University of Twente Student Theses


Quantification of calcification in peripheral arterial disease using dual-energy computed tomography angiography

Wiggers, R.B.M. (2022) Quantification of calcification in peripheral arterial disease using dual-energy computed tomography angiography.

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Embargo date:31 May 2024
Abstract:Peripheral arterial disease (PAD) is associated with a high risk of adverse events such as amputation, even in patients who undergo successful revascularization. Amputation leads to substantial disability and increases mortality rate, which may be up to 50% within 5 years. Identifying patients at high risk of adverse events remains difficult. Previous research has shown that up to 54% of patients undergoing major amputation may not receive any vascular procedure in the year leading up to amputation, underlining the need for better risk stratification. In coronary artery disease, quantitative calcium scores have been established as a robust predictor of adverse events. Based on this result, this study aimed to investigate the potential for quantification of peripheral calcification and its association with clinical outcomes. As a first step towards this goal, a systematic review was conducted. This study found a significant association between more severe calcification and severity of ischemia at clinical presentation, technical success of endovascular treatment and primary patency. Additionally, a trend was observed towards increased rates of major adverse cardiovascular events, all-cause mortality and major adverse limb events, which includes target lesion revascularization and major amputation. However, there were several limitations, including heterogeneity in calcium scores used and the use of imaging not standard in PAD, such as unenhanced computed tomography (CT). Therefore, this study investigated the use of dual-energy CT angiography (CTA) for segmentation of calcifications and quantitative calcium density measurement, to aim towards standardized calcification scoring based on CTA, a standard imaging modality in PAD. To this end, two dual-energy CT-based methods were investigated: material decomposition analysis and virtual non-contrast (VNC) scan generation. Both method were validated in a phantom experiment. Material decomposition analysis showed good separation between contrast agent and calcification and allowed for accurate calcium density scoring; the latter should be confirmed in vivo, preferably through histopathologic analysis. The VNC scan exhibited good suppression of the contrast agent, but also suppressed hydroxyapatite phantom to some extent. In the subsequent patient data analysis, segmentation of calcifications on VNC scans and through material decomposition were compared to reference segmentations based on conventional CTA by means of the Dice similarity coefficient. The material decomposition result had a moderate Dice coefficient, but showed good accuracy with regard to the pattern of calcification and small calcifications. The VNC segmentation performed better, but was time-consuming and laborious. Both methods should be developed further; nevertheless, dual-energy based calcium scoring is promising as a means towards improved risk stratification, which may allow for targeted measures to prevent adverse events in high-risk PAD patients.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine
Programme:Technical Medicine MSc (60033)
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