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.

Effect of temporal resolution on calcium scoring: insights from photon-counting detector CT

To intra-individually investigate the variation of coronary artery calcium (CAC), aortic valve calcium (AVC), and mitral annular calcium (MAC) scores and the presence of blur artifacts as a function of temporal resolution in patients undergoing non-contrast cardiac CT on a dual-source photon counting detector (PCD) CT. This retrospective, IRB-approved study included 70 patients (30 women, 40 men, mean age 78 ± 9 years) who underwent ECG-gated cardiac non-contrast CT with PCD-CT (gantry rotation time 0.25 s) prior to transcatheter aortic valve replacement. Each scan was reconstructed at a temporal resolution of 66 ms using the dual-source information and at 125 ms using the single-source information. Average heart rate and heart rate variability were calculated from the recorded ECG. CAC, AVC, and MAC were quantified according to the Agatston method on images with both temporal resolutions. Two readers assessed blur artifacts using a 4-point visual grading scale. The influence of average heart rate and heart rate variability on calcium quantification and blur artifacts of the respective structures were analyzed by linear regression analysis. Mean heart rate and heart rate variability during data acquisition were 76 ± 17 beats per minute (bpm) and 4 ± 6 bpm, respectively. CAC scores were smaller on 66 ms (median, 511; interquartile range, 220-978) than on 125 ms reconstructions (538; 203-1050, p < 0.001). Median AVC scores [2809 (2009-3952) versus 3177 (2158-4273)] and median MAC scores [226 (0-1284) versus 251 (0-1574)] were also significantly smaller on 66ms than on 125ms reconstructions (p < 0.001). Reclassification of CAC and AVC risk categories occurred in 4% and 11% of cases, respectively, whereby the risk category was always overestimated on 125ms reconstructions. Image blur artifacts were significantly less on 66ms as opposed to 125 ms reconstructions (p < 0.001). Intra-individual analyses indicate that temporal resolution significantly impacts on calcium scoring with cardiac CT, with CAC, MAC, and AVC being overestimated at lower temporal resolution because of increased motion artifacts eventually leading to an overestimation of patient risk.

A Novel Reconstruction Technique to Reduce Stair-Step Artifacts in Sequential Mode Coronary CT Angiography

PURPOSE

Prospective electrocardiography-triggering is one of the most commonly used cardiac computed tomography (CT) scan modes but can be susceptible to stair-step artifacts in the transition areas of an acquisition over multiple cardiac cycles. We evaluated a novel reconstruction algorithm to reduce the occurrence and severity of such artifacts in sequential coronary CT angiography.

MATERIALS AND METHODS

In this institutional review board-approved, retrospective study, 50 consecutive patients (16 females; mean age, 58.9 ± 15.2) were included who underwent coronary CT angiography on a dual-source photon-counting detector CT in the sequential ultra-high-resolution mode with a detector collimation of 120 × 0.2 mm. Each scan was reconstructed without (hereafter called standard reconstruction) and with the novel ZeeFree reconstruction algorithm, which aims to minimize stair-step artifacts. The presence and extent of stair-step artifacts were rated by 2 independent, blinded readers on a 4-point discrete visual scale. The relationship between the occurrences of artifacts was correlated with the average and variability of heart rate and with patient characteristics.

RESULTS

A total of 504 coronary segments were included into the analyses. In standard reconstructions, reader 1 reported stair-step artifacts in 40/504 (7.9%) segments, from which 12/504 led to nondiagnostic image quality (2.4% of all segments). Reader 2 reported 56/504 (11.1%) stair-step artifacts, from which 11/504 lead to nondiagnostic image quality (2.2% of all segments). With the ZeeFree algorithm, 9/12 (75%) and 8/11 (73%) of the nondiagnostic segments improved to a diagnostic quality for readers 1 and 2, respectively. The ZeeFree reconstruction algorithm significantly reduced the frequency and extent of stair-step artifacts compared with standard reconstructions for both readers (P < 0.001, each). Heart rate variability and body mass index were significantly related to the occurrence of stair-step artifacts (P < 0.05).

CONCLUSIONS

Our study demonstrates the feasibility and effectiveness of a novel reconstruction algorithm leading to a significant reduction of stair-step artifacts and, hence, a reduction of coronary segments with a nondiagnostic image quality in sequential ultra-high-resolution coronary photon-counting detector CT angiography.

The Importance of Temporal Resolution for Ultra-High-Resolution Coronary Angiography: Evidence From Photon-Counting Detector CT

PURPOSE

The aim of this study was to assess the effect of temporal resolution on subjective and objective image quality of coronary computed tomography angiography (CCTA) in the ultra-high-resolution (UHR) mode with dual-source photon-counting detector (PCD) CT.

MATERIALS AND METHODS

This retrospective, institutional review board-approved study evaluated 30 patients (9 women; mean age, 80 ± 10 years) undergoing UHR CCTA with a clinical dual-source PCD-CT scanner. Images were acquired with a tube voltage of 120 kV and using a collimation of 120 × 0.2 mm. Gantry rotation time was 0.25 seconds. Each scan was reconstructed using both single-source and dual-source data resulting in an image temporal resolution of 125 milliseconds and 66 milliseconds, respectively. The average heart rate and the heart rate variability were recorded. Images were reconstructed with a slice thickness of 0.2 mm, quantum iterative reconstruction strength level 4, and using the Bv64 and Bv72 kernel for patients without and with coronary stents, respectively. For subjective image quality, 2 experienced readers rated motion artifacts and vessel delineation, or in-stent lumen visualization using 5-point discrete visual scales. For objective image quality, signal-to-noise ratio, contrast-to-noise ratio, stent blooming artifacts, and vessel and stent sharpness were quantified.

RESULTS

Fifteen patients had coronary stents, and 15 patients had no coronary stents. The mean heart rate and heart rate variability during data acquisition were 72 ± 10 beats per minute and 5 ± 6 beats per minute, respectively. Subjective image quality in the right coronary artery, left anterior descending, and circumflex artery was significantly superior in 66 milliseconds reconstructions compared with 125 milliseconds reconstructions for both readers (all P 's < 0.01; interreader agreement, Krippendorff α = 0.84-1.00). Subjective image quality deteriorated significantly at higher heart rates for 125 milliseconds (ρ = 0.21, P < 0.05) but not for 66 milliseconds reconstructions (ρ = 0.11, P = 0.22). No association was found between heart rate variability and image quality for both 125 milliseconds (ρ = 0.09, P = 0.33) and 66 milliseconds reconstructions (ρ = 0.13, P = 0.17), respectively. Signal-to-noise ratio and contrast-to-noise ratio were similar between 66 milliseconds and 125 milliseconds reconstructions (both P 's > 0.05), respectively. Stent blooming artifacts were significantly lower on 66 milliseconds than on 125 milliseconds reconstructions (46.7% ± 10% vs 52.9% ± 8.9%, P < 0.001). Higher sharpness was found in 66 milliseconds than in 125 milliseconds reconstructions both in native coronary arteries (left anterior descending artery: 1031 ± 265 ∆HU/mm vs 819 ± 253 ∆HU/mm, P < 0.01; right coronary artery: 884 ± 352 ∆HU/mm vs 654 ± 377 ∆HU/mm, P < 0.001) and stents (5318 ± 3874 ∆HU/mm vs 4267 ± 3521 ∆HU/mm, P < 0.001).

CONCLUSIONS

Coronary angiography with PCD-CT in the UHR mode profits considerably from a high temporal resolution, resulting in less motion artifacts, superior vessel delineation and in-stent lumen visualization, less stent blooming artifacts, and superior vessel and stent sharpness.

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.

Stent imaging on a clinical dual-source photon-counting detector CT system-impact of luminal attenuation and sharp kernels on lumen visibility

OBJECTIVES

To assess the impact of scan modes and reconstruction kernels using a novel dual-source photon-counting detector CT (PCD-CT) on lumen visibility and sharpness of different stent sizes.

