CN115844325A - Distributed fNIRS brain function imaging system for super-scanning application - Google Patents
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Abstract
The invention discloses a distributed fNIRS brain function imaging system for overscan application, which comprises a host platform for data monitoring and analysis and at least more than 2 wearable imaging terminals; the host platform performs data interaction with the plurality of imaging terminals in a wireless communication mode; the light source driving unit generates a driving signal according to a control command sent by the main control unit; the source-detection array unit generates near infrared light with two wavelengths and different frequencies according to the driving signal, converts an emergent light signal into an electric signal, performs analog-to-digital conversion, and further transmits data to the main control unit; the main control unit receives data and realizes online software phase-locked demodulation based on a reference signal weighting-accumulation strategy to obtain a light intensity value; the wireless communication unit adopts a DMA-based time division multiplexing-double-thread strategy, a response transmission mechanism and a self-correcting data frame to realize the synchronous wireless transmission of the information of the multi-imaging terminal and the host platform; the power supply unit is used for outputting power and abnormal output alarm to the imaging terminal; the method has the characteristics of high-efficiency double-thread work and high-precision data synchronization, and is suitable for data synchronization detection application of a plurality of wearable medical devices.
Description
The technical field is as follows:
the invention relates to the technical field of photoelectric detection, in particular to a distributed fNIRS brain function imaging system for super-scanning application.
Background art:
the brain is the most delicate and complex organ in human body, and can participate and control the brain function activities such as movement, feeling, cognition, memory, emotion control and the like. From the aspect of neuroinformatics research, brain science research is helpful for human to understand the cognitive activity mechanism of the brain and promote the human to further understand and develop the functional potential of the brain; from the aspect of disease treatment and control, the research of brain science is very important for the diagnosis and intervention of nervous system diseases such as infantile autism, alzheimer disease, epilepsy and the like, is helpful for further understanding the relevant brain disease mechanism and provides scientific basis for diagnosis and medical treatment; from the aspect of artificial intelligence technology innovation, the operation mechanism of brain function activities is utilized to promote the artificial intelligence field to realize new development of theories and technologies, new concepts in other subject fields are enabled, and the development process of new technologies such as brain-computer interfaces and the like is promoted. In summary, the study of brain function is not only important to the exploration of brain operation mechanism, but also closely related to the health development of human and the scientific progress of society.
With the development of scientific technology, a large number of instruments for detecting brain functional activities have been developed, such as functional magnetic resonance imaging (fMRI), electroencephalogram (EEG), functional near-infrared spectroscopy (fNIRS), and the like, which have advanced the research of brain science. Currently, most of the research on single-person task-type brain function activities based on the above instruments is carried out, and the brain hemodynamic response of a subject is detected through certain task stimulation. Because the influence of the psychological activities and the surrounding natural environment of the testee on the human body is not considered in the social interaction situation, the research limits the breadth of the research content, and the ecological effect problem may exist in the research result.
Therefore, developing a detection apparatus that can perform simultaneous neuroimaging (overscan) of two or more subjects in a daily situation is an important direction of brain science research. The main technical difficulties of the simultaneous acquisition of multi-person brain function signals are the continuity and the synchronism of signal acquisition of each sampling point, the sensitivity of detection equipment, the anti-interference performance to motion artifacts and the like. The fNIRS super-scanning technology detects the relative change of hemoglobin concentration by using the scattering and absorption characteristics of brain tissue to near-infrared light, and calculates hemodynamic parameters based on the absorption spectrum characteristics of the hemoglobin, so as to obtain the spatial distribution of brain function activation regions, and has good time resolution and spatial resolution. Although a plurality of research teams at home and abroad have developed corresponding large-scale systems and a small number of portable systems, most of the systems are heavy, the limitation on the behavior of a testee is large, the problem that data cannot be continuously and synchronously acquired among devices due to the working mode, transmission delay and the like of a plurality of detection devices in group research is not considered, and the method is not suitable for the research on the function activities of the group brain in a natural situation.
