Comparison of Photon-counting Detector and Energy-integrating Detector CT for Visual Estimation of Coronary Percent Luminal Stenosis

Photon-counting CT: An updated review of clinical results

Photon-counting computed tomography (PCD-CT) is an advancing imaging technology that offers improved spatial resolution, energy-resolved imaging, and spectral post-processing compared to conventional CT. These advantages contribute to increased contrast-to-noise ratio, reduction of metal artifacts and radiation dose and the elimination of electronic noise. Since the introduction of clinical PCD-CT, research topics have expanded beyond technical feasibility to evaluation of the impact on patient care. A previous review outlined the technological principles, early clinical results of PCD-CT and early applications in clinical practice. Since then, photon-counting technology has made significant progress, leading to a growing number of clinical applications across various specialties. This review builds upon prior work by summarizing the latest clinical applications of PCCT, including cardiovascular, thoracic, abdominal, musculoskeletal, neuro and pediatric imaging, while addressing current challenges and future directions for clinical implementation.

Current and future applications of photon-counting computed tomography in cardiovascular medicine

Photon-counting CT (PCCT) represents a transformative advancement in cardiac imaging, addressing key limitations of conventional CT. This review synthesises current evidence to demonstrate how PCCT's superior spatial resolution, enhanced tissue characterisation and multienergy capabilities broaden the diagnostic potential of cardiac CT. Applications include the precise detection and quantification of coronary artery calcifications, evaluation of coronary plaque burden and composition, improved assessment of coronary stents, and comprehensive myocardial tissue characterisation and perfusion analysis. By offering high-quality spectral information and detailed tissue characterisation, PCCT provides a non-invasive alternative for assessing coronary artery disease and myocardial pathology, reducing the need for invasive coronary angiography and cardiac MRI. Despite ongoing challenges in technology and clinical implementation, PCCT has the potential to revolutionise cardiovascular diagnostics, optimise diagnostic workflows and enhance patient care through more accurate, streamlined and comprehensive assessments.

Learned high resolution energy-integrating detector CT angiography: Harnessing the power of ultra-high-resolution photon counting detector CT

BACKGROUND

Coronary computed tomography angiography (cCTA) is a widely used noninvasive diagnostic exam to assess patients for coronary artery disease (CAD). However, the spatial resolution of most CT scanners is limited due to the use of energy-integrating detectors (EIDs).

PURPOSE

To develop a convolutional neural network (Improved LUMEN visualization through Artificial super-resoluTion imagEs (ILUMENATE)) informed by photon-counting-detector (PCD)-CT to improve EID-CT image resolution and determine its impact on cCTA.

MATERIALS AND METHODS

With IRB approval, 30 patients undergoing clinically indicated cCTA were scanned with EID-CT (SOMATOM Force, Siemens Healthineers, Forchheim, Germany) and subsequently with ultra-high-resolution (UHR) PCD-CT (NAEOTOM Alpha, Siemens Healthineers) on the same day. ILUMENATE was trained on eight patient PCD-CT datasets (67,890 patch pairs with 90% for training (61,101), 10% reserved for validation (6,789)) and applied to 22 unseen EID-CT cases. Spatial resolution was evaluated using line profiles and percent diameter stenosis quantified with a severity score assigned. Two experienced radiologists, blinded to image type, selected preferred series and scored images for overall quality, sharpness, and noise comparing original EID-CT and ILUMENATE output.

RESULTS

Visual assessment and line profiles showed substantial resolution improvement with ILUMENATE. Percent diameter stenosis was significantly reduced (mean ± standard deviation: 4.42% ± 4.82%) using ILUMENATE (p < 0.001) with nine lesions shifting down in severity score. Readers preferred ILUMENATE images in 22/22 cases and scored ILUMENATE superiorly for overall quality, sharpness, and noise (p < 0.05).

CONCLUSIONS

ILUMENATE enhanced image resolution, resulting in improved overall image quality, reduced calcium blooming artifacts, and improved lumen visibility in cCTA exams performed using EID-CT. This could potentially allow for improved accessibility to UHR image quality, allowing for more accurate assessment of CAD.

Comparison of radiation dose and image quality for abdominal CT exams using photon-counting and energy-integrating CT: A self-controlled study including optimized patient positioning

INTRODUCTION

Photon-counting detector (PCD) CT represents a major advancement in CT imaging, offering improved image quality and reduced radiation dose compared to traditional energy-integrating detector (EID) CT. This study compared image quality and radiation dose using a self-controlled approach, while evaluating the impact of patient positioning.

