CT Angiography of the Aorta Using Photon-counting Detector CT with Reduced Contrast Media Volume

PCD-CT enables contrast media reduction in abdominal imaging compared to an individualized kV-adapted contrast media injection protocol on EID-CT

OBJECTIVES

This study aims to demonstrate reduced iodine contrast media (CM) in routine abdominal CT scans in portal venous phase (PVP) using a photon-counting detector CT (PCD-CT) compared to total body weight (TBW) and kV-adapted CM injection protocols on a state-of-the-art energy-integrating detector CT (EID-CT) while maintaining sufficient image quality (IQ).

MATERIALS AND METHODS

Consecutive contrast-enhanced abdominal PVP CT scans from an EID-CT (Nov 2022-March 2024) and a PCD-CT (Sep 2023-Dec 2023) were compared. CM parameters (total iodine load (TIL), iodine delivery rate (IDR) and dosing factor (DF)) were reported. An individualized acquisition and CM injection protocol based on TBW and kV was applied for the EID-CT and a TBW adapted CM injection protocol was used for the PCD-CT. Objective IQ was evaluated with mean attenuation (Hounsfield Units, HU), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR)). Subjective IQ was assessed via a 5-point Likert scale by 2 expert readers based on diagnostic confidence.

RESULTS

Based on 91 EID-CT scans and 102 PCD-CT scans a TIL reduction of 20.1 % was observed for PCD-CT. PCD-CT demonstrated significantly higher SNR (9.9 ± 1.7 vs. 9.1 ± 1.8, p < 0.001) and CNR (5.1 ± 1.7 vs. 4.3 ± 1.3, p < 0.001) compared to EID-CT. Subjective IQ assessment showed that all scans had sufficient diagnostic IQ.

CONCLUSIONS

PCD-CT allows for CM reduction while providing higher SNR and CNR compared to EID-CT, using clinical individualized scan and CM injection protocols.

Comparison of low-energy virtual monoenergetic images between photon-counting CT and energy-integrating detectors CT: A phantom study

PURPOSE

The purpose of this study was to assess image quality and dose level using a photon-counting CT (PCCT) scanner by comparison with a dual-source CT (DSCT) scanner on virtual monoenergetic images (VMIs) at low energy levels.

MATERIALS AND METHODS

A phantom was scanned using a DSCT and a PCCT with a volume CT dose index of 11 mGy, and additionally at 6 mGy and 1.8 mGy for PCCT. Noise power spectrum and task-based transfer function were evaluated from 40 to 70 keV on VMIs to assess noise magnitude and noise texture (fav) and spatial resolution on two iodine inserts (f50), respectively. A detectability index (d') was computed to assess the detection of two contrast-enhanced lesions according to the energy level used.

RESULTS

For all energy levels, noise magnitude values were lower with PCCT than with DSCT at 11 and 6 mGy, but greater at 1.8 mGy. fav values were higher with PCCT than with DSCT at 11 mGy (8.6 ± 1.5 [standard deviation [SD]%), similar at 6 mGy (1.6 ± 1.5 [SD]%) and lower at 1.8 mGy (-17.8 ± 2.2 [SD]%). For both inserts, f50 values were higher with PCCT than DSCT at 11- and 6 mGy for all keV levels, except at 6 mGy and 40 keV. d' values were higher with PCCT than with DSCT at 11- and 6 mGy for all keV and both simulated lesions. Similar d' values to those of the DSCT at 11 mGy, were obtained at 2.25 mGy for iodine insert at 2 mg/mL and at 0.96 mGy for iodine insert at 4 mg/mL at 40 keV.

CONCLUSION

Compared to DSCT, PCCT reduces noise magnitude and improves noise texture, spatial resolution and detectability on VMIs for all low-keV levels.

Critical but commonly neglected factors that affect contrast medium administration in CT

OBJECTIVE

Past decades of research into contrast media injections and optimization thereof in radiology clinics have focused on scan acquisition parameters, patient-related factors, and contrast injection protocol variables. In this review, evidence is provided that a fourth bucket of crucial variables has been missed which account for previously unexplained phenomena and higher-than-expected variability in data. We propose how these critical factors should be considered and implemented in the contrast-medium administration protocols to optimize contrast enhancement.

METHODS

This article leverages a combination of methodologies for uncovering and quantifying confounding variables associated with or affecting the contrast-medium injection. Engineering benchtop equipment such as Coriolis flow meters, pressure transducers, and volumetric measurement devices are combined with small, targeted systematic evaluations querying operators, equipment, and the physics and fluid dynamics that make a seemingly simple task of injecting fluid into a patient a complex and non-linear endeavor.

RESULTS

Evidence is presented around seven key factors affecting the contrast-medium injection including a new way of selecting optimal IV catheters, degraded performance from longer tubing sets, variability associated with the mechanical injection system technology, common operator errors, fluids exchanging places stealthily based on gravity and density, wasted contrast media and inefficient saline flushes, as well as variability in the injected flow rate vs. theoretical expectations.

CONCLUSION

There remain several critical, but not commonly known, sources of error associated with contrast-medium injections. Elimination of these hidden sources of error where possible can bring immediate benefits and help to drive standardized and optimized contrast-media injections.

CRITICAL RELEVANCE STATEMENT

This review brings to light the commonly neglected/unknown factors negatively impacting contrast-medium injections and provides recommendations that can result in patient benefits, quality improvements, sustainability increases, and financial benefits by enabling otherwise unachievable optimization.

KEY POINTS

How IV contrast media is administered is a rarely considered source of CT imaging variability. IV catheter selection, tubing length, injection systems, and insufficient flushing can result in unintended variability. These findings can be immediately addressed to improve standardization in contrast-enhanced CT imaging.

Neurovascular Imaging with Ultra-High-Resolution Photon-Counting CT: Preliminary Findings on Image-Quality Evaluation

BACKGROUND AND PURPOSE

The first-generation photon-counting detector CT was recently introduced into clinical practice and represents a promising innovation in high-resolution CT imaging. The purpose of this study was to assess the image quality of ultra-high-resolution photon-counting detector CT compared with energy-integrating detector CT and to explore different reconstruction kernel sharpness levels for the evaluation of intracranial aneurysms.

MATERIALS AND METHODS

Ten patients with intracranial saccular aneurysms who had previously undergone conventional energy-integrating detector CT were prospectively enrolled. CT angiograms were acquired on a clinical dual-source photon-counting detector CT in ultra-high-resolution mode and reconstructed with 4 vascular kernels (Bv36, Bv40, Bv44, Bv48). Quantitative and qualitative image-quality parameters of the intracranial arteries were evaluated. For the quantitative analysis (image noise, SNR, contrast-to-noise ratio), ROIs were manually placed at standard anatomic intracranial and extracranial locations by 1 author. In addition, vessel border sharpness was evaluated quantitatively. For the qualitative analysis, 3 blinded neuroradiologists rated photon-counting detector CT and energy-integrating detector CT image quality for the evaluation of the intracranial vessels (ie, the aneurysms and 9 standard vascular branching locations) on a 5-point Likert-type scale. Additionally, readers independently selected their preferred kernel among the 4 kernels evaluated on photon-counting detector CT.

RESULTS

In terms of quantitative image quality, Bv48, the sharpest kernel, yielded increased image noise and decreased SNR and contrast-to-noise ratio parameters compared with Bv36, the smoothest kernel. Compared with energy-integrating detector CT, the Bv48 kernel offered better quantitative image quality for the evaluation of small intracranial vessels (P < .001). Image-quality ratings of the Bv48 were superior to those of the energy-integrating detector CT and not significantly different from ratings of the B44 reconstruction kernel. When comparing side by side all 4 photon-counting detector reconstruction kernels, readers selected the B48 kernel as the best to visualize the aneurysms in 80% of cases.

