1 Introduction
In China, there are many patients with traumatic craniocerebral injury in urgent need of rescue, but a considerable number of patients with intracranial hemorrhage have delayed diagnosis and treatment because of the failure to diagnose in time. Therefore, cerebral hematoma or cerebral hernia oppresses brain tissue. The brain stem and brain substance are irreversibly damaged. Near-infrared intracranial hemorrhage detection equipment can make accurate judgment on intracranial hemorrhage in a short time. Provide instructions for whether to perform CT / MRI examination. Can significantly improve the patient's chance of survival and recovery of nervous system function. It is mainly used clinically for epidural hemorrhage (EDH), subdural hemorrhage (SDH), superficial cerebral hemorrhage, etc. Its advantages are fast, accurate, and non-invasive, and can be used in emergency centers, hospital clinical departments, and monitoring Ward ICU and field battlefield, etc. But no relevant reports about such equipment have been seen in China. The relatively mature equipment abroad is mainly the CRAINscan instrument produced by the German company Oicrain, which is expensive. We based on the absorption characteristics of hemoglobin to near infrared light and Lambert-Beer law. Design a portable device. Realize non-invasive and direct measurement of human brain tissue, provide a basis for timely monitoring of disease course changes and the formulation of rescue treatment plans.
2 Basic principles
When ignoring scattering. The total absorption of human light by the medium is a linear superposition of the absorption of each chromophore in the medium. According to Beer-Lambert's law, the light intensity It passes through the medium and the incident light intensity I0 satisfies the following relationship:
OD = -lnIt / I0 = μcl
Where μ is the absorption coefficient, C is the medium concentration, and l is the optical path. 0D is optical density, when the wavelength of incident light is constant. OD is a linear function of medium concentration. Normally, the absorption of light on both sides of the human brain is symmetrical. If a blood vessel ruptures and causes internal bleeding, the local blood concentration increases. The absorption of light will increase. By measuring the optical density on both sides of the human brain, you can determine whether there is cerebral hemorrhage in patients with craniocerebral trauma, and provide an indication for the need for further CT or MRI examination.
3 Hardware design
The equipment uses the MSP430 microcontroller as the control core. Its output pulse signal drives LEDs of specific wavelength to produce near infrared light. The near-infrared light source passes through the cranial brain tissue, and the photoelectric sensor in the detection probe collects the optical signal containing the blood oxygen information of the brain tissue. After the photoelectric conversion, the electrical signal is transmitted to the single-chip microcomputer. The processed signal can be stored in the EEPROM or passed LCD display. You can also send the signal to the computer through the USB port for further processing or storage. The system block diagram is shown in Figure 1: 
Figure 1 Device system block diagram
3.1 Detection probe
The probe is composed of a light source, a photoelectric sensor and a front-end conversion circuit. The small round hole is used to fix the light source. The photoelectric sensor is fixed in the middle. The light source is LED. The sensor is S1226 series photoelectric sensor. The dark current is small, and the photosensitive sensitivity is high. The distance between the light source and the sensor is set to 40mm. The average detection depth of the probe is about 3cm, and the light source is driven by a constant current source. And under the control of the pulse signal, the time-division luminescence realizes the function of double detection. The contact surface is designed to be arc-shaped, the edges and the places where the light source and the sensor are placed are raised, to reduce the leakage of the light source, the other parts are designed to be thin, the edges are beveled, making it easy to bend, the base material is medical silicone, to avoid fixing the probe Discomfort to the subject. 
Figure 2 Detection probe
3.2 Host circuit
3. 2. 1 MSP430 one-chip computer
System selection, the 16-bit microcontroller MSP430F149 produced by TI, adopts efficient RISC structure, has 16 fast response interrupts, the highest clock frequency is 8MHz, and the interrupt wake-up time is less than 6 microseconds. Its monolithic integrated multi-channel A / D converter, analog comparator, timer, serial communication interface, numerically controlled oscillator (DCO), hardware multiplier, can meet the application needs of most devices. The JTAG module is preset inside. It has a complete online debugging function, and the on-chip FLASH can be used to easily implement software upgrades.
3.2.2 Signal storage
AT24C512 is a 64KB serial electrical erasable programmable memory produced by Atmel. It is packaged in an 8-pin package and has the characteristics of compact structure and large storage capacity. It is especially suitable for data acquisition systems requiring large-capacity data storage. Its connection circuit with single chip is shown in Figure 3. The single chip microcomputer controls the reading and writing of AT24C512 through the P3 port. P3.0 controls the serial clock input terminal SCL, writes the data on SDA to the memory on the rising edge, and reads the data from the memory on the falling edge and sends it to SDA. P3.1 controls the bidirectional serial data input and output terminal SDA, which is mainly used for the data connection between the memory and the microcontroller. 
