基于编码板和针孔的大视野放射源定位系统

Large field-of-view radioactive source location system based on a coded aperture and pinholes

近年来,基于编码孔径成像技术的γ相机被广泛用于放射源的定位和监测,但其成像视野范围有限。虽然可采用多个编码板探测器同时探测的方式扩大视野范围,但会增加成本且设备较为笨重。因此,该文提出了一种编码板和针孔混合系统,编码板全编码视场角和半伪影视场角分别为19.33°和70.80°,增加的针孔可将系统视野扩展到123.40°。进一步基于vGATE仿真平台进行了Monte Carlo仿真实验,结果显示所设计系统在编码板视野内实现了2.95°的空间角度分辨率,在扩展的针孔视野内实现了6.30°的空间角度分辨率,可对3 m处10mCi的放射源有效成像。

[Objective]Gamma-ray detection using a nuclear radiation locator is critical for monitoring,locating,and processing radioactive sources.In recent years,gamma cameras based on coded aperture imaging techniques have been extensively utilized to identify and monitor radioactive sources.However,these detectors have limitations in terms of the imaging field.To accurately determine the specific location of radioactive sources,constant adjustment of the detection angle is required,which is often time-consuming.To expand the detection field,multiple coded aperture cameras can be used simultaneously,but this approach increases cost and equipment complexity.Some researchers have attempted to combine Compton and coded aperture imaging techniques.While the Compton camera can extend the field-of-view(FOV)to 4π,this method is complicated,costly,and limited to detecting high-energy rays.As a result,the combination of these two techniques proves inadequate when searching for low-energy sources.In this work,we proposed a system and method for locating radioactive sources with a large FOV based on combining a coded aperture with pinholes.This method addresses the limited FOV issue encountered in the aforementioned system.[Methods]The coded aperture component of the system uses a modified uniformly redundant array as the uniform redundant array mask.The base mode class is 11,with a unit size of 3.3 mm×3.3 mm,leading to a total size of 69.3 mm×69.3 mm.The mask thickness is 9 mm,and tungsten is used as the material.The detector section includes a 26×26 NaI(Tl)array,where each crystal pixel has dimensions of 1.45 mm×1.45 mm×6.00 mm.A crystal gap of 0.2 mm exists between each pixel,and the distance between the center of the coded aperture and the position-sensitive sensor is 77.5 mm.For the pinhole part of the system,a tapered pinhole with a center size of 4 mm is used.The pinhole is embedded in a shield with equally large pinholes on all four sides.For performance assessment of the system,Monte Carlo simulation experiments were performed with GATE software.A large FOV radioactive source location system is constructed,and simulation data are produced.MATLAB is employed to process the simulation data,compute the system transmission matrix using the Sidden algorithm,and conduct reconstruction using the maximum likelihood expectation maximization method.The projection and reconstruction results of the point sources at various positions are compared and analyzed.Thus,this work shows a comprehensive analysis and assessment of the developed system for locating radioactive sources with a large FOV using a combination of coded aperture and pinhole imaging techniques.[Results]The results indicate that the full coding and semipseudo-film FOV of the coded aperture camera are 19.33°and 70.80°,respectively,and the added pinhole extends the FOV of the system to 123.40°.The developed system attains an angular resolution of 2.95°within the coded aperture FOV and 6.30°within the extended pinhole FOV,effectively imaging a 10 mCi radioactive source at a distance of 3 m.[Conclusions]The developed wide FOV radiation source location system and method effectively address the limited imaging field of the coded aperture camera.