CONCLUSIONS

Ultra-high-resolution photon-counting detector CT provides improved image quality for neurovascular imaging. Although the less sharp kernels provided superior SNR and contrast-to-noise ratio, the sharpest kernels delivered the best subjective image quality on photon-counting detector CT for the evaluation of intracranial aneurysms.

Photon counting CT clinical adoption, integration, and workflow

Photon counting CT was recently introduced into clinical practice [Rajendran K, Petersilka M, Henning A, Shanblatt ER, Schmidt B, Flohr TG, Ferrero A, Baffour F, Diehn FE, Yu L, Rajiah P, Fletcher JG, Leng S, McCollough CH. First Clinical Photon-counting Detector CT System: Technical Evaluation. Radiology 2022;303(1):130-138. doi: https://doi.org/10.1148/radiol.212579 ]. Photon counting detectors (PCD) afford better spatial resolution, radiation dose efficiency, and iodine contrast-to-noise than EID-CT [Leng S, Bruesewitz M, Tao S, Rajendran K, Halaweish AF, Campeau NG, Fletcher JG, McCollough CH. Photon-counting Detector CT: System Design and Clinical Applications of an Emerging Technology. Radiographics 2019;39(3):729-743. doi: https://doi.org/10.1148/rg.2019180115 ); (Leng S, Rajendran K, Gong H, Zhou W, Halaweish AF, Henning A, Kappler S, Baer M, Fletcher JG, McCollough CH. 150-mum Spatial Resolution Using Photon-Counting Detector Computed Tomography Technology: Technical Performance and First Patient Images. Invest Radiol 2018;53(11):655-662. doi: https://doi.org/10.1097/RLI.0000000000000488 )(Booij R, van der Werf NR, Dijkshoorn ML, van der Lugt A, van Straten M. Assessment of Iodine Contrast-To-Noise Ratio in Virtual Monoenergetic Images Reconstructed from Dual-Source Energy-Integrating CT and Photon-Counting CT Data. Diagnostics (Basel) 2022;12(6). doi: https://doi.org/10.3390/diagnostics12061467 ); (Sawall S, Klein L, Amato C, Wehrse E, Dorn S, Maier J, Heinze S, Schlemmer HP, Ziener CH, Uhrig M, Kachelriess M. Iodine contrast-to-noise ratio improvement at unit dose and contrast media volume reduction in whole-body photon-counting CT. Eur J Radiol 2020;126:108909. doi: https://doi.org/10.1016/j.ejrad.2020.108909 ] while also maintaining multienergy CT (MECT) capabilities[Flohr T, Petersilka M, Henning A, Ulzheimer S, Ferda J, Schmidt B. Photon-counting CT review. Phys Med 2020;79:126-136. doi: https://doi.org/10.1016/j.ejmp.2020.10.030 ]. This article will review the clinical adoption of PCD-CT including protocol development, clinical applications, clinical integration and workflow considerations. Protocol development is institution specific and involves collaborative decision-making among radiologists, physicists, and technologists. Key PCD clinical applications include radiation exposure reduction, intravenous contrast volume reduction, and improved lesion conspicuity. Patients who would most benefit from these improvements may preferentially be scanned with PCD CT. With numerous available reconstructions, radiologists should be strategic in the series sent to PACS for interpretation and routinely sending spectral series to PACS can facilitate integration with clinical workflow. The Society of Abdominal Radiology PCD Emerging Technology Commission endorsed this article.

Photon-Counting Detector CT Angiography Versus Digital Subtraction Angiography in Patients with Peripheral Arterial Disease

RATIONALE AND OBJECTIVES

This study aims to compare the diagnostic confidence of photon-counting detector CT angiography (PCD-CTA) depending on the used vascular reformatting kernels with digital subtraction angiography (DSA) as diagnostic reference standard in peripheral arterial occlusive disease (PAOD).

MATERIAL AND METHODS

In 39 patients, 45 lower extremity PCD-CTA with subsequent DSA were analyzed. Advanced PAOD (Fontaine stage 4) was ascertained in 77.8% of patients. CTA post-processing comprised three vascular kernels (Bv36/48/56). Objective image quality assessment included vessel attenuation, image noise, contrast-to-noise (CNR) and signal-to-noise ratios (SNR). Subjective evaluation of calcium blooming, vessel sharpness, luminal attenuation and image noise was performed by three radiologists. Diagnostic performance and concordance to DSA were assessed.

RESULTS

The luminal attenuation remained kernel-independent constant. With sharper kernels, image noise increased substantially, while SNR and CNR decreased. Subjective reduction of calcium blooming and increased vessel sharpness were noted for the sharp Bv56 kernel. While sensitivity in stenosis quantification was comparable between kernels (81.6% vs. 81.5% vs. 81.0%, p = 0.797), specificity increased slightly higher sharpness (71.1% vs. 76.9% vs. 79.6%, p = 0.067). Diagnostic concordance of stenosis ratings compared to DSA increased likewise (Bv36 vs. Bv56, p = 0.002). Severe crural vessel calcifications had no influence on sensitivity, regardless of kernel selection. Contrarily, specificity was substantially worse in severely calcified tibial vessels but could be improved by using the sharp Bv56 kernel (Bv36 vs. Bv56 p = 0.024). Diagnostic confidence was highest for Bv56.

CONCLUSION

In lower leg PCD-CTA, sharp convolution kernels increase diagnostic confidence compared to DSA by improved vessel delineation and reduced calcium blooming with acceptable image noise.

Optimization of photon counting CT for cardiac imaging in patients with left ventricular assist devices: An in-depth assessment of metal artifacts

PURPOSE

Photon counting CT (PCCT) holds promise for mitigating metal artifacts and can produce virtual mono-energetic images (VMI), while maintaining temporal resolution, making it a valuable tool for characterizing the heart. This study aimed to evaluate and optimize PCCT for cardiac imaging in patients during left ventricular assistance device (LVAD) therapy by conducting an in-depth objective assessment of metal artifacts and visual grading.

METHODS

Various scan and reconstruction settings were tested on a phantom and further evaluated on a patient acquisition to identify the optimal protocol settings. The phantom comprised an empty thoracic cavity, supplemented with heart and lungs from a cadaveric lamb. The heart was implanted with an LVAD (HeartMate 3) and iodine contrast. Scans were performed on a PCCT (NAEOTOM Alpha, Siemens Healthcare). Metal artifacts were assessed by three objective methods: Hounsfield units (HU)/SD measurements (DiffHU and SDARTIFACT), Fourier analysis (AmplitudeLowFreq), and depicted LVAD volume in the images (BloomVol). Radiologists graded metal artifacts and the diagnostic interpretability in the LVAD lumen, cardiac tissue, lung tissue, and spinal cord using a 5-point rating scale. Regression and correlation analysis were conducted to determine the assessment method most closely associated with acquisition and reconstruction parameters, as well as the objective method demonstrating the highest correlation with visual grading.

RESULTS

Due to blooming artifacts, the LVAD volume fluctuated between 27.0 and 92.7 cm3. This variance was primarily influenced by kVp, kernel, keV, and iMAR (R2 = 0.989). Radiologists favored pacemaker iMAR, 3 mm slice thickness, and T3D keV and kernel Bv56f for minimal metal artifacts in cardiac tissue assessment, and 110 keV and Qr40f for lung tissue interpretation. The model adequacy for DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was 0.28, 0.76, 0.29, and 0.99 respectively for phantom data, and 0.95, 0.98, 1.00, and 0.99 for in-vivo data. For in-vivo data, the correlation between visual grading (VGSUM) and DiffHU SDARTIFACT, AmplitueLowFreq, and BloomVol was -0.16, -0.01, -0.48, and -0.40 respectively.

CONCLUSION

We found that optimal scan settings for LVAD imaging involved using 120 kVp and IQ level 80. Employing T3D with pacemaker iMAR, the sharpest allowed vascular kernel (Bv56f), and VMI at 110 keV with kernel Qr40 yields images suitable for cardiac imaging during LVAD-therapy. Volumetric measurements of the LVAD for determination of the extent of blooming artifacts was shown to be the best objective method to assess metal artifacts.

