Use of Multispectral MRI to Monitor Aneurysm Sac Contents After Endovascular Abdominal Aortic Aneurysm Repair

Abstract

To validate a newly developed semi-automatic multispectral magnetic resonance imaging (MRI) tool for quantitatively monitoring aneurysm sac contents in patients after endovascular aneurysm repair (EVAR). MRI studies from 24 EVAR patients were retrospectively analyzed. The precontrast T₁-weighted and T₂-weighted and the postcontrast T₁-weighted images were displayed simultaneously. Two independent observers classified the aneurysm sac voxels into categories for endoleak, unorganized thrombus, or organized thrombus by interactively thresholding the multispectral images relative to the signal intensity of fat. Voxel classification was visualized as a color overlay on the MR images; when the observer changed the thresholds, the color overlay was updated immediately. The volumes of the voxels in each category were calculated and expressed in milliliters. The intra- and interobserver variability for measuring the volumes of endoleak and unorganized and organized thrombus were calculated; a Bland and Altman analysis was applied to determine the mean differences and the repeatability coefficient (RC). Mean aneurysm sac volume was 78 ± 42 mL. The intraobserver mean difference for the endoleak volume was 0.5 ± 1.9 mL with an RC of 3.7 mL; the interobserver mean difference was -0.8 ± 3.6 mL (RC 7.1 mL). The intraobserver mean difference for unorganized thrombus volume was -1.2 ± 4.4 mL (RC 8.6 mL); the interobserver mean difference was 0.3 ± 6.3 mL with an RC of 12.3 mL. The intraobserver mean difference for organized thrombus volume was 0.8 ± 5.0 mL (RC 9.7 mL); the interobserver mean difference was 0.4 ± 6.3 mL (RC 12.4 mL). Reproducible monitoring of aneurysm sac contents in EVAR patients is feasible with multispectral MRI in combination with our semi-automatic post-processing tool.