Dual-source CT Scanner Research Articles

Design of a Monte Carlo model based on dual-source computed tomography (DSCT) scanners for dose and image quality assessment using the Monte Carlo N-Particle (MCNP5) code

Abstract The purpose of this work was to develop and validate a Monte Carlo model for a Dual Source Computed Tomography (DSCT) scanner based on the Monte Carlo N-particle radiation transport computer code (MCNP5). The geometry of the Siemens Somatom Definition CT scanner was modeled, taking into consideration the x-ray spectrum, bowtie filter, collimator, and detector system. The accuracy of the simulation from the dosimetry point of view was tested by calculating the Computed Tomography Dose Index (CTDI) values. Furthermore, typical quality assurance phantoms were modeled in order to assess the imaging aspects of the simulation. Simulated projection data were processed, using the MATLAB software, in order to reconstruct slices, using a Filtered Back Projection algorithm. CTDI, image noise, CT-number linearity, spatial and low contrast resolution were calculated using the simulated test phantoms. The results were compared using several published values including IMPACT, NIST and actual measurements. Bowtie filter shapes are in agreement with those theoretically expected. Results show that low contrast and spatial resolution are comparable with expected ones, taking into consideration the relatively limited number of events used for the simulation. The differences between simulated and nominal CT-number values were small. The present attempt to simulate a DSCT scanner could provide a powerful tool for dose assessment and support the training of clinical scientists in the imaging performance characteristics of Computed Tomography scanners.

High-pitch non-gated scans on the second and third generation dual-source CT scanners: comparison of coronary image quality

ObjectiveTo examine differences in image quality of the coronary arteries when performing high-pitch non-electrocardiography (ECG)-gated scans on the second-generation (2G) and third-generation (3G) dual-source CT scanners. MethodsWe retrospectively examined patients with high-pitch non-ECG-gated CT angiography (CTA) of the chest or chest/abdomen/pelvis. Outpatient scans from 59 patients in the 3G high-pitch group and 53 patients in the 2G high-pitch group were included. Two blinded cardiac imagers independently scored the coronary image quality using a 4-point Likert scale (from completely diagnostic to completely non-diagnostic) and evaluated the presence of coronary artery disease. ResultsDiagnostic image quality of the coronaries in high-pitch CTA exams using 3G scanner was improved compared to 2G scanner, both on a per-vessel basis (45–94% versus 23–86%) and on a per-study basis (34% versus 14%). The 3G group showed a statistically significant improvement in image quality when evaluating the left main coronary, right coronary, and overall coronary arteries. Coronary artery disease was detected in 65% of high-pitch scans. Radiation doses in terms of CTDIvol and DLP were lower for 3G high-pitch scans (7.5 mGy and 491 mGy∗cm) compared to 2G high-pitch scans (14.8 mGy and 911 mGy∗cm). ConclusionsWe found a higher proportion of diagnostic image quality of the coronary arteries in high-pitch non-ECG-gated CTA exams using a 3G dual-source CT scanner, compared to 2G. In scans with diagnostic image quality, underlying coronary artery disease may be confidently diagnosed and should prompt considerations for further management in the appropriate clinical setting.

Assessment of image quality in abdominal computed tomography: Effect of model-based iterative reconstruction, multi-planar reconstruction and slice thickness on potential dose reduction

PurposeTo determine the effect of tube load, model-based iterative reconstruction (MBIR) strength and slice thickness in abdominal CT using visual comparison of multi-planar reconstruction images. MethodFive image criteria were assessed independently by four radiologists on two data sets at 42- and 98-mAs tube loads for 25 patients examined on a 192-slice dual-source CT scanner. Effect of tube load, MBIR strength, slice thickness and potential dose reduction was estimated with Visual Grading Regression (VGR). Objective image quality was determined by measuring noise (SD), contrast-to-noise (CNR) ratio and noise-power spectra (NPS). ResultsComparing 42- and 98-mAs tube loads, improved image quality was observed as a strong effect of log tube load regardless of MBIR strength (p < 0.001). Comparing strength 5 to 3, better image quality was obtained for two criteria (p < 0.01), but inferior for liver parenchyma and overall image quality. Image quality was significantly better for slice thicknesses of 2mm and 3mm compared to 1mm, with potential dose reductions between 24%–41%. As expected, with decrease in slice thickness and algorithm strength, the noise power and SD (HU-values) increased, while the CNR decreased. ConclusionIncreasing slice thickness from 1 mm to 2 mm or 3 mm allows for a possible dose reduction. MBIR strength 5 shows improved image quality for three out of five criteria for 1 mm slice thickness. Increasing MBIR strength from 3 to 5 has diverse effects on image quality. Our findings do not support a general recommendation to replace strength 3 by strength 5 in clinical abdominal CT protocols. However, strength 5 may be used in task-based protocols.

