Virtual monochromatic imaging reduces beam hardening artefacts in cardiac interior photon counting computed tomography: a phantom study with cadaveric specimens

Abstract

In interior cardiac computed tomography (CT) imaging, the x-ray beam is collimated to a limited field-of-view covering the heart volume, which decreases the radiation exposure to surrounding tissues. Spectral CT enables the creation of virtual monochromatic images (VMIs) through a computational material decomposition process. This study investigates the utility of VMIs for beam hardening (BH) reduction in interior cardiac CT, and further, the suitability of VMIs for coronary artery calcium (CAC) scoring and volume assessment is studied using spectral photon counting detector CT (PCD-CT). Ex vivo coronary artery samples (N=18) were inserted in an epoxy rod phantom. The rod was scanned in the conventional CT geometry, and subsequently, the rod was positioned in a torso phantom and re-measured in the interior PCD-CT geometry. The total energy (TE) 10-100 keV reconstructions from PCD-CT were used as a reference. The low energy 10-60 keV and high energy 60-100 keV data were used to perform projection domain material decomposition to polymethyl methacrylate and calcium hydroxylapatite basis. The truncated basis-material sinograms were extended using the adaptive detruncation method. VMIs from 30-180 keV range were computed from the detruncated virtual monochromatic sinograms using filtered back projection. Detrending was applied as a post-processing method prior to CAC scoring. The results showed that BH artefacts from the exterior structures can be suppressed with high (≥100 keV) VMIs. With appropriate selection of the monoenergy (46 keV), the underestimation trend of CAC scores and volumes shown in Bland-Altman (BA) plots for TE interior PCD-CT was mitigated, as the BA slope values were -0.02 for the 46 keV VMI compared to -0.21 the conventional TE image. To conclude, spectral PCD-CT imaging using VMIs could be applied to reduce BH artefacts interior CT geometry, and further, optimal selection of VMI may improve the accuracy of CAC scoring assessment in interior PCD-CT.

Assessing the Sensitivity of Dual-Energy Computed Tomography 3-Material Decomposition for the Detection of Gout

“…Several limitations are present within our study. The use of VMI is known to decrease noise-related and beam-hardening artifacts, 25,26,35 both of which would contribute to the improved performance when combined with 3MD. In this study, we did not investigate the relative contributions of VMI to the detection of MSU when using 3MD.…”

“…Hydroxyapatite is the third material chosen for our implementation of 3MD for these reasons. Virtual monochromatic image is known to reduce beam-hardening artifacts and potentially false-positive findings in DECT 23–26 . To our knowledge, the combination of 3MD and VMI has not been previously described for the detection and quantification of MSU.…”

“…Virtual monochromatic image is known to reduce beam-hardening artifacts and potentially false-positive findings in DECT. [23][24][25][26] To our knowledge, the combination of 3MD and VMI has not been previously described for the detection and quantification of MSU. The purpose of this study was to report the accuracy and precision of 3MD-VMI DECT of MSU and HA phantoms as compared with 2MD and DT postprocessing methods.…”