Photon-Counting Versus Dual-Source CT for Transcatheter Aortic Valve Implantation Planning

BACKGROUND

Cardiovascular CT is required for planning transcatheter aortic valve implantation (TAVI).

PURPOSE

To compare image quality, suitability for TAVI planning, and radiation dose of photon-counting CT (PCCT) with that of dual-source CT (DSCT).

MATERIAL AND METHODS

Retrospective study on consecutive TAVI candidates with aortic valve stenosis who underwent contrast-enhanced aorto-ilio-femoral PCCT and/or DSCT between 01/2022 and 07/2023. Signal-to-noise (SNR) and contrast-to-noise ratio (CNR) were calculated by standardized ROI analysis. Image quality and suitability for TAVI planning were assessed by four independent expert readers (two cardiac radiologists, two cardiologists) on a 5-point-scale. CT dose index (CTDI) and dose-length-product (DLP) were used to calculate effective radiation dose (eRD).

RESULTS

300 patients (136 female, median age: 81 years, IQR: 76-84) underwent 302 CT examinations, with PCCT in 202, DSCT in 100; two patients underwent both. Although SNR and CNR were significantly lower in PCCT vs. DSCT images (33.0 ± 10.5 vs. 47.3 ± 16.4 and 47.3 ± 14.8 vs. 59.3 ± 21.9, P < .001, respectively), visual image quality was higher in PCCT vs. DSCT (4.8 vs. 3.3, P < .001), with moderate overall interreader agreement among radiologists and among cardiologists (κ = 0.60, respectively). Image quality was rated as "excellent" in 160/202 (79.2%) of PCCT vs. 5/100 (5%) of DSCT cases. Readers found images suitable to depict the aortic valve hinge points and to map the femoral access path in 99% of PCCT vs. 85% of DSCT (P < 0.01), with suitability ranked significantly higher in PCCT vs. DSCT (4.8 vs. 3.3, P < .001). Mean CTDI and DLP, and thus eRD, were significantly lower for PCCT vs. DSCT (22.4 vs. 62.9; 519.4 vs. 895.5, and 8.8 ± 4.5 mSv vs. 15.3 ± 5.8 mSv; all P < .001).

CONCLUSION

PCCT improves image quality, effectively avoids non-diagnostic CT imaging for TAVI planning, and is associated with a lower radiation dose compared to state-of-the-art DSCT. Radiologists and cardiologists found PCCT images more suitable for TAVI planning.

Cardiovascular Imaging, Climate Change, and Environmental Sustainability

Environmental exposures including poor air quality and extreme temperatures are exacerbated by climate change and are associated with adverse cardiovascular outcomes. Concomitantly, the delivery of health care generates substantial atmospheric greenhouse gas (GHG) emissions contributing to the climate crisis. Therefore, cardiac imaging teams must be aware not only of the adverse cardiovascular health effects of climate change, but also the downstream environmental ramifications of cardiovascular imaging. The purpose of this review is to highlight the impact of climate change on cardiovascular health, discuss the environmental impact of cardiovascular imaging, and describe opportunities to improve environmental sustainability of cardiac MRI, cardiac CT, echocardiography, cardiac nuclear imaging, and invasive cardiovascular imaging. Overarching strategies to improve environmental sustainability in cardiovascular imaging include prioritizing imaging tests with lower GHG emissions when more than one test is appropriate, reducing low-value imaging, and turning equipment off when not in use. Modality-specific opportunities include focused MRI protocols and low-field-strength applications, iodine contrast media recycling programs in cardiac CT, judicious use of US-enhancing agents in echocardiography, improved radiopharmaceutical procurement and waste management in nuclear cardiology, and use of reusable supplies in interventional suites. Finally, future directions and research are highlighted, including life cycle assessments over the lifespan of cardiac imaging equipment and the impact of artificial intelligence tools. Keywords: Heart, Safety, Sustainability, Cardiovascular Imaging Supplemental material is available for this article. © RSNA, 2024.

Reduction of contrast medium for transcatheter aortic valve replacement planning using a spectral detector CT: a prospective clinical trial

INTRODUCTION

This study investigated the use of dual-energy spectral detector computed tomography (CT) and virtual monoenergetic imaging (VMI) reconstructions in pre-interventional transcatheter aortic valve replacement (TAVR) planning. We aimed to determine the minimum required contrast medium (CM) amount to maintain diagnostic CT imaging quality for TAVR planning.

METHODS

In this prospective clinical trial, TAVR candidates received a standardized dual-layer spectral detector CT protocol. The CM amount (Iohexol 350 mg iodine/mL, standardized flow rate 3 mL/s) was reduced systematically after 15 patients by 10 mL, starting at 60 mL (institutional standard). We evaluated standard, and 40- and 60-keV VMI reconstructions. For image quality, we measured signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and diameters in multiple vessel sections (i.e., aortic annulus: diameter, perimeter, area; aorta/arteries: minimal diameter). Mixed regression models (MRM), including interaction terms and clinical characteristics, were used for comparison.

RESULTS

Sixty consecutive patients (mean age, 79.4 ± 7.5 years; 28 females, 46.7%) were included. In pre-TAVR CT, the CM reduction to 40 mL is possible without affecting the image quality (MRM: SNR: -1.1, p = 0.726; CNR: 0.0, p = 0.999). VMI 40-keV reconstructions showed better results than standard reconstructions with significantly higher SNR (+ 6.04, p < 0.001). Reduction to 30 mL CM resulted in a significant loss of quality (MRM: SNR: -12.9, p < 0.001; CNR: -13.9, p < 0.001), regardless of the reconstruction. Across the reconstructions, we observed no differences in the metric evaluation (p > 0.914).

CONCLUSION

Among TAVR candidates undergoing pre-interventional CT at a dual-layer spectral detector system, applying 40 mL CM is sufficient to maintain diagnostic image quality. VMI 40-keV reconstructions improve the vessel attenuation and are recommended for evaluation.

CLINICAL RELEVANCE STATEMENT

Contrast medium reduction to 40 mL in pre-interventional transcatheter aortic valve replacement CT using dual-energy CT maintains image quality, while 40-keV virtual monoenergetic imaging reconstructions enhance vessel attenuation. These results offer valuable recommendations for interventional transcatheter aortic valve replacement evaluation and potentially improve nephroprotection in patients with compromised renal function.

KEY POINTS

• Patients undergoing transcatheter aortic valve replacement (TAVR), requiring pre-interventional CT, are often multimorbid with impaired renal function. • Using a spectral detector dual-layer CT, contrast medium reduction to 40 mL is feasible, maintaining diagnostic image quality. • The additional application of virtual monoenergetic image reconstructions with 40 keV improves vessel attenuation significantly in clinical practice.

Protocol optimization for abdominal imaging using photon-counting CT: a consensus of two academic institutions

PURPOSE

Photon-counting detector CT (PCD CT) is a promising technology for abdominal imaging due to its ability to provide high spatial and contrast resolution images with reduced patient radiation exposure. However, there is currently no consensus regarding the optimal imaging protocols for PCD CT. This article aims to present the PCD CT abdominal imaging protocols used by two tertiary care academic centers in the United States.

METHODS

A review of PCD CT abdominal imaging protocols was conducted by two abdominal radiologists at different academic institutions. Protocols were compared in terms of acquisition parameters and reconstruction settings. Both imaging centers independently selected similar protocols for PCD CT abdominal imaging, using QuantumPlus mode.

RESULTS

There were some differences in the use of reconstruction kernels and iterative reconstruction levels, however the individual combination at each site resulted in similar image impressions. Overall, the imaging protocols used by both centers provide high-quality images with low radiation exposure.

