Development of Magnetic Resonance Coronary Angiography (MRCA) Stenosis Assessment Quantification Method by Comparison With Coronary Computed Tomography Angiography (CTA)

Background:

Diagnosis of significant stenosis of the coronary artery and managing the ischemia is important to prevent cardiac events. Coronary CT angiography (CTA) is one of the current gold standard methods to assess coronary stenosis as well as coronary angiography (CAG), but both coronary CTA and CAG are limited by radiation exposure or contrast media administration.

Magnetic resonance coronary angiography (MRCA) has its advantage in its ability to assess the coronary artery morphology without radiation or contrast media. Unfortunately, the clinical application of MRCA is still challenging mainly because of technical limitation such as its time-consuming image acquisition, inconsistent image quality, and low spatial resolution.

Optimization of MRCA image acquisition process is under great interest and compressed sensing (CS) is one of the promising methods to reduce the acquisition time. Although it's noise-like granular characteristics is a weakness due to its random k-space data acquisition. The granularity may affect the interpretation of the MRCA images considering the small diameter of the coronary arteries. To solve this problem, post-processing denoising approach with deep learning reconstruction (dDLR) is proposed, however too much image smoothing may lead to unfavorable image blurring or produce artefactual smoothing leading to the removal of clinically meaningful signal intensity drops across the artery. Hence, merely assessing the noise level is insufficient. Evaluation of the optimized images with coronary CTA, which is one of the current gold standards, is inevitable to assess its clinical feasibility.

The lack of a consensus method to assess the coronary stenosis on MRCA is another problem. MRCA interpretation is generally performed visually, but its quantification is clinically important to detect the significant stenosis. A previous study has reported by investigating the signal intensity (SI) profile across the coronary artery and its drop of 35% corresponded to significant stenosis by coronary angiography (CAG). Although this SI drop phenomenon was not observed in a different study on chronic total obstruction cases. One of the hypothesized reasons is that the SI drop in MRCA is affected not only by the stenosis severity but also the plaque characteristics, which is not assessable by CAG. To confirm this hypothesis coronary CTA is needed, which is a robust modality to assess coronary stenosis and plaque characteristics. Comparison between MRCA with CTA has the potential to give better information for developing a robust method to assess MRCA.