Restivo Matthew C, Ramasawmy Rajiv, Bandettini W Patricia, Herzka Daniel A, Campbell-Washburn Adrienne E
Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland.
Magn Reson Med. 2020 Nov;84(5):2364-2375. doi: 10.1002/mrm.28278. Epub 2020 Apr 14.
Low-field MRI offers favorable physical properties for SNR-efficient long readout acquisitions such as spiral and EPI. We used a 0.55 tesla (T) MRI system equipped with high-performance hardware to increase the sampling duty cycle and extend the TR of balanced steady-state free precession (bSSFP) cardiac cine acquisitions, which typically are limited by banding artifacts.
We developed a high-efficiency spiral in-out bSSFP acquisition, with zeroth- and first-gradient moment nulling, and an EPI bSSFP acquisition for cardiac cine imaging using a contemporary MRI system modified to operate at 0.55T. Spiral in-out and EPI bSSFP cine protocols, with TR = 8 ms, were designed to maintain both spatiotemporal resolution and breath-hold length. Simulations, phantom imaging, and healthy volunteer imaging studies (n = 12) were performed to assess SNR and image quality using these high sampling duty-cycle bSSFP sequences.
Spiral in-out bSSFP performed favorably at 0.55T and generated good image quality, whereas EPI bSSFP suffered motion and flow artifacts. There was no difference in ejection fraction comparing spiral in-out with standard Cartesian imaging. Moreover, human images demonstrated a 79% ± 21% increase in myocardial SNR using spiral in-out bSSFP and 50% ± 14% increase in SNR using EPI bSSFP as compared with the reference Cartesian acquisition. Spiral in-out acquisitions at 0.55T recovered 69% ± 14% of the myocardial SNR at 1.5T.
Efficient bSSFP spiral in-out provided high-quality cardiac cine imaging and SNR recovery on a high-performance 0.55T MRI system.
低场磁共振成像（MRI）为诸如螺旋和回波平面成像（EPI）等高信噪比效率的长读出采集提供了良好的物理特性。我们使用了一台配备高性能硬件的0.55特斯拉（T）MRI系统，以提高采样占空比，并延长平衡稳态自由进动（bSSFP）心脏电影采集的重复时间（TR），这种采集通常受带状伪影限制。
我们开发了一种具有零阶和一阶梯度矩归零的高效螺旋进出bSSFP采集方法，以及一种用于心脏电影成像的EPI bSSFP采集方法，使用的是一台经过改装可在0.55T运行的当代MRI系统。设计了TR = 8毫秒的螺旋进出和EPI bSSFP电影成像协议，以保持时空分辨率和屏气时长。进行了模拟、体模成像和健康志愿者成像研究（n = 12），以使用这些高采样占空比的bSSFP序列评估信噪比和图像质量。
螺旋进出bSSFP在0.55T时表现良好，产生了良好的图像质量，而EPI bSSFP则出现了运动和流动伪影。与标准笛卡尔成像相比，螺旋进出成像在射血分数方面没有差异。此外，人体图像显示，与参考笛卡尔采集相比，使用螺旋进出bSSFP时心肌信噪比提高了79%±21%，使用EPI bSSFP时信噪比提高了50%±14%。0.55T时的螺旋进出采集恢复了1.5T时心肌信噪比的69%±14%。
高效的bSSFP螺旋进出在高性能0.55T MRI系统上提供了高质量的心脏电影成像和信噪比恢复。