METHODS

A phantom containing six balloon-expandable stents (2.5 to 9 mm diameter) in silicone tubing was scanned on a PCD-CT with standard (0.6 mm and 0.4 mm thicknesses) and ultra-high-resolution (0.2 mm thickness) modes. With the use of increasing contrast medium concentrations, densities of 0, 200, 400, and 600 HU were achieved. Standard-resolution scans were reconstructed using increasing sharpness kernels, using both polyenergetic quantitative soft tissue "conventional" ((Qr40_c(0.6 mm), Qr40_c(0.4 mm), Qr72_c(0.2 mm)) and vascular (Bv) virtual monoenergetic reconstructions (Bv44_m(0.4 mm), Bv60_m(0.4 mm)) at 70 keV. In-stent lumen visibility, sharpness (max. ΔHU of the stent measured in profile plots), and in-stent noise (standard deviation of HU) were measured.

RESULTS

In-stent lumen visibility was highest for Qr72_c(0.2 mm) (86.5 ± 2.8% to 88.3 ± 2.6%) and in Bv60_m(0.4 mm) reconstructions (77.3 ± 2.9 to 82.7 ± 2.5%). Lumen visibility was lowest in the smallest stent (2.5 mm) ranging from 54.1% in Qr40_c(0.6 mm) to 74.1% in Qr72_c(0.2 mm) and highest in the largest stent (9 mm) ranging from 93.8% in Qr40c(0.6 mm) to 99.1% in the Qr72_c(0.2 mm) series. Lumen visibility decreased by 2.1% for every 200-HU increase in lumen attenuation. Max. ΔHU between stents and stent lumen was highest in Qr72_c(0.2 mm) (ΔHU 892 ± 504 to 1526 ± 517) and Bv60_m(0.4 mm) series (ΔHU 480 ± 357 to 1030 ± 344). Improvement of lumen visibility and sharpness in UHR and Bv60_m(0.4 mm) series was strongest in smaller stent sizes.

CONCLUSION

UHR acquisition mode and sharp reconstruction kernels on a novel PCD-CT system significantly improve in-stent lumen visibility and sharpness-especially for smaller stent sizes.

KEY POINTS

• In-stent lumen visibility and sharpness of stents significantly improve using sharp reconstruction kernels (Bv60) and ultra-high-resolution mode in photon-counting detector computed tomography. • The observed improvement of stent-lumen visibility was highest in smaller stent sizes.

Ultra-high resolution photon-counting coronary CT angiography improves coronary stenosis quantification over a wide range of heart rates - A dynamic phantom study

PURPOSE

To investigate the effect of using photon-counting detector (PCD)-CT with ultra-high resolution (UHR) on stenosis quantification accuracy and blooming artifacts from low to high heart rates in a dynamic motion phantom.

METHOD

Two vessel phantoms (diameter: 4 mm) containing solid calcified lesions (25%, 50% stenoses), filled with different concentrations of iodine, inside an anthropomorphic thorax phantom attached to a coronary motion simulator were used. Scanning was performed on a PCD-CT system using an ECG-gated mode at UHR and standard resolution (SR) (0.2, 0.6 mm slice thickness, respectively). Images were reconstructed at 60, 80 and 100 beats per minute (bpm) (UHR: Bv56 kernel, quantum iterative reconstruction (QIR) level 3; SR: 55 keV, Bv40 kernel, QIR3). Percent diameter stenosis (PDS) and blooming artifacts were measured by two readers.

RESULTS

PDS measurements derived from UHR were more accurate than SR for both lesions at every heart rate (p ≤ 0.005 for all, e.g. 50% lesion SR vs. UHR: at 60 bpm 57.1% [55.2-59.2] vs. 50.0% [48.5-51.2], at 100 bpm 61.0% [58.6-64.3] vs. 52.4% [51.3-54.3]). Overall mean difference across heart rates and lesions compared to the nominal stenoses was 9.2% (Limit of Agreement (LoA), 2.4%/16.0%) for SR vs. 2.4% (LoA, -2.8%/7.5%) for UHR. Blooming artifacts decreased with UHR compared to SR for both lesions at every heart rate (p < 0.001 for all, e.g. 50% lesion SR vs. UHR: at 60 bpm 63.8% [60.6-69.5] vs. 52.5% [50.0-57.5], at 100 bpm 70.2% [64.8-78.1] vs. 56.1% [51.2-60.8]).

CONCLUSIONS

This motion phantom study demonstrates improved stenosis quantification accuracy and reduced blooming artifacts with UHR-PCD-CT compared to SR, independent of heart rate.

Simultaneous assessment of heart and lungs with gated high-pitch ultra-low dose chest CT using artificial intelligence-based calcium scoring

Purpose

The combined testing for coronary artery and pulmonary diseases is of clinical interest as risk factors are shared. In this study, a novel ECG-gated tin-filtered ultra-low dose chest CT protocol (GCCT) for integrated heart and lung acquisition and the applicability of artificial intelligence (AI)-based coronary artery calcium scoring were assessed.

Methods

In a clinical registry of 10481 patients undergoing heart and lung CT, GCCT was applied in 44 patients on a dual-source CT. Coronary calcium scans (CCS) with 120 kVp, 100 kVp, and tin-filtered 100 kVp (Sn100) of controls, matched with regard to age, sex, and body-mass index, were retrieved from the registry (n_total=176, 66.5 (59.4-74.0) years, 52 men). Automatic tube current modulation was used in all scans. In 20 patients undergoing GCCT and Sn100 CCS, Agatston scores were measured both semi-automatically by experts and by AI, and classified into six groups (0, <10, <100, <400, <1000, ≥1000).

Results

Effective dose decreased significantly from 120 kVp CCS (0.50 (0.41-0.61) mSv) to 100 kVp CCS (0.34 (0.26-0.37) mSv) to Sn100 CCS (0.14 (0.11-0.17) mSv). GCCT showed higher values (0.28 (0.21-0.32) mSv) than Sn100 CCS but lower than 120 kVp and 100 kVp CCS (all p < 0.05) despite greater scan length. Agatston scores correlated strongly between GCCT and Sn100 CCS in semi-automatic and AI-based measurements (both ρ = 0.98, p < 0.001) resulting in high agreement in Agatston score classification (κ = 0.97, 95% CI 0.92-1.00; κ = 0.89, 95% CI 0.79-0.99). Regarding chest findings, further diagnostic steps were recommended in 28 patients.

Conclusions

GCCT allows for reliable coronary artery disease and lung cancer screening with ultra-low radiation exposure. GCCT-derived Agatston score shows excellent agreement with standard CCS, resulting in equivalent risk stratification.

How scan parameter choice affects deep learning-based coronary artery disease assessment from computed tomography

Recently, algorithms capable of assessing the severity of Coronary Artery Disease (CAD) in form of the Coronary Artery Disease-Reporting and Data System (CAD-RADS) grade from Coronary Computed Tomography Angiography (CCTA) scans using Deep Learning (DL) were proposed. Before considering to apply these algorithms in clinical practice, their robustness regarding different commonly used Computed Tomography (CT)-specific image formation parameters-including denoising strength, slab combination, and reconstruction kernel-needs to be evaluated. For this study, we reconstructed a data set of 500 patient CCTA scans under seven image formation parameter configurations. We select one default configuration and evaluate how varying individual parameters impacts the performance and stability of a typical algorithm for automated CAD assessment from CCTA. This algorithm consists of multiple preprocessing and a DL prediction step. We evaluate the influence of the parameter changes on the entire pipeline and additionally on only the DL step by propagating the centerline extraction results of the default configuration to all others. We consider the standard deviation of the CAD severity prediction grade difference between the default and variation configurations to assess the stability w.r.t. parameter changes. For the full pipeline we observe slight instability (± 0.226 CAD-RADS) for all variations. Predictions are more stable with centerlines propagated from the default to the variation configurations (± 0.122 CAD-RADS), especially for differing denoising strengths (± 0.046 CAD-RADS). However, stacking slabs with sharp boundaries instead of mixing slabs in overlapping regions (called true stack ± 0.313 CAD-RADS) and increasing the sharpness of the reconstruction kernel (± 0.150 CAD-RADS) leads to unstable predictions. Regarding the clinically relevant tasks of excluding CAD (called rule-out; AUC default 0.957, min 0.937) and excluding obstructive CAD (called hold-out; AUC default 0.971, min 0.964) the performance remains on a high level for all variations. Concluding, an influence of reconstruction parameters on the predictions is observed. Especially, scans reconstructed with the true stack parameter need to be treated with caution when using a DL-based method. Also, reconstruction kernels which are underrepresented in the training data increase the prediction uncertainty.

