Stahl Robert, Krug Roland, Kelley Douglas A C, Zuo Jin, Ma C Benjamin, Majumdar Sharmila, Link Thomas M
Musculoskeletal and Quantitative Imaging Group, Department of Radiology, University of California, San Francisco, CA 94107-0946, USA.
Skeletal Radiol. 2009 Aug;38(8):771-83. doi: 10.1007/s00256-009-0676-z. Epub 2009 Mar 18.
The objectives of the study were to optimize three cartilage-dedicated sequences for in vivo knee imaging at 7.0 T ultra-high-field (UHF) magnetic resonance imaging (MRI) and to compare imaging performance and diagnostic confidence concerning osteoarthritis (OA)-induced changes at 7.0 and 3.0 T MRI.
Optimized MRI sequences for cartilage imaging at 3.0 T were tailored for 7.0 T: an intermediate-weighted fast spin-echo (IM-w FSE), a fast imaging employing steady-state acquisition (FIESTA) and a T1-weighted 3D high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) sequence. Three healthy subjects and seven patients with mild OA were examined. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), diagnostic confidence in assessing cartilage abnormalities, and image quality were determined. Abnormalities were assessed with the whole organ magnetic resonance imaging score (WORMS). Focal cartilage lesions and bone marrow edema pattern (BMEP) were also quantified.
At 7.0 T, SNR was increased (p < 0.05) for all sequences. For the IM-w FSE sequence, limitations with the specific absorption rate (SAR) required modifications of the scan parameters yielding an incomplete coverage of the knee joint, extensive artifacts, and a less effective fat saturation. CNR and image quality were increased (p < 0.05) for SPGR and FIESTA and decreased for IM-w FSE. Diagnostic confidence for cartilage lesions was highest (p < 0.05) for FIESTA at 7.0 T. Evaluation of BMEP was decreased (p < 0.05) at 7.0 T due to limited performance of IM-w FSE.
Gradient echo-based pulse sequences like SPGR and FIESTA are well suited for imaging at UHF which may improve early detection of cartilage lesions. However, UHF IM-w FSE sequences are less feasible for clinical use.
本研究的目的是优化三种用于7.0 T超高场（UHF）磁共振成像（MRI）膝关节活体成像的软骨专用序列，并比较7.0 T和3.0 T MRI下关于骨关节炎（OA）所致改变的成像性能和诊断置信度。
将3.0 T时优化的软骨成像MRI序列调整用于7.0 T：中等加权快速自旋回波（IM-w FSE）序列、采用稳态采集的快速成像（FIESTA）序列以及T1加权三维高空间分辨率容积脂肪抑制扰相梯度回波（SPGR）序列。对3名健康受试者和7名轻度OA患者进行了检查。测定了信噪比（SNR）、对比噪声比（CNR）、评估软骨异常的诊断置信度以及图像质量。采用全器官磁共振成像评分（WORMS）评估异常情况。还对局灶性软骨损伤和骨髓水肿模式（BMEP）进行了量化。
在7.0 T时，所有序列的SNR均升高（p < 0.05）。对于IM-w FSE序列，由于比吸收率（SAR）的限制，需要修改扫描参数，导致膝关节覆盖不完整、伪影广泛且脂肪饱和效果较差。SPGR和FIESTA序列的CNR和图像质量升高（p < 0.05），而IM-w FSE序列的则降低。在7.0 T时，FIESTA序列对软骨损伤的诊断置信度最高（p < 0.05）。由于IM-w FSE序列性能有限，7.0 T时BMEP的评估有所降低（p < 0.05）。
基于梯度回波的脉冲序列如SPGR和FIESTA非常适合超高场成像，这可能有助于早期发现软骨损伤。然而，超高场IM-w FSE序列在临床应用中不太可行。