CONCLUSION

These findings provide valuable insights into the development of standardized protocols for PCD CT abdominal imaging, which can help to ensure consistent as well as high-quality imaging across different institutions and allow for future multicenter research collaborations.

Feasibility of Reduced Iodine Loads for Vascular Assessment Prior to Transcatheter Aortic Valve Implantation (TAVI) Using Spectral Detector CT

Reduced iodine loads for computed tomography (CT)-based vascular assessment prior to transcatheter aortic valve implantation (TAVI) may be feasible in conjunction with a spectral detector CT scanner. This prospective single-center study considered 100 consecutive patients clinically referred for pre-TAVI CT. They were examined on a dual-layer detector CT scanner to obtain an ECG-gated cardiac scan and a non-ECG-gated aortoiliofemoral scan. Either a standard contrast media (SCM) protocol using 80 mL Iohexol 350 mgI/mL (iodine load: 28 gI) or a body-mass-index adjusted reduced contrast media (RCM) protocol using 40-70 mL Iohexol 350 mgI/mL (iodine load: 14-24.5 gI) were employed. Conventional images and virtual monoenergetic images at 40-80 keV were reconstructed. A threshold of 250 HU was set for sufficient attenuation along the arterial access pathway. A qualitative assessment used a five-point Likert scale. Sufficient attenuation in the thoracic aorta was observed for all patients in both groups using conventional images. In the abdominal, iliac, and femoral segments, sufficient attenuation was observed for the majority of patients when using virtual monoenergetic images (SCM: 96-100% of patients, RCM: 88-94%) without statistical difference between both groups. Segments with attenuation measurements below the threshold remained qualitatively assessable as well. Likert scores were 'excellent' for virtual monoenergetic images 50 keV and 55 keV in both groups (RCM: 1.2-1.4, SCM: 1.2-1.3). With diagnostic image quality maintained, it can be concluded that reduced iodine loads of 14-24.5 gI are feasible for pre-TAVI vascular assessment on a spectral detector CT scanner.

Photon-Counting Detector Computed Tomography (PCD-CT): A New Era for Cardiovascular Imaging? Current Status and Future Outlooks

Photon-counting detector computed tomography (PCD-CT) represents a revolutionary new generation of computed tomography (CT) for the imaging of patients with cardiovascular diseases. Since its commercial market introduction in 2021, numerous studies have identified advantages of this new technology in the field of cardiovascular imaging, including improved image quality due to an enhanced contrast-to-noise ratio, superior spatial resolution, reduced artifacts, and a reduced radiation dose. The aim of this narrative review was to discuss the current scientific literature, and to find answers to the question of whether PCD-CT has yet led to a true step-change and significant progress in cardiovascular imaging.

Reduced Intravenous Contrast Dose Portal Venous Phase Photon-Counting Computed Tomography Compared With Conventional Energy-Integrating Detector Portal Venous Phase Computed Tomography

OBJECTIVE

The aim of this study was to compare portal venous phase photon-counting CT (PCCT) using 20 cc less than weight-based contrast dosing with energy-integrating detector CT (EID-CT) using weight-based dosing by quantitative and qualitative analysis.

METHODS

Fifty adult patients who underwent a reduced intravenous contrast dose portal venous phase PCCT from May 1, 2023, to August 10, 2023, and a prior portal-venous EID-CT with weight-based contrast dosing were retrospectively identified. Hounsfield units (HU) and noise (SD of HU) were obtained from region-of-interest measurements on 70-keV PCCT and EID-CT in 4 hepatic segments, the main and right portal vein, and both paraspinal muscles. Signal-to-noise and contrast-to-noise ratios were computed. Three abdominal radiologists qualitatively assessed overall image quality, hepatic enhancement, and confidence for metastasis identification on 5-point Likert scales. Readers also recorded the presence/absence of hepatic metastases. Quantitative variables were compared with paired t tests, and multiple comparisons were accounted for with a Bonferroni-adjusted α level of .0016. Ordinal logistic regression was used to evaluate qualitative assessments. Interreader agreement for hepatic metastases was calculated using Fleiss' κ.

RESULTS

Fifty patients (32 women; mean [SD] age, 64 [13] years) were included. There was no significant difference in hepatic HU, portal vein HU, noise, and signal-to-noise or contrast-to-noise ratio between reduced contrast dose portal venous phase PCCT versus EID-CT (all Ps > 0.0016). Image quality, degree of hepatic enhancement, and confidence for metastasis identification were not different for reduced dose PCCT 70-keV images and EID-CT (P = 0.06-0.69). κ Value for metastasis identification was 0.86 (95% confidence interval, 0.70-1.00) with PCCT and 0.78 (95% confidence interval, 0.59-0.98) with EID-CT.

CONCLUSION

Reduced intravenous contrast portal venous phase PCCT 70-keV images had similar attenuation and image quality as EID-CT with weight-based dosing. Metastases were identified with near-perfect agreement in reduced dose PCCT 70-keV images.

Photon-counting CT-angiography in pre-TAVR aortic annulus assessment: effects of retrospective vs. prospective ECG-synchronization on prosthesis valve selection

To compare the diagnostic value of ultrahigh-resolution CT-angiography (UHR-CTA) compared with high-pitch spiral CTA (HPS-CTA) using a first-generation, dual-source photon-counting CT (PCD-CT) scanner for preprocedural planning of transcatheter aortic valve replacement (TAVR). Clinically referred patients with severe aortic valve stenosis underwent both, retrospective ECG-gated cardiac UHR-CTA (collimation: 120 × 0.2 mm) and prospective ECG-triggered aortoiliac HPS-CTA (collimation: 144 × 0.4 mm, full spectral capabilities) for TAVR planning from August 2022 to March 2023. Radiation dose was extracted from the CT reports, and the effective dose was calculated. Two radiologists analyzed UHR-CTA and HPS-CTA datasets, assessing the image quality of the aortic annulus, with regard to the lumen visibility and margin delineation using a 4-point visual-grading scale (ranges: 4 = "excellent" to 1 = "poor"). Aortic annulus area (AAA) measurements were taken for valve prosthesis sizing, with retrospective UHR-CTA serving as reference standard. A total of 64 patients were included (mean age, 81 years ± 7 SD; 28 women) in this retrospective study. HPS-CTA showed a lower radiation dose, 4.1 mSv vs. 12.6 mSv (p < 0.001). UHR-CTA demonstrated higher image quality to HPS-CTA (median score, 4 [IQR, 3-4] vs. 3 [IQR, 2-3]; p < 0.001). Quantitative assessments of AAA from both CTA datasets were strongly positively correlated (mean 477.4 ± 91.1 mm2 on UHR-CTA and mean 476.5 ± 90.4 mm2 on HPS-CTA, Pearson r2 = 0.857, p < 0.001) with a mean error of 22.3 ± 24.6 mm2 and resulted in identical valve prosthesis sizing in the majority of patients (91%). Patients with lower image quality on HPS-CTA (score value 1 or 2, n = 28) were more likely to receive different sizing recommendations (82%). Both UHR-CTA and HPS-CTA acquisitions using photon-counting CT technology provided reliable aortic annular assessments for TAVR planning. While UHR-CTA offers superior image quality, HPS-CTA is associated with lower radiation exposure. However, severely impaired image quality on HPS-CTA may impact on prosthesis sizing, suggesting that immediate post-scan image evaluations may require complementary UHR-CTA scanning.

