the first sample receiving channel 351, and (iii) second sample light received through the second sample receiving channel 352.

[0087] As shown, the detector may include an optical combiner / 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 configured to provide a digital signal output 307.

[0088] The optical combiner splitter 301 is connected to the reference receive channel 36, the first sample receive channel 351, and the second sample receive channel 352. The optical combiner splitter 301 is configured to receive the first sample light, the second sample light, and the reference light and combine the first sample light, the second sample light, and the reference light to provide a combined optical signal. For example, the first sample receive channel 351 and the second sample receive channel 352 may be combined in a beam combining element. This combining may be achieved using, for example, a fused fiber coupler, a polarization combiner, a beam splitter cube, a diffraction grating, or many other separating / combining optical elements such as photonic lanterns, fiber-free-space-fiber multiplexing optics, etc.

[0089] Each sample receiver channel may comprise a single-mode fiber ("SMF") or few-mode fiber ("FMF"). Each sample receiver channel may be connected to an additional fiber in the form of a multimode fiber ("MMF") or FMF. Each sample receiver channel may be connected to the additional fiber, and may be arranged so that each sample receiver channel (e.g., each SMF or FMF) excites its own unique mode within the additional fiber. The reference channel may be provided by an SMF or FMF (typically an SMF). The reference channel may be connected to the additional fiber, for example, to excite the fundamental mode of the additional fiber. The additional fiber may be arranged to couple light at an FMF or MMF fiber coupler. Alternatively, the sample light in the FMF / MMF may be combined with the reference light using one or more free-space beam combining elements, such as a beamsplitter cube.

[0090] The optical combiner / splitter 301 may be configured to split the resulting combined optical signal into two separate channels, a first optical channel 302a and a second optical channel 302b. For example, this may be a 50:50 (or near 50:50) split. The first optical channel 302a and the second optical channel 302b may be connected to a balanced photodetector 303. Each optical channel may be configured to direct light to an associated photodiode. The balanced detector may be configured to provide an output based on the difference between the outputs from the two photodetectors. The two photodetectors are typically configured so that the beat signals at each photodiode are 180° out of phase with each other, so that coherent AC terms positively couple with each other. The balanced photodetector 303 may be configured to output a current corresponding to the difference between the output currents of the two photodetectors. The balanced photodetector 303 may remove any undesired DC terms from this signal, such as slow fluctuations emanating from the light source 20, or other common-mode effects such as noise.

[0091] The photodetector 30 may be configured to use a current-to-voltage converter to convert the current output from the balanced photodetector 303 to a corresponding voltage. As shown in inset A of FIG. 1 , the converter may include a transimpedance amplifier 304. The voltage output from the transimpedance amplifier 304 may then be amplified using an amplifier 305. The amplifier may be used to limit the electronic frequency of the circuit to scale the output signal to the full range of the ADC and further maximize the SNR. This amplified voltage is then provided to the ADC 306 to be digitized. The ADC 306 includes a digitizer with sufficient bandwidth so that the entire signal bandwidth, including the time-of-flight information, can be digitized without attenuation. As understood in the context of this disclosure and described in more detail below, the ADC may have a digitization bandwidth much greater than that of a single DTOF. By effectively providing more DTOFs in each digitized interferogram, the iNIRS system 10 may utilize a greater proportion of the digitization bandwidth for each ADC 306 of the system 10.

[0092] For example, the digitizer bandwidth may be at least as large as the bandwidth for the combined optical signal (e.g., the digitizer bandwidth may be large enough to process multiple different DTOF distributions contained in a single interferogram). For example, the digitizer may be selected to have a sampling rate high enough that the Nyquist criterion is met for the bandwidth of the signal being processed. A digitizer may be provided as part of each photodetector 30, or the digitizer may be part of the controller 40, which may be connected to each of the photodetectors 30 to receive the electrical signals to be digitized therefrom. For each combined optical signal, a digital signal output 307 is provided that provides a digital representation of that combined optical signal (and therefore of the sample light incident on the photodetector 30 at the moment that the combined optical signal is generated and measured).

[0093] The iNIRS system 10 is configured to acquire multiple digital signal outputs 307 indicative of the sample light incident on the photodetectors 30. In particular, each photodetector 30 is configured to iteratively combine the optical signals (of the first sample, the second sample, and the reference) to provide a digital signal output 307 indicative of each combined optical signal. For example, a time-series digital signal output 307 may be acquired for each photodetector 30, with each subsequent digital signal output 307 relating to a later time point at which the combined optical signal was acquired and measured (the digital signal output 307 indicative of that combined optical signal as acquired and measured). As previously mentioned, each digital signal output 307 may be in the form of interferogram data indicative of an interferogram acquired using the detector 30 (two or more sample light DTOFs may be acquired for that time point at that detector 30).

