Coded Aperture Imaging With MURA For ? Internal Contamination

The ? camera is widely used for the radiation environment monitoring,medical imaging and so on.The gamma camera in this paper is mainly for the imaging of internal contamination.The front-end detector using multi anode position sensitive photomultiplier tube?PSPMT??Cs I crystal and signal readout circuit.It matches position readout circuit to complete the design of digital signal readout circuit and data processing program.In the design,the low-pass filter module prepared by FPGA enhances the signal to noise ratio of the system.As the focus of the paper,MURA coded aperture collimator and image reconstruction algorithm enhance the imaging range and spatial resolution of the system.According to the detection characteristics of internal contamination,sensitivity,imaging field of view,imaging resolution,the paper has chosen Modified Uniformly Redundant Arrays.It designed aperture collimator MURA?37×37? and the manufacturing scheme of MURA collimator has been improved.Using mixed materials,wire processing,combined with 3D printing technology,the MURA coded aperture collimator with good imaging performance was successfully developed.According to the characteristics of rapid detection of internal contamination the Maximum Likelihood Expectation Maximization method is selected to reconstruct the image in the paper.The MLEM algorithm is implemented in Matlab environment.In the experiment of MURA?37×37? in combination with front-end detection,the ¹³⁷Cs source was detected.Imaging focal length of the collimator is b=25.4mm,the unit aperture is pm=2.13 mm.When detecting,the ¹³⁷Cs source is placed in the lead shielding cavity.The distance between ¹³⁷Cs and collimator is a=100mm.The experimental results show,the system can be used to detect the position of the slice ¹³⁷Cs source,the magnification is 1.254,the full code field of view is about 196 mm,the geometric resolution is about 10.437 mm,the angular resolution is about 5.64°.The design meets the requirements.