Phase Contrast Magnetic Resonance Imaging (PCMR) for the Heart
Phase contrast magnetic resonance imaging (PCMR) can be used to measure and quantify blood flow through the heart. Physicians use it to estimate the left ventricle flow, stenotic flow, and the ratio of flow in right and left ventricle from congenital abnormalities. A PCMR is normally performed anytime a scan is ordered to assess aortic, mitral, tricuspid, and pulmonary regurgitation or stenosis. Regurgitation occurs when the valves of the heart do not close properly and results in a backward flow to the heart. A PCMR is also often performed whenever there is a congenital heart disease like an atrial septal defect (ASD), ventricular septal defect (VSD), and patent ductus arteriosus (PDA).
Aortic regurgitation phase contrast magnetic resonance imaging is accomplished by centering the image parallel to the aortic valve from a coronal image. A parasagittal image can also be used and should be center parallel to the aortic valve and PA. It should be centered one inch above the valve. The velocity encoding factor (VENC) will depend on the regurgitation and should be between 250 to 550 cm/second. A high regurgitation causes a high VENC. Normally 40 to 60 phases of the aorta are obtained. Contouring the aorta provides important information. The aorta is contoured at each phase. A flow curve is made from the results of the aortic contouring. The amount of regurgitation is calculated by taking the backward flow and dividing it by the forward flow and multiplying by 100. Forward flow is the amount of blood flowing out of the aorta and to the rest of the body. Backward flow is the amount of blood going back into the left ventricle.