Patent Application
20210228118
This disclosure relates generally to brain activity monitoring and more particularly to brain activity monitoring using infrared light.
Near-infrared Spectroscopy may be used to measure brain activity in the motor cortex by measuring relative changes in oxygen concentration in the brain. Brain activity requires oxygen to use energy, which is known as the hemodynamic response and is the basis for many brain imaging technologies. When a user moves their left hand, the concentration of oxygen will increase in the right motor cortex in the area that controls the hand. The more muscle recruitment and the more complex the movement, the greater the oxygen change.
Individuals with an acquired brain injury (such as a stroke) often have mobility impairments, requiring intensive physical rehabilitation. Rehabilitation promotes recovery by leveraging neuroplasticity (i.e. the brain's ability to change). Brain activity metrics may be used to predict recovery, track progress, and compare the effects of different exercises, potentially allowing clinicians to better tailor therapy to individual patients. There remains a need for brain activity monitoring methods and apparatus.
In accordance with one disclosed aspect there is provided an apparatus for monitoring brain activity of a user. The apparatus includes a plurality of spatially separated emitters operable to generate infrared radiation. The apparatus also includes a plurality of spatially separated infrared radiation detectors, and a plurality of light pipes urged into contact with the user's scalp, each one of the plurality of emitters and detectors having an associated light pipe operable to couple infrared radiation from the emitter into the scalp or to couple infrared radiation from the scalp to the detector. Each detector is operable to produce a signal representing an intensity of infrared radiation generated by a selectively actuated one of the plurality of emitters and received at the detector after traveling on a path through underlying brain tissue, the signals being received by a controller operably configured to process the signals from each detector to determine changes in blood oxygenation within the brain tissue along the path between the respective emitter and detector, and generate a spatial representation of brain activity within in the user's brain based on the processed signals.
The emitters and detectors are disposed on a headset and the controller may be remotely disposed with respect to the headset and the headset may include a transmitter operable to transmit the signals to the controller for processing.
The apparatus may include a headset controller disposed on the headset and operably configured to control functions of the transmitter, the emitters, and the detectors.
The infrared radiation may include near infrared radiation.
The emitter may include a light emitting diode operably configured to produce the infrared radiation at a plurality of wavelengths selected to cause the detector to produce signals that facilitate determination of a blood oxygenation state of the brain tissue underlying each of the spatially separated emitters and associated detectors, the blood oxygenation state being indicative of local cerebral hemodynamics within the brain tissue and facilitating a determination of neural activity within the user's brain.
The plurality of wavelengths may include at least first and second wavelengths selected to fall on either side of the isobestic point for oxygenation and deoxygenation of blood hemoglobin.
The light emitting diode associated with each of the plurality of emitters may be mounted within a headset, the headset being operable to support the plurality of emitters and plurality of detectors in contact with the user's scalp when worn by the user.
The plurality of emitters may include at least one emitter disposed proximate to one of the plurality of detectors and the detector may be operable to produce a shallow path signal representing an intensity of infrared radiation generated after traveling along a shallow path through scalp and bone tissue between the at least one emitter and the detector, at least one emitter disposed spaced apart from one or more of the plurality of detectors and the one or more detectors are operable to produce a deep path signal representing an intensity of infrared radiation generated after traveling along a deep path through the underlying brain tissue between the at least one emitter and the one or more detectors.
The controller may be operably configured to process the shallow path signals to determine shallow path noise, the shallow path noise being used as a basis for filtering the deep path signal to determine the changes in blood oxygenation within the brain tissue.
The controller may be operably configured to process the shallow path signals to determine shallow path noise, the shallow path noise being used as a basis for filtering the deep path signal to determine the changes in blood oxygenation within the brain tissue.
The controller may be operably configured to process the signals by aligning a phase of each of the shallow path signals and deep path signals based on a physiological process component in the signals, performing a principle component analysis on the shallow path signals to determine contamination components associated with physiological processes other than changes in blood oxygenation within the brain tissue, and removing the contamination components from the deep path signals to provide signals representing changes in blood oxygenation within the brain tissue from which the effects of other physiological processes have been filtered.
Performing the principle component analysis may include filtering the shallow path signals to separate the shallow path signals into slow-cycling signals associated with slow-cycling physiological processes and fast-cycling signals associated with fast-cycling physiological processes and performing principle component analysis on each of the shallow path signals, the slow-cycling signals and the fast-cycling signals.
The controller may be operably configured to, prior to performing the principle component analysis, process the phase aligned shallow path signals to generate signals representing oxygenation and deoxygenation of blood hemoglobin, and take a first derivative of the signals representing oxygenation and deoxygenation of blood hemoglobin.