DIRA-3D—a model-based iterative algorithm for accurate dual-energy dual-source 3D helical CT

Quantitative dual-energy computed tomography may improve the accuracy of treatment planning in radiation therapy. Of special interest are algorithms that can estimate material composition of the imaged object. One example of such an algorithm is the 2D model-based iterative reconstruction algorithm DIRA. The aim of this work is to extend this algorithm to 3D so that it can be used with cone-beams and helical scanning. In the new algorithm, the parallel FBP method was replaced with the approximate 3D FBP-based PI-method. Its performance was tested using a mathematical phantom consisting of six ellipsoids. The algorithm substantially reduced the beam-hardening artefact and the artefacts caused by approximate reconstruction after six iterations. Compared to Alvarez-Macovski’s base material decomposition, DIRA-3D does not require geometrically consistent projections and hence can be used in dual-source CT scanners. Also, it can use several tissue-specific material bases at the same time to represent the imaged object.

Coronary artery assessment in Kawasaki disease with dual-source CT angiography to uncover vascular pathology

BackgroundKawasaki disease (KD) is a vasculitis with formation of coronary artery aneurysms (CAAs) that can lead to myocardial ischemia. Echocardiography is the primary imaging modality for the coronary arteries despite limited visualization. Coronary angiography (CAG) is the gold standard yet invasive with high-radiation exposure. To date however, state-of-the-art CT scanners enable high-quality low-dose coronary computed tomographic angiography (cCTA) imaging. The aim of our study in KD is to report (i) the diagnostic yield of cCTA compared to echocardiography, and (ii) the radiation dose.Methods and resultsWe collected data of KD patients who underwent cCTA. cCTA findings were compared with echocardiography results. In 70 KD patients (median age 15.1 years [0.5–59.5 years]; 78% male; 38% giant CAA), the cCTA identified 61 CAAs, of which 34 (56%, with a Z score > 3, in 22 patients) were not detected by echocardiography. In addition, the left circumflex (aneurysmatic in 6 patients) was always visible upon cCTA and not detected upon echocardiography. Calcifications, plaques, and/or thrombi were visualized by cCTA in 25 coronary arteries (15 patients). Calcifications were seen as early as 2.7 years after onset of disease. In 5 patients, the cCTA findings resulted in an immediate change of treatment. The median effective dose (ED) in millisievert differed significantly (p < 0.01) between third-generation dual-source and other CT scanners (1.5 [0.3–9.4] (n = 56) vs 3.8 [1.7–20.0] (n = 14)).ConclusionsThe diagnostic yield of third-generation dual-source cCTA combined with reduced radiation exposure makes cCTA a favorable diagnostic modality to complete the diagnosis and long-term treatment indications for KD.Key Points• cCTA is a favorable diagnostic modality to complete the diagnosis and long-term treatment indications for Kawasaki disease.• Kawasaki disease patients with proven coronary artery involvement on echocardiography require additional imaging.

Impact of heart rate on coronary computed tomographic angiography interpretability with a third-generation dual-source scanner

BackgroundGuidelines suggest coronary computed tomography angiography (CCTA) should be performed with a heart rate (HR) below 60. Third-generation dual-source CT (DSCT) scanners, with improved temporal resolution, and end-systolic acquisition may facilitate imaging at higher HRs. We determined the influence of HR and end-systolic acquisition on image interpretability and quality with a third-generation DSCT. MethodsPatients who underwent CCTA between July 2017 and December 2018 were retrospectively identified. All images were acquired using a SOMATOM Force scanner (Siemens Healthcare). The primary outcome was the presence of any uninterpretable coronary segment. The association between HR and CCTA with uninterpretable segments was assessed with multivariable logistic regression, correcting for demographics and imaging variables. ResultsIn total, 2620 patients were included, mean age 61.4 ± 12.9 years and 61.2% male, with uninterpretable segments present in 229 (8.7%) scans. In multivariable analysis, HR 80–89 was associated with an increased likelihood of having a scan with uninterpretable segments (adjusted odds ratio [OR] 4.53, p < 0.001). However, no significant association was present with end-systolic acquisition (HR 80–89, adjusted OR 2.32, p = 0.125). HR ≥ 90 was associated with a decreased likelihood of good or excellent image quality (adjusted OR 0.26, 95% CI 0.11–0.63, p = 0.003). ConclusionsWith third-generation dual-source CT scanners, patients with HR 60–80 can be imaged without impacting image interpretability. End-systolic image acquisition facilitates imaging at HRs > 80 without increasing non-diagnostic scans. Routine use of systolic gating could omit the need for strict HR control and pre-test beta blockade currently required for CCTA.