The invention content is as follows:
in order to overcome the defects of the prior art, the invention provides a distributed fNIRS brain function imaging system for super-scanning application, which can synchronously and continuously measure the relative change of the brain hemoglobin concentration of a plurality of testees in the social interaction process, and provides an imaging tool which is comfortable to wear, excellent in performance, stable and reliable for the research of synchronous nervous activities between brains.
The invention solves the practical problem by adopting the following technical scheme:
a distributed fNIRS brain function imaging system facing super scanning application comprises a host platform for data monitoring and analysis and at least more than 2 wearable imaging terminals; the host platform performs data interaction with the plurality of imaging terminals in a wireless communication mode, and can continuously and synchronously record and display the change information of the blood oxygen activities of a plurality of testees;
the wearable imaging terminal comprises a source-detection array unit, a light source driving unit, a main control unit, a wireless communication unit and a power supply unit;
the main control unit realizes online software phase-locked demodulation based on a reference signal weighting-accumulation strategy and parallelly collects full-channel measurement data;
the wireless communication unit realizes multi-terminal information synchronous wireless transmission based on a time division multiplexing-double-thread strategy of DMA (direct memory access), eliminates time errors generated by asynchronous communication between a host platform and a plurality of imaging terminals, and simultaneously adopts a response transmission mechanism and a self-correcting data frame to realize time registration, classified storage and error code discrimination, thereby ensuring the synchronism of data detection and the accuracy of transmission.
Further, the main control unit realizes the online software phase-locking demodulation step based on the reference signal weighting-accumulation strategy:
the main control unit discretizes the signals to be demodulated, takes the average value of the previous 30 signals as a baseline value of the current integration time to carry out baseline calibration, and subtracts the baseline value from all discretized signals to be demodulated; and in the integration time, the signal to be detected after baseline calibration and two discrete phase-sensitive detection reference signals are respectively demodulated and accumulated, so that the light intensity value of each sampling point is obtained.
Further, the wireless communication unit time division multiplexing based on DMA-two-thread policy step:
the wireless communication unit carries out continuous online software phase-locked demodulation in each integration time through a CPU thread, and the integration completion mark position 1 is marked when the demodulation is completed;
and the wireless communication unit starts DMA data transmission in the second integration time through the DMA thread, and arranges the demodulated value of the previous integration time into a data frame to be sent to the host platform.
Further, the wireless communication unit employs an acknowledgement transmission mechanism and a self-correcting data frame; wherein:
the acknowledgement transmission mechanism employed by the wireless communication unit has three processes:
the terminal sends permission: the host platform sends a data transmission instruction of a first imaging terminal in a broadcast mode, and the imaging terminal identifies and receives the data transmission instruction through a DMA thread and sends a position 1 of an allowable mark;
and waiting for terminal data: the host platform waits for receiving data in the process, and the imaging terminal sends a data frame to the host platform only when the internal integral completion flag bit and the sending permission flag bit of the imaging terminal are simultaneously set to be 1;
receiving terminal data: the host platform receives data in the process, if the data is transmitted in error, the data frame is discarded, a data re-uploading instruction is sent, and the imaging terminal sends the data frame once again; if the host platform still receives the error, the data is marked as error data, the data is marked on the data set, a data completion instruction is sent to the imaging terminal, and data transmission of the next imaging terminal is started.
When the online software phase-locked demodulation is completed, the main control unit reads the current system clock value as the timestamp information of the data, the light intensity value of each sampling point forms a data bit in the data frame, and then the data frame is sent to the host platform.
Has the advantages that:
1. the invention realizes the data wireless transmission of a plurality of imaging terminals based on the ZigBee communication technology, works based on the time division multiplexing-double-thread strategy of DMA, has higher channel utilization rate, adopts an automatic collision avoidance strategy for bottom firmware, can overflow and lose data frames exceeding the tolerance of the channel, but can not generate data errors and crosstalk, is very convenient for removing and adding the network of each imaging terminal, can be used in a plug-and-play mode, and has very strong self-healing property. Compared with WI-FI communication, the method has the characteristics of low error rate and low power consumption, and is particularly suitable for data transmission application of wearable medical equipment.
