Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
J Cardiovasc Magn Reson. 2009 Nov 19;11(1):49. doi: 10.1186/1532-429X-11-49.
Cardiovascular magnetic resonance (CMR) can potentially quantify aortic valve area (AVA) in aortic stenosis (AS) using a single-slice phase contrast (PC) acquisition at valve level: AVA = aortic flow/aortic velocity-time integral (VTI). However, CMR has been shown to underestimate aortic flow in turbulent high velocity jets, due to intra-voxel dephasing. This study investigated the effect of decreasing intra-voxel dephasing by reducing the echo time (TE) on AVA estimates in patients with AS.
15 patients with moderate or severe AS, were studied with three different TEs (2.8 ms/2.0 ms/1.5 ms), in the main pulmonary artery (MPA), left ventricular outflow tract (LVOT) and 0 cm/1 cm/2.5 cm above the aortic valve (AoV). PC estimates of stroke volume (SV) were compared with CMR left ventricular SV measurements and PC peak velocity, VTI and AVA were compared with Doppler echocardiography. CMR estimates of AVA obtained by direct planimetry from cine acquisitions were also compared with the echoAVA.
With a TE of 2.8 ms, the mean PC SV was similar to the ventricular SV at the MPA, LVOT and AoV0 cm (by Bland-Altman analysis bias +/- 1.96 SD, 1.3 +/- 20.2 mL/-6.8 +/- 21.9 mL/6.5 +/- 50.7 mL respectively), but was significantly lower at AoV1 and AoV2.5 (-29.3 +/- 31.2 mL/-21.1 +/- 35.7 mL). PC peak velocity and VTI underestimated Doppler echo estimates by approximately 10% with only moderate agreement. Shortening the TE from 2.8 to 1.5 msec improved the agreement between ventricular SV and PC SV at AoV0 cm (6.5 +/- 50.7 mL vs 1.5 +/- 37.9 mL respectively) but did not satisfactorily improve the PC SV estimate at AoV1 cm and AoV2.5 cm. Agreement of CMR AVA with echoAVA was improved at TE 1.5 ms (0.00 +/- 0.39 cm2) versus TE 2.8 (0.11 +/- 0.81 cm2). The CMR method which agreed best with echoAVA was direct planimetry (-0.03 cm2 +/- 0.24 cm2).
Agreement of CMR AVA at the aortic valve level with echo AVA improves with a reduced TE of 1.5 ms. However, flow measurements in the aorta (AoV 1 and 2.5) are underestimated and 95% limits of agreement remain large. Further improvements or novel, more robust techniques are needed in the CMR PC technique in the assessment of AS severity in patients with moderate to severe aortic stenosis.
心血管磁共振（CMR）可以通过在瓣口层面使用单次切面相位对比（PC）采集来潜在地定量主动脉瓣狭窄（AS）的主动脉瓣口面积（AVA）：AVA=主动脉流量/主动脉速度时间积分（VTI）。然而，CMR 已被证明在湍流高速射流中会低估主动脉流量，这是由于相位失相造成的。本研究旨在通过降低回波时间（TE）来减少相位失相，从而改善 AS 患者的 AVA 估计值。
对 15 例中重度 AS 患者分别在主肺动脉（MPA）、左心室流出道（LVOT）和主动脉瓣上方 0cm/1cm/2.5cm 处进行三种不同 TE（2.8ms/2.0ms/1.5ms）的 PC 测量，以获得主动脉瓣口的流量（SV）。PC 测量的 SV 与 CMR 左心室 SV 测量值进行比较，PC 峰值速度、VTI 和 AVA 与多普勒超声心动图进行比较。还将电影采集的直接平面测量法获得的 CMR AVA 估计值与超声 AVA 进行比较。
在 TE 为 2.8ms 时，PC SV 在 MPA、LVOT 和 AoV0cm 处与心室 SV 相似（通过 Bland-Altman 分析，偏倚为 +/-1.96SD，分别为 1.3 +/-20.2mL/-6.8 +/-21.9mL/6.5 +/-50.7mL），但在 AoV1 和 AoV2.5 处明显较低（-29.3 +/-31.2mL/-21.1 +/-35.7mL）。PC 峰值速度和 VTI 对多普勒超声心动图估计值的低估约为 10%，一致性中等。将 TE 从 2.8 缩短至 1.5ms 可改善 AoV0cm 处心室 SV 和 PC SV 之间的一致性（分别为 6.5 +/-50.7mL 和 1.5 +/-37.9mL），但不能满意地改善 AoV1cm 和 AoV2.5cm 处的 PC SV 估计值。在 TE 1.5ms 时，CMR AVA 与超声 AVA 的一致性较 TE 2.8ms 时有所改善（0.00 +/-0.39cm2 与 0.11 +/-0.81cm2）。与超声 AVA 一致性最佳的 CMR 方法是直接平面测量法（-0.03cm2 +/-0.24cm2）。
通过降低 TE 至 1.5ms，CMR 主动脉瓣口水平的 AVA 与超声 AVA 的一致性得到改善。然而，主动脉内的流量测量（AoV1 和 2.5）仍被低估，95%的一致性界限仍然很大。在评估中重度主动脉瓣狭窄患者的 AS 严重程度时，CMR PC 技术需要进一步改进或采用新的、更稳健的技术。