Personalized 3D printed coronary models in coronary stenting

3D printing has shown great promise in cardiovascular disease, with reports mainly focusing on pre-surgical planning and medical education. Research on utilization of 3D printed models in simulating coronary stenting has not been reported. In this study, we presented our experience of placing coronary stents into personalized 3D printed coronary models with the aim of determining stent lumen visibility with images reconstructed with different postprocessing views and algorithms. A total of six coronary stents with diameter ranging from 2.5 to 4.0 mm were placed into 3 patient-specific 3D printed coronary models for simulation of coronary stenting. The 3D printed models were placed in a plastic container and scanned on a 192-slice third generation dual-source CT scanner with images reconstructed with soft (Bv36) and sharp (Bv59) kernel algorithms. Thick and thin slab maximum-intensity projection (MIP) images were also generated from the original CT data for comparison of stent lumen visibility. Stent lumen diameter was measured on 2D axial and MIP images, while stent diameter was measured on 3D volume rendering images. 3D virtual intravascular endoscopy (VIE) images were generated to provide intraluminal views of the coronary wall and stent appearances. All of these stents were successfully placed into the right and left coronary arteries but 2 of them did not obtain wall apposition along the complete length. The stent lumen visibility ranged from 54 to 97%, depending on the stent location in the coronary arteries. The mean stent lumen diameters measured on 2D axial, thin and thick slab MIP images were found to be significantly smaller than the actual size (P<0.01). Thick slab MIP images resulted in measured stent lumen diameters smaller than those from thin slab MIP images, with significant differences noticed in most of the measurements (4 out of 6 stents) (P<0.05), and no significant differences in the remaining 2 stents (P=0.19-0.38). In contrast, 3D volume rendering images allowed for more accurate measurements with measured stent diameters close to the actual dimensions in most of these coronary stents, except for the stent placed at the right coronary artery in one of the models due to insufficient expansion of the stent. Images reconstructed with sharp kernel Bv59 significantly improved stent lumen visibility when compared to the smooth Bv36 kernel (P=0.01). 3D VIE was successfully generated in all of the datasets with clear visualization of intraluminal views of the stents in relation to the coronary wall. This preliminary report shows the feasibility of using 3D printed coronary artery models in coronary stenting for investigation of optimal coronary CT angiography protocols. Future studies should focus on placement of more stents with a range of stent diameters in the quest to reduce the need for invasive angiography for surveillance.

Deciphering normal and anomalous viscero-atrial situs on multidetector CT angiography.

Viscero-atrial situs encompasses the laterality, relative position and configuration of the abdominal viscera, the atria of the heart and the tracheobronchial tree. Determining the situs and cardiac position is the first step in the commonly used sequential, segmental approach to the imaging evaluation of congenital heart defects (CHD). Abnormalities of visceroatrial situs and cardiac position are frequently associated with the presence of complex CHDs and accurate assessment of situs abnormalities can help predict the probability and type of the defect. Multidetector CT (MDCT) angiography, with its multiplanar reformatting and volume rendering techniques, offers accurate information about the morphology and three-dimensional relationships of the various cardiac and extra cardiac structures. In this pictorial essay, we present the MDCT imaging findings of the spectrum of abnormalities of visceroatrial situs and cardiac position, using a third generation dual source CT scanner.

