Relative aortic blood pressure using 4D flow MRI: Associations with age and aortic tapering

MRI 4D flow velocity is used to evaluate relative blood pressures in the aorta throughout the cardiac cycle. This (3D+t) pressure mapping is used to assess: 1) relationship between trans-aortic pressure gradient with age and aortic tapering (proximal to distal narrowing in lumen area), 2) effect of temporal resolution. We studied 47 healthy subjects (49±17.6 years, 24 men) who underwent 4D flow MRI, among them 20 were reconstructed in 20 and 50 phases per cardiac cycle. Pressure gradients maps were estimated from velocity fields using the Navier-Stokes equations. Relative pressures were calculated using an iterative algorithm while considering a zero pressure at the aortic valve. Distal (DA) to proximal (PA) aortic pressure gradient decreased with age (r=0.60, p<0.05) and was inversely related to DA/PA areas ratio (r=0.35, p<0.05). Such result is in line with the physiological evidence indicating that in aging DA area tends to equalize with PA area lowering the DA to PA pressure gradient. Peak systolic pressure was higher when considering the 50 phases data. Relative pressures calculated from 4D flow within the whole aortic volume through time are consistent with prior physiological knowledge as demonstrated by their variations with age and with aortic geometry.