Peer-review started: July 21, 2019
First decision: September 21, 2019
Revised: October 11, 2019
Accepted: November 20, 2019
Article in press: November 20, 2019
Published online: January 28, 2020
Automated, accurate, objective, and quantitative medical image segmentation has remained a challenging goal in computer science since its inception. This study applies the technique of convolutional neural networks (CNNs) to the task of segmenting carotid arteries to aid in the assessment of pathology.
To investigate CNN’s utility as an ancillary tool for researchers who require accurate segmentation of carotid vessels.
An expert reader delineated vessel wall boundaries on 4422 axial T2-weighted magnetic resonance images of bilateral carotid arteries from 189 subjects with clinically evident atherosclerotic disease. A portion of this dataset was used to train two CNNs (one to segment the vessel lumen and the other to segment the vessel wall) with the remaining portion used to test the algorithm’s efficacy by comparing CNN segmented images with those of an expert reader.
Overall quantitative assessment between automated and manual segmentations was determined by computing the DICE coefficient for each pair of segmented images in the test dataset for each CNN applied. The average DICE coefficient for the test dataset (CNN segmentations compared to expert’s segmentations) was 0.96 for the lumen and 0.87 for the vessel wall. Pearson correlation values and the intra-class correlation coefficient (ICC) were computed for the lumen (Pearson = 0.98, ICC = 0.98) and vessel wall (Pearson = 0.88, ICC = 0.86) segmentations. Bland-Altman plots of area measurements for the CNN and expert readers indicate good agreement with a mean bias of 1%-8%.
Although the technique produces reasonable results that are on par with expert human assessments, our application requires human supervision and monitoring to ensure consistent results. We intend to deploy this algorithm as part of a software platform to lessen researchers’ workload to more quickly obtain reliable results.
Core tip: Accurate segmentation of carotid arteries is useful in assessing the degree of heart disease in general and vascular diseases (such as atherosclerosis) in particular. Until recently, obtaining accurate segmentation could only be accomplished through the work of an experienced researcher requiring a large investment of time and effort. Over the last several years, the method of convolutional neural networks has demonstrated its efficacy in a number of fields. In this study, we apply this method to magnetic resonance images acquired from subjects with clinically evident atherosclerotic disease and compare the resulting segmentations with those determined by experienced researchers.