The controller may be operably configured to activate selected emitters and detectors to generate signals associated with different paths of travel of the infrared radiation through the brain tissue.
Each light pipe may include a low durometer material that is optically transmissive at wavelengths associated with the infrared radiation, the low durometer material facilitating comfortable optical contact with the scalp of the user.
The light pipe material may have a durometer in a range of between about Shore A durometer 30 and about Shore A durometer 90.
The length of each light pipe may be between about 7 millimeters and 15 millimeters.
Each of the plurality of emitters and detectors may be mounted on a headset that conforms to the scalp of the user and a length of at least about 7 mm of the light pipe may protrude outwardly from a surface of the headset.
Each light pipe may include a coupling surface for coupling infrared radiation between the light pipe and the emitter or detector, a distal lens operably configured to contact the scalp and direct infrared radiation to or from the light pipe, and a guide portion extending between the coupling surface and the distal lens.
The apparatus may include a sheath surrounding at least a portion of the guide portion of each light pipe, the sheath being operably configured to reduce infrared radiation leakage from the guide portion of the light pipe.
The sheath may include an outer surface operably configured to divert the user's hair away from the distal lens when the light pipe is in contact with the scalp.
The guide portion of the light pipe may have a generally cylindrical shape and may have a diameter selected to cause total internal reflection of infrared radiation incident at inner surfaces of the guide portion.
The coupling surface of the light pipe may be operably configured to directly contact a radiating surface of the emitter or a radiation receiving surface of the detector for coupling infrared radiation between the light pipe and the detector.
A cross sectional area of the guide portion may be smaller than a cross sectional area of the coupling surface and the light pipe may further include a tapered transition between the coupling surface and the guide portion and a taper angle of the tapered transition may be selected to prevent infrared radiation leakage from the tapered transition, the tapered transition further providing for mounting of the light pipe to the emitter or detector.
The apparatus may include a headset having a plurality of articulated segments, each articulated segment supporting at least one emitter or detector, the articulated segments each being urged toward the scalp of the user to cause contact between the associated light pipes of the respective emitters or detectors and the scalp.
Each of the plurality of articulated segments may be operably configured to mount a circuit substrate and at least one detector or emitter may be mounted on each circuit substrate.
The apparatus may include a flexible interconnect interconnecting between a headset controller and the plurality of circuit substrates.
The flexible interconnect and the plurality of circuit substrates may be formed as a unitary flexible circuit substrate.
The plurality of detectors are disposed spaced apart along a sprung band having a curvature operable to conform to a corresponding lateral curvature of the user's scalp and urge the plurality of detectors toward the scalp when the band is worn by the user.
The apparatus may further include a plurality of articulated segments disposed forwardly or rearwardly with respect to the sprung band, each articulated segment including at least one emitter and being urged toward the scalp when the band is worn by the user.
The controller may be operably configured to monitor the signal level produced at each detector and to control a level of infrared radiation produced by the selectively actuated emitter to maintain the intensity within a detection range of the detector.
The controller may be further operably configured to generate display data for display as a graphic user interface (GUI) on a screen in communication with the controller, the GUI including a spatial representation of at least one of the emitters and detectors along with display information indicating whether the signal intensity is within the detection range of the associated detector.
The controller may be operably configured to discontinue the monitoring when the signals received from the detectors no longer meet a coupling criterion indicative of a plurality of the emitters or detectors being coupled to the scalp of the user.
The apparatus may include at least one coupling sensor operably configured to generate a coupling signal indicating a state of coupling between the plurality of light pipes and the user's scalp, and the controller may be operably configured to discontinue the monitoring in response to the coupling signal indicating that a coupling criterion is not being met.
The at least one coupling sensor may include at least one of a capacitive sensor that produces a signal indicative of a proximity of the apparatus to the scalp, an acoustic sensor that produces a signal in response to an ambient sound level, an inertial sensor that produces a signal indicative of movement of the apparatus, or one or more of the detectors, an ambient light component in the signal produced by the one or more detectors may be indicative of the apparatus being removed from the scalp and the detector being subject to ambient light radiation.
The controller may be operably configured to process the signal received by at least one of the detectors to extract a cardiac pulse signal representing a detected heartbeat of the user and to monitor the pulse signal to determine whether coupling between the emitters and detectors and the scalp of the user meets a coupling criterion.
The controller may be operably configured to process the signals by extracting a dominant frequency from the signals that falls within a frequency range based on the user's expected heartbeat frequency range.