Radiology: Cardiothoracic Imaging Highlights 2023

Radiology: Cardiothoracic Imaging publishes novel research and technical developments in cardiac, thoracic, and vascular imaging. The journal published many innovative studies during 2023 and achieved an impact factor for the first time since its inaugural issue in 2019, with an impact factor of 7.0. The current review article, led by the Radiology: Cardiothoracic Imaging trainee editorial board, highlights the most impactful articles published in the journal between November 2022 and October 2023. The review encompasses various aspects of coronary CT, photon-counting detector CT, PET/MRI, cardiac MRI, congenital heart disease, vascular imaging, thoracic imaging, artificial intelligence, and health services research. Key highlights include the potential for photon-counting detector CT to reduce contrast media volumes, utility of combined PET/MRI in the evaluation of cardiac sarcoidosis, the prognostic value of left atrial late gadolinium enhancement at MRI in predicting incident atrial fibrillation, the utility of an artificial intelligence tool to optimize detection of incidental pulmonary embolism, and standardization of medical terminology for cardiac CT. Ongoing research and future directions include evaluation of novel PET tracers for assessment of myocardial fibrosis, deployment of AI tools in clinical cardiovascular imaging workflows, and growing awareness of the need to improve environmental sustainability in imaging. Keywords: Coronary CT, Photon-counting Detector CT, PET/MRI, Cardiac MRI, Congenital Heart Disease, Vascular Imaging, Thoracic Imaging, Artificial Intelligence, Health Services Research © RSNA, 2024.

Image quality of abdominal photon-counting CT with reduced contrast media dose: Evaluation of reduced contrast media protocols during the COVID19 pandemic supply shortage

Rationale and objectives

Aim of this study was to assess the impact of contrast media dose (CMD) reduction on diagnostic quality of photon-counting detector CT (PCD-CT) and energy-integrating detector CT (EID-CT).

Methods

CT scans of the abdominal region with differing CMD acquired in portal venous phase on a PCD-CT were included and compared to EID-CT scans. Diagnostic quality and contrast intensity were rated. Additionally, readers had to assign the scans to reduced or regular CMD. Regions-of-interest (ROIs) were placed in defined segments of portal vein, inferior vena cava, liver, spleen, kidneys, abdominal aorta and muscular tissue. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated.

Results

Overall 158 CT scans performed on a PCD-CT and 68 examinations on an EID-CT were analyzed. Overall diagnostic quality showed no significant differences for PCD-CT with standard CMD which scored a median 5 (IQR:5-5) and PCD-CT with 70% CMD scoring 5 (4-5). (For PCD-CT, 71.69% of the examinations with reduced CMD were assigned to regular CMD by the readers, for EID-CT 9.09%. Averaged for all measurements SNR for 50% CMD was reduced by 19% in PCD-CT (EID-CT 34%) and CNR by 48% (EID-CT 56%). Virtual monoenergetic images (VMI)50keV for PCD-CT images acquired with 50% CMD showed an increase in SNR by 72% and CNR by 153%.

Conclusions

Diagnostic interpretability of PCD-CT examinations with reduction of up to 50% CMD is maintained. PCD-CT deducted scans especially with 70% CMD were often not recognized as CMD reduced scans. Compared to EID-CT less decline in SNR and CNR is observed for CMD reduced PCD-CT images. Employing VMI50keV for CMD-reduced PCD-CT images compensated for the effects.

Photon-counting CT in Thoracic Imaging: Early Clinical Evidence and Incorporation Into Clinical Practice

Photon-counting CT (PCCT) is an emerging advanced CT technology that differs from conventional CT in its ability to directly convert incident x-ray photon energies into electrical signals. The detector design also permits substantial improvements in spatial resolution and radiation dose efficiency and allows for concurrent high-pitch and high-temporal-resolution multienergy imaging. This review summarizes (a) key differences in PCCT image acquisition and image reconstruction compared with conventional CT; (b) early evidence for the clinical benefit of PCCT for high-spatial-resolution diagnostic tasks in thoracic imaging, such as assessment of airway and parenchymal diseases, as well as benefits of high-pitch and multienergy scanning; (c) anticipated radiation dose reduction, depending on the diagnostic task, and increased utility for routine low-dose thoracic CT imaging; (d) adaptations for thoracic imaging in children; (e) potential for further quantitation of thoracic diseases; and (f) limitations and trade-offs. Moreover, important points for conducting and interpreting clinical studies examining the benefit of PCCT relative to conventional CT and integration of PCCT systems into multivendor, multispecialty radiology practices are discussed.

Photon-Counting Detector CT Virtual Monoenergetic Images for Coronary Artery Stenosis Quantification: Phantom and In Vivo Evaluation

BACKGROUND. Calcium blooming causes stenosis overestimation on coronary CTA. OBJECTIVE. The purpose of this article was to evaluate the impact of virtual monoenergetic imaging (VMI) reconstruction level on coronary artery stenosis quantification using photon-counting detector (PCD) CT. METHODS. A phantom containing two custom-made vessels (representing 25% and 50% stenosis) underwent PCD CT acquisitions without and with simulated cardiac motion. A retrospective analysis was performed of 33 patients (seven women, 26 men; mean age, 71.3 ± 9.0 [SD] years; 64 coronary artery stenoses) who underwent coronary CTA by PCD CT followed by invasive coronary angiography (ICA). Scans were reconstructed at nine VMI energy levels (40-140 keV). Percentage diameter stenosis (PDS) was measured, and bias was determined from the ground-truth stenosis percentage in the phantom and ICA-derived quantitative coronary angiography measurements in patients. Extent of blooming artifact was measured in the phantom and in calcified and mixed plaques in patients. RESULTS. In the phantom, PDS decreased for 25% stenosis from 59.9% (40 keV) to 13.4% (140 keV) and for 50% stenosis from 81.6% (40 keV) to 42.3% (140 keV). PDS showed lowest bias for 25% stenosis at 90 keV (bias, 1.4%) and for 50% stenosis at 100 keV (bias, -0.4%). Blooming artifacts decreased for 25% stenosis from 61.5% (40 keV) to 35.4% (140 keV) and for 50% stenosis from 82.7% (40 keV) to 52.1% (140 keV). In patients, PDS for calcified plaque decreased from 70.8% (40 keV) to 57.3% (140 keV), for mixed plaque decreased from 69.8% (40 keV) to 56.3% (140 keV), and for noncalcified plaque was 46.6% at 40 keV and 54.6% at 140 keV. PDS showed lowest bias for calcified plaque at 100 keV (bias, 17.2%), for mixed plaque at 140 keV (bias, 5.0%), and for noncalcified plaque at 40 keV (bias, -0.5%). Blooming artifacts decreased for calcified plaque from 78.4% (40 keV) to 48.6% (140 keV) and for mixed plaque from 73.1% (40 keV) to 44.7% (140 keV). CONCLUSION. For calcified and mixed plaque, stenosis severity measurements and blooming artifacts decreased at increasing VMI reconstruction levels. CLINICAL IMPACT. PCD CT with VMI reconstruction helps overcome current limitations in stenosis quantification on coronary CTA.

Evaluation of ECG-Gated, High-Pitch Thoracoabdominal Angiographies With Dual-Source Photon-Counting Detector Computed Tomography

PURPOSE

The aim of this study was to evaluate the radiation dose, image quality, and the potential of virtual monoenergetic imaging (VMI) reconstructions of high-pitch computed tomography angiography (CTA) of the thoracoabdominal aorta on a dual-source photon-counting detector-CT (PCD-CT) in comparison with an energy-integrating detector-CT (EID-CT), with a special focus on low-contrast attenuation.

METHODS

Consecutive patients being referred for an electrocardiogram (ECG)-gated, high-pitch CTA of the thoracoabdominal aorta prior to transcatheter aortic valve replacement (TAVR), and examined on the PCD-CT, were included in this prospective single-center study. For comparison, a retrospective patient group with ECG-gated, high-pitch CTA examinations of the thoracoabdominal aorta on EID-CT with a comparable scan protocol was matched for gender, body mass index, height, and age. Virtual monoenergetic imaging reconstructions from 40 to 120 keV were performed. Enhancement and noise were measured in 7 vascular segments and the surrounding air as mean and standard deviation of CT values. The radiation dose was noted and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Finally, a subgroup analysis was performed, comparing VMI reconstructions from 40 keV to 70 keV in patients with at least a 50% decrease in contrast attenuation between the ascending aorta and femoral arteries.

