Photon counting computed tomography of in-stent-stenosis in a phantom: Optimal virtual monoenergetic imaging in ultra high resolution.

Rationale and objectives: Coronary computed tomography angiography (CCTA) is becoming increasingly important for the diagnostic workup of coronary artery disease, nevertheless, imaging of in-stent stenosis remains challenging. For the first time, spectral imaging in Ultra High Resolution (UHR) is now possible in clinically available photon counting CT. The aim of this work is to determine the optimal virtual monoenergetic image (VMI) for imaging in-stent stenoses in cardiac stents. Materials and methods: 6 stents with inserted hypodense stenoses were scanned in an established phantom in UHR mode. Images were reconstructed with 3 different kernels for spectral data (Qr56, Qr64, Qr72) with varying levels of sharpness. Based on region of interest (ROI) measurements image quality parameters including contrast-to-noise ratio (CNR) were analyzed for all available VMI (40 keV-190 keV). Finally, based on quantitative results and VMI used in clinical routine, a set of VMI was included in a qualitative reading. Results: CNR showed significant variations across different keV levels (p < 0.001). Due to reduced noise there was a focal maximum in the VMI around 65 keV. The peak values were observed for kernel Qr56 at 116 keV with 19.47 ± 8.67, for kernel Qr64 at 114 keV with 13.56 ± 6.58, and for kernel Qr72 at 106 keV with 12.19 ± 3.25. However, in the qualitative evaluation the VMI with lower keV (55 keV) performed best. Conclusions: Based on these experimental results, a photon counting CCTA in UHR with stents should be reconstructed with the Qr72 kernel for the assessment of in-stent stenoses, and a VMI 55 keV should be computed for the evaluation.

Coronary stent imaging in photon counting computed Tomography: Optimization of reconstruction kernels in a phantom.

PURPOSE: Imaging stents and in-stent stenosis remains a challenge in coronary computed tomography angiography (CCTA). In comparison to conventional Computed Tomography, Photon Counting CT (PCCT) provides decisive clinical advantages, among other things by providing low dose ultra-high resolution imaging of coronary arteries. This work investigates the image quality in CCTA using clinically established kernels and those optimized for the imaging of cardiac stents in PCCT, both for in-vitro stent imaging in 400 µm standard resolution mode (SRM) and 200 µm Ultra High Resolution Mode (UHR). METHODS: Based on experimental scans, vascular reconstruction kernels (Bv56, Bv64, Bv72) were optimized. In an established phantom, 10 different coronary stents with 3 mm diameter were scanned in the first clinically available PCCT. Scans were reconstructed with clinically established and optimized kernels. Four readers measured visible stent lumen, performed ROI-based density measurements and rated image quality. RESULTS: Regarding the visible stent lumen, UHR is significantly superior to SRM (p < 0.001). In all levels, the optimized kernels are superior to the clinically established kernels (p < 0.001). One optimized kernel showed a significant reduction of noise compared to the clinically established kernels. Overall image quality is improved with optimized kernels. CONCLUSIONS: In a phantom study PCCT UHR with optimized kernels for stent imaging significantly improves the ability to assess the in-stent lumen of small cardiac stents. We recommend using UHR with an optimized sharp vascular reconstruction kernel (Bv72uo) for imaging of cardiac stent.

Insights into extrinsic foot muscle activation during a 75 min run using T2 mapping.

The extrinsic foot muscles are essentially for controlling the movement path but our knowledge of their behavior during prolonged running is still very limited. Therefore, this study analyzed the time-course of muscle activation using T2 mapping during 75 min of running. In this prospective study, 19 recreational active runners completed 75 min of treadmill running at a constant speed. Interleaved T2 mapping sequences were acquired and segmented at timepoints 0, 2.5, 5, 10, 15, 45, and 75 min. ANOVA for repeated measurements followed by a Tukey post hoc test and Pearson correlation between running speed and initial signal increase at 2.5 min were calculated. All muscles showed a significant signal increase between baseline and 2.5 min (e.g. medial gastrocnemius: + 15.48%; p < 0.01). This was followed by a plateau phase till 15 min for all but the extensor digitorum longus muscle and a significant decrease at 45 or 75 min for all muscles (all p < 0.05). Correlation between running speed and signal increase was negative for all muscles and significant for both gastrocnemii (e.g. medial: r = - 0.57, p = 0.0104) and soleus (r = - 0.47, p = 0.0412). The decrease of relaxation times times in the later running phases was less pronounced for faster runners (≥ 10 km/h). T2 relaxation times do not only decrease after cessation of exercise but already during prolonged running. The lesser initial increase and later decrease in faster runners may indicate training induced changes.