[0094] In the example described herein, the iNIRS system 10 is configured to acquire interferogram data that effectively includes a representation of two separate DTOFs (one for a first sample light and one for a second sample light). In the example of FIG. 1, two sample receiving channels are provided with a delay in one of the sample receiving channels so that one light source 20 and one detector 30 may be used to acquire two separate DTOFs. However, it will be understood that in the context of the present disclosure, similar functionality may be provided by introducing a delay in one of two or more sample delivery channels (in addition to, or as an alternative to, introducing a delay in one of the two or more sample receiving channels). An example of such a mechanism will now be described with reference to FIG. 3a.

[0095] FIG. 3a shows an iNIRS system. The light source 20, detector 30, and object to be imaged are present as in the system of FIG. 1. However, a first sample delivery channel 251 and a second sample delivery channel 252 are present in FIG. 3a. Each sample delivery channel 251, 252 connects the light source 20 to the object to be imaged. The iNIRS system also includes a sample receiving channel and a reference channel 26 (only one of each is shown in FIG. 3a). The detector 30 is positioned to combine reference light carried in the reference channel 26 with sample light carried in the sample receiving channel.

[0096] In FIG. 3a, an additional optical channel length 252a is provided in the second sample delivery channel 252. The additional optical channel length 252a shown in FIG. 3a is arranged to provide the same function as the additional optical channel length 352a shown in FIG. 1. That is, the additional optical channel length 252a is arranged so that a portion of the sample light incident on the detector has a substantially longer time of flight compared to other sample light incident on the detector (where the additional time of flight is due to the sample light traveling along the additional length of the optical channel). In FIG. 3a, the light source 20 is configured to direct a first sample light to the target through the first sample channel 251 and a second sample light to the target through the second sample channel 252. Both the first sample light and the second sample light may be received on the same sample receiving channel. Each of the first sample light and the second sample light may then be combined with a reference light to provide a first beat frequency and a second beat frequency. 1, the additional optical channel length 252a is selected to prevent spectral overlap between the beat frequencies associated with the first sample light and the beat frequencies associated with the second sample light. The light source 20 may be connected to an optical splitter configured to split light from the light source 20 between (i) the first sample light directed to the object along the first sample delivery channel 251, (ii) the second sample light directed to the object along the second sample delivery channel 252 (through the additional optical channel length 252a), and (iii) the reference light directed to the detector 30 along one or more reference channels.

[0097] Another exemplary iNIRS system will now be described with reference to Figure 3b. One advantage of the system of Figure 1 (compared to that of Figure 3a) is that if more light sources are added to the system, the light sources may be combined with the existing two sample receiving channels so that a first sample light and a second sample light may be provided to detector 30 for each light source (where the second sample light has an optical delay compared to the first sample light). Alternatively, as in Figure 3a, if multiple different detectors are added, each detector may have only one sample receiving channel, and that detector may receive the first sample light and the second sample light from the light source.

[0098] 3b shows an iNIRS system comprising a first light source 20a and a second light source 20b. The first light source 20a is (i) connected to the subject via a sample delivery channel 25a and (ii) connected to a detector (e.g., a detector optical combiner 301) via a reference channel 26a. The second light source 20b is (i) connected to the subject via a sample delivery channel 25b and (ii) connected to a detector (e.g., an optical combiner 301) via a reference channel 26b. The system comprises a first sample receiving channel 351 and a second sample receiving channel 352 of the type described above in connection with FIG. 1 (e.g., with an additional optical channel length 352a in the second optical channel 352). The iNIRS system may be arranged such that the first sample receiving channel 251 may receive the first sample light from the first light source 20a and the second sample light from the second light source 20b, and the second sample receiving channel 252 may receive the second sample light from the first light source 20a and the second sample light from the second light source 20b.

[0099] The system may be configured to prevent spectral overlap among the four different received optical signals. For example, one of the reference channels 26a, 26b may have an additional optical channel length designed to introduce a time-of-flight delay into that reference channel. In FIG. 3b, this is illustrated by the additional reference channel length 262b in the second reference channel 26b. This additional optical channel length 262b for the reference channel (second reference channel 26b) and the additional optical channel length 352a for the second sample receive channel 352 may be selected so that all four beat frequency distributions may match in the same interferogram without spectral overlap. Additionally or alternatively, the system may be configured to provide time multiplexing for the operation of two light sources such that only one light source is operating at a time (and thus the additional optical channel length 352 itself may prevent spectral overlap among them in the interferogram, for example, without the need for the additional reference channel length 262b).

[0100] FIG. 3c shows another exemplary iNIRS system. One light source 20 and one detector (although only the detector optical combiner 301 is shown) are present in the iNIRS system of FIG. 3c. The light source 20 is connected to the subject via the sample delivery channel 25 and to the detector (combiner 301) via the reference channel 26. The system of FIG. 3c is similar to that of FIG. 1, except that the system of FIG. 3c includes a third sample receiving channel 353. The third sample receiving channel 353 includes an additional optical channel length 353a, which has a different length relative to the additional optical channel length 352a of the second optical channel 352. The three sample receiving channels are arranged to have different lengths so that three separate beat frequency distributions may be included in one interferogram without spectral overlap. For example, one of the additional optical channel lengths 352a, 353a may be significantly larger than the other to provide an additional increase in time of flight for sample light photons traveling along that channel.