Myocardial Characterization with Extracellular Volume Mapping with a First-Generation Photon-counting Detector CT with MRI Reference

Background Photon-counting detector (PCD) CT provides comprehensive spectral data with every acquisition, but studies evaluating myocardial extracellular volume (ECV) quantification with use of PCD CT compared with an MRI reference remain lacking. Purpose To compare ECV quantification for myocardial tissue characterization between a first-generation PCD CT system and cardiac MRI. Materials and Methods In this single-center prospective study, adults without contraindication to iodine-based contrast media underwent same-day cardiac PCD CT and MRI with native and postcontrast T1 mapping and late gadolinium enhancement for various clinical indications for cardiac MRI (the reference standard) between July 2021 and January 2022. Global and midventricular ECV were assessed with use of three methods: single-energy PCD CT, dual-energy PCD CT, and MRI T1 mapping. Quantitative comparisons among all techniques were performed. Correlation and reliability between different methods of ECV quantification were assessed with use of the Pearson correlation coefficient (r) and the intraclass correlation coefficient. Results The final sample included 29 study participants (mean age ± SD, 54 years ± 17; 15 men). There was a strong correlation of ECV between dual- and single-energy PCD CT (r = 0.91, P < .001). Radiation dose was 40% lower with dual-energy versus single-energy PCD CT (volume CT dose index, 10.1 mGy vs 16.8 mGy, respectively; P < .001). In comparison with MRI, dual-energy PCD CT showed strong correlation (r = 0.82 and 0.91, both P < .001) and good to excellent reliability (intraclass correlation coefficients, 0.81 and 0.90) for midventricular and global ECV quantification, but it overestimated ECV by approximately 2%. Single-energy PCD CT showed similar relationship with MRI but underestimated ECV by 3%. Conclusion Myocardial tissue characterization with photon-counting detector CT-based quantitative extracellular volume analysis showed a strong correlation to MRI. © RSNA, 2023 Supplemental material is available for this article.

Ultra-low-dose computed tomography for torsion measurements of the lower extremities in children and adolescents

BACKGROUND

Quantifying femoral and tibial torsion is crucial in the preoperative planning for derotation surgery in children and adolescents. The use of an ultra-low-dose computed tomography (CT) protocol might be possible for modern CT scanners and suitable for reliable torsion measurements even though the bones are not completely ossified.

METHODS

This is a retrospective review of 77 children/adolescents (mean age 12.7 years) who underwent a lower extremity CT for torsion measurements on a 64-slice scanner. A stepwise dose reduction (70%, 50%, 30% of the original dose) was simulated. Torsion measurements were performed on all image datasets, and image noise, interrater agreement and subjective image quality were evaluated. Effective radiation dose of each original scan was estimated. As proof of concept, 24 children were scanned with an ultra-low-dose protocol, adapted from the 30% dose simulation, and the intra-class correlation coefficient (ICC) was determined. Ethics approval and informed consent were given.

RESULTS

Torsion measurements at the simulated 30% dose level had equivalent interrater agreement compared to the 100% dose level (ICC ≥ 0.99 for all locations and dose levels). Image quality of almost all datasets was rated excellent, regardless of dose. The mean sum of the effective dose of the total torsion measurement was reduced by simulation from 0.460/0.490 mSv (boys/girls) at 100% dose to 0.138/0.147 mSv at 30%. The ICC of the proof-of-concept group was as good as that of the simulated 30% dose level.

CONCLUSION

Pediatric torsion measurements of the lower extremities can be performed using an ultra-low-dose protocol without compromising diagnostic confidence.

Photon-Counting Detector CT-Based Vascular Calcium Removal Algorithm: Assessment Using a Cardiac Motion Phantom

OBJECTIVES

The diagnostic performance of coronary computed tomography angiography is known to be negatively affected by the presence of severely calcified plaques in the coronary arteries. In this article, the performance of a novel image reconstruction algorithm (PureLumen) based on spectral CT data of a first-generation dual-source photon-counting detector computed tomography (PCD-CT) system was assessed in a phantom study. PureLumen tries to remove only the calcified contributions from the image while leaving the rest unmodified.

MATERIALS AND METHODS

The study uses 2 iodine contrast filled vessel phantoms (diameter 4 mm) filled with different concentrations of iodine and equipped with calcified stenosis inserts. Each phantom features 2 separate calcified lesions of 25% and 50% percentage diameter stenosis (PDS) size. The vessel phantoms were mounted inside an anthropomorphic thorax phantom attached to an artificial motion device, simulating realistic cardiac motion at heart rates between 50 beats per minute and 100 beats per minute. Acquisitions were performed using a prospectively electrocardiogram triggered dual-source sequence mode on a PCD-CT system (NAEOTOM Alpha, Siemens Healthineers). Images were reconstructed at 80% of the RR interval with virtual monoenergetic images (Mono) and with additional calcium-removal (PureLumen), both at 65 keV. PureLumen is based on a spectral base material decomposition into iodine and calcium, which aims to reconstruct images without calcium contributions, while leaving all other material contribution unchanged. Stenosis grade was assessed individually for each vessel insert in all reconstructed image series by 2 readers.

RESULTS

The measured median PDS values for the 50% lesion were 56.0% (52.0%, 57.0%) for the Mono case and 50.0% (48.5%, 51.0%) for PureLumen. The 25% lesion median PDS values were 36.0% (29.5%, 39.5%) for Mono and 31.5% (30.5%, 34.0%) for PureLumen. Both lesion sizes demonstrate a significant difference between Mono and PureLumen in their result (P < 0.05) with PureLumen median values being closer to the actual true stenosis size for the 50% and 25% lesion. A visual assessment of the image quality depending on the heart rate yielded good image quality up to a heart rate of 80 beats per minute in the PureLumen case.

CONCLUSIONS

This phantom study shows that a novel calcium-removal image reconstruction algorithm (PureLumen) using a first-generation dual-source PCD-CT effectively decreases blooming artifacts caused by heavily calcified plaques and improves image interpretability. It also shows that PureLumen retains its performance in the presence of motion with simulated heart rates up to 80 beats per minute. Future in vivo clinical studies are needed to confirm the benefits of this type of reconstruction in terms of coronary computed tomography angiography quality and accuracy.