Axial absorbed dose distributions during abdominal computed tomography acquisitions: Measurement and the Monte Carlo simulation study

We aimed to validate Monte Carlo (MC) simulation models against measurements and evaluate the effect of object size on axial absorbed dose distributions during abdominal computed tomography (CT) acquisitions based on MC simulations. A medium-sized abdominal phantom, with holes to insert a pencil ionization chamber, was acquired using a 192-slice dual-source CT scanner at a tube voltage of 120 kVp and a displayed volume CT dose index of 5.0 mGy. Absorbed doses were measured using the pencil ionization chamber and an electrometer, and normalized absorbed doses to center were calculated for all measurement locations. The Particle and Heavy Ion Transport code System version 3.02 was used to simulate normalized absorbed doses of 19 locations through small-, medium-, and large-sized abdominal phantom models with a tube voltage of 120 kVp. In the measurement and MC simulation, the normalized absorbed dose to center in the medium-sized abdominal phantom was 1.48 ± 0.28 and 1.62 ± 0.35, respectively. Higher normalized doses were observed at peripheral regions when the phantom size was larger.

Venous Collateral Pathways in Superior Thoracic Inlet Obstruction: A Systematic Analysis of Anatomy, Embryology, and Resulting Patterns.

OBJECTIVE. For this study, we reviewed 56 standard-of-care CT examinations over a timespan of 2 years from patients with superior thoracic inlet venous obstruction and identified eight thoracic collateral pathways for venous blood return to the right heart. We evaluated each pathway individually from an anatomic and a pathophysiologic perspective for a better understanding of how such pathways form and what patterns can be expected. MATERIALS AND METHODS. All 56 patients were scanned according to our standard CT protocol. Images of the thoracic region were acquired in the craniocaudal direction during breath-holding using a second-generation dual-source CT scanner. Contrast medium was administered via a cubital or antecubital vein; the amount of contrast material ranged from 49 to 81 mL depending on patient body weight. RESULTS. Of the 56 patients, CT showed superior vena cava syndrome exclusively in 22 (39%) patients and showed superior vena cava syndrome and involvement of the left or right brachiocephalic vein or even the subclavian vein in the remaining 34 (61%) patients. We could not find any remarkable feature leading to the formation of only one collateral pathway or to a specific pattern depending on underlying cause or the level or the extent of obstruction. Thus, we believe that there are no specific patterns for how these venous detours form and that they are most probably driven by pressure gradients. CONCLUSION. Recognizing imaging findings associated with venous collateral pathways may prevent misdiagnosis or unnecessary follow-up examinations. Furthermore, knowledge of these collateral pathways and an understanding of the underlying cause can support interventional radiologists and vascular surgeons in planning interventional procedures and revascularization procedures.

Optimized management of urolithiasis by coloured stent-stone contrast using dual-energy computed tomography (DECT)

BackgroundWe analysed in vitro the appearance of commonly used ureteral stents with dual-energy computed tomography (DECT) and we used these characteristics to optimize the differentiation between stents and adjacent stone.MethodsWe analysed in vitro a selection of 36 different stents from 7 manufacturers. They were placed in a self-build phantom model and measured using the SOMATOM® Force Dual Source CT-Scanner (Siemens, Forchheim, Germany). Each sample was scanned at various tube potentials of 80 and 150 peak kilovoltage (kVp), 90 and 150 kVp and 100 and 150 kVp. The syngo Post-Processing Suite software program (Siemens, Forchheim, Germany) was used for differentiation based on a 3–material decomposition algorithm (UA, calcium, urine) according to our standard stone protocol.ResultsStents composed of polyurethane appeared blue and silicon-based stents were red on the image. The determined appearances were constant for various peak kilovoltage (kVp) values. The coloured stent-stone-contrast displayed on DECT improves monitoring, especially of small calculi adjacent to indwelling ureteral stents.ConclusionBoth urinary calculi and ureteral stents can be accurately differentiated by a distinct appearance on DECT. For the management of urolithiasis patients can be monitored more easily and accurately using DECT if the stent shows a different colour than the adjacent stone.

Intermittent CT fluoroscopic guided lung biopsy - Retrospective analysis of success rate, radiation exposure, complications and duration of procedure.

