Molecular Imaging Instrumentation Laboratory, Department of Radiology, Stanford University, Stanford, California, USA.
Department of Mechanical Engineering, Sungkyunkwan University, Suwon, South Korea.
Med Phys. 2023 Jun;50(6):3389-3400. doi: 10.1002/mp.16354. Epub 2023 Apr 7.
Simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) has shown promise in acquiring complementary multiparametric information of disease. However, designing these hybrid imaging systems is challenging due to the propensity for mutual interference between the PET and MRI subsystems. Currently, there are integrated PET/MRI systems for clinical applications. For neurologic imaging, a brain-dedicated PET insert provides superior spatial resolution and sensitivity compared to body PET scanners.
Our first-generation prototype brain PET insert ("PETcoil") demonstrated RF-penetrability and MR-compatibility. In the second-generation PETcoil system, all analog silicon photomultiplier (SiPM) signal digitization is moved inside the detectors, which results in substantially better PET detector performance, but presents a greater technical challenge for achieving MR-compatibility. In this paper, we report results from MR-compatibility studies of two fully assembled second-generation PET insert detector modules.
We studied the effect of the presence of the two second-generation TOF-PET insert detectors on parameters that affect MR image quality and evaluated TOF-PET detector performance under different MRI pulse sequence conditions.
With the presence of operating PET detectors, no RF noise peaks were induced in the MR images, but the relative average noise level was increased by 15%, which led to a 3.1 to 4.2-dB degradation in MR image signal-to-noise ratio (SNR). The relative homogeneity of MR images degraded by less than 1.5% with the two operating TOF-PET detectors present. The reported results also indicated that ghosting artifacts (percent signal ghosting (PSG) ⩽ 1%) and MR susceptibility artifacts (0.044 ppm) were insignificant. The PET detector data showed a relative change of less than 5% in detector module performance between running outside and within the MR bore under different MRI pulse sequences except for energy resolution in EPI sequence (13% relative difference).
The PET detector operation did not cause any significant artifacts in MR images and the performance and time-of-flight (TOF) capability of the former were preserved under different tested MR conditions.
正电子发射断层扫描/磁共振成像（PET/MRI）同时采集疾病的互补多参数信息具有很大的应用潜力。然而，由于 PET 和 MRI 子系统之间存在相互干扰的倾向，因此设计这种混合成像系统具有挑战性。目前已经有临床应用的集成 PET/MRI 系统。对于神经影像学，与体部 PET 扫描仪相比，专用脑部的 PET 插入式探头提供了更高的空间分辨率和灵敏度。
第一代原型脑部 PET 插入式探头（“PETcoil”）证明了其射频穿透性和磁共振兼容性。在第二代 PETcoil 系统中，所有模拟硅光电倍增管（SiPM）信号数字化都移到探测器内部，这使得 PET 探测器性能有了显著提高，但也对实现磁共振兼容性提出了更大的技术挑战。在本文中，我们报告了两个完全组装的第二代 PET 插入式探测器模块的磁共振兼容性研究结果。
我们研究了存在两个第二代时间-of-flight（TOF）-PET 插入式探测器对影响磁共振图像质量的参数的影响，并评估了在不同 MRI 脉冲序列条件下的 TOF-PET 探测器性能。
在运行的 PET 探测器存在的情况下，MR 图像中没有产生 RF 噪声峰，但平均噪声水平增加了 15%，导致 MR 图像信号噪声比（SNR）降低了 3.1 至 4.2dB。当两个运行的 TOF-PET 探测器存在时，MR 图像的相对均匀性降低不到 1.5%。报告的结果还表明，鬼影伪影（信号鬼影百分比（PSG）⩽1%）和磁共振磁化率伪影（0.044ppm）不明显。在不同的 MRI 脉冲序列下，除了 EPI 序列中的能量分辨率（相对差异 13%）外，PET 探测器数据显示在运行于 MR 磁体内部和外部之间时，探测器模块性能的相对变化小于 5%。
PET 探测器的运行不会在 MR 图像中造成任何明显的伪影，并且在不同的测试磁共振条件下，探测器的性能和时间-of-flight（TOF）能力得以保持。
