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

Ultra-high-resolution 40 keV virtual monoenergetic imaging using spectral photon-counting CT in high-risk patients for coronary stenoses

OBJECTIVES

To assess the image quality of ultra-high-resolution (UHR) virtual monoenergetic images (VMIs) at 40 keV compared to 70 keV, using spectral photon-counting CT (SPCCT) and dual-layer dual-energy CT (DECT) for coronary computed tomography angiography (CCTA).

METHODS AND MATERIALS

In this prospective IRB-approved study, 26 high-risk patients were included. CCTA was performed both with an SPCCT in UHR mode and with one of two DECT scanners (iQOn or CT7500) within 3 days. 40 keV and 70 keV VMIs were reconstructed for both modalities. Stenoses, blooming artefacts, and image quality were compared between all four reconstructions.

RESULTS

Twenty-six patients (4 women [15%]) and 28 coronary stenoses (mean stenosis of 56% ± 16%) were included. 40 keV SPCCT gave an overall higher quality score (5 [5, 5]) than 70 keV SPCCT (5 [4, 5], 40 keV DECT (4 [3, 4]) and 70 keV SPCCT (4 [4, 5]), p < 0.001). Less variability in stenosis measurement was found with SPCCT between 40 keV and 70 keV (bias: -1% ± 3%, LoA: 6%) compared with DECT (-6% ± 8%, LoA 16%). 40 keV SPCCT vs 40 keV DECT showed a -3% ± 6% bias, whereas 40 keV SPCCT vs 70 keV DECT showed a -8% ± 6% bias. From 70 keV to 40 keV, blooming artefacts did not increase with SPCCT (mean +2% ± 5%, p = 0.136) whereas they increased with DECT (mean +7% ± 6%, p = 0.005).

CONCLUSION

UHR 40 keV SPCCT VMIs outperformed 40 keV and 70 keV DECT VMIs for assessing coronary artery stenoses, with no impairment compared to 70 keV SPCCT VMIs.

KEY POINTS

Question Use of low virtual mono-energetic images at 40 keV using spectral dual-energy and photon-counting CT systems is not yet established for diagnosing coronary artery stenosis. Findings UHR 40 keV SPCCT enhances diagnostic accuracy in coronary artery assessment. Clinical relevance By combining spectral sensitivity with lower virtual mono-energetic imaging and ultra-high spatial resolution, SPCCT enhances coronary artery assessment, potentially leading to more accurate diagnoses and better patient outcomes in cardiovascular imaging.

Effect of Vessel Attenuation, VMI Level, and Reconstruction Kernel on Pericoronary Adipose Tissue Attenuation for EID CT and PCD CT: An Ex Vivo Porcine Heart Study

BACKGROUND. Pericoronary adipose tissue (PCAT) attenuation and the fat attenuation index (FAI) may serve as markers of inflammation and the risk of adverse cardiac events. However, standardization of relevant CT acquisition and reconstruction parameters is lacking. OBJECTIVE. The purpose of this study was to investigate the influence of vessel attenuation, the virtual monoenergetic image (VMI) level, and the reconstruction kernel on PCAT attenuation and FAI by use of energy-integrating detector (EID) and photon-counting detector (PCD) CT systems in an ex vivo porcine heart model. METHODS. The right coronary artery (RCA) of a porcine heart was injected with saline or varying contrast medium dilutions to achieve vessel attenuation ranging from 0 to 1000 HU. After each injection, the heart was sequentially scanned by EID CT at 120 kVp and PCD CT at 140 kVp at a constant CTDIvol of 10 mGy. For EID CT, polychromatic images were reconstructed with a Qr40 kernel. For PCD CT, VMIs (obtained at 40-80 keV in 10-keV increments) were reconstructed with Qr40, Bv40, and Bv56 kernels. ROIs were placed to measure RCA and PCAT attenuation. FAI was determined using software; histogram analysis was performed to assess voxel attenuation in the volumes of interest for FAI calculation. RESULTS. Correlations were observed between attenuation in the RCA and attenuation in the adjacent PCAT (r = 0.3-1.0) and between vessel attenuation and the FAI (r = -0.9 to 1.0). For PCAT attenuation and the FAI, these associations became progressively weaker when progressively sharper kernels were used. For increasing vessel attenuation on EID CT and for increasing VMI level on PCD CT, FAI histograms showed right shifts in peak attenuation values; the percentage of histogram voxels that met the threshold range for inclusion in FAI calculation was 9-38% for EID CT and 6-39% for PCD CT at VMI levels of 70-80 keV. For PCD CT, use of sharper kernels was associated with left shifts in peak attenuation values and greater percentages of voxels within the threshold range for inclusion in FAI calculation. CONCLUSION. PCAT attenuation and the FAI are influenced by vessel lumen attenuation, the VMI level, and the reconstruction kernel. A minority of pericoronary voxels contribute to FAI measurements for polychromatic EID CT and for PCD CT at high VMI levels. CLINICAL IMPACT. These findings may help standardize acquisition and reconstruction parameters for PCAT attenuation and FAI measurements.

