2023-12-06 17:43:11
Hungarian researchers studied the differences in volume of coronary plaques obtained on virtual monoenergetic reconstructions from photon counting CT. In an article published in the European Journal of Radiology, they show significant volume differences depending on the calcium level of the plaques observed.
Photon counting CT (CP-CT) is a promising technique for the evaluation of coronary arteries with higher spatial and temporal resolution than current generation scanners.
Monoenergetic reconstructions enabled by photon counting CT can improve detection of coronary plaques
Compared to conventional energy-integrating detectors, photon-counting detectors record the energy of each individual photon and directly convert X-ray photons into electrical signals without the need for reflective septa, resulting in improved spatial resolution, noise reduction and improved soft tissue contrast. It has already been demonstrated on histological samples of atherosclerotic plaque that different plaque components and vessel lumens can be accurately differentiated using spectral data from a CT-CP system.
Additionally, this allows for monoenergetic virtual images that can help improve coroscan due to reduced artifacts and contrast-to-noise ratio. Additionally, CP-CT allows for sharper delineation of structures such as calcifications because it provides superior spatial resolution. Therefore, the use of different monoenergetic reconstructions can improve coronary plaque detection. However, monoenergetic virtual images also change the Hounsfield unit (HU) values of voxels and can therefore impact plaque volume estimates that are often made using fixed HU thresholds.
A study to measure the volume differences of plates obtained by monioenergetic virtual images
A Hungarian study published in the European Journal of Radiology aims to evaluate how the quantification of individual plaque components changes with respect to different monoenergetic levels obtained by CT-CP. The researchers carried out dual-source coroscanners and the virtual monoenergetic images were reconstructed between 40 and 180 keV in increments of 10 keV. Polychromatic images at 120 kVp (T3D) were used as reference. Quantitative plaque analysis was performed on the T3D images and the segmentation masks were copied onto the monoenergetic reconstructions. Volumes of calcified plaque (>350 Hounsfield, HU units), noncalcified plaque (30 to 350 HU), and low-attenuation noncalcified plaque (−100 to 30 HU) were calculated using fixed thresholds.
Considerable differences observed depending on the calcium level of the plaque
They analyzed 51 plaques from 51 patients (67% men, mean age 65 ± 12 years). Average attenuation and contrast-to-noise ratio decrease significantly with increasing keV levels, with similar values observed between T3D and 70 keV images (299 ± 209 versus 303 ± 225 HU, for average HU; 15 .5 ± 3.7 vs. 15.8 ± 3.5, p = 0.32 for signal-to-noise ratio). The average volume of non-calcified plaques was comparable between T3D and 100-180 keV reconstructions. There was a decrease in the mean volume of calcified plaques, with a significant difference between all monoenergetic images and T3D. The volume of low attenuation plaques increased with increasing keV levels and all monoenergetic images showed a significant difference from T3D except 50 keV (28.0 ± 30.8 mm3 and 28.6 ± 30.1 mm3, respectively).
The researchers concluded from their work that estimated coronary plaque volumes differ significantly between monoenergetic virtual images. Normalization protocols are needed to achieve comparable results for future studies, particularly for low-attenuation plaque volume which is currently defined using a fixed HU threshold.
Bruno Benque with European Radiology
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