The controller may be operably configured to discontinue the monitoring when the cardiac pulse signals received from the detectors no longer meet the coupling criterion.
The controller may be operably configured to monitor time variations in blood oxygenation within the brain tissue in a region underlying each detector and selectively actuated emitter and to generate data metrics representing a degree of brain activation in each region.
The controller may be further operably configured to generate display data for display as a graphic user interface (GUI) on a screen in communication with the controller, the GUI including a representation of regions of the user's body that correspond to regions of the user's brain that are indicated by the changes in blood oxygenation within the brain tissue to be actuated.
The controller may include a processor circuit, the processor circuit including a graphic processing unit operably configured to accelerate processing of the signals from each of the plurality of detectors to facilitate near real time presentation of results to the user.
Other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific disclosed embodiments in conjunction with the accompanying figures.
In drawings which illustrate disclosed embodiments,
Referring to
Each detector 104 is operable to produce a signal representing an intensity of near infrared radiation generated by a selectively actuated one of the plurality of emitters 102 and received at the detector after traveling on a path through underlying brain tissue. Near infrared radiation (i.e. near infrared light) has a wavelength generally within a range of about 750 nm (nanometers) to 900 nm and is able to travel through skin, tissue, and bone. The near infrared radiation from each emitter 102 thus penetrates the scalp and skull and travels along a path through respective portions of underlying brain tissue, which reflects the radiation back to one or more of the detectors 104. By selectively actuating one of the emitters 102 and one of the detectors 104, the signal produced by the detector may be associated with a region of the user's neurocranium that subtends the emitter and detector. If the emitter 102 and detector 104 are disposed proximate each other, the infrared radiation that reaches the detector will have primarily passed through the superficial scalp and bone tissues and is unlikely to have penetrated brain tissues underlying the bone of the neurocranium. When the emitter 102 and detector 104 are disposed spaced further apart, the infrared radiation that reaches the detector will generally have penetrated the scalp and bone tissues and entered the underlying brain tissue.
In this embodiment, the headset 108 is in wireless communication with a controller 110, which in this embodiment is implemented using a tablet computing device acting as a host controller. The host controller is thus remotely disposed with respect to the emitters 102 and detectors 104, and the headset 108 includes a transmitter (not shown) operable to transmit the signals to the controller 110 for processing. The controller 110 receives the signals generated by the detectors 104, which are processed to determine changes in blood oxygenation within the brain tissue along the path between the respective emitter and detector. Based on the processing of the signals, the controller 110 is able to generate a spatial representation of brain activity within in the user's brain.
In one embodiment each emitter 102 is configured to produce near infrared radiation at two or more wavelengths, which are selected to cause an associated detector to produce signals that facilitate determination of a blood oxygenation state of the underlying brain tissue. For example, first and second wavelengths may be selected that fall on either side of the isobestic point for oxygenation and deoxygenation of blood hemoglobin (Hb) at which deoxy-Hb and oxy-Hb have substantially identical absorption coefficients. For example an emitter that produces wavelengths of 750 nm and 850 nm may be used. In other embodiments the selected wavelengths may fall on the same side of the isobestic point.
The detected intensity of each of the selected wavelengths at the detector 104 is thus indicative of the blood oxygenation state, which in turn is indicative of local cerebral hemodynamics within the brain tissue and facilitates a determination of neural activity within the portion of the user's brain through which the near infrared radiation produced by the emitter has traveled to reach the detector.
In this embodiment the emitters 102 and detectors 104 are disposed on the headset 108 and the controller 110 acts as a host controller, which is remotely disposed with respect to the headset and receives signals transmitted by a transmitter (not shown) on the headset 108. In this embodiment, the headset 108 may further include a headset controller (not shown) disposed on the headset and operably configured to control signal generation and acquisition by the emitters 102 and the detectors 104 and the transmission of these signals to the host controller 110.
In this embodiment the detectors 104 are mounted within a detector enclosure 112, which also houses some of the emitters 102. The remaining emitters are each housed in a separate emitter enclosure 114. One of the emitter enclosures 114 is shown in exploded view in
Referring to
In the embodiment shown the light pipe 106 also includes a sheath 222 surrounding at least a portion of the guide portion 218 of the light pipe. The sheath 222 is optically absorbent at the wavelengths emitted by the emitter 102 and reduces near infrared radiation leakage from the guide portion 218 of the light pipe 106. In some embodiments the sheath 222 may include an outer surface that is ribbed or otherwise configured to divert the user's hair away from the distal lens 220 when the light pipe 106 is in contact with the scalp, thereby improving near infrared radiation coupling between the emitters 102 and the scalp.
