Kilner Philip J, Gatehouse Peter D, Firmin David N
CMR Unit, Royal Brompton Hospital, Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital, Sydney Street, London, UK.
J Cardiovasc Magn Reson. 2007;9(4):723-8. doi: 10.1080/10976640701465090.
Users and manufacturers of cardiovascular magnetic resonance (CMR) systems have, potentially, an unrivalled asset. Phase contrast mapping of velocities through planes transecting the great arteries should provide the most accurate measurements available of cardiac output, shunt flow, aortic or pulmonary regurgitation and, indirectly, of mitral regurgitation. But the reality is that phase contrast velocity mapping remains under-used, and may have become discredited in the eyes of some CMR users and referring clinicians. Even when appropriate methods of acquisition have been used, there can be inaccuracies of flow measurement on some CMR systems caused by background phase errors due to eddy currents or uncorrected concomitant gradients. Measurements of regurgitant or shunt flow can be seriously affected by these errors which should be minimised or corrected by appropriate hardware and software design. If they have not been, inaccuracies can be detected and corrected by repeating identical velocity acquisitions on a static phantom, and subtracting the corresponding apparent phantom velocities from those of the clinical acquisition. For accurate measurements of aortic regurgitation or mitral inflow, motion tracking and velocity correction with respect to the cyclic displacements of the valves are needed, but few if any commercial systems provide this facility. Measurements of jet velocity pose different challenges, mainly related to the size and placement of voxels relative to a narrow jet. Awareness of the potential problems and concerted efforts towards optimisation are needed from manufacturers and users to make appropriate use of phase contrast flow measurement - a unique strength of cardiovascular magnetic resonance.
心血管磁共振（CMR）系统的用户和制造商可能拥有一项无与伦比的资产。通过横切大动脉的平面进行速度的相位对比成像，应该能够提供最准确的心输出量、分流流量、主动脉或肺动脉反流测量值，并且能间接测量二尖瓣反流。但实际情况是，相位对比速度成像的应用仍然不足，在一些CMR用户和转诊临床医生眼中，它可能已经声名扫地。即使采用了合适的采集方法，一些CMR系统上由于涡流或未校正的伴随梯度导致的背景相位误差，仍可能造成流量测量不准确。反流或分流流量的测量会受到这些误差的严重影响，而这些误差应通过适当的硬件和软件设计降至最低或得到校正。如果没有做到这一点，可以通过在静态体模上重复相同的速度采集，并从临床采集的速度中减去相应的体模表观速度，来检测和校正不准确之处。为了准确测量主动脉反流或二尖瓣流入，需要针对瓣膜的周期性位移进行运动跟踪和速度校正，但几乎没有商业系统提供此功能。射流速度的测量面临不同的挑战，主要与相对于狭窄射流的体素大小和放置有关。制造商和用户需要意识到潜在问题并共同努力进行优化，以便恰当地利用相位对比流量测量——这是心血管磁共振的一项独特优势。