2. The invention controls each imaging terminal to carry out light intensity calibration so as to compensate the absorption and scattering difference of brains of different testees, and enables each imaging terminal to reach a similar signal-to-noise ratio level by adjusting the intensity of near infrared light.
3. The imaging terminal adopts a high-precision timer to provide timestamp information for the acquired data, and utilizes a DMA mode to realize that a wireless communication unit directly exchanges data with an internal data memory without passing through a main control unit (CPU), thereby eliminating the time error of asynchronous communication between a host platform and a plurality of imaging terminals; and in the process of receiving the data frame, the host platform performs time registration and channel classification according to the difference of the timestamp bit and the address bit, marks abnormal data (transmission error and overflow loss) before fNIRS data preprocessing, and further analyzes and processes to obtain the individual hemodynamic activity information and the data set of the testee.
Description of the drawings:
FIG. 1 is a block diagram of a distributed fNIRS brain function imaging system for a super-scan application;
FIG. 2 is a flow chart of the operation of the present invention involving on-line software phase-locked demodulation;
FIG. 3 is a schematic circuit diagram of a light source driving unit according to the present invention;
FIG. 4 is a flowchart illustrating the operation of automatically adjusting the light intensity of the light source driving unit according to the present invention;
FIG. 5 is a diagram relating to ZigBee data frame transmission format requirements of the present invention;
FIG. 6 is a timing diagram of the present invention involving a TDM-dual thread policy operation
Fig. 7 is a flow chart of the present invention relating to wireless communications.
Detailed Description
The technical solutions of the present invention are further described in detail with reference to the accompanying drawings and specific embodiments, which are only illustrative of the present invention and are not intended to limit the present invention.
The invention provides a super-scanning application-oriented distributed fNIRS brain function imaging system, which comprises a host platform and a wearable imaging terminal (more than or equal to 2 stations) for data monitoring and analysis; the imaging terminal is used for acquiring blood oxygen information of a plurality of brain area sampling points of a testee in a full-parallel manner; and the host platform is used for processing and analyzing the received data frames to obtain the brain hemodynamic activity information of each testee.
The imaging terminal adopts a high-precision timer to continuously acquire, demodulate and communicate light intensity data and provides timestamp information for the acquired data. When the system data is transmitted in error, data loss can be caused, the time point of the lost data can be quickly identified by using the timestamp, and the subsequent data processing work is facilitated.
The imaging terminal adopts a baseline calibration method, each sampling point collects the front 30 groups of data, the average value of the data is used as a baseline, the subsequent measurement value is calibrated (the value of the baseline is subtracted) by the baseline, and then online software phase-locked demodulation processing is carried out to obtain the original light intensity data of each sampling point.
The imaging terminal comprises a constant current source driving circuit and a feedback type light intensity adjusting circuit, wherein the constant current source driving circuit drives a light source to generate near-infrared modulation light with two wavelengths and different frequencies; the feedback type light intensity adjusting circuit adjusts the magnitude of the driving current by controlling the resistance value change of the resistor.
The imaging terminal is made of flexible black medical self-adhesive silica gel materials to wrap the detector and the light source device, so that the imaging terminal is naturally attached to the contour of a skull, is better attached to the skin, and reduces extra errors and motion artifacts generated by relative motion.
The data frame format in the imaging terminal consists of an address bit, a timestamp bit, a marking bit, a data bit and an end bit; the address bit is a specific serial number of the imaging terminal; the timestamp bits are used to mark the point in time at which the set of data was collected; the marking bit is used for marking whether the group of data is transmitted correctly by the host platform; the data bit is composed of original light intensity data of each sampling point; the end bit is used for judging whether the group of data is transmitted to the end.
The main control unit in the imaging terminal adopts a Direct Memory Access (DMA) hardware transmission method to realize data transmission between the data Memory and the wireless communication unit, solves the conflict of receiving interruption of an external serial port and nesting interruption of a timer, and improves the demodulation efficiency of the main control unit.
