Walker P G, Pedersen E M, Oyre S, Flepp L, Ringgaard S, Heinrich R S, Walton S P, Hasenkam J M, Jorgensen H S, Yoganathan A P
Cardiovascular Fluid Mechanics Laboratory, School of Chemical Engineering, Georgia Institute of Technology, Atlanta, USA.
J Heart Valve Dis. 1995 May;4(3):296-307.
The aim of this study was to compare different (long/short echo time, whole body/small bore scanner) magnetic resonance velocity measurement techniques and their applicability to the measurement of blood velocity downstream of prosthetic heart valves. In-vitro magnetic resonance velocity measurements were performed downstream of four normal and stenotic prosthetic heart valves (St. Jude Medical bileaflet, Monostrut tilting disc, Ionescu-Shiley Pericardial and Starr-Edwards caged-ball) under steady flow conditions in an aortic test chamber. Cross-sectional and longitudinal velocity images were obtained downstreamed of the valves. Magnetic resonance was able to measure all three components of fluid velocity downstream of the valves under normal and stenotic conditions except in regions of turbulence. The velocity was measured across the tube cross-section in 10-15 minutes producing a good visualization of the axial velocity profile. High velocity regions, shear layers and reversed/stagnant regions were identified. The flow rate calculated by integration of the magnetic resonance velocity across the cross-section of the tube was accurate to 5-6% in normal cases and slightly less accurate for stenotic valves. Although signal loss on the modulus image was adverse to the velocity images, it was found that these regions could be used to identify areas of flow disturbance. The high magnetic field, small bore scanner was able to produce images with a resolution of 0.2 x 0.2 x 1.0 mm and was less affected by turbulence producing more detailed flow images. Magnetic resonances has been shown to be a useful new tool in the measurement of the velocity downstream of prosthetic heart valves. In particular it's short data acquisition time and the possibilities to reproduce the same measurements in-vivo make it an attractive alternative to traditional methods.
本研究的目的是比较不同的（长/短回波时间、全身/小口径扫描仪）磁共振速度测量技术及其在人工心脏瓣膜下游血流速度测量中的适用性。在主动脉测试腔的稳定流动条件下，对四个正常和狭窄的人工心脏瓣膜（圣犹达医疗双叶瓣、单支柱倾斜盘瓣、伊奥内斯库-希利心包瓣和斯塔尔-爱德华兹笼球瓣）下游进行体外磁共振速度测量。在瓣膜下游获得横截面和纵向速度图像。除了湍流区域外，磁共振能够测量正常和狭窄条件下瓣膜下游流体速度的所有三个分量。在10 - 15分钟内测量管横截面的速度，可很好地显示轴向速度分布。识别出高速区域、剪切层和反向/停滞区域。通过对管横截面的磁共振速度进行积分计算得到的流量，在正常情况下精确到5 - 6%，对于狭窄瓣膜的精度略低。尽管模量图像上的信号损失对速度图像不利，但发现这些区域可用于识别流动干扰区域。高磁场、小口径扫描仪能够产生分辨率为0.2×0.2×1.0毫米的图像，受湍流影响较小，可产生更详细的流动图像。磁共振已被证明是测量人工心脏瓣膜下游速度的一种有用的新工具。特别是其短的数据采集时间以及在体内重复相同测量的可能性，使其成为传统方法的一个有吸引力的替代方案。
