Pai Vinay M
Department of Radiology, New York University School of Medicine, New York, NY 10016, USA.
Magn Reson Med. 2007 Aug;58(2):419-24. doi: 10.1002/mrm.21297.
Conventional phase-contrast (PC) MRI is limited in the temporal resolution (typically 50 ms) that can be achieved, due to the need to implement bipolar velocity encoding gradients. PC using steady-state free precession (SSFP) has recently been developed to acquire PC data at higher rates without sacrificing contrast-to-noise ratio (CNR). This work presents two multiecho SSFP PC implementations that can be used to increase the time efficiency of PCSSFP. Both approaches (extrinsic and intrinsic) enable reference image lines to be acquired within the same TR as the flow-encoded lines, thus minimizing the scan time and permitting TR-equivalent temporal resolutions. Both approaches have been implemented and tested successfully on human volunteers at 1.5T and 3T. While the intrinsic approach is useful for encoding higher velocity flows in-plane, the extrinsic implementation can be used for studying a wider range of encoding velocities for flow in the imaging plane and through the imaging plane.
传统的相位对比（PC）MRI在可实现的时间分辨率（通常为50毫秒）方面受到限制，这是由于需要实施双极速度编码梯度。最近开发了使用稳态自由进动（SSFP）的PC，以在不牺牲对比度噪声比（CNR）的情况下更高速率地获取PC数据。这项工作提出了两种多回波SSFP PC实现方法，可用于提高PC-SSFP的时间效率。两种方法（外在法和内在法）都能在与流动编码线相同的TR内采集参考图像线，从而将扫描时间降至最低，并允许达到TR等效的时间分辨率。两种方法均已在1.5T和3T的人体志愿者身上成功实施并进行了测试。虽然内在法对于在平面内编码更高速度的流动很有用，但外在法可用于研究成像平面内和穿过成像平面的更广泛的流动编码速度范围。