Prediction of anemia on enhanced computed tomography of the thorax using virtual non-contrast reconstructions.

ABSTRACT: To determine if anemia can be predicted on enhanced computed tomography (CT) examinations of the thorax using virtual non-contrast (VNC) images, in order to support clinicians especially in diagnosing primary asymptomatic patients in daily routine.In this monocentric study, 100 consecutive patients (50 with proven anemia), who underwent a contrast-enhanced CT examination of the thorax due to various indications were included. Attenuation was measured in the descending thoracic aorta, the intraventricular septum, and the left ventricle cavity both in the conventional contrast-enhanced and in the VNC images.Two experienced radiologists annotated the delineation of a dense interventricular septum or a hyperattenuating aortic wall sign for all patients.Hemoglobin levels were then correlated with the measured attenuation values, as well as the visualization of the aortic wall or interventricular septum.Good correlation was shown between hemoglobin levels and CT attenuation values of the left ventricular cavity (r = .59), aorta (r = .56), and ratio between left ventricular cavity and the intraventricular septum (r = .57). Receiver operating characteristic curve revealed ≤ 36.5 hounsfield units (left ventricular cavity) as the threshold for diagnosing anemia. Predicting anemia by visualization of a hyperattenuating aortic wall or a dense interventricular septum yielded a specificity of 98% and 92%, respectively.Predicting anemia on enhanced CT examinations using VNC is feasible. A threshold value of ≤ 36.5 hounsfield units (left ventricular cavity) best defines anemia. Aortic wall or interventricular septum visualization on VNC is a specific anemia indicator.

Comparison of a novel Compressed SENSE accelerated 3D modified relaxation-enhanced angiography without contrast and triggering with CE-MRA in imaging of the thoracic aorta.

To compare a novel Compressed SENSE accelerated ECG- and respiratory-triggered flow-independent 3D isotropic Relaxation-Enhanced Angiography without Contrast and Triggering (modified REACT) with standard non-ECG-triggered 3D contrast-enhanced magnetic resonance angiography (CE-MRA) for imaging of the thoracic aorta in patients with connective tissue diseases (CTD) or other aortic diseases using manual and semiautomatic measurement approaches. This retrospective, single-center analysis of 30 patients (June-December 2018) was conducted by two radiologists, who independently measured aortic diameters on modified REACT and CE-MRA using manual (Multiplanar-Reconstruction) and semiautomatic (Advanced Vessel Analysis) measurement tools on seven levels (inner edge): Aortic annulus and sinus, sinotubular junction, mid- and high-ascending aorta, aortic isthmus, and descending aorta. Bland-Altman analysis was conducted to evaluate differences between the mean values of aortic width and ICCs were calculated to assess interobserver agreement. For each level, image quality was evaluated on a four-point scale in consensus with Wilcoxon matched-pair test used to evaluate for differences between both MRA techniques. Additionally, evaluation time for each measurement technique was noted, which was compared applying one-way ANOVA. When comparing both imaging and measurement methods, CE-MRA (mean difference 0.24 ± 0.27 mm) and the AVA-tool (- 0.21 ± 0.15 mm) yielded higher differences compared to modified REACT (- 0.11 ± 0.11 mm) and the MPR-tool (0.07 ± 0.21 mm) for all measurement levels combined without yielding clinical significance. There was an excellent interobserver agreement between modified REACT and CE-MRA using both tools of measurement (ICC > 0.9). Modified REACT (average acquisition time 06:34 ± 01:36 min) provided better image quality from aortic annulus to mid-ascending aorta (p < 0.05), whereas at distal measurement levels, no significant differences were noted. Regarding time requirement, no statistical significance was found between both measurement techniques (p = 0.08). As a novel non-CE-MRA technique, modified REACT allows for fast imaging of the thoracic aorta with higher image quality in the proximal aorta than CE-MRA enabling a reliable measurement of vessel dimensions without the need for contrast agent. Thus, it represents a clinically suitable alternative for patients requiring repetitive imaging. Manual and semiautomatic measurement approaches provided comparable results without significant difference in time need.

Virtual monoenergetic images preserve diagnostic assessability in contrast media reduced abdominal spectral detector CT.