In the embodiment shown the guide portion 218 has a generally cylindrical shape and has a diameter D selected to cause total internal reflection of near infrared radiation or light rays incident at inner surfaces of the guide portion. In one embodiment the light pipe 106 is molded from a liquid silicone rubber material (such as Lumisil LR 7601/70), which has high optical transmissivity at near infrared radiation wavelengths. Lumisil LR 7601/70 has a refractive index of 1.41, for which the total internal reflection (TIR) critical angle is about 45.2°. A light ray 224 emitted from the center of the radiating surface 216 of the emitter 102 would thus impinge on the outer surface of the guide portion 218 and would be reflected to travel along the outer surface of the guide. Any light rays from the emitter 102 at an angle greater than 45.2° that impinge on the outer surface of the guide portion 218 would escape from the light pipe 106, but would be absorbed in the sheath 222.
In the embodiment shown a cross sectional area of the guide portion 218 is smaller than a cross sectional area of the coupling surface 214 and the light pipe includes a tapered transition 228 between the coupling surface and the guide portion. A taper angle of the tapered portion 228 is selected to prevent near infrared radiation leakage from the tapered transition. In
In one embodiment the guide portion 218 of the light pipe 106 has a diameter of about 4 mm, the tapered portion 228 has a diameter of about 6 mm at the coupling surface 214, and the light pipe has an overall length L of about 9 mm. The plurality of emitters 102 may each be configured generally as shown in
One of the detector enclosures 112 is shown in exploded view in
In this embodiment the emitter 102 is disposed proximate the detector 104 for use as a shallow path emitter. The configuration of the shallow path emitter 102 is generally similar to the configuration described above in connection with
As disclosed above, in one embodiment the light pipe 106 is molded from a liquid silicone rubber material such as Lumisil LR 7601/70, which is a relatively compliant material having a Shore A durometer of 70. The material is biocompatible for skin contact for a period of time that the headset would usually be worn by a user during a brain activity assessment session. The material also has good resistance to environmental and other contaminants. The low durometer of the light pipes 106 facilitates comfortable optical contact with the scalp of the user. The inventors have found that a light pipe material having a durometer in a range of between about Shore A durometer 45 and about Shore A durometer 70 provides an acceptable level of comfort and transmittance of near infrared radiation. However, in some embodiments even more compliant materials having Shore A durometer as low as 30 may be used. Less compressible materials having Shore A durometer as high as 95 may also provide comfort for the user.
The headset 108 of
The emitters 102 include shallow path emitters (labeled as 412-420 in
Each of the shallow path emitters 412-420 is disposed proximate to respective detectors 400-408. In one embodiment the spacing between the shallow path emitters 412-420 and the respective detectors 400-408 is about 8 mm center-to-center. Near infrared radiation that reaches the detector will have traveled over a relatively shallow path through superficial scalp and bone tissues and is unlikely to have penetrated brain tissues underlying the bone of the neurocranium. Accordingly, when one of the shallow path emitters is activated, the adjacent detector produces a shallow path signal. The emitters 422-436 are spaced apart by about 30 mm center-to-center from the nearest detector and near infrared radiation emitted by these emitters thus travels over a deeper path through the underlying brain tissues before reaching the nearest detector. In one embodiment the penetration of the near infrared radiation from the emitters 422-436 is about 15 mm into the underlying brain tissues.
In one embodiment the shallow path signals are used as a basis for filtering noise from the signals produced between the emitters 422-436 and the respective nearest detectors. Noise may be induced by blood flow in the skin, blood flow in the neurocranium, the user's cardiac pulse, movement between the headset 108 and the users scalp, and ambient light, for example. The controller 110 may be operably configured to process the shallow path signals to determine shallow path noise and make corrections to the deep path signals when determining changes in blood oxygenation within the underlying brain tissues.
The detector enclosures 112 and emitter enclosures 114 of the headset 108 act as a plurality of articulated segments which are urged toward the scalp of the user to cause contact between the associated light pipes 106 of the respective emitters 102 or detectors 104 and the scalp. Portions of the headset 108 that operate to urge the detector enclosures 112 toward the user's scalp are shown in exploded view in
The rear portions 200 of the emitter enclosures 114 are shown disposed in pairs, one of the pair being disposed forwardly with respect to the sprung band 500 and the other being disposed rearwardly with respect to the sprung band. Each of the rear portions 200 of the pair of emitter enclosures 114 has a spring 502 that joins between the rear portions and urges them toward the scalp when the headset 108 is worn by the user. The spring 502 causes the rear portions 200 and thus emitter enclosures 114 in each pair to be toed in to conform to a curvature of the user's neurocranium in a direction aligned with the sagittal plane.
