基于SPECT探头的高灵敏编码孔径γ成像系统

Highly sensitive coded aperture gamma imaging system based on a SPECT probe

远距离、大范围、快速检测放射源对国土安全具有重要意义,γ相机可以远距离提取放射性物质位置、强度以及类别等信息,是一种有效的检测工具。由于探测器面积小,且编码孔径的视场(Field of View,FOV)有限,当前编码孔径γ相机的探测效率普遍低。本研究提出一种基于国产的滨松BHP6601型临床单光子发射计算机断层成像(Single Photon Emission Computed Tomography,SPECT)探头的大面积高灵敏度编码孔径γ成像系统研制方案。该探头的固有分辨率为3.55 mm,有效探测面积为510 mm×390 mm,可用于提高辐射成像系统的空间角度分辨率和灵敏度。本研究根据此探测器规格,设计采用修正均匀冗余阵列(Modified Uniformly Redundant Arrays,MURA)编码嵌套模式的编码板,其中心基本单元阵列大小23×23,每个单位孔径大小为22.1 mm×17 mm。成像系统无伪影视场在X方向上和Y方向上分别为57.32°和47.3°;空间角度分辨率在X和Y方向上分别为2.94°和2.28°。采用该方案的γ成像系统对18 m处3.7×107 Bq 137Cs单点源进行测试,采集时间1 s即可精准定位;若对于4 m处的1.11×106 Bq 137Cs定位,采集时间仅需要2 s。仿真测试结果表明:该系统对于远距离或低活度的放射源能快速清晰定位。

[Background]Remote,large-scale,rapid and real-time detection of radioactive sources is of great significance for industrial investigation and environmental remediation.Gama camera can extract information such as the location,intensity and category of radioactive substances from a long distance,and is an effective detection tool.Due to the small detector area and the limited field of view(FOV)of the coded aperture,the detection efficiency of the current coded apertureγcameras is low.[Purpose]This study aims to propose a prototype of large area and highly sensitive coded aperture gamma imaging system based on a SPECT probe.[Methods]First of all,the Hamamatsu BHP6601 single photon emission computed tomography(SPECT)probe with large area of 510 mm×390 mm and high intrinsic spatial resolution of 3.55 mm was selected as the detector of the system.Based on the detector by tectonic analysis,modified uniform redundant arrays(MURA)coding nesting mode was adopted with a rank of 23 and each unit aperture size of 22.1 mm×17 mm.Then,the system transmission matrix is obtained by using the gamma rays emitted from the radioactive sources at different angles of the FOV to reach the detector geometry through the coded aperture.Then,the geometric relationship between the radioactive source and the system is used to analyze and construct different radioactive source events.Next,the cumulative probability based on the system transmission matrix simulates the photon distribution on the detector.Finally,using Maximum Likelihood Expectation Maximization(MLEM)algorithm is built source image.[Results]The results indicate that the non artifact field of view(NAFOV)is 57.32°in the X direction and 47.3°in the Y direction;and the spatial angle resolution is 2.94°in the X direction and 2.28°in the Y direction.Theγcamera can accurately locate 3.7×107 Bq 137Cs single point source in 1 s at the distance of 18 m and 2 s to accurately reconstruct the position of 1.11×106 Bq 137Cs at the distance of 4 m away from the camera.[Conclusions]Theγcamera of this study has a high detection capability for distant or low-activity radiation sources in large range.