OBJECTIVES: To investigate if low-keV virtual monoenergetic images (VMI40keV) from abdominal spectral detector CT (SDCT) with reduced intravenous contrast media application (RCM) provide abdominal assessment similar to conventional images with standard contrast media (SCM) dose. METHODS: 78 patients with abdominal SDCT were retrospectively included: 41 patients at risk for adverse reactions who received 44 RCM examinations with 50 ml and 37 patients who underwent 44 SCM examinations with 100 ml of contrast media (CM) and who were matched for effective body diameters. RCM, SCM images and RCM-VMI40keV were reconstructed. Attenuation and signal-to-noise ratio (SNR) of liver, pancreas, kidneys, lymph nodes, psoas muscle, aorta and portal vein were assessed ROIs-based. Contrast-to-noise ratios (CNR) of lymph nodes vs aorta/portal vein were calculated. Two readers evaluated organ/vessel contrast, lymph node delineation, image noise and overall assessability using 4-point Likert scales. RESULTS: RCM were inferior to SCM images in all quantitative/qualitative criteria. RCM-VMI40keV and SCM images showed similar lymph node and muscle attenuation (p = 0.83,0.17), while for all other ROIs, RCM-VMI40keV showed higher attenuation (p ≤ 0.05). SNR was comparable between RCM-VMI40keV and SCM images (p range: 0.23-0.99). CNR of lymph nodes was highest in RCM-VMI40keV (p ≤ 0.05). RCM-VMI40keV received equivalent or higher scores than SCM in all criteria except for organ contrast, overall assessability and image noise, where SCM were superior (p ≤ 0.05). However, RCM-VMI40keV received proper or excellent scores in 88.6/94.2/95.4% of the referring cases. CONCLUSIONS: VMI40keV counteract contrast deterioration in CM reduced abdominal SDCT, facilitating diagnostic assessment. ADVANCES IN KNOWLEDGE: SDCT-derived VMI40keV provide adequate depiction of vessels, organs and lymph nodes even at notable CM reduction.

Metastatic pulmonary calcification: First report of pulmonary calcium suppression using dual-energy CT.

Metastatic pulmonary calcification is an underdiagnosed metabolic lung disease characterized by diffuse calcium deposition in the lungs, often associated with secondary hyperparathyroidism due to chronic renal failure. A 31-year-old man with chronic renal failure initially presented with diffuse pain symptoms, deterioration of general condition, and respiratory insufficiency. Noncontrast-enhanced computed tomography of the chest was performed using a spectral-detector-based dual-energy CT. It showed multiple, centrilobular, ground-glass opacities, and nodules, ultimately leading to the diagnosis. Calcium suppression proved to be highly useful to classify the pulmonary alterations.

Are left atrial diverticula and left-sided septal pouches relevant additional findings in cardiac CT? Correlation between left atrial outpouching structures and ischemic brain alterations.

PURPOSE: To evaluate the correlation between left atrial diverticula (LAD) and left-sided septal pouches (LSSP) with ischemic brain alterations in MRI. METHODS: A retrospective analysis of 174 patients who received both, a dedicated cardiac CT angiography (CCTA) and a brain MRI examination was performed. Two radiologists independently reviewed all examinations for the presence of LAD and LSSP as well as ischemic alterations of the brain. Subsequently, the correlation between these cardiac and cerebral findings as well as to other potentially related risk factors was assessed. RESULTS: 71 LAD (total prevalence 41%) and 65 LSSP (total prevalence 37%) were identified in 174 patients. Combined prevalence was 10%. Ischemic brain alterations were found in patients with a LAD in 42.3% (30/71) and with a LSSP in 64.6% (42/65). Patients without any anatomical variant in the left atrium showed ischemic brain alterations in 39.4% (26/66). The presence of a LSSP was associated with an increased risk for ischemic brain alterations in multivariate logistic regression analysis after adjusting for other risk factors (OR = 3.57, 95% CI = 0.51-2.09, p <  .01). CONCLUSION: In our study cohort LAD and LSSP are highly prevalent anatomical structures within the left atrium. Patients with LSSP showed an approximated 3.5-fold higher probability for ischemic brain alterations. Therefore, LSSP should be considered as a potential risk factor for cardioembolic strokes and its presence should be stated in cardiac CT reports.

Evaluation of soft-plaque stenoses in coronary artery stents using conventional and monoenergetic images: first in-vitro experience and comparison of two different dual-energy techniques.