As shown in
A block diagram of the electrical and control components of the apparatus 100 is shown in
Referring to
The headset controller 600 also includes an analog to digital converter (ADC) 606. Signals produced at each detector 104 are amplified and conditioned by the circuitry 312 shown in
The headset controller 600 also includes a transmitter 608. The transmitter 608 may be implemented as a Bluetooth wireless interface having a relatively low power consumption which permits the headset controller 600 to be run on battery power (not shown).
In this embodiment the headset controller 600 further includes a coupling sensor 622 in communication with an I/O input 624 of the microcontroller 602 for generating a coupling signal indicating a state of coupling between the plurality of light pipes of the emitters 102 and detectors 104 and the user's scalp. The coupling sensor 622 may be a capacitive sensor disposed on the headset 108 that produces a signal indicative of the proximity of the headset 108 to the scalp of the user. A reduction in sensed capacitance would be indicative of the headset 108 having been moved or removed such that the emitters 102 and detectors 104 are no longer in contact with the user's scalp. Alternatively or additionally, an acoustic sensor such as a microphone may be disposed on the headset 108 to generate a signal that in response to an ambient sound level at the microphone. An increase in sound level at the microphone may indicate that the headset 108 has been moved or removed. In other embodiments an accelerometer may be disposed on the headset 108 to provide inertial signals indicative of movement of the headset. Rapid movements of the headset 108 sensed by the accelerometer may be indicative that the headset 108 has been moved or removed. Another alternative would be to monitor ambient light signals experienced at one or more of the detectors 104. When an ambient light component in the detector signal changes significantly, this may be indicative of the headset 108 being removed from the user's scalp. In one embodiment two or more of the alternative coupling sensors may be implemented to monitor the coupling conditions between the headset 108 and the user's scalp.
In this embodiment the headset controller 600 is in communication with the host controller 110, which includes a microprocessor 630, a memory 632, a wireless radio 634, and a display 636. In the embodiment shown in
In one embodiment the processor circuit 630 may include a graphic processing unit operably configured to accelerate processing of the signals from each of the plurality of detectors 104 to facilitate near real time presentation of results to the user.
The wireless radio 634 implements Bluetooth communication protocols for communicating with the transmitter 608 of the headset controller 600. In other embodiments the wireless radio 634 may implement other wireless protocols for communicating with the transmitter 608, which may be correspondingly configured to implement a wireless protocol other than the Bluetooth protocol.
Referring to
The signal calibration process 700 begins at block 702 when user initiates a signal calibration at the host controller 110. Block 704 directs the microcontroller 602 to determine whether a coupling criterion has been met by reading the coupling sensor 622 and comparing the coupling signal received at the I/O input 624 against a range of values determined to indicate that the coupling to the user's scalp is sufficient. If at block 704, the coupling criterion is not met then the microcontroller 602 is directed to block 706, which directs the microcontroller to transmit a notification to the host controller 110 for display to the user. The user may then relocate the headset on the scalp in an attempt to improve the coupling. Block 706 then directs the microprocessor 602 back to block 704 to re-check the coupling. When at block 704, the coupling criterion is met, the microcontroller 602 is directed to block 708. Block 708 directs the microcontroller 602 to acquire signals from the shallow path emitters 412-420 and the associated detectors. The signal acquisition process for emitter/detector pairs is shown in
The signal calibration process 700 then continues at block 710, which directs the microcontroller 602 to determine whether the signal level produced by each detector for each respective emitter/detector pair falls within a pre-determined signal level criterion. If the signal level criterion is not met at block 710, the microcontroller 602 is directed to block 712, which directs the microcontroller to determine whether the emitter signal level is at a maximum. If the signal level not yet maximized, block 712 directs the microcontroller 602 to block 714, which directs the microcontroller to increase the emitter drive signal level for the emitter. The process then continues by repeating block 708 and 710. If at block 712, the signal level is already maximized, the microcontroller 602 is directed to block 716, which directs the microcontroller to determine whether the detector gain is already at a maximum. If the detector gain has not already been maximized then block 716 directs the microcontroller 602 to block 718 and the gain of the detector is increased. Block 718 may also reduce the emitter drive signal level back to a lower level or a minimum level. Block 718 then directs the microcontroller 602 back to block 708 and blocks 708 and 710 are repeated with the increased detector gain.
