|M.Sc Student||Gorodisky Lior|
|Subject||Quantification of Mitral Regurgitation using Magnetic|
|Department||Department of Electrical Engineering||Supervisors||Professor Moshe Porat|
|Clinical Professor Jonathan Lessick|
|Full Thesis text|
Mitral Regurgitation (MR) is a cardiac disorder, in which the mitral valve does not function properly and allows blood from the left ventricular to flow backwards into the left atrium. The gold standards to assess MR are by echocardiography, using ultrasound and the Doppler effect. Quantitative analysis can be performed by means of the Proximal Isovelocity Surface Area (PISA) method in which the blood volume which regurgitates through the valve is assessed proximal to the regurgitant orifice. Since PISA is based on the Doppler effect, the velocity can be measured only for the component which is parallel to the direction of the ultrasound beam, therefore the surface in which the velocity is equal (PISA) is assumed to be a hemisphere.
The aim of this research was to develop methods to quantify MR severity using Magnetic Resonance Imaging (MRI) 3D velocity imaging and to validate results compared to 2 gold standards: echo-Doppler (qualitative and PISA methods) and MRI anatomic method where MR volume is calculated as the difference between left and right ventricular forward volumes.
A few methods for estimation of the regurgitant blood volume during a heart cycle have been developed and examined - measuring the difference between the forward flows through the aortic valve and mitral valve, measuring the backward flow through the mitral valve and estimating PISA by measuring the 3D surface area of the MR proximal flow convergence. Each method was checked for robustness to the selection of the calculation parameters. In addition, the influence of some properties of the MRI scan were examined, such as selection of the maximal measured velocity, handling of aliasing and using directional velocities. In contrast to Doppler-based PISA, we didn't assume that the PISA shape is hemispheric. Thus our results are based on a more realistic PISA shape. In order to check the validity of the used assumption for echocardiography, the ellipticity of the created PISA was examined. Our results indicate that the observed 3D shape of the PISA envelope by MRI is closer to a hemiellipsoid than a hemisphere.
The regurgitant volumes, calculated by the MRI-PISA method correlate well with the measurements from echocardiography (clinical qualitative evaluation to mild, moderate and severe MR and quantitative evaluation using the PISA method) and also with the anatomic MRI method. Our conclusion is that the MRI-based evaluation of MR is superior to the 2D-PISA approach and may be able to assess MR severity quantitatively without any geometric assumptions.