BACKGROUND: Non-invasive coronary imaging after stent placement remains challenging. Favorable results for dual-energy computed tomography (DECT) derived monoenergetic (MonoE) images have been reported for this purpose. Nowadays, there are different dual-energy techniques available, each with specific advantages and disadvantages. However, for the evaluation of coronaries after stent implantation there is no systematic comparison between different dual-energy techniques. Therefore, the aim of our study was to compare two widely used DECT systems using an in-stent restenosis (ISR) phantom setup. METHODS: Soft-plaque-like stenoses (~50% of lumen) were inserted into ten coronary stents embedded in contrast-filled vessel phantoms. A dual-source CT (DSCT) and a dual-layer CT (DLCT) with comparable acquisition and reconstruction parameters were used. Conventional polyenergetic (PolyE) and MonoE images with 9 different levels (40-120 keV) were calculated. ISR assessability was evaluated by subjective scoring using a 5-point scale and by the following quantitative parameters: image noise, visible lumen diameter (VLD) and ISR contrast-to-noise ratio (CNR). RESULTS: A non-significant trend towards larger VLD in DLCT images was observed. Highest noise was found in low-keV MonoE with significantly higher values for DSCT than for DLCT. Conversely, noise was significantly lower for DSCT at higher-keV MonoE. Peak ISR CNR values were found at low-keV MonoE with no significant difference between both systems. However, for PolyE and mid-energy MonoE, CNRs were significantly higher for DSCT. Subjective image quality was significantly better for PolyE and low-keV MonoE than for high-keV MonoE, also without significant difference between both systems. CONCLUSIONS: Conspicuity of ISR benefits from DECT. Peak CNRs were comparable for both DECT systems and low-keV MonoE offered the highest CNR values and best subjective image quality. In contrast, high-keV MonoE cannot be recommended for stent evaluation due to poor CNR values and therefore significantly limited visualization of stenoses.

Correction to: Imaging of the pulmonary vasculature in congenital heart disease without gadolinium contrast: Intraindividual comparison of a novel Compressed SENSE accelerated 3D modified REACT with 4D contrast-enhanced magnetic resonance angiography.

The original publication of this article [1], contained graphical errors in Figs. 1 and 2. This does not impact the display of the mean differences of the Bland-Altman plots. The updated figures (Fig. 1 and Fig. 2) are published in this correction article.

Imaging of the pulmonary vasculature in congenital heart disease without gadolinium contrast: Intraindividual comparison of a novel Compressed SENSE accelerated 3D modified REACT with 4D contrast-enhanced magnetic resonance angiography.

BACKGROUND: Patients with Congenital heart disease (CHD) require repetitive imaging of the pulmonary vasculature throughout their life. In this study, we compared a novel Compressed SENSE accelerated (factor 9) electrocardiogram (ECG)- and respiratory-triggered 3D modified Relaxation-Enhanced Angiography without Contrast and Triggering (modified REACT-non-contrast-enhanced magnetic resonance angiography (modified REACT-non-CE-MRA)) with standard non-ECG-triggered time-resolved 4D CE-MRA for imaging of the pulmonary arteries and veins in patients with CHD. METHODS: This retrospective analysis of 25 patients (June 2018-April 2019) with known or suspected CHD was independently conducted by two radiologists executing measurements on modified REACT-non-CE-MRA and 4D CE-MRA on seven dedicated points (inner edge): Main pulmonary artery (MPA), right and left pulmonary artery, right superior and inferior pulmonary vein, left superior (LSPV) and inferior pulmonary vein. Image quality for arteries and veins was evaluated on a four-point scale in consensus. RESULTS: Twenty-three of the 25 included patients presented a CHD. There was a high interobserver agreement for both methods of imaging at the pulmonary arteries (ICC ≥ 0.96); at the pulmonary veins, modified REACT-non-CE-MRA showed a slightly higher agreement, pronounced at LSPV (ICC 0.946 vs. 0.895). Measurements in 4D CE-MRA showed higher diameter values compared to modified REACT-non-CE-MRA, at the pulmonary arteries reaching significant difference (e.g. MPA: mean 0.408 mm, p = 0.002). Modified REACT-non-CE-MRA (average acquisition time 07:01 ± 02:44 min) showed significant better image quality than 4D CE-MRA at the pulmonary arteries (3.84 vs. 3.32, p < 0.001) and veins (3.32 vs. 2.72, p = 0.015). CONCLUSIONS: Compressed SENSE accelerated (factor 9) ECG- and respiratory-triggered 3D modified REACT-non-CE-MRA allows for reliable and fast imaging of the pulmonary arteries and veins with higher image quality and slightly higher interobserver agreement than 4D CE-MRA without contrast agent and associated disadvantages. Therefore, it represents a clinically suitable technique for patients requiring repetitive imaging of the pulmonary vasculature, e.g. patients with CHD.

Spectral Photon-Counting Computed Tomography for Coronary Stent Imaging: Evaluation of the Potential Clinical Impact for the Delineation of In-Stent Restenosis.