Tungsten-Based Contrast Agent for Photon-Counting Detector CT Angiography in Calcified Coronaries: Comparison to Iodine in a Cardiovascular Phantom

OBJECTIVES

Calcified plaques induce blooming artifacts in coronary computed tomography angiography (CCTA) potentially leading to inaccurate stenosis evaluation. Tungsten represents a high atomic number, experimental contrast agent with different physical properties than iodine. We explored the potential of a tungsten-based contrast agent for photon-counting detector (PCD) CCTA in heavily calcified coronary vessels.

MATERIALS AND METHODS

A cardiovascular phantom exhibiting coronaries with calcified plaques was imaged on a first-generation dual-source PCD-CT. The coronaries with 3 different calcified plaques were filled with iodine and tungsten contrast media solutions equating to iodine and tungsten delivery rates (IDR and TDR) of 0.3, 0.5, 0.7, 1.0, 1.5, 2.0, 2.5, and 3.0 g/s, respectively. Electrocardiogram-triggered sequential acquisitions were performed in the spectral mode (QuantumPlus). Virtual monoenergetic images (VMIs) were reconstructed from 40 to 190 keV in 1 keV increments. Blooming artifacts and percentage error stenoses from calcified plaques were quantified, and attenuation characteristics of both contrast media were recorded.

RESULTS

Blooming artifacts from calcified plaques were most pronounced at 40 keV (78%) and least pronounced at 190 keV (58%). Similarly, percentage error stenoses were highest at 40 keV (48%) and lowest at 190 keV (2%), respectively. Attenuation of iodine decreased monotonically in VMIs from low to high keV, with the strongest decrease from 40 keV to 100 keV (IDR of 2.5 g/s: 1279 HU at 40 keV, 187 HU at 100 kV, and 35 HU at 190 keV). The attenuation of tungsten, on the other hand, increased monotonically as a function of VMI energy, with the strongest increase between 40 and 100 keV (TDR of 2.5 g/s: 202 HU at 40 keV, 661 HU at 100 kV, and 717 HU at 190 keV). For each keV level, the relationship between attenuation and IDR/TDR could be described by linear regressions ( R2 ≥ 0.88, P < 0.001). Specifically, attenuation increased linearly when increasing the delivery rate irrespective of keV level or contrast medium. Iodine exhibited the highest relative increase in attenuation values at lower keV levels when increasing the IDR. Conversely, for tungsten, the greatest relative increase in attenuation values occurred at higher keV levels when increasing the TDR. When high keV imaging is desirable to reduce blooming artifacts from calcified plaques, IDR has to be increased at higher keV levels to maintain diagnostic vessel attenuation (ie, 300 HU), whereas for tungsten, TDR can be kept constant or can be even reduced at high keV energy levels.

CONCLUSIONS

Tungsten's attenuation characteristics in relation to VMI energy levels are reversed to those of iodine, with tungsten exhibiting high attenuation values at high keV levels and vice versa. Thus, tungsten shows promise for high keV imaging CCTA with PCD-CT as-in distinction to iodine-both high vessel attenuation and low blooming artifacts from calcified plaques can be achieved.

Review: The Role of Dual-Energy Computed Tomography in Detecting Monosodium Urate Deposits in Vascular Tissues

PURPOSE OF REVIEW

To highlight novel findings in the detection of monosodium urate deposits in vessels using dual energy computed tomography, and to discuss the potential clinical implications for gout and hyperuricemia patients.

RECENT FINDINGS

Gout is an independent risk factor for cardiovascular disease. However, classical risk calculators do not take into account these hazards, and parameters to identify patients at risk are lacking. Monosodium urate measured by dual energy computed tomography is a well-established technology for the detection and quantification of monosodium urate deposits in peripheral joints and tendons. Recent findings also suggest its applicability to identify vascular urate deposits. Dual energy computed tomography is a promising tool for detection of cardiovascular monosodium urate deposits in gout patients, to better delineate individuals at increased risk for cardiovascular disease.