Figure 3 LED driver
3.2.3 Light source driving circuit
The light source driving circuit is shown in Fig. 3, the single chip P5.4 foot outputs Vctrl voltage. P5.6 controls the EN enable terminal. When the input voltage is greater than 2.5V, the device works and the output current drives the LED to light up; when the input voltage is less than 2.2V, the LED1, LED2, and LED3 terminals show high impedance. Can't light up.
SET is the input terminal of bias current. Its relationship with the output current of the three LEDs is Iled = 230xIset, and Iled = (Vctrl-Vset) / R, Vset = 1.215V, that is: Iled = 230 (Vctrl-1.215) / R It can be seen that the LED output current is only related to the P5.4 output voltage and resistance R, and turns to emit light under the control of the single chip microcomputer.
3.2.4 LCD display module
LSDl2864CT is a graphic dot matrix liquid crystal display, which is mainly composed of row driver, column driver and full dot matrix liquid crystal display, which can complete graphics and text display. The single chip microcomputer realizes the operation of the status register of the liquid crystal module through the P1 port. P1.0 controls the D / I register selection signal line, P1.1 controls the R / W read and write signal line, P1.2 and P1.3 control the CSI and CS2 chip selection signal lines, P1.4 connects to the / RST terminal, P1. 5 Connect E enable signal line. The P2 port is a data port connected to the 8-bit data line of the LCD module. MSP430 specifically divides two groups of I / O ports for LCD display. Usually the sequence of starting the LCD is: Initialize the read status word to write the instruction code, write the data, and turn on the display. The program code can be divided into modules such as writing instruction code and writing data according to different functions. Enable signal E rising edge trigger is valid.
3.2.5 Computer communication
This system interface chip adopts PDIUSBD12 of PHILIPS Company, it is a high-performance USB interface device, integrated SIE, FIFO memory, transceiver and voltage converter. Module functions include: synchronous pattern recognition, parallel-serial conversion, bit stuffing, destuffing, CRC check / generation, address recognition, etc. Its 8-bit parallel data is connected to the P5 port of MSP430, and A0 is the command and data selection line. When A0 = 0. MSP430 sends data to PDIUSBD12. When AO = 1. Then send the command. The data exchange adopts the interrupt query method, and determines whether the data or command of the upper computer is received by querying whether INT_N is low, and then realizes the data exchange between MSP430 and PDIUSBD12 through the _WR and _RD pins.
4 Software flow
The system software design mainly uses the RISC reduced instruction of MSP430 to mix programming with assembly language and C language. The system is mainly divided into the following parts: (1) System initialization, including system clock calibration, A / D conversion parameter initialization, watchdog initialization, LCD controller initialization, etc .; (2) LCD display section. Including the display of Chinese characters and waveform display; (3) Interrupt processing, including keyboard interrupt processing, signal sampling interruption, abnormal data alarm part, etc .; (4) blood content calculation, blood content calculation by point-by-point differential method. 4 is a flowchart of the main program of the system. After the hardware is initialized. Test if a key is pressed. If there is, the corresponding function of the key is executed. Then the LCD displays the information corresponding to different functions. If no button is pressed, the current measured blood concentration is displayed. Wait for the user's next operation. 
Figure 4 System main program
5 Clinical application
When the instrument is used in the clinic of the hospital, the patient is examined by near infrared spectroscopy. The exploration sites are bilateral frontal, temporal, and occipital. First read and record the blood oxygen value on one side, then sample at the symmetrical site, repeat 2 times, and take the average. The difference between the two was calculated, and the difference ≥ 0.45 was used as a criterion to determine whether there was bleeding, and then a brain CT examination was performed. Results Among the 47 cases, 29 showed CT hemorrhage. 19 of them had subdural hemorrhage. There were 7 patients with epidural hemorrhage and 3 patients with superficial cerebral hemorrhage. Near-infrared light detectors diagnosed 28 patients with cerebral hemorrhage, 24 cases were confirmed by CT, 4 cases were false positives, 2 of them had subcutaneous hematoma; 19 cases were negative by near infrared examination, and 17 cases were confirmed by CT. Of the two false-negative patients, one was subarachnoid hemorrhage and the other was parenchymal hemorrhage.
6 Summary
Because the penetration of near-infrared light is not strong, the attenuation of the human brain tissue is quite strong, and the spatial resolution of the device is not very high. It cannot replace conventional CT examination to quantify and localize intracranial lesions. The advantage is that Make a preliminary diagnosis of the injury quickly without any harm to the human body. The overall design is compact. The operation is simple, the price is cheap, and it has certain practical value. It is expected to achieve good economic benefits after being put into production.
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