Figure 18. Magnitude (top row) and phase (bottom row) images of the pulmonary artery (left column) and aorta (right column). Flow volume is calculated as the product of the mean flow velocity, which is measured on the phase images, and the cross-sectional area of the vessel. Flow in the pulmonary artery (PA) is equivalent to the right ventricular stroke volume (RVSV), and flow in the aorta is equivalent to the left ventricular stroke volume (LVSV).