Abstract：
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/m2) 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 B1 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 mm3. Two experienced radiologists rated the image quality and the impact of B1 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 B1 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.
摘要：
超高场磁共振成像（MRI）（≥7T）具有提供出色的空间分辨率和独特的图像对比度的潜力。除了在这个场强下体内射频传输不均匀性之外，上腹部的成像面临着与运动引起的重影伪影相关的额外挑战。为了应对这些挑战，这项工作的目的是开发一种在7T下具有大视野的高分辨率自由呼吸上腹MRI技术.在七名健康志愿者（五名男性/两名女性，体重指数：19.6-24.8kg/m2），在7T下使用八通道收发阵列线圈。两名志愿者也在3T时接受了检查。在两个单独的采集中扫描了肝脏和肾脏区域.为了使信号激励均匀化，时间交错模式采集(TIAMO)方法与个性化的B1垫片对一起使用，基于23-s笛卡尔快速低角射击(FLASH)采集。利用自由感应衰减导航信号，以0.8×0.8×1.0mm3的空间分辨率重建呼吸门控图像。两位经验丰富的放射科医生对图像质量以及B1不均匀性和运动相关伪影在多点尺度上的影响进行了评估。所有志愿者的图像都显示出有效的水激发，并针对呼吸运动进行了准确的校正。B1不均匀性对图像质量的影响很小，强调多发射TIAMO垫片的功效。高空间分辨率可以很好地描绘小结构，如肾上腺，输尿管近端,隔膜，和小血管，尽管肝脏图像数据中仍然存在一些条纹伪影。在与两名志愿者进行的3T直接比较中，7-T采集显示信噪比分别增加了77%和58%。总的来说,这项工作证明了在7T磁场强度下以亚毫米空间分辨率在上腹部进行自由呼吸MRI的可行性。