[0101] FIG. 3d shows another exemplary iNIRS system. The iNIRS system of FIG. 3d is similar to that of FIG. 3a. However, a single splitter is shown in FIG. 3b to separate light from light source 20 into each of (i) first sample delivery channel 251, (ii) second sample delivery channel 252, and (iii) reference channel 26. For the iNIRS systems of the present disclosure, the combining or separating of three or more separate optical channels may be provided by a single component (as shown in FIG. 1 and FIGS. 3a-3c), or it may be provided by multiple components. In FIG. 3d, two optical splitters, a first optical splitter 24a and a second optical splitter 24b, are provided.

[0102] A first optical splitter 24a is connected to the light source 20 to receive light therefrom. The first optical splitter 24a is positioned to split the light into a sample optical channel and a reference optical channel. A reference channel 26 may extend from the first optical splitter 24a toward a detector where the reference channel 26 is combined with the sample receiving channel of the system. The sample optical channel extends from the first optical splitter 24a to a second optical splitter 24b. The second optical splitter 24b is provided by a separate component relative to the first optical splitter 24a. The second optical splitter 24b is positioned to split the sample light received from the first optical splitter 24a into two sample delivery channels: a first sample delivery channel 251 and a second sample delivery channel 252 (where the second sample delivery channel 252 has an additional optical channel length 252a as described herein). It should be understood that a similar mechanism may be provided for an exemplary system where first, two sample receiving channels are combined into a single sample channel, and then that single sample channel is combined with a reference channel (e.g., by a separate component), and / or first, one sample receiving channel is combined with a reference channel, and then the other sample receiving channel is combined with that combined channel.

[0103] FIG. 3e shows another exemplary iNIRS system. The system of FIG. 3e includes two detectors: a first detector 30a and a second detector 30b. For simplicity, the optical combiner for each detector is shown as a separate component relative to the detector, but it will be understood that the optical combiner may form part of the detector. One light source 20 is shown in FIG. 3e. Light from the light source 20 is split into both (i) a sample delivery channel 25 that delivers sample light toward the object being imaged and (ii) a reference delivery channel 26 that provides reference light to the detectors 30a and 30b. Each of the detectors 30a and 30b has an associated reference receiving channel 36a and 36b, respectively. Each reference receiving channel 36a and 36b is positioned to provide light from the reference channel 26 to its respective detector. For example, the reference channel 26 may include an optical splitter that splits the reference light from the reference channel 26 into each of two reference receive channels 36a, 36b.

[0104] Each of the detectors 30a, 30b is connected to the object being imaged by two sample receive channels. As shown, the first detector 30a is connected to the object by a first detector first sample receive channel 3510a and a first detector second sample receive channel 3520a, one of which has an additional optical channel length (shown in FIG. 3e as channel 3510a) as disclosed herein. Similarly, the second detector 30b is connected to the object by a second detector first sample receive channel 3510b and a second detector second sample receive channel 3520b, again, one of which has an additional optical channel length (shown in FIG. 3e as channel 3520b) as disclosed herein. Thus, as described herein, each of the first detector 30a and the second detector 30b may receive a first sample light and a second sample light, where the difference in time of flight between the two sample receiving channels for each detector 30a, 30b is such that the resulting first beat frequency has no spectral overlap with the resulting second beat frequency.

[0105] Two optical combiners are provided for each of detectors 30a, 30b: (i) one for combining light from the two sample receiving channels into a single combined sample channel, and (ii) one for combining light from the single combined sample channel with reference light from a reference receiving channel. Each detector may include two such optical combiners.

[0106] For the first detector 30a, the first detector first combiner 3011a is connected to both the first detector sample receiving channels 3510a, 3520a and configured to combine light from the two channels 3510a, 3520a into the first detector combined sample channel. The first detector second combiner 3012a is connected to the first reference receiving channel 36a and the first detector combined sample channel to combine the combined sample light with the reference light. The first detector 30a is connected to the first detector second combiner 3012a to receive the combined light from the first detector second combiner 3012a. For the second detector 30b, the second detector first combiner 3011b is connected to both the second detector sample receiving channels 3510b, 3520b and configured to combine light from the two channels 3510b, 3520b into the second detector combined sample channel. The second detector second combiner 3012b is connected to the second reference receive channel 36b and the second detector combined sample channel to combine the combined sample light with the reference light. The second detector 30b is connected to the second detector second combiner 3012b to receive the combined light from the second detector second combiner 3012b. Thus, different light combinations may be provided in stages (e.g., by multiple different components).

[0107] FIG. 3e also illustrates different exemplary functions of this iNIRS system. As described herein, each detector is configured to receive and process first and second sample light data. Thus, each detector may effectively acquire information related to two (or more) different photon distributions for the sample light passing through the object being imaged. For example, one digitizer channel may be used for each detector, and the resulting data acquired from that digitizer channel may exhibit two different beat frequency distributions (i.e., the data may include a first sample light photon distribution and a second sample light photon distribution). In other words, the iNIRS system of the present disclosure may be arranged to more fully utilize the full bandwidth of the digitizer channels (e.g., to acquire more usable data per each digitizer channel). The sample delivery and / or sample receiving channels may be arranged in the object such that the system is configured to acquire two or more photon distributions for similar volumes within the object and / or such that at least some acquired photon distributions are for different volumes within the object.