The host platform comprises a parameter configuration unit, a data processing unit and a real-time monitoring unit, wherein the parameter configuration unit is used for selecting the number of the started imaging terminals, controlling the imaging terminals to carry out light intensity adjustment and transmitting related detection parameters; the data processing unit is used for classifying the detection data of each imaging terminal and marking the data with transmission errors; and the real-time monitoring unit receives the classified data, further analyzes and processes the data to obtain the brain hemodynamic activity information of each testee, and displays the brain hemodynamic activity information in real time.
As shown in fig. 1, a distributed fNIRS brain function imaging system for overscan application is characterized in that: the system comprises a host platform and a wearable imaging terminal (more than or equal to 2 stations) for data monitoring and analysis; the host platform carries out synchronous data interaction with the plurality of imaging terminals in a wireless communication mode, and can continuously and synchronously record and display the change information of the blood oxygen activities of a plurality of testees.
The brain function imaging system comprises a host platform for data monitoring and analysis and at least more than 2 wearable imaging terminals; the host platform performs data interaction with the plurality of imaging terminals in a wireless communication mode, and can continuously record and display the change information of the blood oxygen activities of a plurality of testees;
the wearable imaging terminal comprises a source-detection array unit, a light source driving unit, a main control unit, a wireless communication unit and a power supply unit; wherein:
the light source driving unit consists of a constant current source driving circuit and a feedback type light intensity adjusting circuit;
the main control unit is composed of a timer, an ARM microcontroller, a data memory and online software phase-locked demodulation;
the light source driving unit generates a driving signal according to a control command sent by the main control unit;
the source-detection array unit generates near-infrared light with different frequencies and different wavelengths according to the driving signals and converts emergent light signals into electric signals, performs analog-to-digital conversion and further transmits data to the main control unit;
the main control unit receives data and performs online software phase-locked demodulation processing to obtain a light intensity value; the wireless communication unit adopts a response transmission mechanism and a self-correcting data frame to carry out real-time interaction on the data generated by the main control unit and the data of the host platform;
the power supply unit is used for outputting power and abnormal output alarm to the imaging terminal;
and the host platform transmits the relevant detection parameters to the imaging terminals, receives the data frames of all the imaging terminals, and performs detection recording and classified storage.
Further, the wireless communication unit realizes the multi-terminal information synchronous wireless transmission step based on the time division multiplexing-double-thread strategy of the DMA:
the imaging terminal carries out continuous online software phase-locked demodulation in each integration time through a CPU thread, and the integration completion mark position 1 is marked when the demodulation is completed;
the imaging terminal starts DMA data transmission in the second integral time through a DMA thread, and arranges the demodulated value of the previous integral time into a data frame to be sent to the host platform; wherein:
the wireless communication unit adopts a response transmission mechanism and a self-correcting data frame, and has three processes when data transmission is carried out:
the terminal sends permission: the host platform sends a data transmission instruction of a first imaging terminal in a broadcast mode, and the imaging terminal receives the data transmission instruction through DMA identification and sends a position 1 of an allowable mark;
and waiting for terminal data: the host platform waits for receiving data in the process, and the imaging terminal sends a data frame to the host platform only when the internal integral completion flag bit and the sending permission flag bit of the imaging terminal are simultaneously set to be 1;
receiving terminal data: the host platform receives data in the process, if the data is transmitted in error, the data frame is discarded, a data re-uploading instruction is sent, and the imaging terminal sends the data once again; if the host platform still receives the error at the moment, marking the data as error data, marking the data on the data set, sending a data completion instruction to the imaging terminal, and starting data transmission of the next imaging terminal.
Further, the wireless communication unit adopts a response transmission mechanism and a self-correcting data frame to carry out real-time interaction on the data generated by the main control unit and the data of the host platform:
the data frame format is composed of an address bit, a timestamp bit, a marking bit, a data bit and an end bit;
the address bit is a specific serial number of the imaging terminal;
the timestamp bit is used for marking the time point of acquiring the group of data;
the marking bit is used for marking whether the group of data is transmitted correctly by the host platform;
the data bit is composed of original light intensity data of each sampling point;
the end bit is used for judging whether the group of data is transmitted to the end.