RESULTS

Fifty patients (mean age 77.0±14.5 years; 31 women) were included. The radiation dose was significantly lower on the PCD-CT (4.2±1.4 vs. 7.2±2.2 mGy; p<0.001). With increasing keV, vascular noise, SNR, and CNR decreased. Intravascular attenuation was significantly higher on VMI at levels from 40 to 65, compared with levels of 120 keV (p<0.01 and p<0.005, respectively). On the PCD-CT, SNR was significantly higher in keV levels 40 and 70 (all p<0.001), and CNR was higher at keV levels 40 and 45 (each p<0.001), compared with scans on the EID-CT. At VMI ≤60 keV, image noise was also significantly higher than that in the control group. The subgroup analysis showed a drastically improved diagnostic performance of the low-keV images in patients with low-contrast attenuation.

CONCLUSION

The ECG-gated CTA of the thoracoabdominal aorta in high-pitch mode on PCD-CT have significantly lower radiation dose and higher objective image quality than EID-CT. In addition, low-keV VMI can salvage suboptimal contrast studies, further reducing radiation dose by eliminating the need for repeat scans.

CLINICAL IMPACT

ECG-gated CT-angiographies of the thoracoabdominal aorta can be acquired with a lower radtiation dose and a better image quality by using a dual-source photon-countinge detector CT. Furthermore, the inherent spectral data offers the possiblity to improve undiagnostic images and thus saves the patient from further radiation and contrast application.

Image Quality and Radiation Dose of CTPA With Iodine Maps: A Prospective Randomized Study of High-Pitch Mode Photon-Counting Detector CT Versus Energy-Integrating Detector CT

BACKGROUND. Dual-energy CT pulmonary angiography (CTPA) with energy-integrating detector (EID) technology is limited by the inability to use high-pitch technique. OBJECTIVE. The purpose of this study was to compare the image quality of anatomic images and iodine maps between high-pitch photon-counting detector (PCD) CTPA and dual-energy EID CTPA. METHODS. This prospective study included 117 patients (70 men and 47 women; median age, 65 years) who underwent CTPA to evaluate for pulmonary embolism between March 2022 and November 2022. Fifty-eight patients were randomized to undergo PCD CTPA (pitch, 2.0), and 59 were randomized to undergo EID CTPA (pitch, 0.55). For each examination, 120-kV polychromatic images, 60-keV virtual monogenetic images (VMIs), and iodine maps were reconstructed. One radiologist measured CNR and SNR. Three radiologists independently assessed subjective image quality (on a scale of 1-4, with a score of 1 denoting highest quality). Radiation dose was recorded. RESULTS. SNR and CNR were higher for PCD CTPA than for EID CTPA for polychromatic images and VMIs, for all assessed vessels other than the left upper lobe artery. For example, for PCD CTPA versus EID CTPA, the right lower lobe artery on polychromatic images had an SNR of 34.5 versus 28.0 (p = .003) and a CNR of 29.2 versus 24.4 (p = .001), and on VMIs it had an SNR of 43.2 versus 32.7 (p = .005) and a CNR of 37.4 versus 29.3 (p = .002). For both scanners for readers 1 and 2, the median image quality score for polychromatic images and VMIs was 1, although distributions indicated significantly better scores for PCD CTPA than for EID CTPA for polychromatic images for reader 1 (p = .02) and reader 2 (p = .005) and for VMIs for reader 1 (p = .001) and reader 2 (p = .006). The image quality of anatomic image sets was not different between PCD CTPA and EID CTPA for reader 3 (p > .05). The image quality of iodine maps was not different between PCD CTPA and EID CTPA for any reader (p > .05). For PCD CTPA versus EID CTPA, the CTDIvol was 3.9 versus 4.5 mGy (p = .03), and the DLP was 123.5 mGy × cm versus 157.0 mGy × cm (p < .001). CONCLUSION. High-pitch PCD CTPA provided anatomic images with better subjective and objective image quality versus dual-energy EID CTPA, with lower radiation dose. Iodine maps showed no significant difference in image quality between scanners. CLINICAL IMPACT. CTPA may benefit from the PCD CT technique.

Saving Contrast Media in Coronary CT Angiography with Photon-Counting Detector CT

RATIONALE AND OBJECTIVES

To determine the optimal virtual monoenergetic image (VMI) energy level and the potential of contrast-media (CM) reduction for coronary computed tomography angiography (CCTA) with photon-counting detector CT (PCD-CT).

MATERIALS AND METHODS

In this institutional review board-approved study, patients who underwent CCTA with dual-source PCD-CT with an identical scan protocol and radiation dose were included. In group 1, CCTA was performed with our standard CM protocol (volume: 72-85.2 mL, 370 mg iodine/mL). VMIs were reconstructed from 40 to 60 keV at 5 keV increments. Objective image quality (IQ) (vascular attenuation, image noise, and contrast-to-noise ratio [CNR]) was measured. Two blinded, independent readers rated subjective IQ (overall IQ, subjective image contrast, and subjective noise using a five-point discrete visual scale). Results of group 1 served to determine the best VMI level for CCTA. In group 2, CM volume was reduced by 20%, and in group 3 by another 20%.

RESULTS

A total of 100 patients were enrolled (45 females, mean age 54 ± 13 years). Inter-reader agreement was good-to-excellent for all comparisons (κ > 0.6). In group 1, the best VMI level regarding objective and subjective IQ was 45 keV, which was selected as the reference for groups 2 and 3. For group 2, mean vascular attenuation was 890 Hounsfield units (HU) and mean CNR was 26, with no differences compared to group 1, 45 keV for both objective and subjective IQ. For group 3, mean vascular attenuation was 676 HU and mean CNR was 21, and all patients were rated as diagnostic except one (severe motion artifacts).

CONCLUSION

Increased IQ of PCD-CT can be used for considerable CM volume reduction while still maintaining a diagnostic IQ of CCTA.

An Intra-Individual Comparison of Low-keV Photon-Counting CT versus Energy-Integrating-Detector CT Angiography of the Aorta

This retrospective study aims to provide an intra-individual comparison of aortic CT angiographies (CTAs) using first-generation photon-counting-detector CT (PCD-CT) and third-generation energy-integrating-detector CT (EID-CT). High-pitch CTAs were performed with both scanners and equal contrast-agent protocols. EID-CT employed automatic tube voltage selection (90/100 kVp) with reference tube current of 434/350 mAs, whereas multi-energy PCD-CT scans were generated with fixed tube voltage (120 kVp), image quality level of 64, and reconstructed as 55 keV monoenergetic images. For image quality assessment, contrast-to-noise ratios (CNRs) were calculated, and subjective evaluation (overall quality, luminal contrast, vessel sharpness, blooming, and beam hardening) was performed independently by three radiologists. Fifty-seven patients (12 women, 45 men) were included with a median interval between examinations of 12.7 months (interquartile range 11.1 months). Using manufacturer-recommended scan protocols resulted in a substantially lower radiation dose in PCD-CT (size-specific dose estimate: 4.88 ± 0.48 versus 6.28 ± 0.50 mGy, p < 0.001), while CNR was approximately 50% higher (41.11 ± 8.68 versus 27.05 ± 6.73, p < 0.001). Overall image quality and luminal contrast were deemed superior in PCD-CT (p < 0.001). Notably, EID-CT allowed for comparable vessel sharpness (p = 0.439) and less pronounced blooming and beam hardening (p < 0.001). Inter-rater agreement was good to excellent (0.58-0.87). Concluding, aortic PCD-CTAs facilitate increased image quality with significantly lower radiation dose compared to EID-CTAs.