[0108] As an example, as shown in FIG. 3e, the sample receiving channels 3510a and 3520a of the first detector 30a may be co-located in the object. That is, the two may be located adjacent to each other (e.g., within a threshold distance of each other). Thus, on average, sample light photons traveling from the sample delivery channel 25 to the two sample receiving channels 3510a and 3520a of the first detector 30a may travel through a substantially similar volume of the object (e.g., as shown by the photon paths in FIG. 3e). In other words, the sample light passing through each of the sample receiving channels of the first detector 30a may be effectively used to image the same region of the object. Thus, the first detector 30a may effectively simultaneously acquire two (or more) photon distributions for the same region of the object (e.g., using a single digitizer channel). The system may be configured to process the different photon distributions together, for example, averaging the data acquired from each distribution (i.e., averaging based on distributions acquired using both sample receiving channels).

[0109] As another example, as shown in FIG. 3e, the sample receiving channels 3510b and 3520b of the second detector 30b may be spaced apart in the object. In this case, the same detector (second detector 30b) may be used to simultaneously image two different volumes within the object. As shown in FIG. 3e, the sample light photons received on each channel may, on average, travel through substantially different volumes within the image. Thus, the first sample photon distribution may represent one portion of the object, while the second sample photon distribution may represent a different portion of the object.

[0110] It should be understood that in the context of the present disclosure, different examples may be combined with each other. For example, an iNIRS system may be provided in which there are two sample delivery channels (of different lengths) and two sample receiving channels (of different lengths). The channels may be arranged (e.g., at selected lengths) so that all combinations of the different sample light channel paths fit into the regions of the different sample light channel paths themselves in the resulting interferogram. That is, the channels may be arranged to stack all of the different beat frequency distributions within one interferogram without spectral overlap between the distributions. Similarly, multiple light sources may be used, where some or all of the light sources are connected to the subject via two or more sample delivery channels. Similarly, there may be three or more sample delivery channels and / or sample receiving channels.

[0111] Thus, the present disclosure may provide an iNIRS system in which sample light may travel along two or more different optical paths from the light source to the object and from the object to the detector (regardless of the path taken through the object between the sample delivery channel and the sample receiving channel). The different optical paths may have different lengths so that the resulting beat frequency distributions for different combinations of sample light and reference light may fit into the same interferogram without spectral overlap. Thus, one digitizer channel of the ADC may be used to digitize one interferogram, where the one interferogram contains information indicative of two or more different DTOFs for the sample light. This mechanism may allow more imaging data to be acquired for the object. In other words, this mechanism may allow more data to be acquired without having to increase the number of digitizers in the system. For example, the iNIRS system of the present disclosure may be configured to maximize the number of different beat frequency distributions provided within a single digitized interferogram. That is, for a given digitizer bandwidth, the iNIRS system may be arranged with the maximum number of different distributions present in one interferogram without any spectral overlap between those distributions in that interferogram.

[0112] In each of the examples described herein, each interferogram may provide an indication of all of the sample light photons incident on the detector 30 at a given moment. Two or more different beat frequency distributions associated with different sample light incident on the detector (e.g., first / second) may be present in the interferogram. The controller may be configured to extract a DTOF for each of the sample light beat frequency distributions. Each determined DTOF may provide a distribution indicative of the time of flight for all associated sample light photons incident on the photodetector 30 at a given moment. Each DTOF may include an ensemble average indicative of a number of incident photons (in each of a number of different TOF bins). The intensity for each TOF bin provides an indication of the number of incident photons at that TOF. The phase of a TOF bin (e.g., obtained using Fourier analysis) may indicate the average phase for all of the photons arriving in that TOF bin. As described in more detail below, a number of characteristics of a subject's brain tissue may be determined based on the DTOF data obtained for the subject's brain tissue.

[0113] The iNIRS system 10 may be configured to acquire multiple time-sequential DTOFs for the photodetector 30. This may include an averaged DTOF (where the simultaneously acquired first and second sample light DTOFs are averaged). The digitizer may provide digital outputs indicative of the different measurements, which may optionally be processed in a number of ways to provide and / or use the DTOF data. Examples of these steps will now be described.

[0114] The controller 40 may be configured to receive raw digital interferogram data (e.g., data representing an interferogram obtained by converting the combined optical signal to digital data). This raw interferogram may be divided into individual sweeps of the wavelength-swept emission from the light source 20. For example, the sweep rate of the light source 20 and the time at which the first sweep began may be used to determine a sweep cycle. The data may then be divided into groups, with each group representing an individual sweep. An optional Hilbert transform may be performed on the data at this stage. Data windowing may be performed (e.g., using a Hann or Blackman-Harris window) to reduce side lobes in the data. Fourier analysis, either inverse or normal, may be performed on the data. For example, an inverse Fourier transform may be performed. Fourier analysis may be performed for each wavelength sweep of the light source 20. The resulting data may be in the form of a series of time point spread functions (“TPSFs”), each TPSF corresponding to an associated wavelength sweep. The TPSF data may be processed to remove instrument response functions ("IRFs") from the TPSF data to provide DTOF data. For example, the IRFs may be filtered out (e.g., deconvolved and / or subtracted) using post-processing.

