| During the radiotherapy process,respiratory motion can cause the tumor and organ of thoracic and abdominal surface moving with a certain frequency and amplitude.This can affect the radiotherapy effect,and even cause the radiation damage to the human body.We can monitor the external respiratory motion,infer the tumor motion,and control the relative position of target volume and radiation field through radiotherapy system.This can form a very effective tracking method for respiratory motion problem in current radiotherapy.In view of that the tumor motion of thoracic and abdominal organ caused by respiratory motion can lead to the motion of thoracic and abdominal surface.It is proved that using the respiratory motion of specific points of thoracic and abdominal surface to infer the tumor motion is effective,then using the motion of thoracic and abdominal surface can infer the tumor motion more effectively.In order to analyze the motion regulation of thoracic and abdominal surface,we can measure the 3D motion of thoracic and abdominal surface.In order to solve the 3D motion measurement problem of thoracic and abdominal surface,optical measurement method is recognized as the most practical and potential method.Optical method can be divided into point imaging,line imaging and surface imaging.Surface imaging method is the best option for respiratory motion measurement of human thoracic and abdominal surface.Surface imaging can be divided into capturing one image and capturing multiple images.The former includes binocular vision,Fourier transform profilometry,windowed Fourier transform profilometry and wavelet transform profilometry;The latter includes phase shift profilometry and temporal encoding measurement method.This kind of method has higher measurement accuracy,lower measurement speed.It is not suitable for dynamic 3D measurement.The 3D measurement method of capturing one image is an ideal solution for respiratory motion measurement of human thoracic and abdominal surface.For the respiratory motion of human thoracic and abdominal surface in this paper,we focus on the study of 3D dynamic measurement method,the main work is as follows:1.In view of that the performance of 3D Fourier transform is better than 1D Fourier transform,this paper uses a 3D Fourier fringe analysis wrapped phase extraction method which combines spatial domain with time domain.We take the encoded fringe image sequence of human thoracic and abdominal surface captured by an industrial camera as a 3D volume,use the 3D Fourier transform to convert into frequency domain,then extract the first-order spectrum by frequency domain filtering.Finally the 3D inverse Fourier transform is used to obtain the wrapped phase information.The accuracy of wrapped phase extraction and antiinterference ability can be improved by adding the filtering of time axis.2.For the filtering problem of frequency domain after 3D Fourier transform,this paper uses the 3D Gaussian filter to conduct the frequency domain filtering.We can get the Gaussian filter parameters with individual characteristics by designing and optimizing the filter parameters to reduce the ringing effect,this can improve the accuracy of wrapped phase extraction,and further improve the 3D measurement accuracy of thoracic and abdominal surface.3.Fourier fringe analysis method only has the ability of global analysis,yet wavelet transform has the excellent multi-resolution analysis characteristics.Therefore,this paper uses a 3D wavelet transform wrapped phase extraction method which combines spatial domain with time domain.For the fringe pattern sequence of thoracic and abdominal surface,we conduct the 3D wavelet transform,and select a proper range for the scale parameters.Finally we can obtain the wrapped phase information of fringe pattern sequence by the wavelet coefficients at the wavelet ridge.The proposed method also uses the information of time axis to improve the accuracy of wrapped phase extraction,and further improves the 3D measurement accuracy of thoracic and abdominal surface.The details of thoracic and abdominal surface can be better reflected.4.For the requirement of modern radiotherapy,this paper constructs a 3D measurement method of human thoracic and abdominal surface.We encode three cosine fringe patterns with three different frequencies into the R,G and B channels of one color fringe pattern.The projector projects the color fringe pattern on human thoracic and abdominal surface,the 3CCD industrial camera is used to capture the image.We can get the fringe image sequence of human thoracic and abdominal surface.A color calibration scheme is used to calibrate and separate the encoded fringe images from three channels correctly,the wrapped phase information can be extracted by using the wrapped phase extraction method,the absolute phase information with large range can be obtained by using the temporal phase unwrapping method.Finally the triangular measurement principle is used to get the 3D image sequence of thoracic and abdominal surface.According to the above method,we build the experiment setup through theoretical analysis,and verify the proposed method by measurement experiment.The experiment results show that the proposed method can realize the 3D measurement of human thoracic and abdominal surface during the respiratory process. |