METHODS

This retrospective study analyzed data from 200 patients who underwent abdominal CT scans on both EID (Somatom Definition Flash) and PCD (Naeotom Alpha) scanners. After applying inclusion criteria for proper positioning (within ±20 mm) and stable anatomical conditions, 119 patients were included. Radiation doses were assessed using CTDIvol, and image quality was evaluated via CT numbers, noise levels, signal-to-noise ratio (SNR), SNR to dose (SNRD), and contrast-to-noise ratio to dose (CNRD).

RESULTS

The study found a median radiation dose reduction of 37 % with PCD CT compared to EID CT (p < 0.05). Image quality assessments revealed significant improvements with PCD CT, including reduced noise levels (up to 31 % in contrast-enhanced organs) and enhanced SNRD (33-51 % increase). CNRD improved by 60-76 %, indicating superior imaging performance of PCD CT. However, 36 % of patients on EID were positioned outside the ±20 mm range, which could adversely affect image quality and radiation dose, underscoring the need for more precise patient positioning.

CONCLUSION

This study confirms that PCD CT achieves substantial reductions in radiation dose while enhancing image quality. However, accurate patient positioning is crucial to fully optimize these benefits. Automated tools that ensure proper positioning may be necessary to consistently maintain image quality and reduce radiation exposure.

IMPLICATIONS FOR PRACTICE

PCD CT offers improved patient safety and diagnostic imaging. Automated positioning tools are essential to optimize and consistently maintain image quality and minimize radiation exposure.

Photon-counting detector computed tomography in cardiac imaging

Photon-counting detector computed tomography (PCD-CT) has emerged as a revolutionary technology in CT imaging. PCD-CT offers significant advancements over conventional energy-integrating detector CT, including increased spatial resolution, artefact reduction and inherent spectral imaging capabilities. In cardiac imaging, PCD-CT can offer a more accurate assessment of coronary artery disease, plaque characterisation and the in-stent lumen. Additionally, it might improve the visualisation of myocardial fibrosis through qualitative late enhancement imaging and quantitative extracellular volume measurements. The use of PCD-CT in cardiac imaging holds significant potential, positioning itself as a valuable modality that could serve as a one-stop-shop by integrating both angiography and tissue characterisation into a single examination. Despite its potential, large-scale clinical trials, standardisation of protocols and cost-effectiveness considerations are required for its broader integration into clinical practice. This narrative review provides an overview of the current literature on PCD-CT regarding the possibilities and limitations of cardiac imaging.

Intraindividual Comparison of Ultrahigh-Spatial-Resolution Photon-Counting Detector CT and Energy-Integrating Detector CT for Coronary Stenosis Measurement

BACKGROUND

A recent simulation study proposed that stenosis measurements on coronary computed tomography (CT) angiography are influenced by the improved spatial resolution of photon-counting detector (PCD)-CT. The aim of the current study was to evaluate the impact of ultrahigh-spatial-resolution (UHR) on coronary stenosis measurements and Coronary Artery Disease Reporting and Data System (CAD-RADS) reclassification rates in patients undergoing coronary CT angiography on both PCD-CT and energy-integrating detector (EID)-CT and to compare measurements against quantitative coronary angiography.

METHODS

Patients with coronary calcification on EID-CT (collimation, 192×0.6 mm) were prospectively enrolled for a research coronary CT angiography with UHR PCD-CT (collimation, 120×0.2 mm) within 30 days (between April 1, 2023 and January 31, 2024). PCD-CT was acquired with the same or lower CT dose index and equivalent contrast media volume as EID-CT. Percentage diameter stenosis (PDS) for calcified, partially calcified, and noncalcified lesions were compared between scanners. Patient-level reclassification rates for CAD-RADS were evaluated. The accuracy of PDS measurements was validated against quantitative coronary angiography in patients who underwent invasive coronary angiography.

RESULTS

In total, PDS of 278 plaques were quantified in 49 patients (calcified, 202; partially calcified, 51; noncalcified, 25). PCD-CT-based PDS values were lower than EID-CT measurements for calcified (45.1±20.7 versus 54.6±19.2%; P<0.001) and partially calcified plaques (44.3±19.6 versus 54.9±20.0%; P<0.001), without significant differences for noncalcified lesions (39.1±15.2 versus 39.0±16.0%; P=0.98). The reduction in stenosis degrees led to a 49.0% (24/49) reclassification rate to a lower CAD-RADS with PCD-CT. In a subset of 12 patients with 56 lesions, UHR-based PDS values showed higher agreement with quantitative coronary angiography (mean difference, 7.3%; limits of agreement, -10.7%/25.2%) than EID-CT measurements (mean difference, 17.4%; limits of agreement, -6.9%/41.7%).

CONCLUSIONS

Compared with conventional EID-CT, UHR PCD-CT results in lower PDS values and more accurate stenosis measurements in coronary plaques with calcified components and leads to a substantial Coronary Artery Disease Reporting and Data System reclassification rate in 49.0% of patients.