CN113598761B - A dual-wavelength infrared blood oxygen detection system based on CCD - Google Patents

Abstract

The invention discloses a CCD-based dual-wavelength infrared blood oxygen detection system. The system comprises a multi-wavelength light source emitter, a CCD image sensor and a controller. The invention can realize the measurement of blood oxygen parameters by using the near infrared light spot light source to be matched with the CCD sensor. The light source is small in size and can be applied to any position. The light intensity collecting position can be adjusted to measure multiple angles and multiple depths simultaneously, so that the sensor is suitable for multiple crowds, and is more convenient and practical compared with the single measuring angle and measuring depth of the traditional sensor. The light-emitting source is contacted with the human body, the receiving part uses the CCD sensor to collect continuous frame images of the tested person, and the CCD sensor is not contacted with the skin and is not influenced by the attaching pressure.

Description

A dual-wavelength infrared blood oxygen detection system based on CCD

Technical Field

The invention belongs to the technical field of medical devices and relates to a dual-wavelength infrared blood oxygen detection system based on CCD.

Background Art

Oxygen is one of the important oxygens to maintain human survival. When the human body is severely hypoxic, it will cause damage to certain organs or even shock. Blood oxygen saturation is defined as the ratio of oxygenated hemoglobin concentration to total hemoglobin concentration. It also represents the ability of human blood to carry oxygen. Therefore, blood oxygen saturation has become an indicator for assessing the health of the human circulatory system. Blood oxygen saturation can be divided into arterial oxygen saturation, venous oxygen saturation and pulse oxygen saturation. The normal arterial oxygen saturation is about 97-100%, and the venous oxygen saturation is about 68-77%. Since the penetration and absorption rates of oxygenated hemoglobin and reduced hemoglobin in the blood are different at different wavelengths, the blood oxygen saturation can be calculated in combination with Lambert-Beer's law.

Blood oxygen saturation detection is an important clinical detection method, which has received increasing attention in recent years. Non-invasive monitoring of blood oxygen status of human tissue based on optical measurement is stable and reliable, easy and safe to use, and is currently widely used in surgical monitoring, critical care, and neonatal monitoring. Pulse oximeters are more commonly used in clinical practice to detect human blood oxygen saturation, and the measurement area is the circulatory vascular area at the finger. The second is a patch detection system designed based on near-infrared spectroscopy technology (NIRS), which can detect blood oxygen saturation in the brain and other tissues. However, both have the following disadvantages:

(1) Limited measurement points

The pulse oximeter can only measure the blood oxygen saturation at a single point on the finger. Although the near-infrared spectroscopy (NIRS) detection system can detect different positions according to the sensor's fitting position, it is still impossible to detect certain parts due to the sensor's structural shape.

(2) Sensor design limitations

According to the needs of different groups of people (such as children and adults), sensors with different structures need to be designed. In addition, the angle and depth measured by the sensor are fixed and cannot be changed.

(3) The tightness of the fit will affect the measurement results.

Summary of the invention

The purpose of the present invention is to provide a more convenient detection system for blood oxygen parameters of local tissues of human body in view of the deficiencies of the prior art.

The system includes:

The multi-wavelength light source transmitter fits the position of the human tissue to be detected, and its light source transmitting end is aimed at the position of the human tissue to be detected for blood oxygen parameters, and can emit light sources of two wavelengths, λ1 and λ2;

A CCD image sensor is used to take a picture of the human tissue location where the multi-wavelength light source emitter is located;

The controller is used to obtain the photos transmitted by the CCD image sensor and then perform blood oxygen analysis calculations on them.

Preferably, the CCD image sensor is calibrated before use: the Zhang Zhengyou calibration method is used to adjust the direction of the calibration object or the camera, and some photos of the calibration object in different directions are taken. The least squares method is used to estimate the distortion parameters under the actual radial distortion, and finally the maximum likelihood method is used to optimize and improve the accuracy, thereby obtaining the rotation and translation parameters, as well as the camera distortion parameters.