Tube voltage-independent coronary calcium scoring on a first-generation dual-source photon-counting CT-a proof-of-principle phantom study

To evaluate the accuracy of coronary artery calcium (CAC) scoring at various tube voltages and different monoenergetic image reconstructions on a first-generation dual-source photon-counting detector CT (PCD-CT). A commercially available anthropomorphic chest phantom with calcium inserts was scanned at different tube voltages (90 kV, Sn100kV, 120 kV, and Sn140kV) on a first-generation dual-source PCD-CT system with quantum technology using automatic exposure control with an image quality (IQ) level of 20. The same phantom was also scanned on a conventional energy-integrating detector CT (120 kV; weighted filtered back projection) for reference. Extension rings were used to emulate different patient sizes. Virtual monoenergetic images at 65 keV and 70 keV applying different levels of quantum iterative reconstruction (QIR) were reconstructed from the PCD-CT data sets. CAC scores were determined and compared to the reference. Radiation doses were noted. At an IQ level of 20, radiation doses ranged between 1.18 mGy and 4.64 mGy, depending on the tube voltage and phantom size. Imaging at 90 kV or Sn100kV was associated with a size-dependent radiation dose reduction between 23% and 48% compared to 120 kV. Tube voltage adapted image reconstructions with 65 keV and QIR 3 at 90 kV and with 70 keV and QIR 1 at Sn100kV allowed to calculate CAC scores comparable to conventional EID-CT scans with a percentage deviation of ≤ 5% for all phantom sizes. Our phantom study indicates that CAC scoring with dual-source PCD-CT is accurate at various tube voltages, offering the possibility of substantial radiation dose reduction.

Image Quality Assessment for Clinical Cadmium Telluride-Based Photon-Counting Computed Tomography Detector in Cadaveric Wrist Imaging

OBJECTIVES

Detailed visualization of bone microarchitecture is essential for assessment of wrist fractures in computed tomography (CT). This study aims to evaluate the imaging performance of a CT system with clinical cadmium telluride-based photon-counting detector (PCD-CT) compared with a third-generation dual-source CT scanner with energy-integrating detector technology (EID-CT).

MATERIALS AND METHODS

Both CT systems were used for the examination of 8 cadaveric wrists with radiation dose equivalent scan protocols (low-/standard-/full-dose imaging: CTDIvol = 1.50/5.80/8.67 mGy). All wrists were scanned with 2 different operating modes of the photon-counting CT (standard-resolution and ultra-high-resolution). After reformatting with comparable reconstruction parameters and convolution kernels, subjective evaluation of image quality was performed by 3 radiologists on a 7-point scale. For estimation of interrater reliability, we report the intraclass correlation coefficient (absolute agreement, 2-way random-effects model). Signal-to-noise and contrast-to-noise ratios were calculated to provide semiquantitative assessment of image quality.

RESULTS

Subjective image quality of standard-dose PCD-CT examinations in ultra-high-resolution mode was superior compared with full-dose PCD-CT in standard-resolution mode (P = 0.016) and full-dose EID-CT (P = 0.040). No difference was ascertained between low-dose PCD-CT in ultra-high-resolution mode and standard-dose scans with either PCD-CT in standard-resolution mode (P = 0.108) or EID-CT (P = 0.470). Observer evaluation of standard-resolution PCD-CT and EID-CT delivered similar results in full- and standard-dose scans (P = 0.248/0.509). Intraclass correlation coefficient was 0.876 (95% confidence interval, 0.744-0.925; P < 0.001), indicating good reliability. Between dose equivalent studies, signal-to-noise and contrast-to-noise ratios were substantially higher in photon-counting CT examinations (all P's < 0.001).

CONCLUSIONS

Superior visualization of fine anatomy is feasible with the clinical photon-counting CT system in cadaveric wrist scans. The ultra-high-resolution scan mode suggests potential for considerable dose reduction over energy-integrating dual-source CT.

Photon-Counting Computed Tomography for Coronary Stent Imaging: In Vitro Evaluation of 28 Coronary Stents

OBJECTIVES

The aim of this study was to assess in-stent lumen visibility and quantitative image characteristics of different coronary stents using a novel photon-counting detector (PCD) computed tomography (CT) system in comparison to a state-of-the-art energy-integrating detector (EID) CT scanner.

MATERIALS AND METHODS

In this in vitro phantom study, 28 different coronary stents ranging from 2.25 to 4.5 mm lumen diameter were expanded into plastic tubes filled with contrast agent. Stent-containing plastic tubes were positioned in a custom-made emulsion-filled phantom, which was inserted into an anthropomorphic phantom simulating a medium-sized patient. Computed tomography scans were acquired parallel to the scanners' z axis using a novel cadmium telluride-based PCD CT system (SOMATOM CountPlus; Siemens Healthcare GmbH, Forchheim Germany), operating in 2 different modes (standard-resolution mode [SR] and ultra-high-resolution [UHR] mode), and a latest generation dual-source EID CT system (SOMATOM Force; Siemens Healthcare GmbH, Forchheim). CTDIvol-matched images were reconstructed with comparable convolution kernels and using the same reconstruction parameters. In-stent lumen visibility (in %), increase in in-stent attenuation (expressed as Δ in-stent CT attenuation), and image noise (in Hounsfield unit) were manually measured. Parts of the image analysis (in-stent lumen visibility) were additionally performed in an automated way. Differences were tested using Wilcoxon signed rank test.

RESULTS

The best in-stent lumen visibility was achieved with the PCD-UHR mode and the lowest noise levels with the PCD-SR mode. The median in-stent lumen visibility was significantly higher (P < 0.001) with PCD (SR, 66.7%; interquartile range [IQR], 63.3-72.3; UHR, 68.9%; IQR, 64.4-74.4) compared with EID (65.4%; IQR, 62.2-70.4). The Δ in-stent CT attenuation was significantly lower for PCD in both SR (78 HU; IQR, 46-108; P = 0.024) and UHR (85 HU; IQR, 59-113; P = 0.006) compared with EID (108 HU; IQR, 85-126). Image noise was significantly lower (P < 0.001) for PCD-SR (21 HU; IQR, 21-21) compared with EID images (25 HU; IQR, 24-25.0).

CONCLUSIONS

The PCD provides superior in-stent lumen visibility and quantitative image characteristics when compared with conventional EID.

Energy-integrating-detector multi-energy CT: Implementation and a phantom study

PURPOSE

Multi-energy computed tomography (MECT) has a great potential to enable many novel clinical applications such as simultaneous multi-contrast imaging. The purpose of this study was to implement triple-beam MECT on a traditional energy-integrating-detector (EID) CT platform (EID-MECT).

METHODS

This was accomplished by mounting a z-axis split-filter (0.05 mm Au, 0.6 mm Sn) on Tube A of a dual-source EID CT scanner. With the two split x-ray beams from Tube A and the third beam from Tube B, three beams with different x-ray spectra can be simultaneously acquired. With Tube B operated at 70 or 80 kV and Tube A at 120 or 140 kV, four different triple-beam configurations were calibrated for MECT measurements: 70/Au120/Sn120, 80/Au120/Sn120, 70/Au140/Sn140, and 80/Au140/Sn140 kV. Iodine (I), gadolinium (Gd), bismuth (Bi) samples, and their mixtures were prepared for 2 three-material-decomposition tasks and 1 four-material-decomposition task. For each task, samples were placed in a water phantom and scanned using each of the four triple-beam configurations. For comparison, the same phantom was also scanned using three other dual-energy CT (DECT) or MECT technologies: twin-beam DECT (TB-DECT), dual-source DECT (DS-DECT), and photon-counting-detector CT (PCD-CT), all with optimal x-ray spectrum settings and at equal volume CT dose index (CTDIvol). The phantom for four-material decomposition (I/Gd/Bi/Water imaging) was scanned using the PCD-CT only (140 kV with 25, 50, 75, and 90 keV). Image-based material decomposition was performed to acquire material-specific images, on which the mean basis material concentrations and noise levels were measured and compared across all triple-beam configurations in EID-MECT and various DECT/MECT systems.

RESULTS

The optimal triple-beam configuration was task-dependent with 70/Au120/Sn120, 70/Au140/Sn140, and 70/Au120/Sn120 kV for I/Gd/Water, I/Bi/Water, and I/Gd/Bi/Water material decomposition tasks, respectively. At equal radiation dose level, EID-MECT provided comparable or better quantification accuracy in material-specific images for all three material decomposition tasks, compared to EID-based DECT and PCD-CT systems. In terms of noise level comparison, EID-MECT-derived material-specific images showed lower noise levels than TB-DECT and DS-DECT, but slightly higher than that from PCD-CT in I/Gd/Water imaging. For I/Bi/Water imaging, EID-MECT showed a comparable noise level to DS-DECT, and a much lower noise level than TB-DECT and PCD-CT in all material-specific images. For the four-material decomposition task involving I/Gd/Bi/Water, the bismuth-specific image derived from EID-MECT was slightly noisier, but both iodine- and gadolinium-specific images showed much lower noise levels in comparison to PCD-CT.

