Maï Wilfried, Badea Cristian T, Wheeler Charles T, Hedlund Laurence W, Johnson G Allan
Center for In Vivo Microscopy, Box 3302, Duke University Medical Center, Durham, NC 27710, USA.
Magn Reson Med. 2005 Apr;53(4):858-65. doi: 10.1002/mrm.20400.
One can acquire high-resolution pulmonary and cardiac images in live rodents with MR microscopy by synchronizing the image acquisition to the breathing cycle across multiple breaths, and gating to the cardiac cycle. The precision with which one can synchronize image acquisition to the motion defines the ultimate resolution limit that can be attained in such studies. The present work was performed to evaluate how reliably the pulmonary and cardiac structures return to the same position from breath to breath and beat to beat across the prolonged period required for MR microscopy. Radiopaque beads were surgically glued to the abdominal surface of the diaphragm and on the cardiac ventricles of anesthetized, mechanically ventilated rats. We evaluated the range of motion for the beads (relative to a reference vertebral bead) using digital microradiography with two specific biological gating methods: 1) ventilation synchronous acquisition, and 2) both ventilation synchronous and cardiac-gated acquisitions. The standard deviation (SD) of the displacement was < or =100 microm, which is comparable to the resolution limit for in vivo MRI imposed by signal-to-noise ratio (SNR) constraints. With careful control of motion, its impact on resolution can be limited. This work provides the first quantitative measure of the motion-imposed resolution limits for in vivo imaging.
通过在多次呼吸过程中将图像采集与呼吸周期同步，并与心动周期门控，利用磁共振显微镜可以在活体啮齿动物中获得高分辨率的肺部和心脏图像。将图像采集与运动同步的精确程度决定了此类研究能够达到的最终分辨率极限。开展本研究是为了评估在磁共振显微镜所需的较长时间内，肺部和心脏结构在每次呼吸和每次心跳之间回到相同位置的可靠性。将不透射线的珠子手术粘贴到麻醉、机械通气大鼠的膈肌腹部表面和心室上。我们使用数字微射线摄影术，通过两种特定的生物门控方法评估珠子的运动范围（相对于参考椎体珠子）：1）通气同步采集，以及2）通气同步和心脏门控采集。位移的标准差（SD）≤100微米，这与信噪比（SNR）限制对体内MRI分辨率极限的影响相当。通过仔细控制运动，其对分辨率的影响可以得到限制。这项工作首次对体内成像中运动造成的分辨率极限进行了定量测量。