Preferably, a filter is placed in front of the camera of the CCD image sensor.

The beneficial effects of the present invention are:

The present invention uses a near-infrared point light source in conjunction with a CCD sensor to measure blood oxygen parameters. The light source is small and can be attached to any position. By adjusting the light intensity collection position, multi-angle and multi-depth measurements can be performed simultaneously, which is suitable for a variety of people. Compared with the single measurement angle and measurement depth of traditional sensors, it is more convenient and practical.

The light source of the present invention contacts the human body, and the receiving part uses a CCD sensor to collect continuous frame images of the person being measured. The CCD sensor does not contact the skin and is not affected by the fitting pressure.

The present invention only needs to use a reusable emitting light source and CCD sensor, and can realize multiplexing for multiple groups by controlling the spacing between the collection points and the light source, thus overcoming the problem that traditional patch-type sensors need to use probes of corresponding structures and shapes for corresponding groups in order to meet the needs of different groups, which is cumbersome to use.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a system framework diagram;

FIG2 is a schematic diagram of the contact position between the multi-wavelength light source transmitter and the human body and the first and second collection areas;

FIG3 is a schematic diagram of the propagation path of light in human tissue;

FIG4 is a flow chart of the method of the present invention.

DETAILED DESCRIPTION

The present invention is further analyzed in conjunction with the accompanying drawings and specific embodiments.

A more convenient system for detecting blood oxygen parameters of local tissues of the human body.

The system shown in Figure 1 includes:

The multi-wavelength light source transmitter fits the position of the human tissue to be detected, and its light source transmitting end is aimed at the position of the human tissue to be detected for blood oxygen parameters, and can emit light sources of two wavelengths, λ1 and λ2;

A CCD image sensor is used to take a picture of the human tissue location where the multi-wavelength light source emitter is located;

The controller is used to obtain the photos transmitted by the CCD image sensor and then perform blood oxygen analysis calculations on them.

FIG4 is a flow chart of the method of the present invention.

The blood oxygen analysis calculation specifically includes the following steps:

Step S1: Image preprocessing

Acquire the position image of the human tissue to be detected using light sources of different wavelengths, and perform image preprocessing; in the preprocessed image, the light source emitting end of the light source emitter is taken as the center point, the area with a radius R where the center point is the center of the circle is taken as the center area, the area with a radius R1 where the center point is the center of the circle minus the center area is taken as the first acquisition area, and the area with a radius R2 where the center point is the center of the circle minus the first acquisition area is taken as the second acquisition area, R＜R1＜R2, as shown in Figure 2; Figure 3 is a schematic diagram of the propagation path of light in human tissue;

Preferably, the image preprocessing is to eliminate motion artifacts from the image, specifically as follows:

Taking the position of the human tissue to be detected in the image taken by the CCD image sensor when the light source is not emitted as the reference point, determine whether the distance between the position of the human tissue to be detected in the image when the light source is emitted and when it is not emitted exceeds a threshold (which can be 2mm). If so, it is considered that the position of the human tissue to be detected has moved, and the image collected when the light source is emitted is deleted. Otherwise, it is retained for subsequent operations.

Step S2: Extract the infrared light intensity value of each pixel in the image

2-1: The signal recorded by the CCD sensor is an image of continuous frames. According to the time point, the frame image when the light source is not emitting light, the frame image when the light source is emitting light with the first wavelength, and the frame image when the light source is emitting light with the second wavelength are found, and the grayscale values G ₀ (x, y, t), G ^λ1 (x, y, t), and G ^λ2 (x, y, t) are extracted respectively, where x represents the horizontal coordinate of the current grayscale value point with the light source as the origin; y represents the vertical coordinate of the current grayscale value with the light source as the origin; and t represents the time point of the current image.