[0115] In other words, the iNIRS system 10 may be configured to determine a time-of-flight distribution of a time-ordered sequence of sample light photons incident on one or more detectors. If the object being imaged is a subject's brain, this DTOF data may be processed to provide information about a number of different physical properties of the subject's brain tissue. The DTOF data may be used to determine the optical properties of the medium through which the sample light travels. Each TOF bin in the DTOF may represent a selected volume within the subject's brain, and each DTOF represents the total volume of tissue probed by the photons (e.g., each DTOF may represent a weighted average of the properties of brain tissue and other tissues through which the photons travel, such as the scalp, skull, etc.). The optical properties include scattering and absorption properties of the subject's brain tissue. The DTOF data may be used to determine dynamic properties of the subject's brain tissue, such as how certain properties change over time. This includes how the optical properties evolve over time and properties indicative of movement within the subject's brain tissue (e.g., due to blood flow).

[0116] The controller 40 may store data correlating the time of flight for a sample light photon (or for a TOF bin) to an indication of the average path trajectory for that photon. This may include an indication of the depth of penetration into the subject's brain tissue for that photon and / or an indication of the region of the subject's brain tissue through which that photon traveled from the light source 20 to the light detector 30. The controller 40 may be configured to process the DTOF data by dividing this data into select TOF bins. Within each TOF bin, the data may provide depth-resolved progression data for the subject's brain tissue. That is, because a TOF may be associated with a particular penetration depth or region, each TOF bin may include data indicative of a characteristic associated with the particular penetration depth or region. Thus, the progression of data within each TOF bin may provide an indication of how one or more characteristics of the subject's brain tissue are progressing. For example, if the progression indicates a change in movement (e.g., blood flow), that movement may be identified, such that the region in which the movement is occurring may be identified. In this regard, the decay slope of the TOF resolution may be used to identify how the curve decays over time for a particular TOF (eg, a particular penetration depth / region).

[0117] In other words, the iNIRS system 10 may be configured to perform autocorrelation in which DTOFs for successive wavelength sweeps are combined to assess variations in the optical field at the photodetector 30 over time. The variations may be quantified by the associated variation in DTOF over time. The variations may also be depth-resolved by identifying the associated TOF (and therefore the associated penetration depth / region) at which the variations occur. The controller 40 may be configured to process the data received from the photodetector 30 to provide time-of-flight information, including depth-resolved autocorrelation, for the subject's brain tissue. The controller 40 may be configured to use this information to obtain indications of several different properties of the subject's brain tissue, such as intracranial pressure (“ICP”), blood flow index, arterial elasticity, etc. The properties of the subject's brain tissue may be used in several different forms of neuroimaging and analysis, such as in brain-computer interfaces, to image brain regions to identify potential localized injury or stroke, and / or to monitor neural responses to substances such as drugs.

[0118] As understood in the context of the present disclosure, when a square-law detector is used, the intensity at the detector may be proportional to the square of the total electric field strength. The frequency of the interference fringes present in each interferogram may result from multiplying the rate of change of the light frequency by a time delay. In other words, a Fourier-transformed interferogram containing multiple beat frequencies may be used to indicate the photon time-of-flight associated with the beat frequencies present in the interferogram. In other words, the iNIRS system 10 is configured to measure the phase or frequency shift between photons of light (reference and sample) at the two inputs to the detector and attribute the difference to a characteristic of the intervening brain tissue relative to the sample light.

[0119] In this regard, the optical detector 30 may comprise an optical combiner arranged to combine the received light and provide the combined light (including components of the first and / or second sample light at different beat frequencies) to a signal processing circuit. The detector 30 may be configured to generate an interference pattern based on the difference in optical frequency between the incident sample electric field and the reference electric field, e.g., the detected intensity or power is proportional to the square of the incident electric field, which is the sum of the sample electric field and the reference electric field. Thus, the detected intensity or power (in the form of a photocurrent) may be equal to the square of the sum of the incident sample electric field and the reference electric field. The detector may comprise a photodiode, an avalanche photodiode and / or a high-speed line-scan camera, a streak camera, or a high-speed CCD or CMOS sensor. The detector 30 may be a high-bandwidth detector. For example, the detector 30 may be configured to resolve interference fringes at 100 MHz or higher, such as up to 1 GHz. The detector 30 may comprise a single speckle detector. For example, the optical fiber used in the detector may be single-mode. When a multimode detector is used, the detector may comprise an array of square-law detectors, such as a photodiode array, a focal plane array, a high-speed line-scan camera, or a high-speed CCD array. The detector may also comprise a balanced detector array. The balanced detector array may be configured so that the reference light and the scattered light are combined and then separated (e.g., uniformly) by a pair of out-of-phase detectors, such as a four-port (two inputs, two outputs, 50:50 ratio) fiber coupler or a beam splitter cube. The balanced detector may improve the signal-to-noise ratio of the detected signal by eliminating incoherent portions of the signal. The balanced photodetector may also fully utilize all light transmitted through the interferometer to suppress common noise, such as laser intensity noise.