Intermittent CT fluoroscopic biopsy is a new technology, but has not been studied widely. This study aims to investigate correlation between the radiation dose and fluoroscopic CT exposure factors to establish the low dose parameters for performing percutaneous lung biopsies, as well as the relationship of the mean diameter and depth of lesions with radiation dose, procedure time, success and complication rates. This is a retrospective study to analyse lung biopsies performed using intermittent CT fluoroscopic technique with 18 G semi-automated coaxial gun on 256 slice scanner. A total of 50 patients were included in the study. Biopsy was done in three mAs and KVp settings (30 and 70, 10 and 120, 30 and 120, respectively). The statistical data analysis was performed using SPSS Statistics software. Pneumothorax occurred in 22 % of cases. Sampling rate was 98% but histopathological diagnosis was made in 94% cases. Mean procedure time was 30.5±11.1 minutes. Low dose protocol (30 mAs and 70 KVp) had least radiation exposure during biopsy procedure (p < 0.001) with similar success rate, complications and procedure time (p > 0.05) in comparison with high dose protocol (10 and 120, 30 and 120 mAs and KVp, respectively). Mean diameter of lesions didn't correlate with radiation dose, success rate, complications and duration of procedure (p > 0.05) while significant association was found when depth was correlated with radiation exposure during fluoroscopic biopsy, duration of procedure and complication rates (p < 0.05) while no association was found with success rates. On third generation dual energy source CT scanner, reducing mAs and KVp to 30 and 70 during fluoroscopy biopsy can produce images whose complications and success rates are comparable to high dose CT. In general, intermittent CT fluoroscopy guided lung biopsy has good success rates with acceptable complications, while utilising less radiation dose and procedure time.

Virtual monoenergetic dual-energy CT for evaluation of hepatic and splenic lacerations.

To evaluate the utility of virtual monoenergetic imaging in assessing hepatic and splenic lacerations and to determine the optimal energy level to maximize injury contrast-to-noise ratio. We retrospectively examined 49 contrast-enhanced abdominal CT studies performed on a dual-source dual-energy CT (DECT) scanner with reported liver and/or splenic lacerations. All studies included portal venous phase imaging acquired simultaneously at low (80 or 100kVp) and high (140kVp with tin filtration) energy levels. Conventional 120kVp-equivalent images were generated for routine review by blending the low and high energy acquisitions. Virtual monoenergetic reconstructions were retrospectively generated in 10keV increments from 40 to 90keV. Liver or splenic laceration attenuation, background parenchymal attenuation, and noise were measured on each set of monoenergetic and conventional images. Injury-to-parenchyma contrast and contrast-to-noise ratios (CNR) were calculated. Differences between CNR of monoenergetic series and conventional images were assessed with a paired t test. Liver laceration was identified in 28 patients, and splenic laceration in 22 patients. Background noise was lower at higher monoenergetic levels, with the lowest noise seen at 90keV, less than that of conventional images (stddev 8.0 for 90keV and 8.5 for conventional based on noise of uninjured liver/spleen parenchyma, p < 0.001). For both liver and splenic lacerations, injury-to-parenchyma contrast was greater at lower monoenergetic levels, with maximum at 40keV. Contrast at 40-70keV was significantly greater than that of conventional images (p < 0.001). Injury-to parenchyma CNR was also greater at 40-70keV than that of conventional images and with statistical significance. CNR was highest at 40keV for both liver (6.5 for 40keV and 5.4 for conventional, p < 0.001) and splenic lacerations (7.5 vs. 5.8, p < 0.001). DECT virtual monoenergetic imaging at low keV improves injury-to-parenchyma CNR of hepatic and splenic lacerations compared with traditional polyenergetic reconstructions. Specially, the optimal energy level for assessing both was 40keV.

Ultra-low dose one-step CT angiography for coronary, carotid and cerebral arteries using 128-slice dual-source CT: A feasibility study.

Atherosclerotic diseases are systemic and patient outcomes depend on comprehensive imaging evaluation. Computed tomography angiography (CTA) is a powerful tool used to assess atherosclerosis. However, the scanning protocol is designed for cardiovascular and cerebrovascular imaging, which require considerations into the radiation dose, contrast agent and image quality. The purpose of the present study was to evaluate ultra-low dose one-step CTA for coronary, carotid and cerebral arteries with a low concentration contrast agent. A total of 78 patients were enrolled and randomly divided into two groups: Group A (n=38) and B (n=40). High-pitch CTA for coronary, carotid and cerebral arteries with a tube voltage of 70 or 80 kVp and 40 ml contrast agent (270 mgI/ml) was performed by a 128-slice dual-source CT scanner for group A. Standard high-pitch CTA with a tube voltage of 100 kVp and 60 ml contrast agent (370 mgI/ml) was conducted for group B. The image quality, radiation dose and amount of contrast agent in group A were evaluated and compared with group B. The dose length product for groups A and B was 62.95±21.54 vs. 160.15±15.13 mGy cm, respectively (t=−23.157, P<0.001). The mean total iodine content was 10.8±0 mg for group A and 22.2±0 mg for group B. In total, 99.4% of the arterial segments could be assessed for the two groups (χ2=0.267, P=0.606). The results revealed that ultra-low dose one-step high-pitch CTA can provide assessable image quality, and minimize the radiation dose and contrast agent.

