Radiology and Imaging Sciences and Molecular Biomedical Imaging Laboratory, National Institute of Biomedical Imaging and Bioengineering, Bethesda, MD, USA.
J Cardiovasc Magn Reson. 2012 May 1;14(1):27. doi: 10.1186/1532-429X-14-27.
Myocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in the presence of myocardial fibrosis. The purpose of this study was to evaluate acquisition factors that may result in variation of measured T1 time and ECV including magnetic field strength, cardiac phase and myocardial region.
31 study subjects were enrolled and underwent one cardiovascular MR exam at 1.5 T and two exams at 3 T, each on separate days. A Modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired before and 5, 10, 12, 20, 25 and 30 min after administration of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist) at 1.5 T (exam 1). For exam 2, MOLLI sequences were acquired at 3 T both during diastole and systole, before and after administration of Gd-DTPA (0.15 mmol/kg Magnevist).Exam 3 was identical to exam 2 except gadobenate dimeglumine was administered (Gd-BOPTA; 0.1 mmol/kg Multihance). T1 times were measured in myocardium and blood. ECV was calculated by (ΔR1myocardium/ΔR1blood)*(1-hematocrit).
Before gadolinium, T1 times of myocardium and blood were significantly greater at 3 T versus 1.5 T (28% and 31% greater, respectively, p < 0.001); after gadolinium, 3 T values remained greater than those at 1.5 T (14% and 12% greater for myocardium and blood at 3 T with Gd-DTPA, respectively, p < 0.0001 and 18% and 15% greater at 3 T with Gd-BOPTA, respectively, p < 0.0001). However, ECV did not vary significantly with field strength when using the same contrast agent at equimolar dose (p = 0.2). Myocardial T1 time was 1% shorter at systole compared to diastole pre-contrast and 2% shorter at diastole compared to systole post-contrast (p < 0.01). ECV values were greater during diastole compared to systole on average by 0.01 (p < 0.01 to p < 0.0001). ECV was significantly higher for the septum compared to the non-septal myocardium for all three exams (p < 0.0001-0.01) with mean absolute differences of 0.01, 0.004, and 0.07, respectively, for exams 1, 2 and 3.
ECV is similar at field strengths of 1.5 T and 3 T. Due to minor variations in T1 time and ECV during the cardiac cycle and in different myocardial regions, T1 measurements should be obtained at the same cardiac phase and myocardial region in order to obtain consistent results.
心肌 T1 弛豫时间（T1 时间）和细胞外容积分数（ECV）在心肌纤维化存在时会发生改变。本研究的目的是评估可能导致测量的 T1 时间和 ECV 发生变化的采集因素，包括磁场强度、心脏相位和心肌区域。
31 名研究对象入组，在 1.5T 进行一次心血管磁共振检查，在 3T 进行两次检查，两次检查分别在不同的日子进行。在 1.5T 时（检查 1），在给予 0.15mmol/kg 钆喷替酸二甲葡胺（Gd-DTPA；Magnevist）前和给药后 5、10、12、20、25 和 30min 时采集改良 Look-Locker 反转恢复（MOLLI）序列。对于检查 2，在 3T 时分别在舒张期和收缩期采集 MOLLI 序列，在给予 Gd-DTPA（0.15mmol/kg Magnevist）前后进行。检查 3 与检查 2 相同，只是给予钆贝葡胺（Gd-BOPTA；0.1mmol/kg Multihance）。在心肌和血液中测量 T1 时间。ECV 通过（ΔR1myocardium/ΔR1blood）*（1-红细胞压积）计算。
在给予钆之前，心肌和血液的 T1 时间在 3T 时明显大于 1.5T（分别增加 28%和 31%，p<0.001）；在给予钆之后，3T 值仍然大于 1.5T 值（分别增加 14%和 12%，心肌和血液中的 Gd-DTPA 在 3T 时，p<0.0001；分别增加 18%和 15%，心肌和血液中的 Gd-BOPTA 在 3T 时，p<0.0001）。然而，当使用相同的对比剂以等摩尔剂量时，ECV 与场强无显著差异（p=0.2）。心肌 T1 时间在对比前收缩期比舒张期短 1%，在对比后舒张期比收缩期短 2%（p<0.01）。ECV 值在舒张期平均比收缩期高 0.01（p<0.01 至 p<0.0001）。在所有三个检查中，ECV 值在间隔部比非间隔部心肌高，分别为 0.01、0.004 和 0.07，差异有统计学意义（p<0.0001-0.01）。
ECV 在 1.5T 和 3T 的场强下相似。由于 T1 时间和 ECV 在心脏周期和不同心肌区域中的细微变化，为了获得一致的结果，T1 测量应在相同的心脏相位和心肌区域进行。
