Comprehensive sex-specific and age-dependent analysis of four-dimensional flow cardiovascular magnetic resonance assessed aortic blood flow-related parameters in normal subjects using single-vendor magnetic resonance systems and single-vendor software.

Background: Aortic blood flow characterization by four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) is increasingly performed in aneurysm research. A limited number of studies have established normal values that can aid the recognition of abnormal flow at an early stage. This study aims to establish additional sex-specific and age-dependent reference values for flow-related parameters in a large cohort of healthy adults.

Methods: Two hundred and twelve volunteers were included, and 191 volunteers completed the full study protocol. All underwent 4D flow CMR of the entire aorta. Quantitative values for velocity, vorticity, helicity, as well as total, circumferential, and axial wall shear stress (WSS) were determined for the aortic root (AoR), ascending aorta (AAo), aortic arch, descending aorta (DAo), suprarenal aorta, and infrarenal aorta. Vorticity and helicity were indexed for segment volume (mL).

Results: The normal values were estimated per sex and age group, where significant differences between males (M) and females (F) were found only for specific age groups. More specifically, the following variables were significantly different after applying the false discovery rate correction for multiple testing: 1) velocity in the AAo and DAo in the 60-70 years age group (mean ± SD: (M) 47.0 ± 8.2 cm s^-1 vs (F) 38.4 ± 6.9 cm s^-1, p = 0.001 and, (M) 55.9 ± 9.9 cm s^-1 vs (F) 46.5 ± 5.5 cm s^-1, p = 0.002), 2) normalized vorticity in AoR in the 50-59 years age group ((M) 27,539 ± 5042 s^-1 mL^-1 vs (F) 30,849 ± 7285 s^-1 mL^-1, p = 0.002), 3) axial WSS in the Aao in the 18-29 age group ((M) 1098 ± 203 mPa vs (F) 921 ± 121 mPa, p = 0.002). Good to strong negative correlations with age were seen for almost all variables, in different segments, and for both sexes.

Conclusion: This study describes reference values for aortic flow-related parameters acquired by 4D flow MRI. We observed limited differences between males and females. A negative relationship with age was seen for almost all flow-related parameters and segments.