Attenberger Ulrike I, Rathmann Nils, Sertdemir Metin, Riffel Philipp, Weidner Anja, Kannengiesser Stefan, Morelli John N, Schoenberg Stefan O, Hausmann Daniel
Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, University of Heidelberg, Germany.
MR Applications Development, Siemens Healthcare, Erlangen, Germany.
Z Med Phys. 2016 Jun;26(2):168-76. doi: 10.1016/j.zemedi.2015.06.013. Epub 2015 Aug 20.
Spatially-tailored (RF) excitation pulses in echo-planar imaging (EPI), combined with a decreased FOV in the phase-encoding direction, enable a reduction of k-space acquisition lines, which shortens the echo train length (ETL) and reduces susceptibility artifacts. The purpose of this study was to evaluate the image quality of a zoomed EPI (z-EPI) sequence in diffusion-weighted imaging (DWI) of the prostate in comparison to a conventional single-shot EPI using single-channel (c-EPI1) and multi-channel (c-EPI2) RF excitation, with and without use of an endorectal coil.
33 consecutive patients (mean age: 61 +/- 9 years; mean PSA: 8.67±6.23 ng/ml) with examinations between 10/2012 and 02/2014 were analyzed in this retrospective study. In 26 of 33 patients the initial multiparametric (mp)-MRI was performed on a whole-body 3T scanner (Magnetom Trio, Siemens, Erlangen, Germany) using an endorectal coil (c (conventional)-EPI1). Zoomed-EPI (Z-EPI) examinations of these patients and a complete mp-MRI protocol including c-EPI2 of 7 additional patients were carried out on another 3T wb MR scanner with two-channel dynamic parallel transmit capability (Magnetom Skyra with TimTX TrueShape, Siemens). For z-EPI, the one-dimensional spatially selective RF excitation pulse was replaced by a two-dimensional RF pulse. Degree of image blur and susceptibility artifacts (0=not present to 3= non-diagnostic), maximum image distortion (mm), apparent diffusion coefficient (ADC) values, as well as overall scan preference were evaluated. SNR maps were generated to compare c-EPI2 and z-EPI.
Overall image quality of z-EPI was preferred by both readers in all examinations with a single exception. Susceptibility artifacts were rated significantly lower on z-EPI compared to both other methods (z-EPI vs c-EPI1: p<0.01; z-EPI vs c-EPI2: p<0.01) as well as image blur (z-EPI vs c-EPI1: p<0.01; z-EPI vs c-EPI2: p<0.01). Image distortion was not statistically significantly reduced with z-EPI (z-EPI vs c-EPI1: p=0.12; z-EPI vs c-EPI2: p=0.42). Interobserver agreement for ratings of susceptibility artifacts, image blur and overall scan preference was good. SNR was higher for z-EPI than for c-EPI1 (n=1).
Z-EPI leads to significant improvements in image quality and artifacts as well as image blur reduction improving prostate DWI and enabling accurate fusion with conventional sequences. The improved fusion could lead to advantages in the field of MRI-guided biopsy suspicous lesions and performance of locally ablative procedures for prostate cancer.
在回波平面成像（EPI）中，空间定制的（射频）激发脉冲与相位编码方向上减小的视野相结合，能够减少k空间采集线，从而缩短回波链长度（ETL）并减少磁化率伪影。本研究的目的是评估在前列腺扩散加权成像（DWI）中，与使用单通道（c-EPI1）和多通道（c-EPI2）射频激发的传统单次激发EPI相比，缩放EPI（z-EPI）序列的图像质量，以及是否使用直肠内线圈的情况。
本回顾性研究分析了2012年10月至2014年2月期间连续接受检查的33例患者（平均年龄：61±9岁；平均前列腺特异抗原：8.67±6.23 ng/ml）。在33例患者中的26例中，最初的多参数（mp）MRI是在全身3T扫描仪（Magnetom Trio，西门子，埃尔朗根，德国）上使用直肠内线圈进行的（c（传统）-EPI1）。这些患者的缩放EPI（Z-EPI）检查以及另外7例患者的包括c-EPI2的完整mp-MRI方案，是在另一台具有双通道动态并行发射能力的3T全身MR扫描仪（配备TimTX TrueShape的Magnetom Skyra，西门子）上进行的。对于z-EPI，一维空间选择性射频激发脉冲被二维射频脉冲取代。评估了图像模糊程度和磁化率伪影（0=不存在至3=无法诊断）、最大图像失真（mm）、表观扩散系数（ADC）值以及总体扫描偏好。生成信噪比（SNR）图以比较c-EPI2和z-EPI。
除了一个例外，在所有检查中两位阅片者都更倾向于z-EPI的整体图像质量。与其他两种方法相比，z-EPI上的磁化率伪影评分显著更低（z-EPI与c-EPI1比较：p<0.01；z-EPI与c-EPI2比较：p<0.01），图像模糊程度也是如此（z-EPI与c-EPI1比较：p<0.01；z-EPI与c-EPI2比较：p<0.01）。z-EPI并未使图像失真在统计学上显著降低（z-EPI与c-EPI1比较：p=0.12；z-EPI与c-EPI2比较：p=0.42）。观察者间对磁化率伪影、图像模糊和总体扫描偏好评分的一致性良好。z-EPI的SNR高于c-EPI1（n=1）。
Z-EPI可显著改善图像质量和伪影，并减少图像模糊，从而改善前列腺DWI，并能与传统序列进行准确融合。这种改进的融合可能在MRI引导的活检可疑病变以及前列腺癌局部消融手术领域带来优势。