CONCLUSIONS

For the first time, an EID-based MECT system that can simultaneously acquire three x-ray spectra measurements was implemented on a clinical scanner, which demonstrated comparable or better imaging performance than existing DECT and MECT systems.

Accurate Measurement of Agatston Score Using kVp-Independent Reconstruction Algorithm for Ultra-High-Pitch Sn150 kVp CT

OBJECTIVE

To investigate the accuracy of the Agatston score obtained with the ultra-high-pitch (UHP) acquisition mode using tin-filter spectral shaping (Sn150 kVp) and a kVp-independent reconstruction algorithm to reduce the radiation dose.

MATERIALS AND METHODS

This prospective study included 114 patients (mean ± standard deviation, 60.3 ± 9.8 years; 74 male) who underwent a standard 120 kVp scan and an additional UHP Sn150 kVp scan for coronary artery calcification scoring (CACS). These two datasets were reconstructed using a standard reconstruction algorithm (120 kVp + Qr36d, protocol A; Sn150 kVp + Qr36d, protocol B). In addition, the Sn150 kVp dataset was reconstructed using a kVp-independent reconstruction algorithm (Sn150 kVp + Sa36d, protocol C). The Agatston scores for protocols A and B, as well as protocols A and C, were compared. The agreement between the scores was assessed using the intraclass correlation coefficient (ICC) and the Bland-Altman plot. The radiation doses for the 120 kVp and UHP Sn150 kVp acquisition modes were also compared.

RESULTS

No significant difference was observed in the Agatston score for protocols A (median, 63.05; interquartile range [IQR], 0-232.28) and C (median, 60.25; IQR, 0-195.20) (p = 0.060). The mean difference in the Agatston score for protocols A and C was relatively small (-7.82) and with the limits of agreement from -65.20 to 49.56 (ICC = 0.997). The Agatston score for protocol B (median, 34.85; IQR, 0-120.73) was significantly underestimated compared with that for protocol A (p < 0.001). The UHP Sn150 kVp mode facilitated an effective radiation dose reduction by approximately 30% (0.58 vs. 0.82 mSv, p < 0.001) from that associated with the standard 120 kVp mode.

CONCLUSION

The Agatston scores for CACS with the UHP Sn150 kVp mode with a kVp-independent reconstruction algorithm and the standard 120 kVp demonstrated excellent agreement with a small mean difference and narrow agreement limits. The UHP Sn150 kVp mode allowed a significant reduction in the radiation dose.

Structured Digital Self-Assessment of Patient Anamnesis Prior to Computed Tomography: Performance Evaluation and Added Value

The aim of this study was to evaluate the performance of a tablet-based, digitized structured self-assessment (DSSA) of patient anamnesis (PA) prior to computed tomography (CT). Of the 317 patients consecutively referred for CT, the majority (n = 294) was able to complete the tablet-based questionnaire, which consisted of 67 items covering social anamnesis, lifestyle factors (e.g., tobacco abuse), medical history (e.g., kidney diseases), current symptoms, and the usability of the system. Patients were able to mark unclear questions for a subsequent discussion with the radiologist. Critical issues for the CT examination were structured and automatically highlighted as “red flags” (RFs) in order to improve patient interaction. RFs and marked questions were highly prevalent (69.5% and 26%). Missing creatinine values (33.3%), kidney diseases (14.4%), thyroid diseases (10.6%), metformin (5.5%), claustrophobia (4.1%), allergic reactions to contrast agents (2.4%), and pathological TSH values (2.0%) were highlighted most frequently as RFs. Patient feedback regarding the comprehensibility of the questionnaire and the tablet usability was mainly positive (90.9%; 86.2%). With advanced age, however, patients provided more negative feedback for both (p = 0.007; p = 0.039). The time effort was less than 20 min for 85.1% of patients, and faster patients were significantly younger (p = 0.046). Overall, the DSSA of PA prior to CT shows a high success rate and is well accepted by most patients. RFs and marked questions were common and helped to focus patients’ interactions and reporting towards decisive aspects.

Individualized coronary calcium scoring at any tube voltage using a kV-independent reconstruction algorithm

PURPOSE

We prospectively investigate the feasibility of a patient specific automated tube voltage selection (ATVS)-based coronary artery calcium scoring (CACS) protocol, using a kV-independent reconstruction algorithm, to achieve significant dose reductions while maintaining the overall cardiac risk classification.

METHODS

Forty-three patients (mean age, 61.8 ± 9.0 years; 40% male) underwent a clinically indicated CACS scan at 120kVp, as well as an additional CACS acquisition using an individualized tube voltage between 70 and 130kVp based on the ATVS selection (CARE-kV). Datasets of the additional CACS scans were reconstructed using a kV-independent algorithm that allows for calcium scoring without changing the weighting threshold of 130HU, regardless of the tube voltage chosen for image acquisition. Agatston scores and radiation dose derived from the different ATVS-based CACS studies were compared to the standard acquisition at 120kVp.

RESULTS

Thirteen patients displayed a score of 0 and were correctly identified with the ATVS protocol. Agatston scores derived from the standard 120kVp (median, 33.4; IQR, 0-289.7) and the patient-tailored kV-independent protocol (median, 47.5; IQR, 0-287.5) showed no significant differences (p = 0.094). The intra-class correlation for Agatston scores derived from the two different protocols was excellent (ICC = 0.99). The mean dose-length-product was 29.8 ± 11.9 mGy × cm using the ATVS protocol and 31.7 ± 11.4 mGy × cm using the standard 120kVp protocol (p < 0.001). Additionally, 95% of patients were classified into the same risk category (0, 1-10, 11-100, 101-400, or > 400) using the patient-tailored protocol.

CONCLUSIONS

ATVS-based CACS, using a kV-independent algorithm, allows for high accuracy compared to the standard 120kVp scanning, while significantly reducing radiation dose parameters.

KEY POINTS

• ATVS allows for CT scanning with reduced radiation dose values. • KV-independent CACS is feasible at any tube voltage between 70 and 130 kVp. • ATVS applied to kV-independent CACS can significantly reduce the radiation dose.

Application of Transition-Metal Catalysis, Biocatalysis, and Flow Chemistry as State-of-the-Art Technologies in the Synthesis of LCZ696

LCZ696 is a novel treatment for patients suffering from heart failure that combines the two active pharmaceutical ingredients sacubitril and valsartan in a single chemical compound. While valsartan is an established drug substance, a new manufacturing process suitable for large-scale commercial production had to be developed for sacubitril. The use of chemocatalysis, biocatalysis, and flow chemistry as state-of-the-art technologies allowed to efficiently build up the structure of sacubitril and achieve the defined performance targets.

Multi-energy CT with Triple X-ray Beams: A Feasibility Animal Study

Energy-integrating-detector (EID)-based triple-beam multi-energy CT (TB-MECT) was recently implemented on a dual-source (DS) CT platform by mounting a z-axis split-filter (0.05 mm Au, 0.6 mm Sn) on one of the two tubes. The purpose of this work is to perform a feasibility animal study on this new MECT platform for a small bowel imaging task using two contrast agents, iodine and bismuth. Optimal triple-beam configurations, 70/Au140/Sn140 kV were determined in a phantom study for this task and applied in the animal study for best material decomposition imaging performance. The results demonstrated that the TB-MECT can successfully separate and quantify the two contrast agents from one single scan for the task of small bowel imaging.

