Design of intracranial hemorrhage detection equipment based on MSP430 microcontroller

1 Introduction

In China, there are many patients with traumatic brain injury who are in urgent need of emergency treatment, but a considerable number of patients with intracranial hemorrhage are delayed in rescue and treatment due to the failure to make timely diagnosis. As a result, brain hematoma or brain herniation compresses brain tissue, causing irreversible damage to the brainstem and brain parenchyma. Near-infrared intracranial hemorrhage detection equipment can make accurate judgments on intracranial hemorrhage in a short time, providing indications for whether to implement CT/MRI examinations. It can significantly improve the patient's survival rate and recovery of nervous system function. In clinical practice, it is mainly used for epidural hemorrhage (EDH), subdural hemorrhage (SDH), superficial brain parenchymal hemorrhage, etc. Its advantages are fast, accurate, and non-destructive. It can be used in emergency centers, hospital clinical departments, ICUs, and field battlefields. However, there are no related reports on such equipment in China. The more mature equipment abroad is mainly the CRAINscan instrument produced by Oicrain Company in Germany, which is expensive. We designed a portable device based on the absorption characteristics of hemoglobin to near-infrared light and Lambert-Beer's law. It can achieve non-invasive and direct measurement of human brain tissue, providing a basis for timely monitoring of disease course changes and formulation of emergency treatment plans.

2 Basic principles

When scattering is ignored, the total absorption of incident light by the medium is the linear superposition of the absorption of each chromophore in the medium. According to the Beer-Lambert law, the intensity of light It passing through the medium and the incident light intensity I0 satisfy the following relationship:

OD = -lnIt/I0 = μcl

Where μ is the absorption coefficient, C is the medium concentration, and l represents the optical path. OD is the optical density. When the wavelength of the incident light is constant, OD is a linear function of the medium concentration. Under normal circumstances, 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. Therefore, by measuring the optical density on both sides of the human brain, it can be determined whether there is cerebral hemorrhage in patients with craniocerebral trauma, and provide an indication for whether further CT or MRI examination is needed.

3 Hardware Design

The device uses the MSP430 microcontroller as the control core. Its output pulse signal drives the LED of a specific wavelength to produce near-infrared light. The near-infrared light source passes through the brain tissue, and the photoelectric sensor in the detection probe collects the light signal containing the blood oxygen information of the brain tissue. After photoelectric conversion, the electrical signal is transmitted to the microcontroller. The processed signal can be stored in the EEPROM or displayed on the LCD. The signal can also be transmitted to the computer through the USB port for further processing or storage. The system block diagram is shown in Figure 1:

Figure 1 Equipment system block diagram

3.1 Detection probe

The probe consists of a light source, a photoelectric sensor and a front-end conversion circuit. The small round hole is used to fix the light source, and the photoelectric sensor is set in the middle. The light source is LED, and the sensor is S1226 series photoelectric sensor. It has a small dark current and high photosensitivity. The distance between the light source and the sensor is set to 40mm. The average detection depth of the probe is about 3cm. The light source is driven by a constant current source. And under the control of the pulse signal, the light is emitted in time to realize the function of dual measurement. The contact surface is designed to be arc-shaped, and the edges and the parts where the light source and sensor are placed are raised to reduce the leakage of the light source. The rest of the parts are designed to be very thin, and the edges have bevels to make it easy to bend. The base material is medical silicone to avoid discomfort to the person being tested when fixing the probe.

Figure 2 Detection probe

3.2 Host circuit

3.2.1 MSP430 MCU

System selection, TI's 16-bit single-chip microcomputer MSP430F149, 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 single chip integrates multi-channel A/D converter, analog comparator, timer, serial communication interface, digital control oscillator (DCO), hardware multiplier, which can meet the application needs of most devices. It has a preset JTAG module inside. It has complete online debugging function and can use the on-chip FLASH to easily implement software upgrades.

3.2.2 Signal Storage

AT24C512 is a 64KB serial electrically erasable programmable memory produced by Atmel. It adopts 8-pin package, has the characteristics of compact structure and large storage capacity, and is particularly suitable for data acquisition systems with large-capacity data storage requirements. Its connection circuit with the microcontroller is shown in Figure 3. The microcontroller 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 and sends it to SDA on the falling edge. P3.1 controls the bidirectional serial data input and output terminal SDA, which is mainly used for 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 Figure 3. The single chip microcomputer P5.4 pin outputs the 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 present high impedance and cannot light up.

SET is the bias current input terminal. 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 the resistor R, and they emit light in turn under the control of the microcontroller.

3.2.4 LCD Module

LSDl2864CT is a graphic dot matrix LCD display, which is mainly composed of row driver, column driver and full dot matrix LCD display, and can display graphics and text. The single chip microcomputer realizes the operation of the LCD module status register 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 select signal lines, P1.4 connects to the /RST terminal, and P1.5 connects to the E enable signal line. The P2 port is a data port connected to the 8-bit data line of the LCD module. MSP430 specially divides two groups of I/O ports for LCD display. Usually the order of starting the LCD is: initialize read status word write instruction code, write data, and turn on the display. The program code can be divided into modules such as write instruction code and write data according to different functions. The enable signal E is triggered by the rising edge.