If at block 716 the detector gain is at a maximum, the microcontroller 602 is directed to block 720. Block 720 directs the microcontroller to transmit a notification message to the host controller 110 causing a message to be displayed for the user on the host controller. The user may adjust the headset position and elect to re-check, in which case block 722 directs the microcontroller 602 back to block 708 to repeat signal acquisition of the shallow path signals for the adjusted headset position. Alternatively, the user may elect to continue with the headset coupling as-is, in which case block 722 directs the microcontroller 602 to block 724.
Block 724 then directs the microcontroller 602 to determine whether a cardiac pulse signal has been detected. The microcontroller 602 is directed to extract a cardiac pulse signal from the signal received at the detector, which is relatively strong compared to other signal components and also has a well-known waveform that facilitates extraction. If at block 724 the cardiac pulse signal is not detected, the microcontroller 602 is directed to block 726, which directs the microcontroller to transmit a notification message to the host controller 110. The user may then adjust the headset position and elect to re-check, in which case block 728 directs the microcontroller 602 back to block 708 to repeat the shallow path signal acquisition for the new headset position. Alternatively, the user may elect to continue with the coupling as-is, in which case block 728 directs the microcontroller 602 to block 730.
If at block 724 the cardiac pulse signal is detected in the shallow path signal, the microcontroller 602 is directed to block 730. The cardiac pulse signal provides an additional determination of the effectiveness of the coupling between the headset 108 and the user's scalp and is further used to perform filtering to remove physiological effects from signals not related to changes in blood oxygenation that are indicative of brain activity.
The signal calibration process 700 then continues at block 730, which directs the microcontroller 602 to repeat the process for the deep path emitter/detector pairs substantially as described above in connection with the shallow path signals. The signal levels for driving the deep path emitters 422-436 and the detector gain is thus calibrated at blocks 730-740 to bring the signals within the signal level criterion for successful detection by the associated detectors. When the emitter drive signal level and detector gain are maximized and the user has adjusted the headset position and elected to re-check at block 744, the microcontroller 602 is directed back to block 708 to repeat the signal acquisition for shallow path emitters at the new headset position.
The microcontroller 602 is also directed to determine whether the cardiac pulse signal is detected for the deep path emitter/detector pairs at block 746. When the pulse signal is not detected at block 746 and the user has adjusted the headset position and elected to re-check at block 750, the microcontroller 602 is directed back to block 708 to repeat the signal acquisition for shallow path emitters. If the signal level criterion is met at block 732 and the cardiac pulse is detected at block 746, the signal calibration process 700 successfully ends at block 752.
Referring to
If the coupling criterion is met at block 764, block 768 then directs the microcontroller 602 to generate data representing a digital waveform for driving the emitters 102. In one embodiment the modulation waveform is a sinewave having a frequency in the kilohertz range and a duration of about 4 milliseconds. Other embodiments may implement different waveforms, frequencies, and/or duration. Block 768 also directs the microcontroller 602 to store the waveform data in the DAC buffer 614. In one embodiment the same digital waveform may be used for signal acquisition from each of the different emitter/detector pairs with a calibration scaling factor being applied to the waveform for each emitter/detector pair as determined by the signal calibration process 700.
The signal acquisition process 760 then continues at block 770, which directs the microcontroller 602 to select an emitter/detector pair that is to be activated for signal acquisition. The process 760 may be used to acquire signals from one emitter/detector pair or from a group of emitter/detector pairs, as in the case of the signal calibration process 700. Each of the emitters 102 is paired with one of the detectors 104, which as a pair define a measurement channel that can be activated. Block 770 directs the microcontroller 602 to cause the selected detector 104 to be configured for receiving signals via the analog to digital converter 606. Block 770 also directs the microcontroller 602 to configure the drive signal conditioning block 604 via the I/O signal 620 to connect the selected emitter to produce near infrared radiation. In embodiments where the emitter is operably configured to produce near infrared radiation at multiple wavelengths, the drive signal conditioning block 604 may also configure the emitter to selectively enable each of the wavelength sources in the emitter to generate the respective wavelengths.
Block 772 then directs the microcontroller 602 to cause the digital to analog converter 612 to read the digital modulation waveform data stored in the DAC buffer 614 and to commence conversion of the digital data into an analog waveform. If the signal calibration process 700 has already been performed, the microcontroller 602 would also apply any determined calibration factor for driving the emitter at a signal level that produces sufficient signal at the associated detector. The analog waveform at the output 616 is thus connected through appropriate drive signal buffers in the drive signal conditioning block 604 to the selected emitter, which then generates a frequency burst having a duration and drive level set by the digital modulation data and the determined signal level calibration factor. The selected emitter couples near infrared radiation through the scalp, which travels through the underlying tissue such that at least a portion of reaches the selected detector and produces an analog signal representing the received near infrared radiation. In embodiments where the emitter 102 includes multiple wavelength sources, each wavelength is activated separately to facilitate generation of separate signals at the detector for each wavelength.
