Courtesy of Prof Giles Roditi and Dr Pauline Hall Barrientos, this image demonstrates 4D Flow magnetic resonance angiography (MRA), a technique of time-resolved phase-contrast MRI for investigating flow fields. This animated image shows an example of 4D flow in the thoracic aorta; colour stream lines are derived from emitter planes placed in the ascending aorta and at two points in the descending thoracic aorta. A rainbow colour coding denotes slow (blue) through to fast (red) flow velocities.

In this example image, a patient with an aneurysmal dilation of the ascending aorta and chronic dissection of the descending aorta shows higher velocity flow in the true lumen of the descending aorta (feeding visceral vessels such as the superior mesenteric artery) compared to the false lumen in systole. There is also a high velocity jet of aortic valve incompetence in diastole regurgitant into the left ventricle.