The wireless communication unit comprises a self-correcting data frame and a time division multiplexing-double-thread strategy, wherein the data frame consists of an address bit, a timestamp bit, a marking bit, a data bit and an ending bit, the timestamp bit is determined by a high-precision timer, the precision is 10ms, and the time synchronism of data acquisition among a plurality of imaging terminals is ensured; the time division multiplexing-double-thread strategy adopts ZigBee based on IEEE802.15.4 bottom layer protocol, realizes data interaction between a data memory in a main control unit and a ZigBee data buffer in a DMA mode, eliminates time errors existing in asynchronous communication, and realizes high-precision multi-imaging terminal continuity detection.
Further, the constant current source driving circuit drives the light source to generate near infrared modulation light with two wavelengths and different frequencies; the feedback light intensity adjusting circuit adjusts the process of driving current by controlling the resistance value change of the resistor; wherein:
the feedback type light intensity adjusting circuit receives a preset light intensity value range input by a host platform, adjusts the gear of the resistor to the minimum value, turns on an excitation light source of a first sampling point and carries out online software phase-locked demodulation;
judging whether the gear is the maximum gear, if so, directly finishing the light intensity adjustment of the channel, and otherwise, further judging whether the light intensity is in a preset range; if the sampling point is not in the preset range, the gear is increased for further measurement, and if the sampling point is in the range, the next sampling point is adjusted until all the sampling points are adjusted.
Further, the main control unit receives the data and performs online software phase-locked demodulation processing to obtain a light intensity value: generating 8 groups of square wave signals with the interval of 31Hz between 86Hz and 303Hz through a timer, wherein each group of square wave signals consists of two paths of square waves with the same frequency and without phase shift and 90-degree phase shift and are used as phase-sensitive detection reference signals for on-line software phase-locked demodulation;
the main control unit discretizes the signals to be demodulated, takes the average value of the previous 30 signals as a baseline value of the current integration time to carry out baseline calibration, and subtracts the baseline value from all the values of the signals to be demodulated; within the integration time, respectively demodulating the signal to be detected after baseline calibration and two discrete phase-sensitive detection reference signals to obtain a light intensity value of each sampling point;
when the online software phase-locked demodulation is completed, reading the value of the system clock as a timestamp, wherein the time representation precision is 10ms; the light intensity values of the sampling points form data bits in the data frame, and the timestamp bits are determined by the system clock, so that the data frame is sent to the host platform.
Further, the host platform comprises a parameter configuration unit, a data processing unit and a real-time monitoring unit, wherein:
the parameter configuration unit is used for selecting the number of the started imaging terminals, controlling the imaging terminals to adjust light intensity and transmitting related detection parameters;
the data processing unit is used for classifying the detection data of each imaging terminal and marking the data with transmission errors;
and the real-time monitoring unit receives the classified data, further analyzes and processes the data to obtain the brain hemodynamic activity information of each testee, and displays the brain hemodynamic activity information in real time.
The source-detection array unit is connected with the main control unit and the light source driving unit and is used for emitting near infrared light modulated light with different frequencies according to a control command of the main control unit, converting an emergent light signal into an electric signal, performing analog-to-digital conversion, and transmitting data to the main control unit for demodulation processing;
the power supply unit comprises a power supply management unit and a lithium battery power supply, and the power supply management unit is used for outputting a stable power supply and giving an alarm in abnormal output.
And the host platform transmits the relevant detection parameters to the imaging terminals, receives the data frames of all the imaging terminals, and performs detection recording and classified storage.
In order to obtain Optical imaging of a brain function region, an Optical topological imaging (OT) technology is adopted for imaging, the principle is that light intensity change information of each sampling point is converted into variation of hemoglobin concentration by using a modified Lambert-beer law, and then a two-dimensional image is obtained through interpolation.