A comparison study of radiation effective dose in ECG-Gated Coronary CT Angiography and calcium scoring examinations performed with a dual-source CT scanner

In this report we have evaluated radiation effective dose received by patients during ECG-gated CCTA examinations based on gender, heart rate, tube voltage protocol and body mass index (BMI). A total of 1,824 patients were retrospectively recruited (1,139 men and 685 women) and they were divided into Group 1 (CCTA with calcium scoring), Group 2 (CCTA without calcium scoring) and Group 3 (only calcium scoring), where the association between gender, heart rate, tube voltage protocol and body mass index (BMI) were analysed. Examinations were performed using a retrospective ECG-gated CCTA protocol and the effective doses were calculated from the dose length product with a conversion coefficient of 0.026 mSv.mGy−1cm−1. No significant differences were observed in the mean effective dose between gender in all groups. The mean estimated dose was significantly higher when the heart rate was lower in Group 1 (p < 0.001) and Group 2 (p = 0.002). There were also significant differences between the mean effective dose in tube voltage protocol and BMI among the three groups. The mean effective dose was positively correlated with BMI (p < 0.001), but inversely related to the heart rate. This study supported the theory that a high heart rate, low tube voltage and low BMI could significantly reduce radiation dose exposure.

In Vivo Analysis of Urinary Stones With Dual-Energy Computed Tomography.

Formation mechanisms and treatment of the urinary stones are different, depending on their chemical structure. Therefore, determining the stone type plays a key role in planning treatment and preventive measures. Computed tomography (CT), with the use of dual-energy technology in recent years, has made it possible to do in vivo analysis of urinary stones. In this study, we aimed to evaluate the diagnostic efficacy of dual-energy CT (DECT) and compare its results with in vitro analysis, which is accepted as a gold standard for analysis of urinary stones. The DECT examinations were performed on 373 patients using 128-slice dual-source CT scanner. Analysis of attenuation ratios in the high and low kilovoltage peak values of the stone was performed at workstation, and stones were classified as hydroxyapatite, calcium oxalate, cystine, and uric acid. On follow-up, the stone was obtained in 35 patients as a result of surgery or passed spontaneously. The DECT analysis and in vitro analysis results were compared and statistically evaluated. In all patients, 136 hydroxyapatite, 160 calcium oxalate, 57 uric acid, and 20 cystine stones were detected with DECT. In vitro analyses of the stones were performed in 35 patients, and 8 hydroxyapatite, 18 calcium oxalate, 6 uric acid, and 3 cystine stones were revealed. When DECT analysis results were compared with in vitro analysis results, stone types were detected correctly in 32 (91.4%) patients and incorrectly in 3 (8.6%) patients. Especially all uric acid and cystine stones were correctly detected with DECT. With advanced postprocess analysis methods, DECT is able to analyze urinary stones. The DECT is found superior especially in detecting uric acid and cystine stones. Its success in detecting hydroxyapatite and calcium oxalate stones is also high. When in vivo analyses of the stones are performed with DECT, it will be possible to make a contribution to the personalization and optimization of the treatment.

Prevalence of Decreased Myocardial Blood Flow in Symptomatic Patients with Patent Coronary Stents: Insights from Low-Dose Dynamic CT Myocardial Perfusion Imaging.