CT Myocardial Perfusion and CT-FFR versus Invasive FFR for Hemodynamic Relevance of Coronary Artery Disease

Background CT-derived fractional flow reserve (CT-FFR) and dynamic CT myocardial perfusion imaging enhance the specificity of coronary CT angiography (CCTA) for ruling out coronary artery disease (CAD). However, evidence on comparative diagnostic value remains scarce. Purpose To compare the diagnostic accuracy of CCTA plus CT-FFR, CCTA plus CT perfusion, and sequential CCTA plus CT-FFR and CT perfusion for detecting hemodynamically relevant CAD with that of invasive angiography. Materials and Methods This secondary analysis of a prospective study included patients with chest pain referred for invasive coronary angiography at nine centers from July 2016 to September 2019. CCTA and CT perfusion were performed with third-generation dual-source CT scanners. CT-FFR was assessed on-site. Independent core laboratories analyzed CCTA alone, CCTA plus CT perfusion, CCTA plus CT-FFR, and a sequential approach involving CCTA plus CT-FFR and CT perfusion for the presence of hemodynamically relevant stenosis. Invasive coronary angiography with invasive fractional flow reserve was the reference standard. Diagnostic accuracy metrics and the area under the receiver operating characteristic curve (AUC) were compared with the Sign test and DeLong test. Results Of the 105 participants (mean age, 64 years ± 8 [SD]; 68 male), 49 (47%) had hemodynamically relevant stenoses at invasive coronary angiography. CCTA plus CT-FFR and CCTA plus CT perfusion showed no evidence of a difference for participant-based sensitivities (90% vs 90%, P > .99), specificities (77% vs 79%, P > .99) and vessel-based AUCs (0.84 [95% CI: 0.77, 0.91] vs 0.83 [95% CI: 0.75, 0.91], P = .90). Both had higher participant-based specificity than CCTA alone (54%, both P < .001) without evidence of a difference in sensitivity between CCTA (94%) and CCTA plus CT perfusion (P = .50) or CCTA plus CT-FFR (P = .63). The sequential approach combining CCTA plus CT-FFR with CT perfusion achieved higher participant-based specificity than CCTA plus CT-FFR (88% vs 77%, P = .03) without evidence of a difference in participant-based sensitivity (88% vs 90%, P > .99) and vessel-based AUC (0.85 [95% CI: 0.77, 0.93], P = .78). Compared with CCTA plus CT perfusion, the sequential approach showed no evidence of a difference in participant-based sensitivity (P > .99), specificity (P = .06), or vessel-based AUC (P = .54). Conclusion There was no evidence of a difference in diagnostic accuracy between CCTA plus CT-FFR and CCTA plus CT perfusion for detecting hemodynamically relevant CAD. A sequential approach combining CCTA plus CT-FFR with CT perfusion led to improved participant-based specificity with no evidence of a difference in sensitivity compared with CCTA plus CT-FFR. ClinicalTrials.gov registration no.: NCT02810795 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Sinitsyn in this issue.

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.

Virtual calcium removal in calcified coronary arteries with photon-counting detector CT-first in-vivo experience

Purpose

To evaluate the feasibility and accuracy of quantification of calcified coronary stenoses using virtual non-calcium (VNCa) images in coronary CT angiography (CCTA) with photon-counting detector (PCD) CT compared with quantitative coronary angiography (QCA).

Materials and methods

This retrospective, institutional-review board approved study included consecutive patients with calcified coronary artery plaques undergoing CCTA with PCD-CT and invasive coronary angiography between July and December 2022. Virtual monoenergetic images (VMI) and VNCa images were reconstructed. Diameter stenoses were quantified on VMI and VNCa images by two readers. 3D-QCA served as the standard of reference. Measurements were compared using Bland-Altman analyses, Wilcoxon tests, and intraclass correlation coefficients (ICC).

Results

Thirty patients [mean age, 64 years ± 8 (standard deviation); 26 men] with 81 coronary stenoses from calcified plaques were included. Ten of the 81 stenoses (12%) had to be excluded because of erroneous plaque subtraction on VNCa images. Median diameter stenosis determined on 3D-QCA was 22% (interquartile range, 11%-35%; total range, 4%-88%). As compared with 3D-QCA, VMI overestimated diameter stenoses (mean differences -10%, p < .001, ICC: .87 and -7%, p < .001, ICC: .84 for reader 1 and 2, respectively), whereas VNCa images showed similar diameter stenoses (mean differences 0%, p = .68, ICC: .94 and 1%, p = .07, ICC: .93 for reader 1 and 2, respectively).

Conclusion

First experience in mainly minimal to moderate stenoses suggests that virtual calcium removal in CCTA with PCD-CT, when feasible, has the potential to improve the quantification of calcified stenoses.