Here’s the image I was trying to get before New Year’s. This shows flow entering the right atrium of a normal subject’s heart. Blood flow is shown by the white pencils. Vorticity (the amount of spin of a bit of fluid) is shown by the colored arrows. Only the strongest velocity and vorticity is shown here, to keep the image from getting too cluttered. The right atrium is shown in transparent white, and the right ventricle is the big triangular shape in yellow. Flow is entering the atrium from the top, through the superior vena cava (SVC). You can see vorticity ringing the flow, since it is being generated at the SVC surface. Flow up from the bottom, through the inferior vena cava (IVC), is more complicated. Venous (return) flow from the liver comes in and wraps around behind the main IVC flow from the lower abdomen. The two flows mix as they enter through the bottom of the atrium. This is useful, since you want all the important chemicals from your liver to mix with the rest of your blood before it gets pumped to your lungs and beyond. Too bad this type of imaging (4DMRI) can’t give more details about the mixing process.