A Blooming correction technique for improved vasa vasorum detection using an ultra-high-resolution photon-counting detector CT

Ex vivo coronary calcium volume quantification using a high-spatial-resolution clinical photon-counting-detector computed tomography

Purpose

Coronary artery calcification (CAC) is an important indicator of coronary disease. Accurate volume quantification of CAC is challenging using computed tomography (CT) due to calcium blooming, which is a consequence of limited spatial resolution. Ex vivo coronary specimens were scanned on an ultra-high-resolution (UHR) clinical photon-counting detector (PCD) CT scanner, and the accuracy of CAC volume estimation was compared with a state-of-the-art conventional energy-integrating detector (EID) CT, a previous-generation investigational PCD-CT, and micro-CT.

Approach

CAC specimens (n = 13 ) were scanned on EID-CT and PCD-CT using matched parameters (120 kV, 9.3 mGy CTDI vol ). EID-CT images were reconstructed using our institutional routine clinical protocol for CAC quantification. UHR PCD-CT data were reconstructed using a sharper kernel. An image-based denoising algorithm was applied to the PCD-CT images to achieve similar noise levels as EID-CT. Micro-CT images served as the volume reference standard. Calcification images were segmented, and their volume estimates were compared. The CT data were further compared with previous work using an investigational PCD-CT.

Results

Compared with micro-CT, CT volume estimates had a mean absolute percent error of 24.1 % ± 25.6 % for clinical PCD-CT, 60.1 % ± 48.2 % for EID-CT, and 51.1 % ± 41.7 % for previous-generation PCD-CT. Clinical PCD-CT absolute percent error was significantly (p < 0.01 ) lower than both EID-CT and previous generation PCD-CT. The mean calcification CT number and contrast-to-noise ratio were both significantly (p < 0.01 ) higher in clinical PCD-CT relative to EID-CT.

Conclusions

UHR clinical PCD-CT showed reduced calcium blooming artifacts and further enabled improved accuracy of CAC quantification beyond that of conventional EID-CT and previous generation PCD-CT systems.

Measurement of enhanced vasa vasorum density in a porcine carotid model using photon counting detector CT

Purpose

The onset of atherosclerosis is preceded by changes in blood perfusion within the arterial wall due to localized proliferation of the vasa vasorum. The purpose of this study was to quantify these changes in spatial density of the vasa vasorum using a research whole-body photon-counting detector CT (PCD-CT) scanner and a porcine model.

Approach

Vasa vasorum angiogenesis was stimulated in the left carotid artery wall of anesthetized pigs ( n = 5 ) while the right carotid served as a control. After a 6-week recovery period, the animals were scanned on the PCD-CT prior to and after injection of iodinated contrast. Annular regions of interest were used to measure wall enhancement in the injured and control arteries. The exact Wilcoxon-signed rank test was used to determine whether a significant difference in contrast enhancement existed between the injured and control arterial walls.

Results

The greatest arterial wall enhancement was observed following contrast recirculation. The wall enhancement measurements made over these time points revealed that the enhancement was greater in the injured artery for 13/16 scanned arterial regions. Using an exact Wilcoxon-signed rank test, a significantly increased enhancement ratio was found in injured arteries compared with control arteries ( p = 0.013 ). Vasa vasorum angiogenesis was confirmed in micro-CT scans of excised arteries.

Conclusions

Whole-body PCD-CT scanners can be used to detect and quantify the increased perfusion occurring within the porcine carotid arterial wall resulting from an increased density of vasa vasorum.

Quantification of Coronary Calcification using High-Resolution Photon-Counting-Detector CT and an Image Domain Denoising Algorithm

Coronary artery calcification (CAC) is an important indicator of coronary disease. Accurate volume quantification of coronary calcification, especially calcifications smaller than a few mm, using computed tomography (CT) is challenging due to calcium blooming, which is a consequence of limited spatial resolution. In this study, ex-vivo coronary specimens were scanned on a clinical photon-counting detector (PCD) CT scanner and the estimated coronary calcification volume were compared with a conventional energy-integrating detector (EID) CT. Scans were performed using the same tube potential and radiation dose (120 kV, 9.3 mGy CTDI_vol). EID-CT images were reconstructed using our routine clinical protocol for CAC quantification. PCD-CT images were reconstructed using a sharper reconstruction kernel than that was supported by the EID-CT scanner, resulting in improved resolution but higher image noise levels. An image-based denoising algorithm was applied to the PCD-CT images to achieve similar noise levels as the EID-CT images. Calcifications were segmented to estimate the volume. Micro-CT images of the same calcifications were acquired and served as the reference standard. PCD-CT images showed reduced calcium blooming artifacts compared to EID-CT. Calcification volume estimates were found to overestimate the micro-CT volumes by 9 ± 12% for PCD-CT data, and 24 ± 18% for the EID-CT data. Volume quantification accuracy of the current PCD-CT system was also found to be superior to a previous-generation investigational PCD-CT scanner with larger detector pixels.