康普顿相机的成像分辨分析与模拟
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摘要
相较于传统的γ射线的成像系统,康普顿相机的高效率优势使其在重离子放疗的实时监测中极具潜力.中科院近代物理研究所已经建成一座具有完全知识产权的重离子治癌示范装置,且正在进行全国范围的推广.鉴于重离子治癌的广阔前景,本工作对康普顿相机的成像分辨本领进行了分析和Geant 4模拟,并根据反投影算法进行了图像重建.分析及模拟结果显示,当探测单元的位置分辨为2 mm,其导致的成像分辨与能量分辨为5%时导致的成像分辨相差约10%.对于几百keV的γ射线,探测器的相对能量分辨很容易好于1.0%.因此,相较于能量分辨,探测晶体单元的位置分辨本领对重建图像的质量起主导作用.
Compared with traditional gamma-ray imaging equipment, the Compton camera is a very promising imaging device in nuclear medicine and molecular imaging, and has a strong potential application in monitoring beams in heavy-ion-therapy because of its high efficiency feature. A demonstration device for heavy ion cancer treatment with complete intellectual property right has been built at Institute of Modern Physics, Chinese Academy of Sciences in Wuwei city of Gansu Province. At present the device is being up-graded, and the heavy ion cancer treatment is being generalized in national wide. In view of the broad prospects of heavy ion cancer treatment, the imaging resolution of Compton camera is analyzed theoretically, and three errors effecting the imaging resolution, which are energy resolution, position resolution of detector and the Doppler effect, are determined. Then the three errors are simulated by using the Geant 4 packages. The physical process in simulation is selected as the G4 EMPenelopePhysics model, which makes the atomic shell cross section data for low energy physical process used directly. The Compton camera geometry consists of two layers of detectors.The layer close to γ source is called detector and the other one is called absorption detector. The material of scatter detector is selected as low-Z silicon and carbon, and the absorb detector is high-Z germanium. The thickness value of scatter detector and absorb detector are both 20 mm. The spacing between the two layers is100 mm. The simulation results by Geant 4 are used to reconstruct the image of point-like γ source through using the back-projection algorithm. The simulation results and the re-constructed images indicate that the difference between the image full width at half maximum induced by 2 mm position resolution and that induced by 5.0% relative energy resolution of scatter detector is about 10%, and amount to that by the Doppler effect of Silicon. For the γ ray with energies of several hundred keV, the energy resolution of Si detectors is easily better than 1.0% in practice. Therefore, the detector's position resolution dominates the image quality of the Compton camera. Considering the Doppler effect, manufacturing techniques and imaging efficiency, 2.0 mm-sized crystal unit and 1.0% energy resolution power is suggested for practically manufacturing the Compton camera.
Compared with traditional gamma-ray imaging equipment, the Compton camera is a very promising imaging device in nuclear medicine and molecular imaging, and has a strong potential application in monitoring beams in heavy-ion-therapy because of its high efficiency feature. A demonstration device for heavy ion cancer treatment with complete intellectual property right has been built at Institute of Modern Physics, Chinese Academy of Sciences in Wuwei city of Gansu Province. At present the device is being up-graded, and the heavy ion cancer treatment is being generalized in national wide. In view of the broad prospects of heavy ion cancer treatment, the imaging resolution of Compton camera is analyzed theoretically, and three errors effecting the imaging resolution, which are energy resolution, position resolution of detector and the Doppler effect, are determined. Then the three errors are simulated by using the Geant 4 packages. The physical process in simulation is selected as the G4 EMPenelopePhysics model, which makes the atomic shell cross section data for low energy physical process used directly. The Compton camera geometry consists of two layers of detectors.The layer close to γ source is called detector and the other one is called absorption detector. The material of scatter detector is selected as low-Z silicon and carbon, and the absorb detector is high-Z germanium. The thickness value of scatter detector and absorb detector are both 20 mm. The spacing between the two layers is100 mm. The simulation results by Geant 4 are used to reconstruct the image of point-like γ source through using the back-projection algorithm. The simulation results and the re-constructed images indicate that the difference between the image full width at half maximum induced by 2 mm position resolution and that induced by 5.0% relative energy resolution of scatter detector is about 10%, and amount to that by the Doppler effect of Silicon. For the γ ray with energies of several hundred keV, the energy resolution of Si detectors is easily better than 1.0% in practice. Therefore, the detector's position resolution dominates the image quality of the Compton camera. Considering the Doppler effect, manufacturing techniques and imaging efficiency, 2.0 mm-sized crystal unit and 1.0% energy resolution power is suggested for practically manufacturing the Compton camera.
引文
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[2]Shakirin G,Braess H,Fiedler F,et al.2011 Phys.Med.Biol.56 1281
[3]Enghardt W,Crespo P,Fiedler F,et al.2004 Nucl.Instrum.Meth.A 525 284
[4]Nishio T,Ogino T,Nomura K,et al.2006 Med.Phys.334190
[5]Amaldi U,Hajdas W,Iliescu S,et al.2010 Nucl.Instrum.Meth.A 617 248
[6]Henriquet P,Testa E,Chevallier M,et al.2012 Phys.Med.Biol.57 4655
[7]Agodi C,Battistoni G,Bellini F,et al.2012 Phys.Med.Biol.57 5667
[8]Gwosch K,Hartmann B,Jakubek J,et al.2013 Phys.Med.Biol.58 3755
[9]Borm V,Joulaeizadeh L,Beekman F,et al.2012 Phys.Med.Biol.57 297
[10]Testa M,Bajard M,Chevallier M,et al.2010 Radiat.Environ.Biophy.49 337
[11]Krimmer J,Ley J L,Abellan C,et al.2015 Nucl.Instrum.Meth.A 787 98
[12]Peterson S W,Robertson D,Polf J,et al.2010 Phys.Med.Biol.55 6841
[13]Seo H,Park J H,Ushakov A,et al.2011 J.Instrum.6C01024
[14]Kurosawa S,Kubo H,Ueno K,et al.2012 Curr.Appl.Phys.12 364
[15]Kormoll T,Fiedler F,Schone S,et al.2011 Nucl.Instrum.Meth.A 626-627 114
[16]Llosa G,Cabello J,Callier S,et al.2013 Nucl.Instrum.Meth.A 718 130
[17]Schoenfelder V,Himer A,Schneider K,et al.1973 Nucl.Instrum.Meth.107 385
[18]Todd R W,Nightingale J M,Everett D B,et al.1974 Nature251 132