Cashen T A, Carr J C, Shin W, Walker M T, Futterer S F, Shaibani A, McCarthy R M, Carroll T J
Department of Biomedical Engineering, Northwestern University, Feinberg School of Medicine of Northwestern University, Chicago, IL, USA.
AJNR Am J Neuroradiol. 2006 Apr;27(4):822-9.
A method is presented for high-temporal-resolution MR angiography (MRA) using a combination of undersampling strategies and a high-field (3T) scanner. Currently, the evaluation of cerebrovascular disorders involving arteriovenous shunting or retrograde flow is accomplished with conventional radiographic digital subtraction angiography, because of its high spatial and temporal resolutions. Multiphase MRA could potentially provide the same diagnostic information noninvasively, though this is technically challenging because of the inherent trade-off between signal intensity-to-noise ratio (S/N), spatial resolution, and temporal resolution in MR imaging.
Numerical simulations addressed the choice of imaging parameters at 3T to maximize S/N and the data acquisition rate while staying within specific absorption rate limits. The increase in S/N at 3T was verified in vivo. An imaging protocol was developed with S/N, spatial resolution, and temporal resolution suitable for intracranial angiography. Partial Fourier imaging, parallel imaging, and the time-resolved echo-shared acquisition technique (TREAT) were all used to achieve sufficient undersampling.
In 40 volunteers and 10 patients exhibiting arteriovenous malformations or fistulas, intracranial time-resolved contrast-enhanced MRA with high acceleration at high field produced diagnostic-quality images suitable for assessment of pathologies involving arteriovenous shunting or retrograde flow. The technique provided spatial resolution of 1.1 x 1.1 x 2.5 mm and temporal resolution of 2.5 seconds/frame. The combination of several acceleration methods, each with modest acceleration, can provide a high overall acceleration without the artifacts of any one technique becoming too pronounced.
By taking advantage of the increased S/N provided by 3T magnets over conventional 1.5T magnets and converting this additional S/N into higher temporal resolution through acceleration strategies, intracranial time-resolved MRA becomes feasible.
本文介绍了一种使用欠采样策略和高场（3T）扫描仪相结合的高时间分辨率磁共振血管造影（MRA）方法。目前，由于传统放射数字减影血管造影具有高空间和时间分辨率，因此对涉及动静脉分流或逆流的脑血管疾病的评估是通过传统放射数字减影血管造影来完成的。多期MRA有可能无创地提供相同的诊断信息，尽管这在技术上具有挑战性，因为在磁共振成像中，信号强度与噪声比（S/N）、空间分辨率和时间分辨率之间存在固有的权衡。
数值模拟解决了在3T时成像参数的选择问题，以在保持特定吸收率限制的同时最大化S/N和数据采集率。在体内验证了3T时S/N的增加。开发了一种适用于颅内血管造影的具有S/N、空间分辨率和时间分辨率的成像方案。部分傅里叶成像、并行成像和时间分辨回波共享采集技术（TREAT）都用于实现足够的欠采样。
在40名志愿者和10名患有动静脉畸形或瘘管的患者中，高场下具有高加速的颅内时间分辨对比增强MRA产生了适用于评估涉及动静脉分流或逆流的病变的诊断质量图像。该技术提供了1.1×1.1×2.5mm的空间分辨率和2.5秒/帧的时间分辨率。几种加速方法的组合，每种方法都有适度的加速，可以提供高总体加速，而不会使任何一种技术的伪影变得过于明显。
通过利用3T磁体比传统1.5T磁体提供的更高S/N，并通过加速策略将这种额外的S/N转换为更高的时间分辨率，颅内时间分辨MRA变得可行。