[0120] In the context of the present disclosure, it will be understood that the examples described herein are not intended to be limiting. Instead, the examples illustrate specific potential ways of implementing the claimed technology. For example, the iNIRS system 10 is described with a continuous optical cable providing a channel and a probe connecting the channel to the subject's scalp. However, it will be understood that the probe itself may be part of the optical channel, or that a probe may not be provided at all. Similarly, the reference channel feature is intended only to illustrate that reference light is delivered from the light source to the photodetector via an optical channel (rather than through the subject's brain tissue). For example, if multiple light sources are provided, each light source may have one reference channel for each photodetector, where the reference channel directly connects the light source to the photodetector. In this case, there may be no reference connection in the system at all. Additionally or alternatively, if multiple light sources are used, reference light may be transmitted in a common reference optical channel, where a portion of the reference light is acquired from the common reference optical channel for each of the photodetectors. The light source may also be positioned to deliver light to one of multiple different locations on the subject's scalp. For example, the light source may be connected to multiple different sample delivery channels, each extending toward the subject's scalp (e.g., from an optical splitter).

[0121] It will be understood that the particular arrangements shown for the detector signal processing circuits need not be considered limiting. Each photodetection arrangement may be configured to combine the first sample light, the second sample light, and the reference light to provide a combined optical signal having components at one or more first beat frequencies and one or more second beat frequencies, and process the combined optical signal to determine one or more characteristics of the subject's brain tissue. Any suitable signal processing and / or conversion circuitry may be used for this purpose. For example, a transimpedance amplifier may not be required (e.g., depending on the photodetector or ADC, current-to-voltage conversion may not be required, or it may be performed in a different manner). Similarly, balanced photodetectors need not be used; instead, a single photodetector, such as a photodiode, may be used. Similarly, the arrangements with ADCs shown in the figures 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.

[0122] From the foregoing, it will be understood that the examples shown in the figures are illustrative only and include features that may be generalized, eliminated, or replaced as described and claimed herein. Referring generally to the figures, it will be understood that schematic functional block diagrams are used to illustrate the functionality of the systems and apparatus described herein. In addition, processing functions may also be provided by devices supported by electronic devices. However, it will be understood that functionality need not be so divided and should not be construed to imply any particular hardware structure other than that described and claimed below. The functionality of one or more of the elements shown in the figures may be further subdivided and / or distributed throughout the apparatus of the present disclosure. In some examples, the functionality of one or more elements shown in the figures may be integrated into a single functional unit.

[0123] As will be understood by those skilled in the art in the context of this disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspect of the present disclosure may be combined with any of the other aspects of the present disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to operation of a particular element of apparatus may be provided in a method that does not use that particular type of apparatus. In addition, unless some other feature is explicitly described as essential to the operation of that feature, each feature of each of the examples is intended to be separable from the feature with which it is combined. Each of the separable features may, of course, be combined with any of the other features of the example with which it is described, or with any of the other features or combinations of features with respect to any of the other examples described herein. Furthermore, equivalents and modifications not described above may be employed without departing from the invention.

[0124] Certain features of the methods described herein may be implemented in hardware, and one or more functions of an apparatus may be implemented in method steps. It will be understood that, in the context of this disclosure, the methods described herein do not necessarily have to be performed in the order described, nor necessarily in the order shown in the figures. Thus, aspects of the present disclosure described with reference to a product or apparatus are also intended to be implemented as a method, and vice versa. The methods described herein may be implemented in a computer program, or in hardware, or any combination of a computer program and hardware. Computer programs include software, middleware, firmware, and any combination of software, middleware, and firmware. The program may be provided as a signal or network message, or recorded on a computer-readable medium, such as a tangible computer-readable medium capable of storing a computer program in a non-transitory form. Hardware includes computers, handheld devices, programmable processors, general-purpose processors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and arrays of logic gates.

[0125] Any controller of the present disclosure may be implemented using fixed logic, such as an assembly of logic gates, or programmable logic, such as software and / or computer program instructions executed by a processor. The controller may include a central processing unit (CPU) connected to a graphics processing unit (GPU) and associated memory, and associated memory. Other types of programmable logic include programmable processors, programmable digital logic, such as field programmable gate arrays (FPGAs), tensor processing units (TPUs), erasable programmable read-only memory (EPROMs), electrically erasable programmable read-only memory (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 or optical cards, other types of machine-readable media suitable for storing electronic instructions, or any suitable combination thereof. In particular, any controller of the present disclosure may be provided by an ASIC.

[0126] Other examples and modifications of the present disclosure will be apparent to those skilled in the art in light of the present disclosure.