Reduced versus standard dose contrast volume for contrast-enhanced abdominal CT in overweight and obese patients using photon counting detector technology vs. second-generation dual-source energy integrating detector CT

PURPOSE

To compare image quality of contrast-enhanced abdominal-CT using 1st-generation Dual Source Photon-Counting Detector CT (DS-PCD-CT) versus 2nd-generation Dual-Source Energy Integrating-Detector CT (DS-EID-CT) in patients with BMI ≥ 25, applying two different contrast agent volumes, vendor proposed protocols and different virtual monoenergetic images (VMI).

METHOD

68 overweight (BMI ≥ 25 kgm2) patients (median age: 65 years; median BMI 33.3 kgm2) who underwent clinically indicated, portal-venous contrast-enhanced abdominal-CT on a commercially available 1st-generation DS-PCD-CT were prospectively included if they already have had a pre-exam on 2nd-generation DS-EID-CT using a standardized exam protocol. Obesity were defined by BMI-calculation (overweight: 25-29.9, obesity grade I: 30-34.9; obesity grade II: 35-39.9; obesity grade III: > 40) and by the absolute weight value. Body weight adapted contrast volume (targeted volume of 1.2 mL/kg for the 1st study and 0.8 mL/kg for the 2nd study) was applied in both groups. Dual Energy mode was used for both the DS-PCD-CT and the DS-EID-CT. Polychromatic images and VMI (40 keV and 70 keV) were reconstructed for both the DS-EID-CT and the DS-PCD-CT data (termed T3D). Two radiologists assessed subjective image quality using a 5-point Likert-scale. Each reader drew ROIs within parenchymatous organs and vascular structures to analyze image noise, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR).

RESULTS

Median time interval between scans was 12 months (Min: 6 months; Max: 36 months). BMI classification included overweight (n = 10, 14.7 %), obesity grade I (n = 38, 55.9 %), grade II (n = 13, 19.1 %) and grade III (n = 7, 10.3 %). The SNR achieved with DS-PCD-CT at QIR level 3was 12.61 vs. 11.47 (QIR 2) vs. 10.53 (DS-EID-CT), irrespective of parenchymatous organs. For vessels, the SNR were 16.73 vs. 14.20 (QIR 2) vs. 12.07 (DS-EID-CT). Moreover, the obtained median noise at QIR level 3 was as low as that of the DS-EID-CT (8.65 vs. 8.65). Both radiologists rated the image quality higher for DS-PCD-CT data sets (p < 0.05). The highest CNR was achieved at 40 keV for both scanners. T3D demonstrated significantly higher SNR and lower noise level compared to 40 keV and 70 keV. Median CTDIvol and DLP values for DS-PCD-CT and DS-EID-CT were 10.90 mGy (IQR: 9.31 - 12.50 mGy) vs. 16.55 mGy (IQR: 15.45 - 18.17 mGy) and 589.50 mGy * cm (IQR: 498.50 - 708.25 mGy * cm) vs. 848.75 mGy * cm (IQR: 753.43 - 969.58 mGy * cm) (p < 0.001).

CONCLUSION

Image quality can be maintained while significantly reducing the contrast volume and the radiation dose (27% and 34% lower DLP and 31% lower CDTIvol) for abdominal contrast-enhanced CT using a 1st-generation DS-PCD-CT. Moreover, polychromatic reconstruction T3D on a DS-PCD-CT enables sufficient diagnostic image quality for oncological imaging.

A prospective study comparing the quality of coronary computed tomography angiography images from photon counting and energy integrating detector systems

BACKGROUND

As guidelines endorse the use of computed tomography (CT) for examining coronary artery disease (CAD), it is important to compare the advantages and disadvantages of the novel photon counting detector CT (PCD-CT) technology with the established energy integrating detector CT (EID-CT).

PURPOSE

To compare the image quality of coronary computed tomography angiography (CCTA) and the Agatston scores (AS) derived from EID-CT and PCD-CT.

MATERIAL AND METHODS

In this prospective observational study, 28 patients underwent clinical calcium score and CCTA scans on an EID-CT and a PCD-CT scanner. CCTA images were qualitatively analyzed by five observers using visual grading characteristics. The correlation and agreement of the AS were assessed using Spearman's rank correlation and Bland-Altman plots.

RESULTS

This qualitative analyses demonstrated a high fraction of "good" or "excellent" ratings for the image criteria in both CT systems. The sharpness of the distal lumen and image quality regarding motion artifacts were rated significantly higher for EID-CT (P < 0.05). However, the sharpness of coronary calcification was rated significantly higher for PCD-CT (P < 0.05). Spearman's rank correlation and Bland-Altman plots showed good correlation (P = 0.95) and agreement regarding the AS between EID-CT and PCD-CT.

CONCLUSION

Both CT systems exhibited high CCTA image quality. The sharpness of calcifications was rated significantly higher for PCD-CT. A good correlation was observed between the AS derived from the two systems.

Low-iodine 40-keV virtual monoenergetic CT angiography of the lower extremities

Introduction

To evaluate a reduced iodine volume protocol for lower extremity CT angiography (CTA) using dual-energy CT (DECT).

Methods

This retrospective study included consecutive patients who underwent lower extremity CTA from June to December 2022. A 10 ml 1:1 mixed test bolus was performed, followed by a 40 ml full bolus at a 2.5/s injection rate, using 400 mg/ml iodine contrast media. Conventional and 40 keV virtual monoenergetic images (VMI) were reconstructed. For both reconstructions, five main artery segments were assessed with a 3-point image quality score as well as quantitative attenuation, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements with diagnostic quality thresholds (respectively >150 HU and >3).

Results

Forty patients were included in the study (mean age 68 ± 12 yo). 200 artery segments were assessed. Median qualitative image scores were 3 [IQR, 3, 3] for both reconstructions. 40 keV VMI upgraded qualitative scores for 51 (26%) of patients, including 9 (5%) from nondiagnostic to diagnostic quality. 40 keV VMI obtained attenuation and CNR diagnostic quality for respectively 100% and 100% of segments, compared with 96% and 98% for conventional images (p < 0.001). Distal artery segments showed the most differences between 40 keV VMI and conventional images.

Conclusion

A low-iodine lower extremity CTA protocol is feasible, with 40 keV virtual monoenergetic spectral reconstruction enabling maintained diagnostic image quality at the distal artery segments.

Clinical Applications of Photon-counting CT: A Review of Pioneer Studies and a Glimpse into the Future

CT systems equipped with photon-counting detectors (PCDs), referred to as photon-counting CT (PCCT), are beginning to change imaging in several subspecialties, such as cardiac, vascular, thoracic, and musculoskeletal radiology. Evidence has been building in the literature underpinning the many advantages of PCCT for different clinical applications. These benefits derive from the distinct features of PCDs, which are made of semiconductor materials capable of converting photons directly into electric signal. PCCT advancements include, among the most important, improved spatial resolution, noise reduction, and spectral properties. PCCT spatial resolution on the order of 0.25 mm allows for the improved visualization of small structures (eg, small vessels, arterial walls, distal bronchi, and bone trabeculations) and their pathologies, as well as the identification of previously undetectable anomalies. In addition, blooming artifacts from calcifications, stents, and other dense structures are reduced. The benefits of the spectral capabilities of PCCT are broad and include reducing radiation and contrast material dose for patients. In addition, multiple types of information can be extracted from a single data set (ie, multiparametric imaging), including quantitative data often regarded as surrogates of functional information (eg, lung perfusion). PCCT also allows for a novel type of CT imaging, K-edge imaging. This technique, combined with new contrast materials specifically designed for this modality, opens the door to new applications for imaging in the future.

