Emvalomenos Gaelle, Trajanovska Sofie, Pham Binh T T, Doughty Peter, Burnet Jerome, Smith Isabelle, Garipov Ruslan, Gregoire Marie-Claude, Sunn Nana, McGrath John, Meikle Steven R
Sydney School of Health Sciences, The University of Sydney, Camperdown, NSW, 2050, Australia.
Brain and Mind Centre, The University of Sydney, 100 Mallett Street, Camperdown, NSW, 2050, Australia.
EJNMMI Phys. 2021 Oct 9;8(1):68. doi: 10.1186/s40658-021-00415-1.
This study aimed to evaluate the performance of a preclinical PET insert in three configurations: as a stand-alone unit outside the MRI bore, inside the bore of a cryogen-free 3T MRI and, finally, while performing simultaneous PET/MRI studies.
The PET insert consists of two rings of six detectors, each detector comprising 8 × 12 SiPMs reading out dual offset layers of pixelated LYSO crystals with a 1.4-mm pitch. The inner diameter is 60 mm, transaxial field of view (FoV) 40 mm and axial FoV 98 mm. Evaluation was based on NEMA NU 4-2008 guidelines with appropriate modifications. Spatial resolution and sensitivity were measured inside and outside the MR bore. Image quality, count rate and quantitative performance were measured in all three configurations. The effect of temperature stability on PET sensitivity during fast spin echo sequences was also evaluated. B field homogeneity and T1 and T2 relaxation times were measured using a water-filled phantom, with and without simultaneous PET operation. Finally, PET and MRI scans of a mouse injected with 10 MBq [F]NaF and a mouse injected with 16 MBq [F]FDG were performed in sequential and simultaneous modes.
Peak absolute sensitivity was 10.15% with an energy window of 250-750 keV. Absolute sensitivity values outside and inside the MR bore with MR idle agreed to within 0.1%. Outside the MR bore, spatial resolution was 1.21/1.59 mm FWHM (radial/tangential) 5 mm from the centre of the FoV which compared well with 1.19/1.26 mm FWHM inside the MR bore. There were no substantial differences between all three scan configurations in terms of peak NEC rate (175 kcps at 17 MBq), scatter or random fractions. Uniformity and recovery coefficients were also consistent between scanning modes. B field homogeneity and T1 and T2 relaxation times were unaltered by the presence of the PET insert. No significant differences were observed between sequential and simultaneous scans of the animals.
We conclude that the performance of the PET insert and MRI system is not significantly affected by the scanning mode.
本研究旨在评估一款临床前PET插入件在三种配置下的性能：作为独立单元置于MRI孔外、置于无液氦3T MRI的孔内，以及最后在进行PET/MRI同步研究时的性能。
PET插入件由两个包含六个探测器的环组成，每个探测器由8×12个硅光电倍增管（SiPM）组成，用于读出像素化LYSO晶体的双偏移层，像素间距为1.4毫米。内径为60毫米，横向视野（FoV）为40毫米，轴向视野为98毫米。评估基于NEMA NU 4 - 2008指南并进行了适当修改。在MR孔内外测量空间分辨率和灵敏度。在所有三种配置下测量图像质量、计数率和定量性能。还评估了快速自旋回波序列期间温度稳定性对PET灵敏度的影响。使用充水体模测量B场均匀性以及T1和T2弛豫时间，测量时PET插入件分别处于工作和不工作状态。最后，对注射了10 MBq [F]NaF的小鼠和注射了16 MBq [F]FDG的小鼠进行PET和MRI扫描，扫描模式包括顺序扫描和同步扫描。
在能量窗为250 - 750 keV时，峰值绝对灵敏度为10.15%。在MR闲置时，MR孔内外的绝对灵敏度值相差在0.1%以内。在MR孔外，距视野中心5毫米处的空间分辨率为1.21/1.59毫米半高宽（径向/切向），与MR孔内的1.19/1.26毫米半高宽相比表现良好。在所有三种扫描配置下，峰值标准化等效计数率（在17 MBq时为175 kcps）、散射分数或随机分数方面均无实质性差异。扫描模式之间的均匀性和恢复系数也一致。PET插入件的存在未改变B场均匀性以及T1和T2弛豫时间。在对动物进行顺序扫描和同步扫描之间未观察到显著差异。
我们得出结论，PET插入件和MRI系统的性能不受扫描模式的显著影响。
