Evaluation of Aortic Valve Stenosis Using Cardiovascular Magnetic Resonance

Abstract

Background-Accurate quantification of aortic valve stenosis (AVS) is needed for relevant management decisions. However, transthoracic Doppler echocardiography (TTE) remains inconclusive in a significant number of patients. Previous studies demonstrated the usefulness of phase-contrast cardiovascular magnetic resonance (PC-CMR) in noninvasive AVS evaluation. We hypothesized that semiautomated analysis of aortic hemodynamics from PC-CMR might provide reproducible and accurate evaluation of aortic valve area (AVA), aortic velocities, and gradients in agreement with TTE. Methods and Results-We studied 53 AVS patients (AVA TTE =0.87±0.44 cm 2 ) and 21 controls (AVA TTE =2.96±0.59 cm 2 ) who had TTE and PC-CMR of aortic valve and left ventricular outflow tract on the same day. PC-CMR data analysis included left ventricular outflow tract and aortic valve segmentation, and extraction of velocities, gradients, and flow rates. Three AVA measures were performed: AVA CMR1 based on Hakki formula, AVA CMR2 based on continuity equation, AVA CMR3 simplified continuity equation=left ventricular outflow tract peak flow rate/aortic peak velocity. Our analysis was reproducible, as reflected by low interoperator variability (<4.56±4.40%). Comparison of PC-CMR and TTE aortic peak velocities and mean gradients resulted in good agreement (r=0.92 with mean bias=−29±62 cm/s and r=0.86 with mean bias=−12±15 mm Hg, respectively). Although good agreement was found between TTE and continuity equationbased CMR-AVA (r>0.94 and mean bias=−0.01±0.38 cm 2 for AVA CMR2 , −0.09±0.28 cm 2 for AVA CMR3 ), AVA CMR1 values were lower than AVA TTE especially for higher AVA (mean bias=−0.45±0.52 cm 2 ). Besides, ability of PC-CMR to detect severe AVS, defined by TTE, provided the best results for continuity equation-based methods (accuracy >94%). Conclusions-Our Defrance et al Phase-Contrast Evaluation of Aortic Valve Stenosis 605on phase-contrast (PC) imaging demonstrated the ability of velocity-encoded sequences to characterize AVS by evaluating: peak transvalvular velocity, 12 AVA using the continuity equation, [5][6][7][8][9][10] or Hakki formula 7,11 derived from the Gorlin equation. The evaluation of AVA and hemodynamic parameters in the aforementioned PC-CMR studies was mostly based on manual delineation [5][6][7][8]10,11 of the aortic valve and the LVOT, which is subjective and time-consuming, rendering the usefulness of CMR in clinical routine for AVS evaluation limited. In addition, among these studies, some used the estimation of LVOT area from its diameter. [5][6][7][8] Although this strategy complies with TTE measurements, it does not take full advantage of PC-CMR data, which when combined with an accurate segmentation enable a direct estimation of the LVOT stroke volume (SV LVOT ) while taking into account the shape of the outflow tract. Clinical Perspective on p 612Accordingly, our first objective was to design a semiautomated analysis of LVOT and aortic valve PC-CMR data, which would enable an accurate evaluation of AVA, mean and maximal...

Volumetric velocity measurements in restricted geometries using spiral sampling: a phantom study

“…Recent investigations using 2D throughplane PC for pressure estimation have also proven successful in clinical application, and confirmed the need for short echo times [11][12][13].The necessity to reduce echo times suggest the combination of phase-contrast with a non-Cartesian readout scheme, such as radial or spiral readouts, as these sequences begin their k-space traversal in the centre of k-space, thus reducing the time between excitation and sampling. Ultra-short echo time sequences (UTE sequences) in combination with radial readouts have recently been shown to improve velocity and flow measurements in restrictions in vitro as well as in vivo using sub-millisecond echo times [14].…”

“…Hence, in several 2D throughplane PC studies of maximum velocity and flow determinations in stenotic vessels, a multi-slice procedure was used [11,20]. With the advent of three-dimensional, three-directional velocity encoding sequences (here denoted 4D PC) [21][22][23], the possibility has emerged to quantify velocity and flow in multiple 4 dimensions, and in addition to visualize blood flow by streamlines and pathlines.…”

“…Neglecting the other velocity components could potentially reduce imaging times by 50% without losing the crucial information, which is the maximum velocity in the stenotic jet. This approach would be an extension of the multi-acquisition 2D throughplane PC reported [11,20], with the benefit of control over relative slice positioning and simultaneous acquisitions. However, studies characterising the behaviour of 3D throughplane PC and 4D PC sequences in controlled, restricted geometries are sparse [35,36], warranting a thorough phantom study of properties and performances of different types of sequences.…”

Accurate Assessment of Aortic Stenosis

“…Despite these limitations, multiple studies have sought to investigate the use of MRI for measuring the EOA, by using MRI data in combination with either the continuity or modified forms of the Gorlin equation to calculate EOA. [70][71][72][73][74][75] Studies have also attempted to directly measure the vena contracta of the peak systolic jet in AS patients by calculating the width of the jet with the use of velocity data. This direct measurement does not rely on any assumptions that may be necessary while calculating EOA from catheterization or echocardiography.…”

“…Přes tyto limitace se řada studií snažila hodnotit použití MR při měření EOA kombinováním údajů z MR buď s kontinuitou nebo modifi kovanými formami Gorlinovy rovnice pro výpočet EOA. [70][71][72][73][74][75] Autoři studií se rovněž pokusili přímo měřit jet ve VC ve vrcholové fázi systoly u pacientů s AS vypočítá-váním šířky jetu pomocí údajů o rychlosti. Toto přímé měření není založeno na žádných předpokladech, které jsou nutné při vypočítávání EOA katetrizací nebo echokardiografi cky.…”