Impact of Cardiac Motion on coronary artery calcium scoring using a virtual non-iodine algorithm on photon-counting detector CT: a dynamic phantom study

This study assessed the impact of cardiac motion and in-vessel attenuation on coronary artery calcium (CAC) scoring using virtual non-iodine (VNI) against virtual non-contrast (VNC) reconstructions on photon-counting detector CT. Two artificial vessels containing calcifications and different in-vessel attenuations (500, 800HU) were scanned without (static) and with cardiac motion (60, 80, 100 beats per minute [bpm]). Images were post-processed using a VNC and VNI algorithm at 70 keV and quantum iterative reconstruction (QIR) strength 2. Calcium mass, Agatston scores, cardiac motion susceptibility (CMS)-indices were compared to physical mass, static scores as well as between reconstructions, heart rates and in-vessel attenuations. VNI scores decreased with rising heart rate (p < 0.01) and showed less underestimation than VNC scores (p < 0.001). Only VNI scores were similar to the physical mass at static measurements, and to static scores at 60 bpm. Agatston scores using VNI were similar to static scores at 60 and 80 bpm. Standard deviation of CMS-indices was lower for VNI-based than for VNC-based CAC scoring. VNI scores were higher at 500 than 800HU (p < 0.001) and higher than VNC scores (p < 0.001) with VNI scores at 500 HU showing the lowest deviation from the physical reference. VNI-based CAC quantification is influenced by cardiac motion and in-vessel attenuation, but least when measuring Agatston scores, where it outperforms VNC-based CAC scoring.

Technical Basics and Clinical Benefits of Photon-Counting CT

ABSTRACT

Novel photon-counting detector CT (PCD-CT) has the potential to address the limitations of previous CT systems, such as insufficient spatial resolution, limited accuracy in detecting small low-contrast structures, or missing routine availability of spectral information. In this review article, we explain the basic principles and potential clinical benefits of PCD-CT, with a focus on recent literature that has grown rapidly since the commercial introduction of a clinically approved PCD-CT.

[CT technology: photon-counting detector computed tomography]

BACKGROUND

Photon-counting detector computed tomography (PCD-CT) is a CT technology that overcomes many limitations of conventional detectors. Direct conversion of photons hitting the detector into electrical signals combined with more sensitive and accurate photon detection simultaneously allows spectral evaluation and also potential reduction in radiation exposure to the patient. The combination of energy thresholds and elimination of detector septa allows for a reduction of electronic noise, an increase of spatial resolution, and an improvement of dose efficiency.

ACHIEVEMENTS

Recent research has confirmed significantly reduced image noise, reduced radiation dose, increased spatial resolution, improved iodine signal, and a reduction in artifacts. Spectral imaging potentiates these effects and also allows retrospective calculation of virtual monoenergetic images, virtual noncontrast images or iodine maps. Thus, the photon-counting technique offers the possibility of using various contrast agents, with the prospect of single-scan multiphase imaging or visualization of specific metabolic processes. Therefore, further research and complementary approval processes are necessary for clinical application. Likewise, further research is needed to develop and validate optimal settings and reconstructions for a wide variety of situations, as well as to test new application possibilities.

CONCLUSIONS

The only photon-counting detector CT device available on the market to date received clinical approval in 2021. It remains to be seen which other applications will become possible through improvements in hardware and software. This technology has already demonstrated an impressive superiority compared with the current standard of CT imaging, especially regarding high-resolution imaging of detailed structures and examinations with high radiation exposure.

Radiology: Cardiothoracic Imaging Highlights 2022

Since its inaugural issue in 2019, Radiology: Cardiothoracic Imaging has disseminated the latest scientific advances and technical developments in cardiac, vascular, and thoracic imaging. In this review, we highlight select articles published in this journal between October 2021 and October 2022. The scope of the review encompasses various aspects of coronary artery and congenital heart diseases, vascular diseases, thoracic imaging, and health services research. Key highlights include changes in the revised Coronary Artery Disease Reporting and Data System 2.0, the value of coronary CT angiography in informing prognosis and guiding treatment decisions, cardiac MRI findings after COVID-19 vaccination or infection, high-risk features at CT angiography to identify patients with aortic dissection at risk for late adverse events, and CT-guided fiducial marker placement for preoperative planning for pulmonary nodules. Ongoing research and future directions include photon-counting CT and artificial intelligence applications in cardiovascular imaging. Keywords: Pediatrics, CT Angiography, CT-Perfusion, CT-Spectral Imaging, MR Angiography, PET/CT, Transcatheter Aortic Valve Implantation/Replacement (TAVI/TAVR), Cardiac, Pulmonary, Vascular, Aorta, Coronary Arteries © RSNA, 2023.

Dual-Source Photon-Counting Computed Tomography-Part III: Clinical Overview of Vascular Applications beyond Cardiac and Neuro Imaging

Photon-counting computed tomography (PCCT) is an emerging technology that is expected to radically change clinical CT imaging. PCCT offers several advantages over conventional CT, which can be combined to improve and expand the diagnostic possibilities of CT angiography. After a brief description of the PCCT technology and its main advantages we will discuss the new opportunities brought about by PCCT in the field of vascular imaging, while addressing promising future clinical scenarios.

[New contrast agents for photon-counting computed tomography]

BACKGROUND

The introduction of energy-selective photon-counting detectors into clinical practice represents the next milestone in computed tomography (CT). In addition to significantly higher resolution, these detectors allow the implicit acquisition of dual or multispectral data in a single measurement through the use of typically freely selectable thresholds. This capability reignited the interest in new contrast agents based on heavy elements, so-called high‑z elements, for clinical CT.

OBJECTIVE

The present article aims to investigate the potential suitability of different chemical elements as contrast agents and to discuss possible clinical applications, for example, K‑edge imaging or simultaneous application of different contrast agents.

CONCLUSION

First preclinical experiments as well as experiments in large animals could demonstrate potential advantages of contrast agents based on heavy elements. For example, such contrast agents promise a significant increase in image contrast compared to conventional iodine-based agents.

[Update: Small bowel diseases in computed tomography and magnetic resonance imaging]

CLINICAL/METHODICAL ISSUE

Radiological procedures play a crucial role in the diagnosis of small bowel disease. Due to a broad and quite nonspecific spectrum of symptoms, clinical evaluation is often difficult, and endoscopic procedures require significant manpower, are time-consuming and expensive. In contrast, radiologic imaging can provide important information about morphologic and functional variations of the small bowel and help to identify various disease entities, such as inflammation, tumors, vascular problems, and obstruction.

STANDARD RADIOLOGICAL METHODS

The most common radiological modalities in small bowel diagnostics include ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and fluoroscopy. Each of these modalities has its own advantages and limitations, and the choice of imaging modality depends on clinical symptoms and suspected diagnosis in addition to availability.

METHODOLOGICAL INNOVATIONS

In recent years, significant progress has been made, especially in cross-sectional imaging modalities, as a result of new and further technical developments.

PERFORMANCE

These range from increasing detail resolution to functional and molecular imaging techniques that go far beyond simple morphology. In addition, information technology (IT) applications, which include artificial intelligence and radiomics, are assuming an increasing role.

ACHIEVEMENTS

Many of the methods mentioned are still in early stages and need to be further developed for daily practice, but some have already found their way into clinical routine.

PRACTICAL RECOMMENDATIONS

The aim of this work is to provide a review of the most important disease entities of the small intestine, including new and innovative diagnostic approaches.

Photon-counting detector CT: early clinical experience review

Since its development in the 1970s, X-ray CT has emerged as a landmark diagnostic imaging modality of modern medicine. Technological advances have been crucial to the success of CT imaging, as they have increasingly enabled improvements in image quality and diagnostic value at increasing radiation dose efficiency. With recent advances in engineering and physics, a novel technology has emerged with the potential to surpass several shortcomings and limitations of current CT systems. Photon-counting detector (PCD)-CT might substantially improve and expand the applicability of CT imaging by offering intrinsic spectral capabilities, increased spatial resolution, reduced electronic noise and improved image contrast. In this review we sought to summarize the first clinical experience of PCD-CT. We focused on most recent prototype and first clinically approved PCD-CT systems thereby reviewing initial publications and presenting corresponding clinical cases.