Dimitriou Praxitelis, Kähäri Anders, Emilsson Kent, Thunberg Per
Department of Radiology, Örebro University Hospital, Sweden.
Acta Radiol. 2012 Nov 1;53(9):995-1003. doi: 10.1258/ar.2012.120261. Epub 2012 Sep 14.
Magnetic resonance (MR) imaging and echocardiography both allow assessment of aortic valve stenosis. In MR the aortic valve area (AvA) is measured using planimetry while in transthoracic echocardiography (TTE) AvA is usually calculated by applying the continuity equation.
To compare the measured stenotic aortic valve areas using five different MR-acquisition alternatives with the corresponding area values calculated by TTE.
The aortic valve was imaged in 14 patients, with diagnosed aortic valve stenosis, using balanced steady state free precession (bSSFP) gradient echo (GE) and phase contrast imaging (PC). Three adjacent slices were planned to encompass the aortic valve and the aortic valve area was measured using planimetry. The two sets of complex valued images generated by the PC sequence formed three kinds of images that could be used for aortic valve area measurements: the magnitude image (PC/Mag), the modulus (PCA/M), and phase difference (PCA/P) between the two complex images, respectively. The valve area from TTE was calculated using the continuity equation. A cut-off of <1.0 cm(2) was used as a criteria for severe stenosis.
The mean area differences between the different MR acquisitions and TTE method were -0.05 ± 0.37 cm(2) (GE), -0.18 ± 0.46 cm(2) (bSSFP), 0.27 ± 0.43 cm(2) (PC/Mag), 0.15 ± 0.32 cm(2) (PCA/P), and 0.26 ± 0.27 cm(2) (PCA/M). The valve area was significantly overestimated using PCA/M that, in turn, implied a significant underestimation of the aortic valve stenosis severity compared to the assessments using TTE.
The smallest area valve difference between TTE and an MR-acquisition alternative is obtained with gradient echo images. The use of PCA/M leads to significant differences in planimetry measurements of the aortic valve orifice and the gradation of the stenosis severity compared to TTE.
磁共振（MR）成像和超声心动图都可用于评估主动脉瓣狭窄。在MR成像中，主动脉瓣面积（AvA）通过平面测量法进行测量，而在经胸超声心动图（TTE）中，AvA通常通过应用连续性方程来计算。
比较使用五种不同MR采集方案测量的狭窄主动脉瓣面积与通过TTE计算得到的相应面积值。
对14例诊断为主动脉瓣狭窄的患者的主动脉瓣进行成像，采用平衡稳态自由进动（bSSFP）梯度回波（GE）和相位对比成像（PC）。计划采集三个相邻层面以覆盖主动脉瓣，并使用平面测量法测量主动脉瓣面积。由PC序列生成的两组复值图像形成了三种可用于主动脉瓣面积测量的图像：幅度图像（PC/Mag）、模量（PCA/M）以及两幅复图像之间的相位差（PCA/P）。通过连续性方程计算TTE的瓣膜面积。以<1.0 cm²作为重度狭窄的标准。
不同MR采集方案与TTE方法之间的平均面积差异分别为：-0.05±0.37 cm²（GE）、-0.18±0.46 cm²（bSSFP）、0.27±0.43 cm²（PC/Mag）、0.15±0.32 cm²（PCA/P）和0.26±0.27 cm²（PCA/M）。使用PCA/M时瓣膜面积被显著高估，这反过来意味着与使用TTE的评估相比，主动脉瓣狭窄严重程度被显著低估。
梯度回波图像在TTE与MR采集方案之间产生的瓣膜面积差异最小。与TTE相比，使用PCA/M会导致主动脉瓣口平面测量以及狭窄严重程度分级出现显著差异。
