Search

Aortic aneurysm is associated with aberrant blood flow and wall shear stress (WSS). This can be studied by coupling magnetic resonance imaging (MRI) with computational fluid dynamics (CFD). For patient-specific simulations, extra attention should be given to the variation in segmentation of the MRI data-set and its effect on WSS. We performed CFD simulations of blood flow in the aorta for ten different volunteers and provided corresponding WSS distributions. The aorta of each volunteer was segmented four times. The same inlet and outlet boundary conditions were applied for all segmentation variations of each volunteer. Steady-state CFD simulations were performed with inlet flow based on phase-contrast MRI during peak systole. We show that the commonly used comparison of mean and maximal values of WSS, based on CFD in the different segments of the thoracic aorta, yields good to excellent correlation (0.78-0.95) for rescan and moderate to excellent correlation (0.64-1.00) for intra- and interobserver reproducibility. However, the effect of geometrical variations is higher for the voxel-to-voxel comparison of WSS. With this analysis method, the correlation for different segments of the whole aorta is poor to moderate (0.43-0.66) for rescan and poor to good (0.48-0.73) for intra- and interobserver reproducibility. Therefore, we advise being critical about the CFD results based on the MRI segmentations to avoid possible misinterpretation. While the global values of WSS are similar for different modalities, the variation of results is high when considering the local distributions., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: In patients with Marfan syndrome (MFS), increased aortic wall stiffening may lead to progressive aortic dilatation. Aortic Pulse Wave Velocity (PWV), a marker of wall stiffness can be assessed regionally, using in-plane multi-directional velocity-encoded MRI. This study examined the diagnostic accuracy of regional PWV for prediction of regional aortic luminal growth during 2-year follow-up in MFS patients., Methods: In twenty-one MFS patients (mean age 36 ± 15 years, 11 male) regional PWV and aortic luminal areas were assessed by 1.5 T MRI. At 2-year follow-up, the incidence of luminal growth, defined as mean luminal diameter increase >2mm was determined for five aortic segments (S1, ascending aorta; S2, aortic arch; S3, thoracic descending aorta, S4, supra-renal and S5, infra-renal abdominal aorta). Regional PWV at baseline was considered increased when exceeding age-related normal PWV (healthy volunteers (n=26; mean age 30 ± 10 years, 15 male)) by two standard-errors. Sensitivity and specificity of regional PWV-testing for prediction of regional luminal growth were determined., Results: Regional PWV at baseline was increased in 17 out of 102 segments (17%). Significant luminal growth at follow-up was reported in 14 segments (14%). The specificity of regional PWV-testing was ≥ 78% for all aortic segments, sensitivity was ≤ 33%., Conclusions: Regional PWV was significantly increased in MFS patients as compared to healthy volunteers within similar age range, in all aortic segments except the ascending aorta. Furthermore, regional PWV-assessment has moderate to high specificity for predicting absence of regional aortic luminal growth for all aortic segments in MFS patients., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Magnetic resonance imaging (MRI) can be used to distinguish bone marrow (BM) from cartilage and may therefore be used to measure BM volume in intact bones. We used MRI to measure the total human fetal BM volume in intact fetuses during the second trimester of pregnancy and determined the contribution of the individual bones to the total compartment. The total BM volume ranged from 934 microL at 17 to 18 weeks to 4563 microL at 22 to 23 weeks of gestation. The largest contributor to the total BM volume was the spine, constituting 26.4% +/- 2.7% of the total volume. By analyzing leukocyte content and percentages of CD34+ cells, lymphocytes, granulocytes, and monocytes of determined volumes, absolute numbers of these cell populations in BM could be measured. The cellular composition of the BM compartment did not significantly change throughout the second trimester of gestation. Absolute white blood cell counts per fetus increased from 111 x 10(6) at 16 to 17 weeks to 1229 x 10(6) at 21 to 22 weeks. The absolute numbers of CD34+ cells increased from 25 x 10(6) at 16 to 17 weeks to 256 x 10(6) at 21 to 22 weeks. Similar analysis of liver and spleen revealed comparable absolute numbers of CD34+ cells in BM and liver throughout the second trimester of gestation. In fetal liver, CD34+ cells differentiate into red cells, myeloid cells, and platelets, while lymphopoiesis mainly occurs in BM or spleen. Combining MRI and cell counts provides a method to quantify specific cell populations in fetal compartments. This study may enable better evaluation of fetal diagnostics and therapies.