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Validation of a robust method for quantification of three-dimensional growth of the thoracic aorta using deformable image registration
Journal article   Open access   Peer reviewed

Validation of a robust method for quantification of three-dimensional growth of the thoracic aorta using deformable image registration

Zhangxing Bian, Jiayang Zhong, Jeffrey Dominic, Gary E Christensen, Charles R Hatt and Nicholas S Burris
Medical physics (Lancaster), Vol.49(4), pp.2514-2530
04/2022
DOI: 10.1002/mp.15496
PMCID: PMC9305918
PMID: 35106769
url
https://doi.org/10.1002/mp.15496View
Published (Version of record) Open Access

Abstract

Accurate assessment of thoracic aortic aneurysm (TAA) growth is important for appropriate clinical management. Maximal aortic diameter is the primary metric that is used to assess growth, but it suffers from substantial measurement variability. A recently proposed technique, termed Vascular Deformation Mapping (VDM), is able to quantify three-dimensional aortic growth using clinical computed tomography angiography (CTA) data using an approach based on deformable image registration (DIR). However, the accuracy and robustness of VDM remains undefined given the lack of a ground truth from clinical CTA data, and furthermore the performance of VDM relative to standard manual diameter measurements is unknown. To evaluate the performance of the VDM pipeline for quantifying aortic growth we developed a novel and systematic evaluation process to generate 76 unique synthetic CTA growth phantoms (based on 10 unique cases) with variable degrees and locations of aortic wall deformation. Aortic deformation was quantified using two metrics: Area Ratio (AR), defined as the ratio of surface area in triangular mesh elements, and the magnitude of deformation in the normal direction (DiN) relative to the aortic surface. Using these phantoms, we further investigated the effects on VDM's measurement accuracy resulting from factors that influence quality of clinical CTA data such as respiratory translations, slice thickness and image noise. Lastly, we compare the measurement error of VDM TAA growth assessments against two expert raters performing standard diameter measurements of synthetic phantom images. Across our population of 76 synthetic growth phantoms, the median absolute error was 0.063 (IQR: 0.073-0.054) for AR and 0.181mm (IQR: 0.214-0.143mm) for DiN. Median relative error was 1.4% for AR and 3.3% for DiN at the highest tested noise level (CNR = 2.66). Error in VDM output increased with slice thickness, with highest median relative error of 1.5% for AR and 4.1% for DiN at slice thickness of 2.0 mm. Respiratory motion of the aorta resulted in maximal absolute error of 3% AR and 0.6 mm in DiN, but bulk translations in aortic position had a very small effect on measured AR and DiN values (relative errors < 1%). VDM-derived measurements of magnitude and location of maximal diameter change demonstrated significantly high accuracy and lower variability compared to two expert manual raters (p<0.03 across all comparisons). VDM yields accurate, three-dimensional assessment of aortic growth in TAA patients and is robust to factors such as image noise, respiration-induced translations and differences in patient position. Further, VDM significantly outperformed two expert manual raters in assessing the magnitude and location of aortic growth despite optimized experimental measurement conditions. These results support validation of the VDM technique for accurate quantification of aortic growth in patients and highlight several important advantages over diameter measurements. This article is protected by copyright. All rights reserved.
 thoracic aortic aneurysm vascular deformation mapping deformable registration

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