Claims

1. 1. An interferometric near-infrared spectroscopy (iNIRS) system comprising: a light emitting mechanism comprising a light source configured to provide a wavelength-swept emission of light; a light detection mechanism including an interferometric photodetector; With The iNIRS system includes: a first optical channel path arranged to (i) extend between the light source and the object to deliver first sample light from the light source to the object, and (ii) extend between the object and the detector to deliver first sample light received from the object to the detector; a second optical channel path disposed to (i) extend between the light source and the object to deliver second sample light from the light source to the object, and (ii) extend between the object and the detector to deliver second sample light received from the object to the detector; a reference light channel path disposed to extend between the light source and the detector for delivering reference light from the light source to the detector along a reference channel; a plurality of optical channels arranged to define The detector comprises: combining the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light; configured to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light; the first optical channel path has a different length relative to the second optical channel path to prevent spectral overlap between the first beat frequency and the second beat frequency; An iNIRS system characterized by:

2. a portion of the first optical channel path sharing a common optical channel with a portion of the second optical channel path; The iNIRS system of claim 1 .

3. the common optical channel (i) connects the light source to the object, or (ii) connects the object to the detector; The iNIRS system of claim 2.

4. The plurality of optical channels include: a sample delivery channel connected to the light source and arranged to be connected to the object for directing first and second sample lights from the light source towards the object; a first sample receiving channel arranged to be coupled to the object to receive a first sample light from the object; a second sample receiving channel arranged to be coupled to the object to receive second sample light from the object; With The first optical channel path comprises: the sample delivery channel; the first sample receive channel; With The second optical channel path is the sample delivery channel; the second sample receive channel; With the first sample receiving channel having a different length relative to the second sample receiving channel, thereby providing a length difference between the first optical channel path and the second optical channel path; The iNIRS system of any one of claims 1 to 3.

5. The iNIRS system includes: an analog-to-digital converter (ADC) configured to obtain sample data including a representation of the first beat frequency and the second beat frequency detected by the photodetector; Equipped with The iNIRS system of any one of claims 1 to 3.

6. the iNIRS system is configured to use a single ADC channel to acquire the sample data for both the first beat frequency and the second beat frequency. The iNIRS system of claim 5.

7. The system comprises: a controller configured to process the sample data to obtain (i) first sample data including an indication of the first beat frequency detected by the photodetector; and (ii) second sample data including an indication of the second beat frequency detected by the photodetector; Equipped with The iNIRS system of claim 5.

8. The processing of the sample data includes: separating the first sample data from the second sample data based on an indication of a beat frequency; Including, The iNIRS system of claim 7.

9. the controller is configured to process the sample data such that (i) the first sample data includes a detected beat frequency less than a threshold frequency, and (ii) the second sample data includes a detected beat frequency greater than the threshold frequency. The iNIRS system of claim 8.

10. the controller is configured to (i) obtain first time-of-flight data for the first sample light based on the first sample data, and (ii) obtain second time-of-flight data for the second sample light based on the second sample data; The iNIRS system of claim 7.

11. the controller is configured to average the first time-of-flight data and the second time-of-flight data to provide combined time-of-flight data. The iNIRS system of claim 10.

12. the controller is configured to align the first time-of-flight data with the second time-of-flight data based on a time offset associated with the length difference between the first optical channel path and the second optical channel path. The iNIRS system of claim 10.

13. Aligning the first time-of-flight data with respect to the second time-of-flight data comprises: (i) applying a fixed time offset related to the difference in duration it takes light to travel along the first optical channel path and the second optical channel path; and (ii) applying a time offset based on aligning one or more features in the first time-of-flight data with corresponding features in the second time-of-flight data. The iNIRS system of claim 12.

14. the difference in length between the first optical channel path and the second optical channel path is at least as great as a distance corresponding to an expected time span for a distribution of time-of-flight (DTOF) associated with the first sample light; The iNIRS system of any one of claims 1 to 3.

15. The iNIRS system includes: a plurality of optical channels arranged to define three or more optical channel paths (i) extending between the light source and the object, and (ii) arranged to extend between the object and the detector; With each of the optical channel paths having a different length to prevent spectral overlap between beat frequencies associated with each of the optical channel paths; The iNIRS system of any one of claims 1 to 3.

16. the number of different optical channel paths is selected based on a digitization bandwidth for a single ADC channel.

16. The iNIRS system of claim 15.

17. the number of optical channel paths is selected to maximize utilization of the complete digitization bandwidth while preventing spectral overlap between the beat frequencies associated with each respective optical channel path; 17. The iNIRS system of claim 16.

18. The light detection mechanism includes: a beam combining element for combining light from the different sample receiving channels into a single channel; Equipped with The iNIRS system of claim 4.

19. the light source is a first light source, The light-emitting mechanism is second light source, With the interferometric photodetector is positioned to receive first sample light from the second light source, second sample light from the second light source, and second reference light from the second light source; The iNIRS system of any one of claims 1 to 3.

