MRI磁场对小动物PET空间分辨率影响的仿真研究
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摘要
目的:研究不同强度的磁场对正电子自由程以及小动物正电子发射断层成像(PET)的空间分辨率的影响。方法:利用蒙特卡罗工具GATE软件建立磁兼容的小动物PET仿真模型,对放射性核素18F、11C、13N、15O及22Na在人体中水、肺、骨不同物质的正电子自由程进行仿真,并依据美国电气制造商协会(NEMA)NU4-2008标准要求对PET空间分辨率进行测量,分析磁场对自由程和空间分辨率的影响。结果:磁场对不同核素正电子自由程和空间分辨率的影响不同,对于18F和22Na等低能核素,9.4 T场强下自由程则分别减少24.5%和20.9%,但空间分辨率并无显著改变。对于15O和11C高能核素,自由程则分别减少61.5%和42.2%,空间分辨率也随着场强增加而提升,但在场强>7 T后基本趋于稳定。结论:小动物PET的空间分辨率在垂直磁场方向有一定提升,提升的幅度与正电子自由程和磁场强度相关。
Objective: To research the effect of magnetic field of different intensity on the positron range and the spatial resolution of positron emission tomography(PET) of small animal. Methods: Monte Carlo tool(GATE software) was applied to establish simulation model of small animal PET which was compatible with magnetic field. And the positron ranges of various substance of radionuclide included 18 F, 11 C, 13 N, 15 O and 22 Na in the water, lung and bone of human body were simulated. According to the requirement of NEMA NU4-2008 standard to measure spatial resolution of PET, and analyze the influence of magnetic field on the positron range and spatial resolution. Results: The influence of magnetic field for different positron range and spatial resolution was different. For nuclide with low power, such as 18 F and 22 Na, the positron range under 9.4 T field intensity were 24.5% and 20.9%, respectively, while the spatial resolution was no significantly changed. For nuclide with high power, such as 15 O and 11 C, the positron range were reduced 61.5% and 42.4%, respectively, and the spatial resolution also enhanced with the increasing of field intensity and it basically entered stability while field intensity was more than 7 T. Conclusion: The spatial resolution of small animal PET is promoted at the direction that was vertical to magnetic field, and the promoted range is relevant with positron range and magnetic field intensity.
Objective: To research the effect of magnetic field of different intensity on the positron range and the spatial resolution of positron emission tomography(PET) of small animal. Methods: Monte Carlo tool(GATE software) was applied to establish simulation model of small animal PET which was compatible with magnetic field. And the positron ranges of various substance of radionuclide included 18 F, 11 C, 13 N, 15 O and 22 Na in the water, lung and bone of human body were simulated. According to the requirement of NEMA NU4-2008 standard to measure spatial resolution of PET, and analyze the influence of magnetic field on the positron range and spatial resolution. Results: The influence of magnetic field for different positron range and spatial resolution was different. For nuclide with low power, such as 18 F and 22 Na, the positron range under 9.4 T field intensity were 24.5% and 20.9%, respectively, while the spatial resolution was no significantly changed. For nuclide with high power, such as 15 O and 11 C, the positron range were reduced 61.5% and 42.4%, respectively, and the spatial resolution also enhanced with the increasing of field intensity and it basically entered stability while field intensity was more than 7 T. Conclusion: The spatial resolution of small animal PET is promoted at the direction that was vertical to magnetic field, and the promoted range is relevant with positron range and magnetic field intensity.
引文
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[2]Cherry SR.Multimodality imaging:beyond PET/CT and SPECT/CT[J].Semin Nucl Med,2009,39(5):348-353.
[3]Vaquero JJ,Kinahan P.Positron Emission Tomography:Current Challenges and Opportunities for Technological Advances in Clinical and Preclinical Imaging Systems[J].Annu Rev Biomed Eng,2015,17:385-414.
[4]Hammer BE,Christensen NL.Measurement of positron range in matter in strong magnetic fields[J].Nuclear Science IEEE Transactions on,1995,42(4):1371-1376.
[5]Kraus R,Delso G,Ziegler SI.Simulation Study of Tissue-Specific Positron Range Correction for the New Biograph m MR Whole-Body PET/MR System[J].IEEE Transactions on Nuclear Science,2012,59(5):1900-1909.
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[7]Jan S,Santin G,Strul D,et al.GATE:a simulation toolkit for PET and SPECT[J].Phys Med Biol,2004,49(19):4543.
[8]Espa?a S,FRAILE LM,HERRAIZ JL,et al.Performance evaluation of Si PM photodetectors for PET imaging in the presence of magnetic fields[J].Nuclear Inst and Methods in Physics Research A,2009,613(2):308-316.
[9]Cherry SR,Sorenson J,Phelps ME,et al.Physics in Nuclear Medicine[J].J Nucl Med,2013,54(7):85.
[10]Raylman RR,Hammer BE,Christensen NL.Combined MRI-PET scanner:a Monte Carlo evaluation of the improvements in PET resolution due to the effects of a static homogeneous magnetic field[J].IEEE Transactions on Nuclear Science,1996,43(4):2406-2412.
[11]Hammer BE,Christensen NL,Heil BG.Use of a magnetic field to increase the spatial resolution of positron emission tomography[J].Med Phys,1994,21(12):1917-1920.
[12]Agostinelli S,Allison J,Amako K,et al.Geant4-a simulation toolkit[J].Nuclear Instruments and Methods in Physics Research,2003,506(3):250-303.
[13]Thielemans K,Tsoumpas C,Mustafovic S,et al.STIR:software for tomographic image reconstruction release 2[J].Phys Med Biol,2012,57(4):867-883.
[14]金永杰.核医学仪器与方法[M].哈尔滨:哈尔滨工程大学出版社,2010.
[15]Luboldt W,Z?phel K,Wunderlich G,et al.Visualization of Somatostatin Receptors in Prostate Cancer and its Bone Metastases with Ga-68-DOTATOC PET/CT[J].Mol Imaging Biol,2010,12(1):78-84.
[16]Mc Bride WJ,Zanzonico P,Sharkey RM,et al.Bispecific antibody pretargeting PET(immunoP ET)with an 124I-labeled hapten-peptide[J].J Nucl Med,2006,47(10):1678-1688.