Malis Vadim, Vucevic Diana, Bae Won C, Yamamoto Asako, Kassai Yoshimori, Lane John, Hsiao Albert, Nakamura Katsumi, Miyazaki Mitsue
Department of Radiology, University of California San Diego, San Diego, CA, USA.
Department of Radiology, VA San Diego Healthcare System, San Diego, CA, USA.
Magn Reson Med Sci. 2024 Sep 5. doi: 10.2463/mrms.mp.2023-0158.
Fresh blood imaging (FBI) utilizes physiological blood signal differences between diastole and systole, causing a long acquisition time. The purpose of this study is to develop a fast FBI technique using a centric k - k k-space trajectory (cFBI) and an exponential refocusing flip angle (eFA) scheme with fast longitudinal restoration.
This study was performed on 8 healthy subjects and 2 patients (peripheral artery disease and vascular disease) with informed consent, using a clinical 3-Tesla MRI scanner. A numeric simulation using extended phase graph (EPG) and phantom studies of eFA were carried out to investigate the restoration of longitudinal signal by lowering refocusing flip angles in later echoes. cFBI was then acquired on healthy subjects at the popliteal artery station to assess the effect of varying high/low flip ratios on the longitudinal restoration effects. In addition, trigger-delays of cFBI were optimized owing to the long acquisition window in zigzag centric k - k k-space trajectory. After optimizations, cFBI images were compared against standard FBI (sFBI) images in terms of scan time, motion artifacts, Nyquist N/2 artifacts, blurring, and overall image quality. We also performed two-way repeated measures analysis of variance.
cFBI with eFA achieved nearly a 50% scan time reduction compared to sFBI. The high/low flip angle of 180/2 degrees with lower refocusing pulses shows fast longitudinal restoration with the highest blood signals, yet also more sensitive to the background signals. Overall, 180/30 degrees images show reasonable blood signal recovery while minimizing the background signal artifacts. After the trigger delay optimization, maximum intensity projection image of cFBI after systole-diastole subtraction demonstrates less motion and N/2 artifacts than that of sFBI.
Together with eFA for fast longitudinal signal restoration, the proposed cFBI technique achieved a 2-fold reduction in scan time and improved image quality without major artifacts.
新鲜血液成像（FBI）利用舒张期和收缩期之间的生理血液信号差异，导致采集时间较长。本研究的目的是开发一种快速FBI技术，使用中心k - k k空间轨迹（cFBI）和具有快速纵向恢复的指数重聚焦翻转角（eFA）方案。
本研究在8名健康受试者和2名患者（外周动脉疾病和血管疾病）身上进行，所有受试者均签署了知情同意书，使用临床3特斯拉MRI扫描仪。进行了使用扩展相位图（EPG）的数值模拟和eFA的体模研究，以研究通过降低后续回波中的重聚焦翻转角来恢复纵向信号。然后在健康受试者的腘动脉部位采集cFBI，以评估不同高/低翻转比在纵向恢复效果上的影响。此外，由于锯齿形中心k - k k空间轨迹中的采集窗口较长，对cFBI的触发延迟进行了优化。优化后，将cFBI图像与标准FBI（sFBI）图像在扫描时间、运动伪影、奈奎斯特N/2伪影、模糊和整体图像质量方面进行比较。我们还进行了双向重复测量方差分析。
与sFBI相比，采用eFA的cFBI扫描时间减少了近50%。具有较低重聚焦脉冲的180/2度高/低翻转角显示出快速的纵向恢复，血液信号最高，但对背景信号也更敏感。总体而言，180/30度图像显示出合理的血液信号恢复，同时将背景信号伪影降至最低。在触发延迟优化后，收缩期 - 舒张期相减后的cFBI最大强度投影图像显示出比sFBI更少的运动和N/2伪影。
结合用于快速纵向信号恢复的eFA，所提出的cFBI技术在扫描时间上减少了两倍，并且在没有重大伪影的情况下提高了图像质量。
