Pai Alex, Li Xiaojuan, Majumdar Sharmila
Department of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94720, USA.
Magn Reson Imaging. 2008 Nov;26(9):1215-20. doi: 10.1016/j.mri.2008.02.017. Epub 2008 May 23.
T2 mapping has been used widely in detecting cartilage degeneration in osteoarthritis. Several scanning sequences have been developed in the determination of T2 relaxation times of tissues. However, the derivation of these times may vary from sequence to sequence. This study seeks to evaluate the sequence-dependent differences in T2 quantitation of cartilage, muscle, fat and bone marrow in the knee joint at 3 T.
Three commercial phantoms and 10 healthy volunteers were studied using 3 T MR. T2 relaxation times of the phantoms, cartilage, muscle, subcutaneous fat and marrow were derived using spin echo (SE), multiecho SE (MESE), fast SE (FSE) with varying echo train length (ETL), spiral and spoiler gradient (SPGR) sequences. The differences between these times were then evaluated using Student's t test. In addition, the signal-to-noise ratio (SNR) efficiency and coefficient of variation of T2 from each sequence were calculated.
The average T2 relaxation time was 36.38+/-5.76 ms in cartilage and 34.08+/-6.55 ms in muscle, ranging from 27 to 45 ms in both tissues. The times for subcutaneous fat and marrow were longer and more varying, ranging from 41 to 143 ms and from 42 to 160 ms, respectively. In FSE acquisition, relaxation time significantly increases as ETL increases (P<.05). In cartilage, the SE acquisition yields the lowest T2 values (27.52+/-3.10 ms), which is significantly lower than those obtained from other sequences (P<.002). T2 values obtained from spiral acquisition (38.27+/-6.45 ms) were higher than those obtained from MESE (34.35+/-5.62 ms) and SPGR acquisition (31.64+/-4.53 ms). These differences, however, were not significant (P>.05).
T2 quantification can be a valuable tool for the diagnosis of degenerative disease. Several different sequences exist to quantify the relaxation times of tissues. Sequences range in scan time, SNR efficiency, reproducibility and two- or three-dimensional mapping. However, when choosing a sequence for quantitation, it is important to realize that several factors affect the measured T2 relaxation time.
T2 映射已广泛用于检测骨关节炎中的软骨退变。在确定组织的 T2 弛豫时间方面已开发了几种扫描序列。然而，这些时间的推导可能因序列而异。本研究旨在评估 3T 时膝关节软骨、肌肉、脂肪和骨髓 T2 定量中序列依赖性差异。
使用 3T MR 对三个商用体模和 10 名健康志愿者进行研究。使用自旋回波（SE）、多回波 SE（MESE）、具有不同回波链长度（ETL）的快速 SE（FSE）、螺旋和扰相梯度（SPGR）序列推导体模、软骨、肌肉、皮下脂肪和骨髓的 T2 弛豫时间。然后使用学生 t 检验评估这些时间之间的差异。此外，计算每个序列的 T2 的信噪比（SNR）效率和变异系数。
软骨的平均 T2 弛豫时间为 36.38±5.76 ms，肌肉为 34.08±6.55 ms，两种组织的范围均为 27 至 45 ms。皮下脂肪和骨髓的时间更长且变化更大，分别为 41 至 143 ms 和 42 至 160 ms。在 FSE 采集时，弛豫时间随着 ETL 的增加而显著增加（P<.05）。在软骨中，SE 采集产生的 T2 值最低（27.52±3.10 ms），显著低于从其他序列获得的值（P<.002）。从螺旋采集获得的 T2 值（38.27±6.45 ms）高于从 MESE 获得的值（34.35±5.62 ms）和 SPGR 采集获得的值（31.64±4.53 ms）。然而，这些差异不显著（P>.05）。
T2 定量可以成为诊断退行性疾病的有价值工具。存在几种不同的序列来定量组织的弛豫时间。序列在扫描时间、SNR 效率、可重复性以及二维或三维映射方面有所不同。然而，在选择用于定量的序列时，重要的是要认识到有几个因素会影响测量的 T2 弛豫时间。
