From the Department of Radiology, Boston Children's Hospital, Boston, MA (R. Nosrati, F.C., O.A., K.P., R. Nichols, P.C., M.A.B., A.T., S.B., S.K.W.); and Harvard Medical School, Boston, MA (R. Nosrati, F.C., O.A., K.P., R. Nichols, P.C., M.A.B., A.T., S.B., S.K.W.).
Invest Radiol. 2024 Dec 1;59(12):805-812. doi: 10.1097/RLI.0000000000001092. Epub 2024 Jun 10.
The T1-weighted GRE (gradient recalled echo) sequence with the Dixon technique for water/fat separation is an essential component of abdominal MRI (magnetic resonance imaging), useful in detecting tumors and characterizing hemorrhage/fat content. Unfortunately, the current implementation of this sequence suffers from several problems: (1) low resolution to maintain high pixel bandwidth and minimize chemical shift; (2) image blurring due to respiratory motion; (3) water/fat swapping due to the natural ambiguity between fat and water peaks; and (4) off-resonance fat blurring due to the multipeak nature of the fat spectrum. The goal of this study was to evaluate the image quality of water/fat separation using a high-resolution 3-point Dixon golden angle radial acquisition with retrospective motion compensation and multipeak fat modeling in children undergoing abdominal MRI.
Twenty-two pediatric patients (4.2 ± 2.3 years) underwent abdominal MRI on a 3 T scanner with routine abdominal protocol and with a 3-point Dixon radial-VIBE (volumetric interpolated breath-hold examination) sequence. Field maps were calculated using 3D graph-cut optimization followed by fat and water calculation from k-space data by iteratively solving an optimization problem. A 6-peak fat model was used to model chemical shifts in k-space. Residual respiratory motion was corrected through soft-gating by weighting each projection based on the estimated respiratory motion from the center of the k-space. Reconstructed images were reviewed by 3 pediatric radiologists on a PACS (picture archiving and communication systems) workstation. Subjective image quality and water/fat swapping artifact were scored by each pediatric radiologist using a 5-point Likert scale. The VoL (variance of Laplacian) of the reconstructed images was used to objectively quantify image sharpness.
Based on the overall Likert scores, the images generated using the described method were significantly superior to those reconstructed by the conventional 2-point Dixon technique ( P < 0.05). Water/fat swapping artifact was observed in 14 of 22 patients using 2-point Dixon, and this artifact was not present when using the proposed method. Image sharpness was significantly improved using the proposed framework.
In smaller patients, a high-quality water/fat separation with sharp visualization of fine details is critical for diagnostic accuracy. High-resolution golden angle radial-VIBE 3-point Dixon acquisition with 6-peak fat model and soft-gated motion correction offers improved image quality at the expense of an additional ~1-minute acquisition time. Thus, this technique offers the potential to replace the conventional 2-point Dixon technique.
用于水/脂分离的 T1 加权 GRE（梯度回波）序列与 Dixon 技术是腹部 MRI（磁共振成像）的重要组成部分，可用于检测肿瘤并对出血/脂肪含量进行特征描述。不幸的是，目前该序列的实现存在几个问题：（1）为了保持高像素带宽和最小化学位移，分辨率较低；（2）由于呼吸运动导致图像模糊；（3）由于脂肪峰和水峰之间的自然歧义，导致水/脂交换；（4）由于脂肪谱的多峰性质，导致离共振脂肪模糊。本研究的目的是评估在儿童腹部 MRI 中使用高分辨率 3 点 Dixon 黄金角度径向采集、回顾性运动补偿和多峰脂肪建模进行水/脂分离的图像质量。
22 例儿科患者（4.2±2.3 岁）在 3T 扫描仪上进行腹部 MRI 检查，使用常规腹部方案和 3 点 Dixon 径向-VIBE（容积内插屏气检查）序列。通过 3D 图割优化计算场图，然后通过迭代求解优化问题从 k 空间数据中计算脂肪和水。使用 6 峰脂肪模型对 k 空间中的化学位移进行建模。通过基于 k 空间中心估计的呼吸运动对每个投影进行加权，通过软门控校正残留呼吸运动。在 PACS（图像存档和通信系统）工作站上，由 3 名儿科放射科医生对重建图像进行评估。每位儿科放射科医生使用 5 分李克特量表对主观图像质量和水/脂交换伪影进行评分。使用重建图像的拉普拉斯方差（VoL）客观量化图像锐度。
根据总体李克特评分，与常规 2 点 Dixon 技术重建的图像相比，使用所描述方法生成的图像明显更好（P＜0.05）。在 22 例患者中，有 14 例使用 2 点 Dixon 技术观察到水/脂交换伪影，而使用提出的方法则不存在该伪影。使用提出的框架，图像锐度得到显著改善。
在较小的患者中，具有精细细节锐利可视化的高质量水/脂分离对于诊断准确性至关重要。高分辨率黄金角度径向-VIBE 3 点 Dixon 采集、6 峰脂肪模型和软门控运动校正可提高图像质量，但需要额外约 1 分钟的采集时间。因此，该技术有可能取代常规的 2 点 Dixon 技术。