Spectral Beam Shaping in Unenhanced Chest CT Examinations: A Phantom Study on Dose Reduction and Image Quality

RATIONALE AND OBJECTIVES

This study aimed to determine the optimal tube potential for unenhanced chest computed tomographies (CTs) with age-related phantoms.

MATERIALS AND METHODS

Three physical anthropomorphic phantoms (newborn, 5-year-old child, and adult) were scanned on a third-generation dual-source CT using CAREkV in semi-mode and CAREDose4D (ref. KV: 120; ref. mAs 50). Scans were performed with all available tube potentials (70-150 kV and Sn150 kV). The lowest volume computed tomography dose index (CTDI_vol) was selected to perform additional Sn100-kV scans with matched and half (Sn100-half) CTDI_vol value. Image quality was evaluated on the basis of contrast-to-noise ratio (CNR).

RESULTS

For the newborn phantom, 70-110 kV was selected as the optimal range (0.36-0.37 mGy). Using Sn150 kV led to an increase in radiation dose (0.75 mGy) without improving CNR (96.9 vs 101.5). Sn100-half showed a decrease in CNR (73.1 vs 101.5). The lowest CTDI_vol for the child phantom was achieved between 100 and 120 kV (0.78-0.80 mGy). Using Sn150 kV increased radiation dose (1.02 mGy) without improvement of CNR (92.4 vs 95.8). At Sn100-half CNR was decreased (61.4 vs 95.8). For adults, 140 and 150 kV revealed the lowest CTDI_vol (2.68 and 2.67 mGy). The Sn150 kV scan delivered comparable CNR (54.4 vs 56.6), but a lower CTDI_vol (2.08 mGy). At Sn100-half CNR was comparable to the 150 kV scan (58.1 vs 56.6).

CONCLUSION

Unenhanced chest CT performed at 100 kV or 150 kV with tin filtration enables radiation dose reduction for the adult phantom, but not for the pediatric phantoms.

Combined Electrocardiography- and Respiratory-Triggered CT of the Lung to Reduce Respiratory Misregistration Artifacts between Imaging Slabs in Free-Breathing Children: Initial Experience

Objective

Cardiac and respiratory motion artifacts degrade the image quality of lung CT in free-breathing children. The aim of this study was to evaluate the effect of combined electrocardiography (ECG) and respiratory triggering on respiratory misregistration artifacts on lung CT in free-breathing children.

Materials and Methods

In total, 15 children (median age 19 months, range 6 months–8 years; 7 boys), who underwent free-breathing ECG-triggered lung CT with and without respiratory-triggering were included. A pressure-sensing belt of a respiratory gating system was used to obtain the respiratory signal. The degree of respiratory misregistration artifacts between imaging slabs was graded on a 4-point scale (1, excellent image quality) on coronal and sagittal images and compared between ECG-triggered lung CT studies with and without respiratory triggering. A p value < 0.05 was considered significant.

Results

Lung CT with combined ECG and respiratory triggering showed significantly less respiratory misregistration artifacts than lung CT with ECG triggering only (1.1 ± 0.4 vs. 2.2 ± 1.0, p = 0.003).

Conclusion

Additional respiratory-triggering reduces respiratory misregistration artifacts on ECG-triggered lung CT in free-breathing children.

In vitro evaluation of a new iterative reconstruction algorithm for dose reduction in coronary artery calcium scoring

Background

Coronary artery calcium (CAC) scoring is a widespread tool for cardiac risk assessment in asymptomatic patients and accompanying possible adverse effects, i.e. radiation exposure, should be as low as reasonably achievable.

Purpose

To evaluate a new iterative reconstruction (IR) algorithm for dose reduction of in vitro coronary artery calcium scoring at different tube currents.

Material and Methods

An anthropomorphic calcium scoring phantom was scanned in different configurations simulating slim, average-sized, and large patients. A standard calcium scoring protocol was performed on a third-generation dual-source CT at 120 kVp tube voltage. Reference tube current was 80 mAs as standard and stepwise reduced to 60, 40, 20, and 10 mAs. Images were reconstructed with weighted filtered back projection (wFBP) and a new version of an established IR kernel at different strength levels. Calcifications were quantified calculating Agatston and volume scores. Subjective image quality was visualized with scans of an ex vivo human heart.

Results

In general, Agatston and volume scores remained relatively stable between 80 and 40 mAs and increased at lower tube currents, particularly in the medium and large phantom. IR reduced this effect, as both Agatston and volume scores decreased with increasing levels of IR compared to wFBP (P < 0.001). Depending on selected parameters, radiation dose could be lowered by up to 86% in the large size phantom when selecting a reference tube current of 10 mAs with resulting Agatston levels close to the reference settings.

Conclusion

New iterative reconstruction kernels may allow for reduction in tube current for established Agatston scoring protocols and consequently for substantial reduction in radiation exposure.

Accuracy and Radiation Dose Reduction Using Low-Voltage Computed Tomography Coronary Artery Calcium Scoring With Tin Filtration

This study prospectively investigated the accuracy and radiation dose reduction of CT coronary artery calcium scoring (CACS) using a 100 kVp acquisition protocol with tin filtration (Sn100 kVp) compared with the standard 120 kVp acquisition protocol; 70 patients (59% men, 62.1 ± 10.7 years) who underwent a clinically indicated CACS acquisition using the standard 120 kVp protocol on a third-generation dual-source CT system were enrolled. An additional Sn100 kVp CACS scan was performed. Agatston scores and categories, percentile-based risk categorization, and radiation dose estimates were derived from 120 and Sn100 kVp studies and compared. Median Agatston scores from the Sn100 and 120 kVp acquisitions were 38.2 and 41.2, respectively (p <0.0001). Excellent correlation of Agatston scores was found between the 2 acquisitions (r = 0.99, p <0.0001). Although the Agatston scores were systematically lower with Sn100 than with 120 kVp, the comparison of Agatston score categories and percentile-based cardiac risk categories showed excellent agreement (κ = 0.98 and κ = 0.98). Image noise was 26.3 ± 5.7 Hounsfield units in Sn100 kVp and 17.6 ± 4.1 Hounsfield units in 120 kVP scans (p <0.0001). The dose-length product was 14.1 ± 3.7 mGy·cm with Sn100 kVp and 58.5 ± 23.5 mGy·cm with 120 kVp scans (p <0.0001), resulting in a significantly lower effective radiation dose (0.19 ± 0.05 vs 0.82 ± 0.32 mSv, p <0.0001) for Sn100 kVp scans. CACS using a low-voltage tin filtration protocol shows excellent correlation and agreement with the standard method with regard to the Agatston score and subsequent cardiac risk categorization, while achieving a 75% reduction in radiation dose.

Reconstructions Using RIF in Motion Mapping Technique Have Substantially Less Arrhythmogenic Artifacts in Dual-source Coronary CTA

RATIONALE AND OBJECTIVES

Particularly for patients with heart arrhythmias, conventional BestSystole (BS) and BestDiastole (BD) reconstruction techniques in computed tomography (CT) frequently show artifacts that hinder the readability of the coronary tree. To address this problem, this paper presents an alternative reconstruction method that combines the technique "reconstructions with identical filling" (RIF) with motion mapping: This new technique is called "RIF in motion mapping" (RIMM). This study compares the diagnostic quality of images generated with RIMM to that of the other reconstruction techniques.

MATERIALS AND METHODS

Having shown major artifacts in standard reconstructions, the CT datasets of 23 patients with suspected coronary artery disease or prior to transcatheter aortic valve replacement were selected manually. Each dataset was evaluated with four reconstruction techniques: BS, BD, RIF, and RIMM. Two radiologists, blinded to the applied reconstruction type, then evaluated the entire coronary tree of each sample using the 15-segment American Heart Association model and the six-grade Likert scale.

