Department of Nuclear Medicine, Technische Universität München, Munich, Germany.
J Nucl Med. 2012 Jun;53(6):845-55. doi: 10.2967/jnumed.111.098608. Epub 2012 Apr 25.
The recently introduced first integrated whole-body PET/MR scanner allows simultaneous acquisition of PET and MRI data in humans and, thus, may offer new opportunities, particularly regarding diagnostics in oncology. This scanner features major technologic differences from conventional PET/CT devices, including the replacement of photomultipliers with avalanche photodiodes and the need for MRI-based attenuation correction. The aim of this study was to evaluate the comparability of clinical performance between conventional PET/CT and PET/MR in patients with oncologic diseases.
Thirty-two patients with different oncologic diagnoses underwent a single-injection, dual-imaging protocol consisting of a PET/CT and subsequent PET/MR scan. PET/CT scans were performed according to standard clinical protocols (86 ± 8 min after injection of 401 ± 42 MBq of (18)F-FDG, 2 min/bed position). Subsequently (140 ± 24 min after injection), PET/MR was performed (4 min/bed position). PET images of both modalities were reconstructed iteratively. Attenuation and scatter correction as well as regional allocation of PET findings were performed using low-dose CT data for PET/CT and Dixon MRI sequences for PET/MR. PET/MR and PET/CT were compared visually by 2 teams of observers by rating the number and location of lesions suspicious for malignancy, as well as image quality and alignment. For quantitative comparison, standardized uptake values (SUVs) of the detected lesions and of different tissue types were assessed.
Simultaneous PET/MR acquisition was feasible with high quality in short acquisition time (≤ 20 min). No significant difference was found between the numbers of suspicious lesions (n = 80) or lesion-positive patients (n = 20) detected with PET/MR or PET/CT. Anatomic allocation of PET/MR findings by means of the Dixon MRI sequence was comparable to allocation of PET/CT findings by means of low-dose CT. Quantitative evaluation revealed a high correlation between mean SUVs measured with PET/MR and PET/CT in lesions (ρ = 0.93) and background tissue (ρ = 0.92).
This study demonstrates, for what is to our knowledge the first time, that integrated whole-body PET/MR is feasible in a clinical setting with high quality and in a short examination time. The reliability of PET/MR was comparable to that of PET/CT in allowing the detection of hypermetabolic lesions suspicious for malignancy in patients with oncologic diagnoses. Despite different attenuation correction approaches, tracer uptake in lesions and background correlated well between PET/MR and PET/CT. The Dixon MRI sequences acquired for attenuation correction were found useful for anatomic allocation of PET findings obtained by PET/MR in the entire body. These encouraging results may form the foundation for future studies aiming to define the added value of PET/MR over PET/CT.
评估常规 PET/CT 和 PET/MR 在不同肿瘤疾病患者中的临床性能是否具有可比性。
32 名不同肿瘤诊断的患者接受了单次注射、双成像方案，包括 PET/CT 和随后的 PET/MR 扫描。PET/CT 扫描按照标准临床方案进行（注射 401 ± 42MBq [18]F-FDG 后 86 ± 8min，2min/床位）。随后（注射后 140 ± 24min），进行 PET/MR（4min/床位）。两种方式的 PET 图像均进行迭代重建。使用低剂量 CT 数据进行衰减和散射校正，使用 Dixon MRI 序列进行 PET/MR 的区域分配。2 个观察组分别对两种模态的图像进行视觉比较，通过评价疑似恶性病变的病变数量和位置、图像质量和配准情况进行比较。对于定量比较，评估了检测到的病变和不同组织类型的标准化摄取值（SUV）。
在短采集时间（≤20min）内，同时进行 PET/MR 采集是可行的，且具有高质量。通过 PET/MR 或 PET/CT 检测到的可疑病变（n=80）或阳性病变患者（n=20）数量无显著差异。通过 Dixon MRI 序列对 PET/MR 发现的病变进行解剖分配与通过低剂量 CT 对 PET/CT 发现的病变进行分配的结果具有可比性。定量评估显示，在病变（ρ=0.93）和背景组织（ρ=0.92）中，通过 PET/MR 和 PET/CT 测量的平均 SUV 值之间存在高度相关性。
本研究首次证明，在临床环境中，集成式全身 PET/MR 是可行的，具有高质量和短的检查时间。在检测疑似恶性肿瘤的高代谢病变方面，PET/MR 的可靠性与 PET/CT 相当。尽管衰减校正方法不同，但病变和背景中的示踪剂摄取在 PET/MR 和 PET/CT 之间相关性良好。为衰减校正而采集的 Dixon MRI 序列对于在全身范围内对通过 PET/MR 获得的 PET 发现进行解剖分配非常有用。这些令人鼓舞的结果可能为未来旨在定义 PET/MR 相对于 PET/CT 的附加价值的研究奠定基础。
