Image-Quality Assessment of Polyenergetic and Virtual Monoenergetic Reconstructions of Unenhanced CT Scans of the Head: Initial Experiences with the First Photon-Counting CT Approved for Clinical Use

Abstract

In 2021, the first clinical photon-counting CT (PCCT) was introduced. The purpose of this study is to evaluate the image quality of polyenergetic and virtual monoenergetic reconstructions in unenhanced PCCTs of the head. A total of 49 consecutive patients with unenhanced PCCTs of the head were retrospectively included. The signals ± standard deviations of the gray and white matter were measured at three different locations in axial slices, and a measure of the artifacts below the cranial calvaria and in the posterior fossa between the petrous bones was also obtained. The signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated for all reconstructions. In terms of the SNRs and CNRs, the polyenergetic reconstruction is superior to all virtual monoenergetic reconstructions (p < 0.001). In the MERs, the highest SNR is found in the 70 keV MER, and the highest CNR is in the 65 keV MER. In terms of artifacts below the cranial calvaria and in the posterior fossa, certain MERs are superior to polyenergetic reconstruction (p < 0.001). The PCCT provided excellent image contrast and low-noise profiles for the differentiation of the grey and white matter. Only the artifacts below the calvarium and in the posterior fossa still underperform, which is attributable to the lack of an artifact reduction algorithm in image postprocessing. It is conceivable that the usual improvements in image postprocessing, especially with regard to glaring artifacts, will lead to further improvements in image quality.

Low-Dose High-Resolution Photon-Counting CT of the Lung: Radiation Dose and Image Quality in the Clinical Routine

“…Sartoretti et al provide further information on these novel QIR algorithms [ 18 ]. Both preclinical studies using PCCT prototypes and early studies with the first PCCT scanner that is approved for clinical use show promising results [ 15 , 16 , 19 , 20 , 21 ].…”

Photon Counting CT Angiography of the Head and Neck: Image Quality Assessment of Polyenergetic and Virtual Monoenergetic Reconstructions

“…However, the noise also increased to the same extent so that the MER did not perform better compared to the PER in terms of SNR and CNR in most cases. It is expected that the post-processing of the MER will be improved in the near future and that the noise can be further minimized [ 8 ]. Considering the qualitative analysis of the present study, the MERs do not yet offer improvements for clinical reporting.…”

“…MERs can be calculated in a wide range of energy levels, which are expressed in kiloelectron volts (keV) [ 7 ]. MERs can be used according to their respective strengths, which are relevant in neurovascular imaging: MERs with low keV levels provide increased soft tissue and iodine contrast, allowing for enhanced visualization of brain lesions and vessels [ 3 , 5 , 8 ], while higher keV levels can be used to reduce beam hardening artifacts; e.g., in order to improve vessel assessment after neurovascular interventions [ 9 , 10 ].…”

Photon-counting detector CT: early clinical experience review

“…The use of VMI for routine clinical PCD-CT imaging has exemplarily been shown for abdominal imaging, 28,66 cardiac CT [69][70][71] and coronary calcium quantification, 72 high-pitch CT angiography of the aorta, 67 lung 35,73 and brain imaging. 74 The benefits of low keV VMI include better visualization of small low-contrast structures and increased iodine signal. For CT angiography examinations, the latter may be particularly promising as high pitch CTA together with low keV VMI may set new standards in terms of radiation and contrast media dose reductions.…”