To study the prevalence and clinical characteristics of decreased myocardial blood flow (MBF) quantified by dynamic computed tomography (CT) myocardial perfusion imaging (MPI) in symptomatic patients without in-stent restenosis. Thirty-seven (mean age, 71.3 ± 10 years; age range, 48-88 years; 31 males, 6 females) consecutive symptomatic patients with patent coronary stents and without obstructive de novo lesions were prospectively enrolled to undergo dynamic CT-MPI using a third-generation dual-source CT scanner. The shuttle-mode acquisition technique was used to image the complete left ventricle. A bolus of contrast media (50 mL; iopromide, 370 mg iodine/mL) was injected into the antecubital vein at a rate of 6 mL/s, followed by a 40-mL saline flush. The mean MBF value and other quantitative parameters were measured for each segment of both stented-vessel territories and reference territories. The MBFratio was defined as the ratio of the mean MBF value of the whole stent-vessel territory to that of the whole reference territory. An MBFratio of 0.85 was used as the cut-off value to distinguish hypoperfused from non-hypoperfused segments. A total of 629 segments of 37 patients were ultimately included for analysis. The mean effective dose of dynamic CT-MPI was 3.1 ± 1.2 mSv (range, 1.7-6.3 mSv). The mean MBF of stent-vessel territories was decreased in 19 lesions and 81 segments. Compared to stent-vessel territories without hypoperfusion, the mean MBF and myocardial blood volume were markedly lower in hypoperfused stent-vessel territories (77.5 ± 16.6 mL/100 mL/min vs. 140.4 ± 24.1 mL/100 mL/min [p < 0.001] and 6.4 ± 3.7 mL/100 mL vs. 11.5 ± 4 mL/100 mL [p < 0.001, respectively]). Myocardial hypoperfusion in stent-vessel territories was present in 48.6% (18/37) of patients. None of clinical parameters differed statistically significantly between hypoperfusion and non-hypoperfusion subgroups. Decreased MBF is commonly present in patients who are symptomatic after percutaneous coronary intervention, despite patent stents and can be detected by dynamic CT-MPI using a low radiation dose.

Metal Artifact Reduction Computed Tomography of Arthroplasty Implants: Effects of Combined Modeled Iterative Reconstruction and Dual-Energy Virtual Monoenergetic Extrapolation at Higher Photon Energies.

The aim of this study was to compare the effects of combined virtual monoenergetic extrapolation (VME) of dual-energy computed tomography data and iterative metal artifact reduction (iMAR) at higher photon energies on low- and high-density metal artifacts and overall image quality of the ankle arthroplasty implants with iMAR, weighted filtered back projection (WFBP), and WFBP-based VME. Total ankle arthroplasty implants in 6 human cadaver ankles served as surrogates for arthroplasty implants. All specimens underwent computed tomography with a 2 × 192-slice dual-source computed tomography scanner at tube voltages of 80 and tin-filtered 150 kVp to produce mixed 120 kVp equivalent polychromatic and virtual monoenergetic extrapolated images at 150 and 190 keV (VME 150 and VME 190, respectively). By implementing the WFBP and iMAR reconstruction algorithms on polychromatic, VME 150 and VME 190 data, 6 image datasets were created: WFBP-Polychromatic, iMAR-Polychromatic, WFBP-VME 150, WFBP-VME 190, iMAR-VME 150, and iMAR-VME 190. High-density and low-density artifacts were separately quantified with a threshold-based computer algorithm. After anonymization and randomization, 2 observers independently ranked the datasets for overall image quality. Repeated measures analysis of variance, Friedman, and Cohen weighted κ tests were applied for statistical analysis. A conservative P value of less than 0.001 was considered statistically significant. iMAR-VME 190 keV and iMAR-VME 150 keV created the least amount of high-density artifacts (all P < 0.001), whereas iMAR-Polychromatic was the most effective method to mitigate low-density streaks (P < 0.001). For low- and high-density artifacts, polychromatic iMAR acquisition was superior to WFBP-VME 150 keV and WFBP-VME 190 keV (all P < 0.001). On sharp kernel reconstructions, readers ranked the overall image quality of iMAR-Polychromatic images highest (all P < 0.001). Similarly, on soft tissue kernel reconstructions, readers ranked iMAR-Polychromatic images highest with a statistically significant difference over other techniques (all P < 0.001), except for iMAR-VME 150 keV (P = 0.356). In computed tomography imaging of ankle arthroplasty implants, iMAR reconstruction results in fewer metal artifacts and better image quality than WFBP reconstruction for both polychromatic and virtual monoenergetic data. The combination of iMAR and VME at higher photon energies results in mixed effects on implant-induced metal artifacts, including decreased high-density and increased low-density artifacts, which in combination does not improve image quality over iMAR reconstruction of the polychromatic data. Our results suggest that, for ankle arthroplasty implants, the highest image quality is obtained by iMAR reconstruction of the polychromatic data without the need to implement VME at high-energy levels.

