Lindley Marc D, Kim Daniel, Morrell Glen, Heilbrun Marta E, Storey Pippa, Hanrahan Christopher J, Lee Vivian S
From the *Department of Physics, and †Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT; and ‡Center for Biomedical Imaging, New York University School of Medicine, New York, NY.
Invest Radiol. 2015 Feb;50(2):101-7. doi: 10.1097/RLI.0000000000000106.
Fresh blood imaging (FBI) is a useful noncontrast magnetic resonance angiographic (MRA) method for the assessment of peripheral arterial disease, particularly for imaging patients with poor renal function. Compared with 1.5 T, 3 T enables higher signal-to-noise ratio and/or spatiotemporal resolution in FBI. Indeed, previous studies have reported successful FBI of the calf station at 3 T. However, FBI of the thigh station at 3 T has been reported to suffer from signal void in the common femoral artery of 1 thigh only because of the radial symmetry in transmit radiofrequency field (B1+) variation. We sought to increase the signal of femoral artery in FBI at 3 T using high-permittivity dielectric padding.
We performed FBI and B1+ mapping of the thigh station at 3 T in 13 human subjects to compare the following 3 dielectric padding settings: no padding, commercially available thick (approximately 5 cm) dielectric padding, and high-permittivity thin (approximately 2 cm) dielectric padding. We characterized the radial symmetry in B1+ variation as well as its impact on the FBI signal at baseline and how dielectric padding improves B1+ and FBI. We evaluated the quality of 3 FBI MRA acquisitions using quantitative (ie, contrast-to-noise ratio of femoral arteries) and qualitative (ie, conspicuity of femoral arteries) analyses.
With the subjects positioned on the magnetic resonance table in feet-first, supine orientation, the radial symmetry in B1+ variation attenuates the signal in the right common femoral artery. The signal void can be improved partially with commercial padding and improved further with high-permittivity padding. Averaging the results over the 13 subjects, the mean B1+, contrast-to-noise ratio, and conspicuity scores for the right common femoral artery were significantly higher with high-permittivity padding than with commercial padding and baseline (P < 0.001).
Our study shows that high-permittivity dielectric padding can be used to increase the signal of femoral artery in FBI at 3 T.
新鲜血液成像（FBI）是一种用于评估外周动脉疾病的有用的非对比磁共振血管造影（MRA）方法，尤其适用于对肾功能不佳的患者进行成像。与1.5T相比，3T在FBI中能够实现更高的信噪比和/或时空分辨率。事实上，先前的研究已报道在3T下成功进行了小腿部位的FBI。然而，据报道，3T下大腿部位的FBI仅在一侧大腿的股总动脉中出现信号缺失，这是由于发射射频场（B1 +）变化的径向对称性所致。我们试图使用高介电常数介电垫来增加3T下FBI中股动脉的信号。
我们对13名人类受试者进行了3T下大腿部位的FBI和B1 +映射，以比较以下3种介电垫设置：无垫、市售厚（约5cm）介电垫和高介电常数薄（约2cm）介电垫。我们在基线时表征了B1 +变化的径向对称性及其对FBI信号的影响，以及介电垫如何改善B1 +和FBI。我们使用定量（即股动脉的对比噪声比）和定性（即股动脉的显见度）分析评估了3次FBI MRA采集的质量。
当受试者以脚先入、仰卧的姿势位于磁共振检查台上时，B1 +变化的径向对称性会减弱右侧股总动脉中的信号。使用市售垫可部分改善信号缺失，而使用高介电常数垫可进一步改善。对13名受试者的结果进行平均后，高介电常数垫组右侧股总动脉的平均B1 +、对比噪声比和显见度评分显著高于市售垫组和基线组（P < 0.001）。
我们的研究表明，高介电常数介电垫可用于增加3T下FBI中股动脉的信号。
