Quantifying Mitral Stenosis
Mitral stenosis (MS) or mitral valve stenosis is the restrictive opening of the mitral valve (MV) resulting in an increase in the gradient pressure across the valve. MRI analysis quantifies MS severity by mitral valve area (MVA), using planimetry and pressure half-time.
The MVA is planimetered directly from gated steady-state free precession (SSFP) images that are acquired as a series of thin, parallel slices, which are oriented perpendicularly to the mitral valve. The MV measurement must be made at the tips of the mitral valve cusps, where the valve is narrowest. Traces should include all blood (white) and exclude calcified cusps (Fig.1).
Stenotic severity may be determined accordingly:
|Tb.1. Mitral stenosis severity scale||MV area (cm2)||Pressure Half-Time (ms)|
II. Pressure Half-Time (PHT):
MVA also may be obtained by acquiring pressure half-time (PHT)—the time (ms) required for the pressure gradient across the mitral valve to fall to half of its peak value. The cardiac phase containing the greatest amount of blood (whitest region) is selected on the phase contrast series; then an oval-shaped region of interest (ROI) inside the area of the MV is selected (Fig.2). This ROI should contain the maximum possible blood volume inside the MV. Using software, a graph of the blood flow through the MV may be obtained, showing the PHT value (Fig.2), which then is employed in the following equation to obtain the MVA and the corresponding MS severity (Tb.1):