目的:对RF场可穿透的椭圆形PET插入物进行MRI兼容性研究,该插入物将MRI内置人体RF线圈作为发射器和接收器。
方法:使用十二个电浮动RF屏蔽PET探测器模块来构建主轴为440mm的原型椭圆形PET插入物,350毫米的短轴,和225毫米的轴向长度。PET检测器模块的电浮动通过使用塑料带将电缆屏蔽与检测器屏蔽隔离来实现。对发射(B1)射频场进行了研究,图像信噪比(SNR),以及3T临床MRI系统中均匀圆柱形(直径:160mm,长度:260mm)体模(NaClNiSO4溶液)的RF脉冲幅度(Verio,西门子,Erlangen,德国)。
结果:椭圆形插入物的B1图与仅MRI场反应相似。与仅MRI值相比,信噪比降低51%,45%,59%的人被看到,分别,对于自旋回波(SE),梯度回波(GE),和回声平面(EPI)图像的情况下的椭圆形PET插入。此外,SE所需的RF脉冲幅度,GE,和EPI序列是,分别,1.93、1.85和1.36倍。然而,椭圆形插入物的平均射频接收灵敏度降低了30%。
结论:原型浮动PET插入物是临床MRI系统的安全问题,并且该兼容性研究为开发用于现有MRI系统的大型身体尺寸浮动PET插入件提供了间隙。由于插入件的射频屏蔽,与仅使用MRI的病例相比,需要相对较大的射频功率.由于这一点,也由于身体线圈的低射频灵敏度,SNR大大降低。
OBJECTIVE: To perform an MRI compatibility
study of an RF field-penetrable oval-shaped PET insert that implements an MRI built-in body RF coil both as a transmitter and a receiver.
METHODS: Twelve electrically floating RF shielded PET detector modules were used to construct the prototype oval PET insert with a major axis of 440 mm, a minor axis of 350 mm, and an axial length of 225 mm. The electric floating of the PET detector modules was accomplished by isolating the cable shield from the detector shield using plastic tape. Studies were conducted on the transmit (B1) RF field, the image signal-to-noise ratio (SNR), and the RF pulse amplitude for a homogeneous cylindrical (diameter: 160 mm and length: 260 mm) phantom (NaCl + NiSO4 solution) in a 3 T clinical MRI system (Verio, Siemens, Erlangen, Germany).
RESULTS: The B1 maps for the oval insert were similar to the MRI-only field responses. Compared to the MRI-only values, SNR reductions of 51%, 45%, and 59% were seen, respectively, for the spin echo (SE), gradient echo (GE), and echo planar (EPI) images for the case of oval PET insert. Moreover, the required RF pulse amplitudes for the SE, GE, and EPI sequences were, respectively, 1.93, 1.85, and 1.36 times larger. However, a 30% reduction in the average RF reception sensitivity was observed for the oval insert.
CONCLUSIONS: The prototype floating PET insert was a safety concern for the clinical MRI system, and this compatibility
study provided clearance for developing a large body size floating PET insert for the existing MRI system. Because of the RF shield of the insert, relatively large RF powers compared to the MRI-only case were required. Because of this and also due to low RF sensitivity of the body coil, the SNRs reduced largely.