2-2: The infrared light intensity value at the pixel point (x, y) at time t is calculated based on the gray value of the frame image, see formula (1)-(2):

g ^λ1 (x,y,t)＝G ^λ1 (x,y,t)-G ₀ (x,y,t) Formula (1)

g ^λ2 (xi,y,t)＝G ^λ2 (x,y,t)-G ₀ (x,y,t) Formula (2)

Wherein g ^λ1 (x, y, t) represents the infrared light intensity value of the first wavelength at time t, and g ^λ2 (x, y, t) represents the infrared light intensity value of the second wavelength at time t.

Step S3: According to the infrared light intensity values of all pixel points (x, y) at time t in each area, the light intensity value of each area is obtained after homogenization, as follows:

Where n represents the number of pixel points (x, y) at a certain area position (i.e., the light source position, the first acquisition area or the second acquisition area);

Since the position of the person being measured may move relative to the initial moment during long-term continuous measurement, the compensation coefficient ρ needs to be added to the light intensity value after extraction. The calculation method of ρ is as follows;

Where G ₀ (x, y, t ₀ ) represents the light intensity value of the pixel point (x1, y1) at the light source position at time t ₀ when the light source is not emitting light, G ₀ (x, y, t) represents the light intensity value of (x1, y1) at time t when the light source is not emitting light, ρ(t) represents the light intensity compensation coefficient at time t, and t ₀ represents the initial time.

The actual light intensity is

in Indicates the light intensity value of the first wavelength at a certain area position (i.e., the light source position, the first collection area, or the second collection area) at time t. It represents the light intensity value of the second wavelength at a certain area position (i.e., the light source position, the first collection area or the second collection area) at time t.

Step S4: oxygen saturation calculation

According to formulas (6)-(7), the light intensity values of the first wavelength and the second wavelength at the center of the first acquisition area and the second acquisition area are obtained: Then, the optical density change is calculated according to formulas (8) and (9), as follows:

in and Respectively represent the first wavelength optical density of the first acquisition area and the second acquisition area, represents the light intensity value of the first wavelength at the light source position, and the subscripts 0, r1 and r2 represent the light source position, the first collection area and the second collection area respectively;

Similarly, the optical density formula of λ2 is as follows:

The ratio of the absorption coefficients of the tissue under test at different wavelengths is calculated based on ΔOD ^λ1 and ΔOD ^λ2 as follows:

The oxygen saturation rSO ₂ is calculated according to the oxygen saturation formula as follows:

Where _CHbO2 represents the concentration of oxygenated hemoglobin, _CHb represents the concentration of deoxygenated hemoglobin, represents the extinction coefficient of deoxyhemoglobin at wavelength λ1, It represents the extinction coefficient of oxygenated hemoglobin at wavelength λ1.

Step S5: Calculation of hemoglobin concentration change

According to formulas (6)-(7), the light intensity values of the second acquisition area at the initial time and the current time t1 are obtained as follows: and The change in hemoglobin concentration ΔC _tHb is calculated as follows:

ΔC _tHb =ΔC _HbO2 +ΔC _Hb formula (14)

Wherein DPF ^λ1 represents the differential path factor, which is obtained by simulation or table lookup; ΔC _HbO2 represents the calculated change in oxygenated hemoglobin concentration; and ΔC _Hb represents the change in deoxygenated hemoglobin concentration.

In this embodiment, λ1 and λ2 are 760nm and 850nm respectively.

When the light intensity value of the multi-wavelength light source transmitter is distinguishable, the farther the collection point is from the light source, the deeper the detection depth. The relationship between the detection depth and the distance between the CCD image sensor and the multi-wavelength light source transmitter is as follows:

Where d represents the detection depth;

If the head blood oxygen is tested, the tissue thickness includes the scalp and sebum thickness, skull thickness, cerebrospinal fluid thickness and brain gray matter thickness. According to empirical values, the preferred detection depth for adults is 15-20mm, and the detection depth for children is 10-15mm.

