Sablong Raphaël, Rengle A, Ramgolam A, Saint-Jalmes H, Beuf O
IEEE Trans Biomed Eng. 2014 Jan;61(1):162-70. doi: 10.1109/TBME.2013.2278712. Epub 2013 Sep 5.
Prospective synchronization of MRI acquisitions on living organisms involves the monitoring of respiratory and heart motions. The electrocardiogram (ECG) signal is conventionally used to measure the cardiac cycle. However, in some circumstances, obtaining an uncorrupted ECG signal recorded on small animals with radio frequency (RF) pulses and gradient switching is challenging. To monitor respiratory motion, an air cushion associated with a pressure sensor is commonly used but the system suffers from bulkiness. For many applications, the physiological gating information can also be derived from an MR navigated signal. However, a compact device that can simultaneously provide respiratory and cardiac information, for both prospective gating and physiological monitoring, is desirable. This is particularly valid since small volume coils or dedicated cardiac RF coil arrays placed directly against the chest wall are required to maximize measurement sensitivity. An optic-based device designed to synchronize MRI acquisitions on small animal's respiratory and heart motion was developed using a transmit-receive pair of optical fibers. The suitability of the developed device was assessed on mice ( n = 10) and was based on two sets of experiments with dual cardiac and respiratory synchronization. Images acquired with prospective triggering using the optical-based signal, ECG, and the pressure sensor during the same experiment were compared between themselves in the first set. The second set compared prospective technique using optical-based device and ECG to a retrospective technique. The optical signal that was correlated to both respiratory and heart motion was totally unaffected by radiofrequency pulses or currents induced by the magnetic field gradients used for imaging. Mice heart MR images depict low-visible motion artifacts with all sensors or techniques used. No significant SNR differences were found between each series of image. Full fiber-optic-based signal derived from heart and respiratory motion was suitable for prospective triggering of heart MR imaging. The fiber optic device performed similarly to the ECG and air pressure sensors, while providing an advantage for imaging with dedicated cardiac array coils by reducing bulk. It can be an attractive alternative for small animal MRI in difficult environments such as limited space and strong gradient switching.
对活体生物进行磁共振成像（MRI）采集的前瞻性同步涉及对呼吸和心脏运动的监测。传统上使用心电图（ECG）信号来测量心动周期。然而，在某些情况下，在小动物身上用射频（RF）脉冲和梯度切换获取未受干扰的ECG信号具有挑战性。为了监测呼吸运动，通常使用与压力传感器相关联的气垫，但该系统体积庞大。对于许多应用，生理门控信息也可以从磁共振导航信号中获取。然而，需要一种紧凑的设备，能够同时提供呼吸和心脏信息，用于前瞻性门控和生理监测。这一点尤其重要，因为需要使用直接贴靠胸壁的小体积线圈或专用心脏RF线圈阵列来最大化测量灵敏度。利用一对收发光纤开发了一种基于光学的设备，用于同步小动物呼吸和心脏运动的MRI采集。在小鼠（n = 10）上评估了所开发设备的适用性，并基于两组双心脏和呼吸同步实验。在第一组实验中，比较了在同一实验期间使用基于光学信号、ECG和压力传感器进行前瞻性触发采集的图像。第二组实验将使用基于光学设备和ECG的前瞻性技术与回顾性技术进行了比较。与呼吸和心脏运动相关的光学信号完全不受用于成像的磁场梯度所感应的射频脉冲或电流的影响。使用所有传感器或技术获取的小鼠心脏MR图像显示出低可见度的运动伪影。各系列图像之间未发现显著的信噪比差异。源自心脏和呼吸运动的全光纤信号适用于心脏MR成像的前瞻性触发。光纤设备的性能与ECG和气压传感器相似，同时通过减少体积为使用专用心脏阵列线圈成像提供了优势。对于在诸如空间有限和强梯度切换等困难环境中的小动物MRI而言，它可能是一种有吸引力的替代方案。