The signal acquisition process 760 then continues at block 774, which directs the microcontroller 602 to cause the analog to digital converter 606 to convert the analog signal received at the selected detector into digital data representation, which is received at the input 618 of the microcontroller as a digital data stream. For an emitter 102 that operates at multiple wavelengths, digital data streams for each wavelength will thus be produced by the detector. Block 776 then directs the microcontroller 602 to process the digital data signals. During the signal calibration process 700 the microcontroller 602 processes the digital data representation to determine signal level and to extract a cardiac pulse signal, if present. Optionally, the processing at block 776 may further involve the microcontroller 602 causing the transmitter 608 to transmit the digital signal to the host controller 110 via the wireless Bluetooth connection for further processing by the host controller.
The process 760 then continues at block 778, which directs the microcontroller 602 to determine whether signals have been acquired for all required emitter/detector pairs. If there remain further signals to be acquired, the microcontroller 602 is directed to block 770, which directs the microcontroller to select the next emitter/detector pair for activation and blocks 772-778 are repeated for the next emitter/detector pair. If at block 778 there are no further signals to be acquired, the microcontroller 602 is directed to block 780 where the signal acquisition process ends.
Following completion of the signal calibration process 700, a user assessment session may be commenced in which signals are acquired from the various the emitter/detector pairs for the duration of the session. For example, referring back to
Referring to
A brain activity assessment commences at block 802 when a user launches the application and the microprocessor 630 is directed to execute the codes stored in the storage location 652 of the memory 632. The application may initially go through a process of receiving user details that will be associated with the assessment session. Block 804 then directs the microprocessor 630 to attempt to establish a wireless connection between the wireless radio 634 of the host controller 110 and the transmitter 608 on the headset 108. If at block 804 no wireless connection is established, the microprocessor 630 is directed to repeat block 804.
If at block 804 a wireless connection with the headset 108 is established, the microprocessor 630 is directed to block 806. Block 806 directs the microprocessor 630 to determine whether the coupling criterion for the headset 108 has been met. As described above in connection with the signal calibration process 700 and signal acquisition process 760, when it is determined by the headset controller 600 that the headset 108 has been removed or moved on the user's scalp such that the coupling criterion is no longer met, a message is transmitted to the host controller 110. Block 806 thus directs the microprocessor 630 to determine whether the coupling criterion is currently being met at the headset 108. If the coupling criterion is not being met, block 808 directs the microprocessor 630 to cause a user notification (not shown) to be generated and displayed on the display 636 to prompt the user to put on or relocate the headset.
If at block 806 the coupling criterion is being met, block 806 directs the microprocessor 630 to block 810, which directs the microprocessor to transmit an instruction via the wireless radio 634 to the headset controller 600 to initiate the signal calibration process 700 shown in
Block 814 then directs the microprocessor 630 to generate data to cause a graphical depiction of the signal quality to be displayed on the display 636 of the host controller 110 to provide feedback to the user for properly locating the headset 108 on the user's scalp. Referring to
Referring back to
While at block 816 the signal level criterion is currently not being met, the graphical depiction 900 includes a status indicator 910 “Calibrating”, which indicates that the signal quality is still being evaluated. If at block 816 the signal level criterion is currently being met, the microprocessor 630 is directed to block 818, which directs the microprocessor 630 to change the displayed screen to the state shown in
The assessment process 800 then continues at block 820, which directs the microprocessor 630 to wait until the user has activated the “Continue” status indicator 910 to continue with the assessment. When the user activates the “Continue” status indicator 910, block 820 directs the microprocessor 630 to block 822. Block 822 directs the microprocessor 630 to continue to receive the digital signal representations from the headset 108 and to process the signals to determine results for the assessment. Generally the signals received at the detectors will have significant noise and may also have significant components due to physiological processes such as the cardiac pulse that may obscure blood oxygenation information in the signals. The processing of the signals is described in more detail later herein.
Block 824 then directs the microprocessor 630 to generate and display results of the assessment. In one embodiment the microprocessor 630 causes a result screen shown in
Referring back to
If at block 824 the assessment session is determined to have been discontinued, the microprocessor 630 is directed to block 826, where the microprocessor is directed to display a brain activity result summary. An example of the summary is shown in
As disclosed above, the processing of the signals at block 822 may involve steps that suppress components of the signal that do not relate to blood oxygenation changes within brain tissue. For example, physiological processes unrelated to brain activity such as the cardiac pulse, respiration, changes in blood pressure, have an effect on how the infrared radiation is absorbed by tissues through which the radiation travels between the emitters 102 and detectors 104. Signals unrelated to brain activity are herein referred to as “contamination signals”.
