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首页> 外文期刊>Nuclear Science, IEEE Transactions on >Evaluation of the Effect of Magnetic Field on PET Spatial Resolution and Contrast Recovery Using Clinical PET Scanners and EGSnrc Simulations
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Evaluation of the Effect of Magnetic Field on PET Spatial Resolution and Contrast Recovery Using Clinical PET Scanners and EGSnrc Simulations

机译：使用临床PET扫描仪和EGSnrc模拟评估磁场对PET空间分辨率和对比度恢复的影响

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摘要

We describe an evaluation of the effect of the magnetic field on the PET spatial resolution and contrast recovery for short and long range positron emitters using experimental phantoms scanned on clinical PET/CT and PET/MR scanners as well as using electron transport simulations. A (a short range positron emitter) point source surrounded by Lucite, a (a relatively long range positron emitter) line source surrounded by water, and a contrast phantom with various sphere sizes were scanned on Siemens’ Biograph-mMR (magnetic field strength: 3 Tesla) and Biograph-40 (no magnetic field). The electron transport simulations were performed from 0T to 11T for , , and for the point source, line source, and the contrast phantom. It was observed that the magnetic field has very small effect () on the resolution of short range nuclides such as based on both simulation and experimental results as expected. For long range nuclides such as slight improvements in spatial resolution and contrast recovery were observed on the plane perpendicular to the direction of the magnetic field from phantom experiments and simulations with 3T magnetic field for the human scanner. The degree of improvement is proportional to the positron range of the nuclides as well - s the strength of the magnetic field, and it saturates at for all nuclides used in this study according to simulation results. For the plane parallel to the direction of the magnetic field, worse resolution and better contrast recovery were observed due to more positron annihilations deposited along the direction of the magnetic field (i.e. re-distribution of positrons). With regard to the results obtained from the simulations for a scanner with better intrinsic resolution (2 mm PSF), the improvement in FWHM saturates at a higher field strength () as compared to that for a human scanner (4.7 mm PSF). However, worse FWHM was observed in all directions at 3T as compared to that at 0T due to re-distribution of positrons and the interaction between the low frequency high energy positrons and the scanner’s narrower intrinsic resolution kernel, while the FWTM and contrast recovery still improve at 3T. FWHM was observed to improve with higher magnetic field strength (). It was also found that the intrinsic resolution of the PET scanner needs to be worse/wider than 2.35 mm to observe an improvement in FWHM for a point source in water under a 3T magnetic field as compared to that under 0T. In addition, a directionally dependent resolution modeling which accounts for the effect of the magnetic field in iterative PET reconstruction was observed to improve the resolution recovery and produce more uniform resolution in all directions within the magnetic field.
机译：我们描述了使用在临床PET / CT和PET / MR扫描仪上扫描的实验体模以及电子传输模拟对磁场对短距离和长距离正电子发射器PET空间分辨率和对比度恢复的影响的评估。在Siemens的Biograph-mMR上扫描了一个被Lucite包围的（短距离正电子发射器）点光源，一个被水包围的（一个相对长距离的正电子发射器）线源以及具有各种球体尺寸的对比体模（磁场强度： 3特斯拉）和Biograph-40（无磁场）。对，以及点源，线源和对比体模从0T到11T进行了电子传输模拟。可以观察到，磁场对短距离核素的分辨率影响很小（例如，基于模拟和实验结果）。对于长距离核素，在人体模型的幻影实验和3T磁场模拟中，在垂直于磁场方向的平面上观察到空间分辨率和对比度恢复方面的轻微改善。改善程度与核素的正电子范围以及磁场强度成正比，根据模拟结果，对于本研究中使用的所有核素，改善程度都达到饱和。对于平行于磁场方向的平面，观察到较差的分辨率和更好的对比度恢复，这是由于沿磁场方向沉积了更多的正电子hil灭（即，正电子重新分布）。从具有更好的固有分辨率（2毫米PSF）的扫描仪的仿真结果来看，与人类扫描仪（4.7毫米PSF）相比，FWHM的改进在更高的场强（）下饱和。但是，由于正电子的重新分布以及低频高能正电子与扫描仪较窄的本征分辨率内核之间的相互作用，在3T时在各个方向观察到的FWHM均比在0T时差，而FWTM和对比度恢复仍在改善在3T。观察到FWHM随着较高的磁场强度而改善（）。还发现，PET扫描仪的固有分辨率需要比2.35 mm差/宽一些，才能观察到3T磁场下水中点源的FWHM与0T下相比有所改善。另外，观察到了方向相关的分辨率模型，该模型考虑了磁场在迭代PET重建中的作用，以改善分辨率恢复并在磁场内的所有方向上产生更均匀的分辨率。

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