Wherein A represents the absorbance of the channel, I 0 And I respectively represent the intensity of the initial incident light and the diffuse reflected light,
denotes the absorption coefficient, C, of two haemoglobins at an incident wavelength of lambda HbO 、C HbR Indicating the concentration of two haemoglobins, DPF (λ) the differential path factor, r the distance of the light source from the detector and G the loss of light intensity by substances other than haemoglobin. The resting state of the testee at the beginning of measurement is taken as reference, and the change of the diffuse reflection light intensity is measured in real time, so that the change of the brain HbO and the brain HbR is detected:
wherein Δ a represents the amount of change in absorbance;
I λ respectively representing the resting state of the testee and the diffuse reflection light intensity measured in real time. Due to the inclusion of Delta C HbO 、ΔC HbR Two unknowns, two wavelengths of near infrared light are needed to solve:
therefore, the relative variation of the hemoglobin concentration of each sampling point is obtained, and then a two-dimensional activation image of the brain area to be detected at a certain time point is obtained in an interpolation mode.
As shown in fig. 2, the wearable imaging terminal discretizes the signal to be demodulated, takes the average value of the first 30 signals as the baseline value of the current integration time, then performs baseline calibration, and subtracts the baseline value from all the signal values to be demodulated. And in the integration time, the signal to be detected after baseline calibration and two discrete phase-sensitive detection reference signals are respectively demodulated, so that the light intensity value of each sampling point is obtained. The imaging terminal adopts two cascaded high-precision timers to form a system clock which runs all the time. When the demodulation is completed, the value of this system clock is read as a time stamp, and the time representation accuracy is 10ms. The light intensity values of the sampling points form data bits in the data frame, and the timestamp bits are determined by the system clock, so that the data frame is sent to the host platform.
As shown in fig. 3, the light source driving unit in the wearable imaging terminal is an 8-channel modulatable constant current LED driving circuit, and the working principle is that when the analog switch is acted by a modulation signal, the analog switch is connected to a reference voltage V REF When the operational amplifier is in a 'virtual short' state, the resistor R S Voltage on is reference voltage V REF (ii) a Field effect tube U GS Greater than the internal turn-on voltage, the drain and source are turned on due to the action on the resistor R S Upper reference voltage V REF Constant and negative feedback action of the circuit, current i flowing through the LED D Keeping constant current, changing reference voltage V by resistor REF Thereby changing the driving current to the target value.
As shown in fig. 4, the wearable imaging terminal first receives a preset light intensity range input by the host platform, adjusts the shift of the resistor to a minimum value, turns on the excitation light source of the first sampling point, and performs online software phase-locked demodulation. And judging whether the gear is the maximum gear, if so, directly finishing the light intensity adjustment of the channel, and otherwise, further judging whether the light intensity is in a preset range. If the sampling point is not in the preset range, the gear is increased for further measurement, and if the sampling point is in the range, the next sampling point is adjusted until all the sampling points are adjusted.
As shown in table 1, each light source of the wearable imaging terminal is composed of two LEDs with 775nm wavelength and 855nm wavelength, and there are 8 LEDs in total for 4 excitation light sources. The main control unit generates 8 square wave signals with different frequencies between 86Hz and 303Hz and 31Hz intervals for modulating 8 LEDs, and the light intensity change information of a plurality of sampling points in a brain area is measured in a full-parallel mode based on a frequency division multiplexing method.
TABLE 1LED modulation frequency
As shown in fig. 5, the ZigBee receiving data frame in the wearable imaging terminal has a length of 1-100 bytes, a certain time interval T0 (minimum 15 ms) is required between data frames to divide the packet correctly, and theoretically the maximum transmission rate is 100byte × 1000ms/15ms =6.7kb/s.
As shown in fig. 6, the wearable imaging terminal performs time division multiplexing-dual-thread policy work, the CPU thread performs continuous online software phase-locked demodulation within each integration time, and when demodulation is completed, the integration completion flag is set to 1; the DMA thread starts DMA data transmission in the second integral time, and arranges the demodulated value of the previous integral time into a data frame to be sent to the host platform. The response transmission mechanism is set in consideration of the problem of time division multiplexing transmission of a plurality of imaging terminals. There are three processes when an imaging terminal performs data transmission: 1. the terminal sends a grant. The host platform sends the data transmission command of the first imaging terminal in a broadcast mode, and the imaging terminal receives the data transmission command through DMA identification and sends the position 1 of the permission mark. 2. And waiting for terminal data. The host platform waits for receiving data in this process, and transmits a data frame to the host platform only when the internal integration completion flag bit and the transmission permission flag bit of the imaging terminal are simultaneously set to 1. 3. And receiving terminal data. The host platform receives the data in the process, if the data is transmitted in error, the data frame is discarded, the data is sent to upload the command again, and the imaging terminal sends the data once again. If the host platform still receives the error, the data is marked as error data, the data is marked on the data set, a data completion instruction is sent to the imaging terminal, and data transmission of the next imaging terminal is started.