RESULTS

Of the 345 analyzed coronary segments, the RIMM technique showed a significant number of images with reliable diagnostic quality (n = 228, 66%) as compared to RIF (P = 0.002) and BS/BD reconstructions (P < 0.001). Per coronary segment, vessel, and patient, the RIMM technique scored significantly better than the conventional BS/BD reconstructions (P = 0.003) and better than the RIF reconstructions with regard to the right coronary artery (P = 0.041).

CONCLUSIONS

This new technique works: Using RIMM on the worst CT images substantially erased many of these artifacts, thereby enabling the radiologists to clearly visualize these segments. As RIMM considerably eliminates artifacts, this new CT reconstruction technique can help make a fast reliable evaluation of a patient's coronary tree. Thus, this enhanced visualization of cardiac images by RIMM avoids the need for further invasive diagnostic procedures.

Radiation dose reduction in parasinus CT by spectral shaping

INTRODUCTION

Spectral shaping aims to narrow the X-ray spectrum of clinical CT. The aim of this study was to determine the image quality and the extent of radiation dose reduction that can be achieved by tin prefiltration for parasinus CT.

METHODS

All scans were performed with a third generation dual-source CT scanner. A study protocol was designed using 100 kV tube voltage with tin prefiltration (200 mAs) that provides image noise levels comparable to a low-dose reference protocol using 100 kV without spectral shaping (25 mAs). One hundred consecutive patients were prospectively enrolled and randomly assigned to the study or control group. All patients signed written informed consent. The study protocol was approved by the local Institutional Review Board and applies to the HIPAA. Subjective and objective image quality (attenuation values, image noise, and contrast-to-noise ratio (CNR)) were assessed. Radiation exposure was assessed as volumetric CT dose index, and effective dose was estimated. Mann-Whitney U test was performed for radiation exposure and for image noise comparison.

RESULTS

All scans were of diagnostic image quality. Image noise in air, in the retrobulbar fat, and in the eye globe was comparable between both groups (all p > 0.05). CNR_{eye globe/air} did not differ significantly between both groups (p = 0.7). Radiation exposure (1.7 vs. 2.1 mGy, p < 0.01) and effective dose (0.055 vs. 0.066 mSv, p < 0.01) were significantly reduced in the study group.

CONCLUSION

Radiation dose can be further reduced by 17% for low-dose parasinus CT by tin prefiltration maintaining diagnostic image quality.

Dose reduction potential of iterative reconstruction algorithms in neck CTA-a simulation study

OBJECTIVES

This study aimed to determine the degree of radiation dose reduction in neck CT angiography (CTA) achievable with Sinogram-affirmed iterative reconstruction (SAFIRE) algorithms.

METHODS

10 consecutive patients scheduled for neck CTA were included in this study. CTA images of the external carotid arteries either were reconstructed with filtered back projection (FBP) at full radiation dose level or underwent simulated dose reduction by proprietary reconstruction software. The dose-reduced images were reconstructed using either SAFIRE 3 or SAFIRE 5 and compared with full-dose FBP images in terms of vessel definition. 5 observers performed a total of 3000 pairwise comparisons.

RESULTS

SAFIRE allowed substantial radiation dose reductions in neck CTA while maintaining vessel definition. The possible levels of radiation dose reduction ranged from approximately 34 to approximately 90% and depended on the SAFIRE algorithm strength and the size of the vessel of interest. In general, larger vessels permitted higher degrees of radiation dose reduction, especially with higher SAFIRE strength levels. With small vessels, the superiority of SAFIRE 5 over SAFIRE 3 was lost.

CONCLUSIONS

Neck CTA can be performed with substantially less radiation dose when SAFIRE is applied. The exact degree of radiation dose reduction should be adapted to the clinical question, in particular to the smallest vessel needing excellent definition.

In Vitro Comparison of Second- and Third-generation Dual-source CT for Coronary Stent Visualization at Different Tube Potentials

RATIONALE AND OBJECTIVES

The study aimed to evaluate in vitro stent lumen visibility of coronary stents in a second- and third-generation dual-source computed tomography (CT) system at 100 and 120 kVp tube potential.

MATERIALS AND METHODS

Twenty-six coronary stents ranging from 2.25 to 4.0 mm in diameter were implanted in a coronary vessel phantom. Scans were performed at 100 and 120 kVp tube potential. Evaluation was performed using a medium-sharp kernel in both systems (B46f in the second-generation and Bv49 in the third-generation model) and a sharp (Bv59) convolution kernel optimized for vascular imaging in the third-generation CT.

RESULTS

The median visible stent lumen diameter in the second-generation system was higher at 120 kVp with a median of 62.0% compared to 56.3% at 100 kVp (P < 0.001). The median visible diameter in the third-generation system was significantly higher applying the Bv49 kernel with 66.7% at 120 kVp and 61.1% at 100 kVp (both P < 0.001). When applying the Bv59 kernel, visible stent lumen further increased to 69.3% at 120 kVp and 66.7% at 100 kVp. Additionally, stent lumen was assessed using full width at half maximum, resulting in a comparable increase in luminal diameter at corresponding tube potential.

CONCLUSIONS

Third-generation dual-source CT provides superior stent lumen visibility at equivalent tube potential and at reduced tube potential of 100 kVp when compared to 120 kVp in a second-generation system, at least when manually assessed.

Feasibility of Respiratory-gated High-pitch Spiral CT:: Free-breathing Inspiratory Image Quality

RATIONALE AND OBJECTIVES

This study aimed to develop and implement a respiratory-gated setup for dual-source computed tomography (CT) at high pitch to examine patients in a reproducible inspiratory phase.

MATERIALS AND METHODS

Twenty-one patients underwent free-breathing respiratory-gated chest CT using a high-pitch scan mode no more than 6 months after inspiratory breath-held nongated CT, which serves as reference. Scan parameters were as follows: pitch = 3.4, 128 × 0.6 mm collimation, 0.28 s gantry rotation time, and 150 ref.mAs per tube at 120 kV. The examinations were triggered using the tidal wave provided by a respiratory-gating system as input signal. Image quality was assessed focusing on artifacts and delineation of the anatomical and pathological structures. Lung volumes were measured on both free-breathing and reference examinations.

RESULTS

All examinations were performed without complications. Image quality was high with both protocols. Significantly less motion artifacts were recorded with the high-pitch mode compared to the reference (P = 0.02). Most of the artifacts were located in the peripheral parts of the lower lobes for the study group and in the central part of the left lower lobe for the reference. Average total lung volume was 4.5 ± 1.5 L in respiratory-gated examinations and 5.8 ± 0.9 L in examinations with breath-hold in inspiration.

CONCLUSIONS

High-pitch chest CT scanning during free breathing minimizes motion artifacts, improving image quality in patients with limited breath-holding abilities. To assure scanning in an inspiratory phase, data acquisition should be triggered with a respiratory-gating system.

Computed Tomography Angiography of Carotid Arteries and Vertebrobasilar System: A Simulation Study for Radiation Dose Reduction

Computed tomography angiography (CTA) of carotid arteries and vertebrobasilar system is a standardized procedure with excellent image quality, but radiation exposure remains a matter of concern. The aim of this study is to examine to what extent radiation dose can be lowered in relation to a standard protocol by simulating examinations with lower tube currents applying a dedicated software.Lower tube current was simulated by a dedicated noise insertion and reconstruction software (ReconCT). In a phantom study, true scans were performed with different dose protocols and compared to the results of simulated dose reductions of the same degree, respectively. In a patient study, 30 CTAs of supra-aortic vessels were reconstructed at a level of 100%, 75%, 50%, and 25% of the initial dose. Objective and subjective image analyses were performed.No significant noise differences between true scans and simulated scans of mimicked contrasted vessels were found. In the patient study, the quality scores of the 4 dose groups differed statistically significant; this difference vanished for the comparison of the 100% and 75% datasets after dichotomization into the categories of diagnostic and nondiagnostic image quality (P = .50).This study suggests an easy-to-implement method of simulating CTAs of carotid arteries and vertebrobasilar system with lower tube current for dose reduction by artificially adding noise to the original raw data. Lowering the radiation dose in a moderate extent to 75% of the original dose levels does not significantly alter the diagnostic image quality.

