Department of Medical Imaging, Radboud University Medical Center, Nijmegen, the Netherlands.
Erwin L Hahn Institute for MR Imaging, Essen, Germany.
NMR Biomed. 2024 Oct;37(10):e5180. doi: 10.1002/nbm.5180. Epub 2024 May 22.
Ultrahigh field magnetic resonance imaging (MRI) (≥ 7 T) has the potential to provide superior spatial resolution and unique image contrast. Apart from radiofrequency transmit inhomogeneities in the body at this field strength, imaging of the upper abdomen faces additional challenges associated with motion-induced ghosting artifacts. To address these challenges, the goal of this work was to develop a technique for high-resolution free-breathing upper abdominal MRI at 7 T with a large field of view. Free-breathing 3D gradient-recalled echo (GRE) water-excited radial stack-of-stars data were acquired in seven healthy volunteers (five males/two females, body mass index: 19.6-24.8 kg/m) at 7 T using an eight-channel transceive array coil. Two volunteers were also examined at 3 T. In each volunteer, the liver and kidney regions were scanned in two separate acquisitions. To homogenize signal excitation, the time-interleaved acquisition of modes (TIAMO) method was used with personalized pairs of B shims, based on a 23-s Cartesian fast low angle shot (FLASH) acquisition. Utilizing free-induction decay navigator signals, respiratory-gated images were reconstructed at a spatial resolution of 0.8 × 0.8 × 1.0 mm. Two experienced radiologists rated the image quality and the impact of B inhomogeneity and motion-related artifacts on multipoint scales. The images of all volunteers showcased effective water excitation and were accurately corrected for respiratory motion. The impact of B inhomogeneity on image quality was minimal, underscoring the efficacy of the multitransmit TIAMO shim. The high spatial resolution allowed excellent depiction of small structures such as the adrenal glands, the proximal ureter, the diaphragm, and small blood vessels, although some streaking artifacts persisted in liver image data. In direct comparisons with 3 T performed for two volunteers, 7-T acquisitions demonstrated increases in signal-to-noise ratio of 77% and 58%. Overall, this work demonstrates the feasibility of free-breathing MRI in the upper abdomen at submillimeter spatial resolution at a magnetic field strength of 7 T.
超高场磁共振成像（MRI）（≥7T）具有提供更高空间分辨率和独特图像对比度的潜力。除了在该场强下身体内的射频发射不均匀性外，上腹部成像还面临与运动引起的鬼影伪影相关的其他挑战。为了应对这些挑战，本工作的目标是开发一种在 7T 下用于大视野高分辨率自由呼吸上腹部 MRI 的技术。在 7T 下，使用 8 通道收发阵列线圈，对 7 名健康志愿者（5 名男性/2 名女性，体重指数：19.6-24.8kg/m）进行了自由呼吸 3D 梯度回波（GRE）水激发径向堆叠星状数据采集。其中两名志愿者也在 3T 下进行了检查。在每个志愿者中，肝脏和肾脏区域分别在两次采集过程中进行扫描。为了均匀信号激发，使用基于 23s 笛卡尔快速低角度 shot（FLASH）采集的个性化 B 匀场对模式的时间交错采集（TIAMO）方法进行采集。利用自由感应衰减导航信号，在 0.8×0.8×1.0mm 的空间分辨率下重建呼吸门控图像。两名有经验的放射科医生对图像质量以及 B 不均匀性和运动相关伪影对多点的影响进行了评分。所有志愿者的图像均显示出有效的水激发效果，并且可以准确校正呼吸运动。B 不均匀性对图像质量的影响很小，突出了多发射 TIAMO 匀场的有效性。高空间分辨率可以极好地描绘出小结构，如肾上腺、近端输尿管、横膈膜和小血管，尽管在肝脏图像数据中仍存在一些条纹伪影。与两名志愿者的 3T 直接比较显示，7T 采集的信号噪声比提高了 77%和 58%。总的来说，本工作证明了在 7T 场强下以亚毫米空间分辨率进行自由呼吸上腹部 MRI 的可行性。