As shown in table 2, when ZigBee transmits data in the wearable imaging terminal, an acknowledgement transmission mechanism is adopted, and whether data reception is normal or wrong, the data transmission time of one imaging terminal is constant 90ms, the minimum integration time adopted by the system depends on the number of enabled imaging terminals, and the specific calculation basis is as follows: the minimum integration time is more than or equal to the number of the enabled imaging terminals multiplied by 90ms.
TABLE 2 minimum integration time for different number of imaging terminals
As shown in fig. 6, the wearable imaging terminal time division multiplexing-dual thread policy does not affect each other when operating, which is characterized in that a CPU and a DMA occupy buses alternately in a time division manner, the occupied bus time is short, and one imaging terminal only performs a DMA data transmission process within an integration time. The modulation frequency of the near infrared light is between 86Hz and 303Hz, the interval is 31Hz, and the sampling frequency of 1K is selected according to the Nyquist sampling theorem. Because the integration time of 1000ms and the sampling frequency of 1K are selected, the imaging terminal generates timer interruption every 1ms for a CPU to occupy a bus, reads the sampling value of the ADC, and writes the accumulated value after demodulation operation into the memory 1. After the demodulation of one integration time is finished, the CPU writes the demodulated value into the memory 2, clears the memory 1, and starts the demodulation of the next integration time. After the CPU finishes occupying the bus, the DMA obtains bus control, accesses and reads the data of the memory 2, transmits the demodulation value of the previous integral time, and empties the memory 2 after the data transmission is finished. The memory 1 stores the accumulated value used for the demodulation operation in the current integration time, and the memory 2 stores the demodulated value of the last integration time.
As shown in fig. 7, the wireless communication unit first establishes a network by the host platform ZigBee, and configures network parameters and network identifiers to wait for a network access request of a child node; the imaging terminal ZigBee sends a network access request in each channel in a broadcasting mode, and waits for a device network access request to reply; the ZigBee of the host platform receives the equipment network access request and replies response information, wherein the response information comprises network parameters and a network identifier (the default is an MAC address); the ZigBee of the imaging terminal selects a node network with the best signal quality, and sends response reply information (the MAC address and the equipment attribute of the imaging terminal) to request for joining; after receiving the response information, the host platform ZigBee can unicast and send the target equipment, and a network short address is allocated in a distributed addressing mode for receiving and sending data in the network; the imaging terminal ZigBee broadcasts and sends a device statement containing the short address and the MAC address of the imaging terminal in the network, if some devices find that the addresses of the devices are the same as the addresses of the devices, address conflict broadcast information is sent, and all the devices with conflicts need to replace the addresses.
The system comprises the following components:
1. the source-detection array unit of the imaging terminal adopts patch type LEDs of Ois-775 and Ois-855 models produced by OSA-OPTO company of Germany as system light sources, wherein the Ois-775 is a 775nm light source, the Ois-855 is a 855nm light source, the detector adopts OPT101, an analog-to-digital converter AD7606 is used for synchronous sampling, and data are transmitted to the main control unit through an SPI communication protocol.
2. The main control unit of the imaging terminal adopts STM32F407 and is mainly used for generating timestamp information of detection data, a modulation signal of a light source and a reference signal required by demodulation, receiving voltage information acquired by an ADC (analog to digital converter), performing online software phase-locked demodulation, DMA (direct memory access) data transmission and the like.
3. The light source driving unit of the imaging terminal is sequentially connected through a voltage reference chip LM4132, an operational amplifier LMV324 and an N-channel field effect transistor IRLMS2002 to form a constant current source driving circuit, and square wave modulation of a light source is achieved through an analog switch ADG 734.
