Development Of Fiber-free Parallel-Plane Diffuse Optical Tomography System For Breast Imaging

The incidence rate of breast cancer ranks first in the female malignant tumor in China,and it shows an increasing trend year by year.Compared with commonly used breast cancer image detection methods such as mammography,Diffuse Optical Tomography(DOT)has the advantages of being noninvasive to the human body,low in cost,and easy to popularize.The geometric structure of traditional breast DOT system includes circular,semi-circle,cup,oval and parallel-plane.Compared with other system structures,the parallel-plane DOT system has the advantages of high signal level,less motion artifacts,and adaptability to breasts of different sizes.However,in the current parallel-plane systems,PMT or CCD is often used for optical signal detection,and fiber is used for optical signal transmission.This causes problems such as high system cost,high complexity,and poor consistency between channels.Aiming at the above problems,this thesis builds a fiber-free parallel-plane DOT system for breast based on the patch-type electronic devices.The main work is as follows:1.Research and development of fiber-free parallel-plane DOT system.The system built in this thesis includes a source module,a detection module and a mechanical motion module.In the source module,this thesis uses patch-type three-wavelength LEDs with wavelengths of 660nm,750nm,and 840nm.The peak and half-width of three wavelengths are tested using a spectrometer,and a triode-based driver circuit is designed.In the detection module,a new photoelectric conversion device SiPM is used as the detector.In the mechanical motion module,the two-slider translation stage is used to realize the movement of the two flat plates.At the software,this thesis has developed a set of control software for system work,which implements functions such as control of mechanical movement,detection of system status,setting of system parameters,and data collection of the system.2.Methodology of imaging and analysis process for fiber-free parallel-plane DOT system.First of all,this thesis proposes a method for acquiring the contour of the measured object based on the rapid scanning in view of the shortcomings of the built system in the imaging process.Through simulation test,the fitting error of this method is determined.At the same time,in the presence of errors,the reconstruction of the absorbing heterogeneous body can still be achieved.Secondly,the system uses the open source software NIRFAST for image reconstruction,and the reconstruction result of this software is in the form of finite element mesh,which is not conducive to the preservation and analysis of the results.In this regard,this thesis implements a method of transforming a tetrahedral finite element mesh to a three-dimensional voxel.Through simulation testing,this method can accurately achieve the conversion of grid to voxel.3.Phantom experiments are performed to verify the imaging performance of the system.Firstly,this thesis uses a polyformaldehyde phantom with good stability and high processing accuracy to test the imaging positioning accuracy of the system.The experimental results show that the reconstruction accuracy of the system is not more than 2mm in the reconstruction results of the slice parallel to the plate at three wavelengths.Secondly,the contrast restoration performance of the system is tested by using agarose phantoms with easy control of optical parameters.The experimental results show that for heterogeneous bodies with absorption coefficients twice as much as the background,the system can reconstruct its contrast with background absorption coefficients better,and for heterogeneous bodies with absorption coefficients three times the background,the system restores contrast slightly lower.Finally,the oxygenated and deoxygenated rabbit blood was used to test the system’s multi-wavelength imaging performance.The experimental results show that the system can accurately recover the change trend of the absorption coefficients of the two chromophores at three different wavelengths,and can realize the material decomposition of the two chromophores.