Guttman Michael A, Kellman Peter, Dick Alexander J, Lederman Robert J, McVeigh Elliot R
Laboratory of Cardiac Energetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Magn Reson Med. 2003 Aug;50(2):315-21. doi: 10.1002/mrm.10504.
Reduced field-of-view (FOV) acceleration using time-adaptive sensitivity encoding (TSENSE) or unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD) can improve the depiction of motion in real-time MRI. However, increased computational resources are required to maintain a high frame rate and low latency in image reconstruction and display. A high-performance software system has been implemented to perform TSENSE and UNFOLD reconstructions for real-time MRI with interactive, on-line display. Images were displayed in the scanner room to investigate image-guided procedures. Examples are shown for normal volunteers and cardiac interventional experiments in animals using a steady-state free precession (SSFP) sequence. In order to maintain adequate image quality for interventional procedures, the imaging rate was limited to seven frames per second after an acceleration factor of 2 with a voxel size of 1.8 x 3.5 x 8 mm. Initial experiences suggest that TSENSE and UNFOLD can each improve the compromise between spatial and temporal resolution in real-time imaging, and can function well in interactive imaging. UNFOLD places no additional constraints on receiver coils, and is therefore more flexible than SENSE methods; however, the temporal image filtering can blur motion and reduce the effective acceleration. Methods are proposed to overcome the challenges presented by the use of TSENSE in interactive imaging. TSENSE may be temporarily disabled after changing the imaging plane to avoid transient artifacts as the sensitivity coefficients adapt. For imaging with a combination of surface and interventional coils, a hybrid reconstruction approach is proposed whereby UNFOLD is used for the interventional coils, and TSENSE with or without UNFOLD is used for the surface coils.
使用时间自适应灵敏度编码（TSENSE）或通过利用时间维度对重叠部分进行傅里叶编码去伪影（UNFOLD）来降低视野（FOV）加速，可以改善实时磁共振成像（MRI）中运动的描绘。然而，在图像重建和显示中，需要增加计算资源以维持高帧率和低延迟。已实现了一个高性能软件系统，用于执行TSENSE和UNFOLD重建以实现实时MRI，并具有交互式在线显示功能。图像在扫描室中显示以研究图像引导程序。展示了使用稳态自由进动（SSFP）序列对正常志愿者和动物心脏介入实验的示例。为了在介入程序中保持足够的图像质量，在加速因子为2且体素大小为1.8×3.5×8 mm的情况下，成像速率限制为每秒七帧。初步经验表明，TSENSE和UNFOLD均可改善实时成像中空间和时间分辨率之间的折衷，并且在交互式成像中能良好运行。UNFOLD对接收线圈没有额外限制，因此比灵敏度编码（SENSE）方法更灵活；然而，时间图像滤波会模糊运动并降低有效加速度。提出了一些方法来克服在交互式成像中使用TSENSE所带来的挑战。在改变成像平面后，TSENSE可能会被暂时禁用，以避免在灵敏度系数适应时出现瞬态伪影。对于结合使用表面线圈和介入线圈的成像，提出了一种混合重建方法，即对介入线圈使用UNFOLD，对表面线圈使用带或不带UNFOLD的TSENSE。
