Bernstein M A, Huston J, Lin C, Gibbs G F, Felmlee J P
Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Magn Reson Med. 2001 Nov;46(5):955-62. doi: 10.1002/mrm.1282.
Initial experience with intracranial and cervical MRA at 3.0T is reported. Phantom measurements (corrected for relaxation effects) show S/N (3.0T) = 2.14 +/- 0.08 x S/N (1.5T) in identical-geometry head coils. A 3.0T 3DTOF intracranial imaging protocol with higher-order autoshimming was developed and compared to 1.5T 3DTOF in 12 patients with aneurysms. A comparison by two radiologists showed the 3.0T to be significantly better (P < 0.001) for visualization of the aneurysms. The feasibility of cervical and intracranial contrast enhanced MR angiography (CEMRA) at 3.0T is also examined. The relaxivity of the gadolinium contrast agent decreases by only about 4-7% when the field strength is increased from 1.5 to 3.0T. Cervical 3.0T CEMRA was obtained in eight patients, two of whom had 1.5T studies available for direct comparison. Image comparison suggests 3.0T to be a favorable field strength for cervical CEMRA. Voxel volumes of 0.62-0.73 mm(3) (not including zero-filling) were readily achieved at 3.0T with the use of a single-channel transmit-receive head or cervical coil, a 25 mL bolus of gadoteridol, and a 3D pulse sequence with a 66% sampling efficiency. This spatial resolution allowed visualization of intracranial aneurysms, carotid dissections, and atherosclerotic disease including ulcerations. Potential drawbacks of 3.0T MRA are increased SAR and T()(2) dephasing compared to 1.5T. Image comparison suggests signal loss due to T()(2) dephasing will not be substantially more problematic than at 1.5T. The dependence of RF power deposition on TR for CEMRA is calculated and discussed.
本文报道了3.0T场强下颅内和颈部MRA的初步经验。模体测量（校正了弛豫效应）显示，在相同几何形状的头部线圈中，S/N（3.0T）= 2.14±0.08×S/N（1.5T）。开发了一种采用高阶自动匀场的3.0T 3DTOF颅内成像方案，并与12例动脉瘤患者的1.5T 3DTOF进行比较。两位放射科医生的比较结果显示，3.0T在动脉瘤可视化方面明显更好（P < 0.001）。还研究了3.0T场强下颈部和颅内对比增强磁共振血管造影（CEMRA）的可行性。当场强从1.5T增加到3.0T时，钆对比剂的弛豫率仅降低约4 - 7%。对8例患者进行了颈部3.0T CEMRA检查，其中2例有1.5T的研究结果可供直接比较。图像比较表明，3.0T是颈部CEMRA的有利场强。在3.0T场强下，使用单通道发射 - 接收头部或颈部线圈、25 mL钆特醇团注以及采样效率为66%的3D脉冲序列，很容易实现0.62 - 0.73 mm³的体素体积（不包括零填充）。这种空间分辨率能够显示颅内动脉瘤、颈动脉夹层以及包括溃疡在内的动脉粥样硬化疾病。与1.5T相比，3.0T MRA的潜在缺点是比吸收率（SAR）增加和T₂失相。图像比较表明，T₂失相导致的信号丢失不会比1.5T时更严重。计算并讨论了CEMRA中射频功率沉积对重复时间（TR）的依赖性。
