| According to the latest data from the WHO's international agency for research on cancer(IARC),breast cancer is the No.1 killer of women's health worldwide and has become a major public health problem in the current society.Early accurate diagnosis can improve the 5-year survival rate of breast cancer patients to more than 95%,so early accurate diagnosis and timely treatment is particularly important.Currently,X-ray target,MRI,B-mode ultrasound,and other imaging methods cannot meet the needs of breast cancer early screening.Ultrasound CT technology has the advantages of not being interfered by the upper and lower tissues,good penetrating characteristics and high imaging resolution,and has become the most promising imaging method for accurate early diagnosis of breast cancer.However,the traditional piezoelectric ultrasound transducers used in the abroad equipment reported.In order to solve the processing technology difficulty and high cost of high density ring array,therefore,it is urgent to develop a low-cost,comfortable,safe,high sensitivity,high specificity of breast cancer diagnostic equipment to achieve early accurate diagnosis of breast cancer,which is also the direction and trend of breast cancer diagnostic research.The configuration scheme of ultrasound transducer and the effective image reconstruction algorithm are the basis for the development of breast ultrasound CT imaging system.This paper focuses on the configuration scheme of the new ultrasound transducer based on PMUT array,carries out the development of the new breast ultrasonic CT system,and at the same time studies on the corresponding breast ultrasonic tomography technology,and obtains high-resolution breast ultrasound imaging.(1)According to the particularity of breast soft tissue,a novel 3D breast ultrasound CT system based on PMUT linear array was proposed.The feature is that four 1×128 PMUT arrays are vertically crossed 90 degrees on the PMMA fixture,and the array length is parallel to the circular axis and surrounds the breast tissue to achieve cylindrical and non-contact measurement.The array length is parallel to the circular axis and roughly parallel to the central axis of the breast,surrounded by the mammary gland,achieving cylindrical and non-contact measurement.It can collect both reflected and transmitted signals,the maximum detection aperture is ?18cm×13cm.A prototype platform of the system was built.According to the characteristics of the system platform,an algorithm of breast ultrasound tomography based on circular scanning was proposed.The breast model I(with a 5 cm mass in the center)was used for experimental analysis and the preliminary test of the system prototype was conducted.The experimental results show that the size,position and contour of the internal mass could be detected,which verifies the feasibility of the system and the effectiveness of the algorithm.(2)The interaction between ultrasound and breast tissue can lead to complex scattering mechanism,so an adaptive time-gain compensation based breast ultrasound tomography algorithm was proposed to overcome the problem of ultrasonic signal attenuation.Based on the circular scanning algorithm,the attenuation coefficient is automatically evaluated by using the spectrum cross-correlation method,and the compensation of pulse echo signal is realized by combining TGC technology.Field II was used for simulation analysis,and the specific algorithm flow was given.Meanwhile,breast model I was used for quantification and comparative analysis of the imaging quality of horizontal sections.The experimental results showed that PSNR and RMSE improved by 34.6% and 49.3%,which effectively improved the detection ability of internal masses.(3)In order to overcome the problem that two-dimensional ultrasound image sequence is not conducive to the comprehensive and intuitive observation of pathological tissues,a new multi-perspective ultrasound tomography technique based on cylindrical scan is proposed.With the dynamic focusing technology centered on FPGA and the cylindrical scanning detection scheme designed,the ultrasonic transducer was rotated 90 degrees at an interval of 2 degrees to obtain the volume data of the breast model and reconstruct the data.Combined with the B-scan algorithm,circular scanning algorithm and volume rendering imaging algorithm,vertical slice imaging,horizontal slice imaging and three-dimensional imaging were realized.Experimental analysis was performed using breast model II(with one 2cm mass in the center and six 1cm masses in the superficial).The experimental results show that the size,position,number and contour of the tumor can be directly and accurately detected,and even the image of the injection pinhole can be seen.In addition,the entire breast contour from the chest wall to the nipple was clearly visible,and the detection performance of the system was further improved.(4)Reflection imaging is beneficial to the detection of the shape and contour of the lesion,while transmission imaging is easy to distinguish the difference of the information inside the lesion.Reflection imaging is beneficial to the detection of the shape and contour of the lesion,while transmission imaging is easy to distinguish the difference of the information inside the lesion.The imaging coordinate system of isometric fan-beam moving along the PMUT array was established by using the designed test scheme of spatial composite image reconstruction.MATLAB was used to establish the digital breast model,including the tissue types of fat,gland,cyst,fibroma,cancer and calcification point,and to quantify and compare the imaging quality under different reconstruction schemes.MATLAB was ultilized to establish the digital breast model,including the tissue types of fat,gland,cyst,fibroma,cancer and calcification point,and to quantify and compare the imaging quality under different reconstruction schemes. |
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