If muscle blood oxygen is tested, tissue thickness includes epidermal thickness and sebum thickness. According to empirical values, the preferred detection depth is 10-15 mm. The greatest influence on the detection depth is sebum thickness, which varies from person to person. The empirical value is for normal people, but for obese and thin people, the empirical value is not effective. In the present invention, the sebum thickness h of the muscle tissue of the tested part is first measured with a sebum thickness meter during the test. Assuming that the epidermal thickness is s, which is generally 3 mm, then Ri _≥ 2h+s.

In addition, in order to ensure that sufficient blood oxygen information is collected, R2-R1>5mm is required, and 10mm is generally used.

The CCD image sensor is calibrated before use: Zhang Zhengyou calibration method is used to adjust the direction of the calibration object or the camera, and take some photos of the calibration object in different directions. The least squares method is used to estimate the distortion parameters under the actual radial distortion, and finally the maximum likelihood method is used to optimize and improve the accuracy, thereby obtaining the rotation and translation parameters, as well as the camera distortion parameters.

The above embodiments are not limitations of the present invention, and the present invention is not limited to the above embodiments. As long as the requirements of the present invention are met, they belong to the protection scope of the present invention.

Claims (9)

1. A dual-wavelength infrared blood oxygen detection system based on CCD, characterized by comprising: The multi-wavelength light source transmitter fits the position of the human tissue to be detected, and its light source transmitting end is aimed at the position of the human tissue to be detected for blood oxygen parameters, and can emit light sources of two wavelengths, λ1 and λ2; A CCD image sensor is used to take a picture of the human tissue location where the multi-wavelength light source emitter is located; A controller is used to obtain the photos transmitted by the CCD image sensor and then perform blood oxygen analysis calculation on them; The blood oxygen analysis calculation specifically includes the following steps: Step S1: Image preprocessing Acquire the position image of the human tissue to be detected using light sources of different wavelengths, and perform image preprocessing; in the preprocessed image, the light source emitting end of the light source emitter is taken as the center point, the area with a radius R where the center point is the center of the circle is taken as the center area, the area with a radius R1 where the center point is the center of the circle minus the center area is taken as the first acquisition area, and the area with a radius R2 where the center point is the center of the circle minus the first acquisition area is taken as the second acquisition area, R＜R1＜R2; Step S2: Extract the infrared light intensity value of each pixel in the image 2-1: Find the frame image when the light source is not emitting light, the frame image when the light source of the first wavelength emits light, and the frame image when the light source of the second wavelength emits light according to the time point, and extract the grayscale values G ₀ (x, y, t), G ^λ1 (x, y, t), G ^λ2 (x, y, t) respectively, where x represents the horizontal coordinate of the current grayscale value point with the light source as the origin; y represents the vertical coordinate of the current grayscale value with the light source as the origin; t represents the time point of the current image; 2-2: The infrared light intensity value at the pixel point (x, y) at time t is calculated based on the gray value of the frame image, see formula (1)-(2): g ^λ1 (x,y,t)＝G ^λ1 (x,y,t)-G ₀ (x,y,t) Formula (1) g ^λ2 (x,y,t)＝G ^λ2 (x,y,t)-G ₀ (x,y,t) Formula (2) Where g ^λ1 (x, y, t) represents the infrared light intensity value of the first wavelength at time t, and g ^λ2 (x, y, t) represents the infrared light intensity value of the second wavelength at time t; Step S3: According to the infrared light intensity values of all pixel points (x, y) at time t in each area, the light intensity value of each area is obtained after homogenization, as follows: Where n represents the number of pixel points (x, y) at a certain area position (i.e., the light source position, the first acquisition area or the second acquisition area); The compensation coefficient ρ is calculated as follows; Where G ₀ (x, y, t ₀ ) represents the light intensity value of the pixel point (x1, y1) at the light source position at time t ₀ when the light source is not emitting light, G ₀ (x, y, t) represents the light intensity value of (x1, y1) at time t when the light source is not emitting light, ρ(t) represents the light intensity compensation coefficient at time t, and t ₀ represents the initial time; The actual light intensity is in Indicates the light intensity value of the first wavelength at a certain area position (i.e., the light source position, the first collection area, or the second collection area) at time t. Indicates the light intensity value of the second wavelength at a certain area position (i.e., the light source position, the first collection area or the second collection area) at time t; Step S4: oxygen saturation calculation According to formulas (6)-(7), the light intensity values of the first wavelength and the second wavelength at the center of the first acquisition area and the second acquisition area are obtained: Then, the optical density change is calculated according to formulas (8) and (9), as follows: in and Respectively represent the first wavelength optical density of the first acquisition area and the second acquisition area, The light intensity value of the first wavelength representing the position of the light source; Similarly, the optical density formula of λ2 is as follows: The ratio of the absorption coefficients of the tissue under test at different wavelengths is calculated based on ΔOD ^λ1 and ΔOD ^λ2 as follows: The oxygen saturation rSO ₂ is calculated according to the oxygen saturation formula as follows: Where _CHbO2 represents the concentration of oxygenated hemoglobin, _CHb represents the concentration of deoxygenated hemoglobin, represents the extinction coefficient of deoxyhemoglobin at wavelength λ1, represents the extinction coefficient of oxygenated hemoglobin at wavelength λ1; Step S5: Calculation of hemoglobin concentration change According to formulas (6)-(7), the light intensity values of the second acquisition area at the initial time and the current time t1 are obtained as follows: and The change in hemoglobin concentration ΔC _tHb is calculated as follows: ΔC _tHb =ΔC _HbO2 +ΔC _Hb formula (14) Wherein DPF ^λ1 represents the differential path factor, which is obtained by simulation or table lookup; ΔC _HbO2 represents the calculated change in oxygenated hemoglobin concentration; and ΔC _Hb represents the change in deoxygenated hemoglobin concentration. 2. A CCD-based dual-wavelength infrared blood oxygen detection system according to claim 1, characterized in that step S1 image preprocessing is to eliminate motion artifacts from the image. 3. According to the CCD-based dual-wavelength infrared blood oxygen detection system of claim 2, the image preprocessing is specifically as follows: Taking the position of the human tissue to be detected in the image taken by the CCD image sensor when the light source is not emitted as the reference point, determine whether the distance between the position of the human tissue to be detected in the image when the light source is emitted and the position when it is not emitted exceeds the threshold. If so, it is considered that the position of the human tissue to be detected has moved, and the image collected when the light source is emitted is deleted. Otherwise, it is retained for subsequent operations. 4. A CCD-based dual-wavelength infrared blood oxygen detection system according to claim 1, characterized in that λ1 and λ2 are 760nm and 850nm respectively. 5. According to the CCD-based dual-wavelength infrared blood oxygen detection system of claim 1, the relationship between the detection depth and the collection area of the multi-wavelength light source transmitter is as follows: Where d represents the detection depth. 6. A CCD-based dual-wavelength infrared blood oxygen detection system according to claim 1, characterized in that if the head blood oxygen is tested, when the detection object is an adult, the detection depth of the multi-wavelength light source transmitter is 15 to 20 mm, and when the detection object is a child, the detection depth of the multi-wavelength light source transmitter is 10 to 15 mm. 7. A dual-wavelength infrared blood oxygen detection system based on CCD according to claim 1, characterized in that if muscle blood oxygen is tested, the detection depth of the multi-wavelength light source transmitter is 10-15mm; the collection area radius _Ri ≥2h+s, i=1,2, where h represents the sebum thickness of the muscle tissue of the tested part, and s represents the epidermal thickness. 8. A CCD-based dual-wavelength infrared blood oxygen detection system according to claim 1, characterized in that R2-R1>5mm. 9. A CCD-based dual-wavelength infrared blood oxygen detection system according to claim 1, characterized in that R2-R1=10mm.