As disclosed above in connection with
There are some difficulties in performing the filtering of the deep path signals in that the physical processes and structures of the circulatory system may cause a variable delay between contamination signals generated for different deep path and shallow path measurement channels due to these channels being spaced apart about and within the user's neurocranium. There may also be differences between how the physiological process manifest for different deep path and shallow path measurement channels. A flowchart including blocks of code for directing the microprocessor 630 of the host controller 110 to implement block 822 of the process 800 is shown in
Block 1002 then directs the microprocessor 630 to determine the relative phase of each of the extracted cardiac pulse signals using one of the channels as a reference channel. Block 1004 then directs the microprocessor 630 to estimate a time delay for each channel relative to the reference channel (i.e. the reference channel is assumed to have zero time delay). The process 822 then continues at block 1006, which directs the microprocessor 630 to align the deep path and shallow path signals for all the measurement channels. The processed signals at block 1006 thus have the variable delays due to the manifestation of the physiological processes on the respective signals all aligned so that the contamination signals are substantially aligned in time for all measurement channels.
In some embodiments, the absence of a cardiac pulse signal in detected signals may be taken as being indicative that the coupling criterion is no longer being met. The headset controller 600 or the host controller 110 may be operably configured to process the signal received by at least one of the detectors to extract a pulse signal representing a detected heartbeat of the user and to monitor the pulse signal to determine whether coupling between the emitters and detectors and the scalp of the user meets a coupling criterion. A dominant frequency may be extracted from the detected signals, and if the frequency falls within a frequency range based on the user's expected heartbeat frequency range, then the coupling criterion will be considered to be met. The cardiac pulse signal may thus be used in addition to or instead of the coupling signal produced by the coupling sensor 622 (shown in
Block 1008 then directs the microprocessor 630 to process signals for each channel and at each wavelength to extract components associated with blood oxygenation. For example, in embodiments where a dual wavelength emitter having wavelengths of 750 nm and 850 nm is used, the components for each of these wavelengths may be extracted from the signals for each channel to yield a signal that is indicative of blood oxygenation associated with the channel.
Block 1010 then directs the microprocessor 630 to compute a first derivative of the signal produced at block 1008. The inventors have found that signals that reflect a rate of change in blood oxygenation are less noisy than raw blood oxygenation signals.
The process 822 then continues at block 1012, which directs the microprocessor 630 to preform principal component analysis (PCA) on the combined shallow path signals to generate an estimate for the contamination signals. In one embodiment the principal component analysis is applied more than once to the processed shallow path signals to differentiate between faster-cycling signals (for example cardiac pulse in the 0.5 Hz-2 Hz range) and slower-cycling signals (for example respiration in the 0.01 Hz-0.1 Hz range). For example, a first principal component analysis may be performed on the shallow path signals produced at block 1010. This may be followed by a second principal component analysis on a high pass filtered version of the signals produced at block 1010 to selectively retain only fast-cycling signals. A further principal component analysis may be performed on a low pass filtered version of the signals produced at block 1010 to selectively retain only slow-cycling signals. The inventors have found that it is possible for a simple single-pass principal component analysis applied to the signals at block 1010 may capture either one of these fast or slow cycling components while possibly missing the other.
Block 1014 then directs the microprocessor 630 to compute a linear regression on the deep path signal produced at block 1010 for each deep path measurement channel. The linear regression predicts the deep path measurements as an additive function of all the contamination signals obtained by the principal component analysis, thereby estimating the influence of each contamination signal and providing a formula to then remove these influences from the deep path signals. The resulting signals have the influence of contamination signals substantially reduced to provide a signal representing changes in blood oxygenation that can be used to produce the result screen 920 shown in
Functions described above as being implemented on either the host controller 110 or the headset controller 600 may be moved between the controllers or implemented on another controller (not shown).
On other embodiments the headset controller 600 may be implemented using more than one microcontroller located on the headset 108.
While specific embodiments have been described and illustrated, such embodiments should be considered illustrative only and not as limiting the disclosed embodiments as construed in accordance with the accompanying claims.
This application claims the benefit of provisional patent application 62/694447 entitled “SYSTEM AND METHOD FOR A USABLE DEVICE FOR MONITORING BRAIN ACTIVITY”, filed on Jul. 6, 2018 and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2019/050935 | 7/5/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62694447 | Jul 2018 | US |