Leadless Cardiac Pacemaker (LCP) without Diagnostic Relevant Artifacts in DualSource and DualEnergy-CT Examinations in First- to Third-Generation DSCT Scanner

To identify the influence and artifact burden in cardiac CT imaging of a leadless cardiac pacemaker (LCP) performed with all three generations of DualSource CT (DSCT) Scanners. The LCP was examined in DSCT scanners of the first to third generation using DualEnergy (DECT) and DSCT as well as alterations of the current-time product. For DECT examinations, virtual monoenergetic images were computed manually on a dedicated workstation. Virtual voltage was manually selected by subjective assessment of the lowest artifact burden. Systematic variations of the pacemaker angle to the gantry were assessed, too. The angle was successively increased by 10°, ranging from 0° to 90°. Artifact burden was quantified on a five-point Likert scale (1- no artifacts, 2- few artifacts, 3- moderate artifacts, 4- many artifacts, and 5- massive artifacts). Likert values of 1-3 were considered diagnostic and assessed by two board-certified radiologists in consensus. In total, 200 examinations were analyzed, a mean Likert value of 1.93 ± 0.61 was found overall. None of the images were assessed Likert value >3. The positioning evaluation showed a clear and significant reduction of artifact burden toward lower angles, (0°: 1.4 ± 0.5 vs. 90° 2.55 ± 0.51). At scanner level, second-generation DSCT performed significantly better (1.68 ± 0.47) than both other scanners. Comparison of technique (DECT vs. DSCT) revealed a significantly improved image quality in DSCT examinations. LCP can be safely examined in DSCT scanner of the first to third generation with the evaluated protocols and techniques, which are currently in use. Artifact burden can be significantly reduced by aligning or approaching the LCP's longitudinal axis toward the scanner's z-axis.

Abstract 16693: Standalone Quantitative 18 F-NaF Coronary PET Fused With Prior Deep-Inspiration Coronary CT Angiography for Improved Patient Workflow

Introduction: 18 F-NaF PET holds promise in distinguishing high-risk plaques in patients with coronary artery disease. The current imaging protocol requires a hybrid single-session acquisition of coronary computed tomography angiography (CTA) and PET. This approach does not allow high-risk patient selection for 18 F-NaF imaging based on prior CTA findings. We aimed to determine whether prior deep inspiration CTA fused with a subsequent PET-only scan allows reliable evaluation of coronary 18 F-NaF uptake. Methods: Twenty-five patients (age 65±6 years, 68% males) underwent clinical CTA (CTA1) on a dual-source CT scanner and subsequently combined 18 F-NaF PET/CTA (CTA2) imaging on a hybrid PET/CT scanner within 16 [9,28] days. We fused CTA1 with 18 F-NaF PET (PET) and compared the visual pattern of activity, maximal standard uptake values (SUVmax) and target to background ratio (TBR) measurements on prior-CTA (PET/CTA1) versus hybrid (PET/CTA2) cardiac motion corrected PET images. Results: On PET/CTA2, 118 coronary plaques were identified. Thirty-six coronary segments from 14 (56%) patients had high 18 F-NaF uptake (TBR&gt;1.25), while 82 segments had lesions with 18 F-NaF TBR ≤1.25. Uptake in all lesions was categorized identically on co-registered PET/CTA1. There was no difference in 18 F-NaF uptake between PET/CTA1 and PET/CTA2 (SUVmax: 1.46±0.59 vs. 1.45±0.57, p=0.53; TBR:1.28±0.55 vs. 1.26±0.53, p=0.41). Repeatability of uptake measurements was excellent with intraclass correlation coefficients of 0.98 (95% CI 0.97 to 0.99, p&lt;0.001) and 0.94 (95% CI 0.92 to 0.96, p&lt;0.001) and limits of agreement of ±0.18 and ±0.19 for SUVmax and TBR respectively. Conclusions: Coronary CTA/PET protocol with CTA first followed by PET-only allows for reliable and reproducible quantification of 18 F-NaF coronary uptake. This approach may facilitate selection of high-risk patients for PET-only imaging based on results from prior CTA, providing a practical workflow for clinical application.