4D MRI virtual catheter automatically evaluates aortic flow

A newly created four-dimensional (4D) virtual catheter technique allows for reproducible, automated estimation of blood flow in patients with congenital bicuspid aortic valve (BAV), reported authors of an Oct. 8 study published in Radiology.

BAV is the most common congenital heart defect and is often associated with severe aortopathy—a disease of the aorta—explained first author Mohammed S. M. Elbaz, PhD, and colleagues. Other 4D flow MRI techniques have shed some insight into the causes of aortopathy, but translating the imaging method to clinical use has been tough. 

“To address these limitations, we propose to use 4D flow MRI as the basis for a personalized noninvasive mathematical model that mimics the catheter-based probing of intra-aortic hemodynamics: a virtual catheter,” Elbaz, with Northwestern University’s Feinberg School of Medicine, and co-authors wrote. “We hypothesize that the proposed virtual catheter technique would enable a reproducible and systematic quantitative identification of altered volumetric time-resolved intra-aortic hemodynamics along the aorta center in patients with BAV.”

Elbaz and colleagues retrospectively collected data from 57 patients with BAV and 34 healthy participants who underwent an aortic 4D flow MRI between November 2011 and August 2014. Healthy patients who underwent test-retest exams within two weeks were used to determine reproducibility. Volumetric intra-aortic hemodynamics were automatically taken using 4D flow MRI within the virtual catheter.

The virtual technique demonstrated “high” reproducibility in measuring intra-aortic blood flow dynamics, including kinetic energy, viscous energy loss and vorticity. Those with BAV had higher viscous energy loss and vorticity values along the center volume of the aorta vessel compared to healthy patients.

“An important challenge in assessing intra-aortic hemodynamics at 4D flow MRI is the known variations in aorta size and shape among different individuals, disease stages, and even during healthy aging in the same individual,” the researchers explained. “Our proposed virtual catheter can automatically adapt to each patient-specific aorta shape and size to ensure reliable patient-specific evaluation and systematic comparison among patients."

In a related editorial, Dimitris Mitsouras, PhD, and Michael D. Hope, MD, both with the University of California San Francisco’s Department of Radiology and Biomedical Imaging, explained more research will be needed to verify the study results.

The “last hurdle” to doing so, they explained, is well-designed longitudinal studies to identify and standardize key parameters that affect treatment for BAV-associated aortopathy.

“Elbaz et al offer a set of readily measured and reproducible hemodynamic markers,” the editorialists concluded. “These markers have the potential to add to or modulate our existing arsenal of measurements in 4D flow MRI with which we continue our journey toward improving risk stratification for this disease.”