20. the light detection mechanism is a first light detection mechanism, The iNIRS system includes: a second light detection mechanism; With The second light detection mechanism A second detector; With The plurality of optical channels include: a third optical channel path disposed to (i) extend between the light source and the object to deliver third sample light from the light source to the object, and (ii) extend between the object and the second detector to deliver third sample light received from the object to the second detector; a fourth optical channel path disposed to (i) extend between the light source and the object to deliver fourth sample light from the light source to the object, and (ii) extend between the object and the second detector to deliver fourth sample light received from the object to the second detector; a second reference light channel path disposed to extend between the light source and the second detector for delivering reference light from the light source to the second detector along a second reference channel; and arranged to define The second detector is combining the reference light with the third sample light to provide optical signals at a plurality of third beat frequencies between the third sample light and the reference light; configured to combine the reference light with the fourth sample light to provide optical signals at a plurality of fourth beat frequencies between the fourth sample light and the reference light; the third optical channel path has a different length relative to the fourth optical channel path to prevent spectral overlap between the third beat frequency and the fourth beat frequency. The iNIRS system of any one of claims 1 to 3.

21. the iNIRS system is configured to average data obtained from each of the first through fourth detected beat frequencies; 21. The iNIRS system of claim 20.

22. The plurality of optical channels include: a first sample delivery channel connected to the light source and arranged to be connected to the object for directing first sample light from the light source towards the object; a second sample delivery channel connected to the light source and arranged to be connected to the object for directing second sample light from the light source towards the object; a sample receiving channel arranged to be connected to the object to receive first and second sample lights from the object; With The first optical channel path comprises: the first sample delivery channel; the sample receive channel; With The second optical channel path is the second sample delivery channel; the sample receive channel; With the first sample delivery channel having a different length relative to the second sample delivery channel, thereby providing a length difference between the first optical channel path and the second optical channel path; The iNIRS system of any one of claims 1 to 3.

23. The plurality of optical channels include: a first sample delivery channel connected to the light source and positioned to be connected to the object for directing light from the first light source towards the object; a second sample delivery channel connected to the light source and arranged to be connected to the object for directing light from the second light source towards the object; a first sample receiving channel arranged to be connected to the object to receive from the object first sample light from the first sample delivery channel and first sample light from the second sample delivery channel; a second sample receiving channel arranged to be connected to the object to receive second sample light from the first sample delivery channel and second sample light from the second sample delivery channel from the object; With the first sample delivery channel has a different length than the second sample delivery channel and the first sample receiving channel has a different length than the second sample receiving channel to prevent spectral overlap between (i) a first beat frequency for the first sample light from the first sample delivery channel, (ii) a first beat frequency for the first sample light from the second sample delivery channel, (iii) a second beat frequency for the second sample light from the first sample delivery channel, and (iv) a second beat frequency for the second sample light from the second sample delivery channel; The iNIRS system of any one of claims 1 to 3.

24. 1. An interferometric near-infrared spectroscopy (iNIRS) system comprising: a light emitting mechanism comprising: a light source configured to provide a wavelength-swept emission of light; a sample delivery channel connected to the light source and positioned to be connected to an object for directing light from the light source towards the object; and a reference channel connected to the light source for receiving light from the light source; a first sample receiving channel arranged to be connected to the object to receive first sample light from the object; a second sample receiving channel arranged to be connected to the object to receive second sample light from the object, each of the first sample light and the second sample light comprising light emitted from the light source; and an interferometric photodetector connected to: (i) the first sample receiving channel to receive the first sample light; (ii) the second sample receiving channel to receive the second sample light; and (iii) the reference channel to receive reference light; With The photodetector combining the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light; configured to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light; the first sample receive channel has a different length relative to the second sample receive channel to prevent spectral overlap between the first beat frequency and the second beat frequency; An iNIRS system characterized by:

25. 1. An interferometric near-infrared spectroscopy (iNIRS) system comprising: a light emitting mechanism comprising: a light source configured to provide a wavelength-swept emission of light; a first sample delivery channel connected to the light source and arranged to be connected to an object to direct light from the light source towards the object; a second sample delivery channel connected to the light source and arranged to be connected to the object to direct light from the light source towards the object; and a reference channel connected to the light source to receive light from the light source; a sample receiving channel arranged to be connected to the object to receive first and second sample light from the object, the first sample light comprising light emitted from the light source that has traveled along the first sample delivery channel, and the second sample light comprising light emitted from the light source that has traveled along the second sample delivery channel; and a light detection mechanism comprising: an interferometric light detector connected to: (i) the sample receiving channel to receive the first and second sample light; and (ii) the reference channel to receive a reference light. With The interferometric photodetector comprises: combining the reference light with the first sample light to provide optical signals at a plurality of first beat frequencies between the first sample light and the reference light; configured to combine the reference light with the second sample light to provide optical signals at a plurality of second beat frequencies between the second sample light and the reference light; the first sample delivery channel having a different length relative to the second sample delivery channel to prevent spectral overlap between the first beat frequency and the second beat frequency; An iNIRS system characterized by:

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