4. The power supply unit of the imaging terminal adopts DM02-2805 and 1800mAh polymer lithium batteries, can provide a stable power supply and an abnormity alarm function, and the lithium batteries have large capacity and small volume and meet the requirements of wearable equipment.
5. The wireless communication unit adopts a 2.4G radio frequency transceiving chip CC2530 based on a ZigBee communication protocol, a radio frequency front-end chip CC2591 and an antenna module, has the characteristics of high hardware integration level, strong signal, low error rate and low power consumption, and is suitable for a small-data-volume and multi-node wireless radio frequency network.
6. The host platform is designed by adopting LabView software, performs data interaction with each imaging terminal through a wireless communication unit, processes, records and classifies the received data to obtain a concentration time change curve of hemoglobin, OT optical imaging and a data set.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (4)
1. A distributed fNIRS brain function imaging system for overscan application, comprising: the brain function imaging system comprises a host platform for data monitoring and analysis and at least more than 2 wearable imaging terminals; the host platform performs data interaction with the plurality of imaging terminals in a wireless communication mode, and can continuously and synchronously record and display the change information of the blood oxygen activities of a plurality of testees;
the wearable imaging terminal comprises a source-detection array unit, a light source driving unit, a main control unit, a wireless communication unit and a power supply unit;
the main control unit realizes online software phase-locked demodulation based on a reference signal weighting-accumulation strategy and parallelly collects full-channel measurement data;
the wireless communication unit realizes multi-terminal information synchronous wireless transmission based on a time division multiplexing-double-thread strategy of DMA (direct memory access), eliminates time errors generated by asynchronous communication between a host platform and a plurality of imaging terminals, and simultaneously adopts a response transmission mechanism and a self-correcting data frame to realize time registration, classified storage and error code discrimination, thereby ensuring the synchronism of data detection and the accuracy of transmission.
2. The distributed fNIRS brain function imaging system for hyperspectral applications of claim 1, wherein: the main control unit realizes the online software phase-locking demodulation step based on the reference signal weighting-accumulation strategy:
the main control unit discretizes the signals to be demodulated, takes the average value of the previous 30 signals as a baseline value of the current integration time to carry out baseline calibration, and subtracts the baseline value from all discretized signals to be demodulated; and in the integration time, the signal to be detected after baseline calibration and two discrete phase-sensitive detection reference signals are respectively demodulated and accumulated, so that the light intensity value of each sampling point is obtained.
3. The distributed fNIRS brain function imaging system for hyperspectral applications of claim 1, wherein: the wireless communication unit based on DMA time division multiplexing-double thread strategy steps:
the wireless communication unit carries out continuous online software phase-locked demodulation in each integration time through a CPU thread, and when the demodulation is completed, the integration completion mark position is marked as 1;
and the wireless communication unit starts DMA data transmission in the second integration time through the DMA thread, and arranges the demodulated value of the previous integration time into a data frame to be sent to the host platform.
4. The distributed fNIRS brain function imaging system for hyperspectral applications of claim 1, wherein: the wireless communication unit adopts a response transmission mechanism and a self-correcting data frame step; the response transmission mechanism adopted by the wireless communication unit has three processes:
the terminal sends permission: the host platform sends a data transmission instruction of a first imaging terminal in a broadcast mode, and the imaging terminal identifies and receives the data transmission instruction through a DMA thread and sends a position 1 of an allowable mark;
and waiting for terminal data: the host platform waits for receiving data in the process, and the imaging terminal sends a data frame to the host platform only when the internal integral completion flag bit and the sending permission flag bit of the imaging terminal are simultaneously set to be 1;
receiving terminal data: the host platform receives data in the process, if the data is transmitted in error, the data frame is discarded, a data re-uploading instruction is sent, and the imaging terminal sends the data frame once again; if the host platform still receives the error, marking the data as error data, marking the data on the data set, sending a data completion instruction to the imaging terminal, and starting data transmission of the next imaging terminal;
when the online software phase-locked demodulation is completed, the main control unit reads the current system clock value as the timestamp information of the data, the light intensity value of each sampling point forms a data bit in the data frame, and then the data frame is sent to the host platform.
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