Unenhanced third-generation dual-source chest CT using a tin filter for spectral shaping at 100kVp

OBJECTIVE

To prospectively investigate image quality and radiation dose of 100kVp spectral shaping chest CT using a dedicated tin filter on a 3rd generation dual-source CT (DSCT) in comparison to standard 100kVp chest CT.

METHODS

Sixty patients referred for a non-contrast chest on a 3rd generation DSCT were prospectively included and examined at 100kVp with a dedicated tin filter. These patients were retrospectively matched with patients that were examined on a 2nd generation DSCT at 100kVp without tin filter. Objective and subjective image quality was assessed in various anatomic regions and radiation dose was compared.

RESULTS

Radiation dose was decreased by 90% using the tin filter (3.0 vs 0.32mSv). Soft tissue attenuation and image noise was not statistically different for both examination techniques (p>0.05), however image noise was found to be significantly higher in the trachea when using the additional tin filter (p=0.002). SNR was found to be statistically similar in pulmonary tissue, significantly lower when measured in air and significantly higher in the aorta for the scans on the 3rd generation DSCT. Subjective image quality with regard to overall quality and image noise and sharpness was not statistically significantly different (p>0.05).

CONCLUSION

100kVp spectral shaping chest CT by means of a tube-based tin-filter on a 3rd generation DSCT allows 90% dose reduction when compared to 100kVp chest CT on a 2nd generation DSCT without spectral shaping.

Influence of trigger type, tube voltage and heart rate on calcified plaque imaging in dual source cardiac computed tomography: phantom study

Background

To investigate the impact of high pitch cardiac CT vs. retrospective ECG gated CT on the quantification of calcified vessel stenoses, with assessment of the influence of tube voltage, reconstruction kernel and heart rate.

Methods

A 4D cardiac movement phantom equipped with three different plaque phantoms (12.5%, 25% and 50% stenosis at different calcification levels), was scanned with a 128-row dual source CT scanner, applying different trigger types (gated vs. prospectively triggered high pitch), tube voltages (100-120 kV) and heart rates (50–90 beats per minute, bpm). Images were reconstructed using different standard (B26f, B46f, B70f) and iterative (I26f, I70f) convolution kernels. Absolute and relative plaque sizes were measured and statistically compared. Radiation dose associated with the different methods (gated vs. high pitch, 100 kV vs. 120 kV) were compared.

Results

Compared to the known diameters of the phantom plaques and vessels both CT-examination techniques overestimated the degrees of stenoses. Using the high pitch CT-protocol plaques appeared larger (0.09 ± 0.31 mm, 2 ± 8 percent points, PP) in comparison to the ECG-gated CT-scans. Reducing tube voltage had a similar effect, resulting in higher grading of the same stenoses by 3 ± 8 PP. In turn, sharper convolution kernels lead to a lower grading of stenoses (differences of up to 5%). Pairwise comparison of B26f and I26f, B46f and B70f, and B70f and I70f showed differences of 0–1 ± 6–8 PP of the plaque depiction. Motion artifacts were present only at 90 bpm high pitch experiments. High-pitch protocols were associated with significantly lower radiation doses compared with the ECG-gated protocols (258.0 mGy vs. 2829.8 mGy CTDI_vol, p ≤ 0.0001).

Conclusion

Prospectively triggered high-pitch cardiac CT led to an overestimation of plaque diameter and degree of stenoses in a coronary phantom. This overestimation is only slight and probably negligible in a clinical situation. Even at higher heart rates high pitch CT-scanning allowed reliable measurements of plaque and vessel diameters with only slight differences compared ECG-gated protocols, although motion artifacts were present at 90 bpm using the high pitch protocols.

Closing in on the K edge: coronary CT angiography at 100, 80, and 70 kV-initial comparison of a second- versus a third-generation dual-source CT system

PURPOSE

To prospectively evaluate radiation and contrast medium requirements for performing high-pitch coronary computed tomographic (CT) angiography at 70 kV using a third-generation dual-source CT system in comparison to a second-generation dual-source CT system.

MATERIALS AND METHODS

All patients gave informed consent for this institutional review board-approved study. Forty-five patients (median age, 52 years; 27 men) were imaged in high-pitch mode with a third-generation dual-source CT system at 70 kV (n = 15) or with a second-generation dual-source CT system at 80 or 100 kV (n = 15 for each). Tube voltage was based on body mass index: 80 or 70 kV for less than 26 kg/m(2) versus 100 kV for 26-30 kg/m(2). For the 80- and 100-kV protocols, 80 mL of contrast material was injected, versus 45 mL for the 70-kV protocol. Data were reconstructed by using a second-generation iterative reconstruction algorithm for second-generation dual-source CT and a recently introduced third-generation iterative reconstruction algorithm for third-generation dual-source CT. Objective image quality was measured for various regions of interest, and subjective image quality was evaluated with a five-point Likert scale.

RESULTS

The signal-to-noise ratio of the coronary CT angiography studies acquired with 70 kV was significantly higher (70 kV: 14.3-17.6 vs 80 kV: 7.1-12.9 vs 100 kV: 9.8-12.9; P < .0497) than those acquired with the other two protocols for all coronary arteries. Qualitative image quality analyses revealed no significant differences between the three CT angiography protocols (median score, 5; P > .05). The mean effective dose was 75% and 108% higher (0.92 mSv ± 0.3 [standard deviation] and 0.78 mSv ± 0.2 vs 0.44 mSv ± 0.1; P < .0001), respectively, for the 80- and 100-kV CT angiography protocols than for the 70-kV CT angiography protocol.

CONCLUSION

In nonobese patients, third-generation high-pitch coronary dual-source CT angiography at 70 kV results in robust image quality for studying the coronary arteries, at significantly reduced radiation dose (0.44 mSv) and contrast medium volume (45 mL), thus enabling substantial radiation dose and contrast medium savings as compared with second-generation dual-source CT.

Performance of turbo high-pitch dual-source CT for coronary CT angiography: first ex vivo and patient experience

OBJECTIVES

To evaluate image quality, maximal heart rate allowing for diagnostic imaging, and radiation dose of turbo high-pitch dual-source coronary computed tomographic angiography (CCTA).

METHODS

First, a cardiac motion phantom simulating heart rates (HRs) from 60-90 bpm in 5-bpm steps was examined on a third-generation dual-source 192-slice CT (prospective ECG-triggering, pitch 3.2; rotation time, 250 ms). Subjective image quality regarding the presence of motion artefacts was interpreted by two readers on a four-point scale (1, excellent; 4, non-diagnostic). Objective image quality was assessed by calculating distortion vectors. Thereafter, 20 consecutive patients (median, 50 years) undergoing clinically indicated CCTA were included.

RESULTS

In the phantom study, image quality was rated diagnostic up to the HR75 bpm, with object distortion being 1 mm or less. Distortion increased above 1 mm at HR of 80-90 bpm. Patients had a mean HR of 66 bpm (47-78 bpm). Coronary segments were of diagnostic image quality for all patients with HR up to 73 bpm. Average effective radiation dose in patients was 0.6 ± 0.3 mSv.

CONCLUSIONS

Our combined phantom and patient study indicates that CCTA with turbo high-pitch third-generation dual-source 192-slice CT can be performed at HR up to 75 bpm while maintaining diagnostic image quality, being associated with an average radiation dose of 0.6 mSv.

KEY POINTS

• CCTA is feasible with the turbo high-pitch mode. • Turbo high-pitch CCTA provides diagnostic image quality up to 73 bpm. • The radiation dose of high-pitch CCTA is 0.6 mSv on average.