OBJECTIVES: In-stent restenosis (ISR) is one of the main long-term complications after coronary stent placement, and the ability to evaluate ISR noninvasively using coronary computed tomography (CT) angiography remains challenging. For this application, spectral photon-counting CT (SPCCT) has the potential to increase image quality and reduce artifacts due to its advanced detector technology.Our study aimed to verify the technical and clinical potential of a novel SPCCT prototype using an ISR phantom setup. MATERIALS AND METHODS: Soft plaque-like restenosis (45 HU; approximately 50% of the stent lumen) were inserted into 10 different coronary stents (3 mm diameter), which were placed in a vessel phantom and filled with a contrast agent (400 HU). A research prototype SPCCT and a clinical dual-layer CT (DLCT; IQon; Philips) with comparable acquisition and reconstruction parameters were used to scan the phantoms. Conventional polyenergetic (PolyE) and monoenergetic (MonoE) images with 4 different energy levels (40, 60, 90, 120 keV) were reconstructed. Qualitative (delineation of the stenosis and adjacent residual lumen using a 5-point Likert scale) and quantitative (image noise, visible lumen diameter, lumen diameter adjacent to the stenosis, contrast-to-noise ratio of the restenosis) parameters were evaluated for both systems. RESULTS: The qualitative results averaged over all reconstructions were significantly superior for SPCCT compared with DLCT (eg, subjective rating of the best reconstruction of each scanner: DLCT PolyE: 2.80 ± 0.42 vs SPCCT MonoE 40 keV: 4.25 ± 1.03). Stenosis could be clearly detected in 9 and suspected in 10 of the 10 stents with both SPCCT and DLCT. The residual lumen next to the stenosis was clearly delineable in 7 of 10 stents (0.64 ± 0.11 mm or 34.97% of the measured stent lumen) with SPCCT, while it was not possible to delineate the residual lumen for all stents using DLCT. The measured diameter of the lumen within the stent was significantly higher for SPCCT compared with DLCT in all reconstructions with the best results for the MonoE 40 keV images (SPCCT: 1.80 ± 0.17 mm; DLCT: 1.50 ± 0.31 mm). The image noise and the contrast-to-noise ratio were better for DLCT than for SPCCT (contrast-to-noise ratio: DLCT MonoE 40: 31.58 ± 12.54; SPCCT MonoE 40: 4.64 ± 1.30). CONCLUSIONS: Spectral photon-counting CT allowed for the noninvasive evaluation of ISR with reliable results regarding the residual lumen for most tested stents and the clear identification or suspicion of stenosis for all stents. In contrast, the residual lumen could not be detected for a single stent using DLCT.

Venous-phase chest CT with reduced contrast medium dose: Utilization of spectral low keV monoenergetic images improves image quality.

PURPOSE: Intravenous contrast administration is crucial in many CT examinations but also poses a potential risk to the patient. Monoenergetic images (MonoE) of dual-energy CT systems can virtually increase iodine attenuation and might improve image quality (IQ) if contrast dose is reduced. In this study, we investigated the influence of MonoE on lymph node (LN) delineation and IQ in chest CT examinations with significantly reduced contrast dose (50 %) of a novel dual-layer CT (DLCT). METHOD: 30 patients with clinically indicated reduced contrast dose underwent venous-phase chest DLCT scans. Conventional polyenergetic (PolyE) and MonoE images at 40 keV were calculated. The contrast difference of hilar lymph nodes (LN-CD) to the adjacent right pulmonary artery, their signal-to-noise (SNR) and contrast-to-noise-ratio (CNR) were determined. Subjective IQ was evaluated by 2 readers with respect to LN delineation and overall contrast enhancement (CE) using a 5-point-Likert-scale. RESULTS: LN-CD, SNR and CNR were significantly higher in MonoE than in PolyE images (LN-CD 92.3 ±â€¯37.9 vs. 33.1 ±â€¯14.5 HU, SNR 8.4 ±â€¯3.4 vs. 4.0 ±â€¯1.2, CNR 9.2 ±â€¯6.3 vs. 2.6 ±â€¯1.5; all p < 0.01). The LN delineation (3.7 ±â€¯0.9 vs.1.8 ±â€¯0.7; p < 0.01) and the CE (3.9 ±â€¯0.7 vs. 2.3 ±â€¯0.7; p < 0.01) were rated significantly better for MonoE than for PolyE images. There was no MonoE examination classified as non-diagnostic. CONCLUSIONS: Subjective and objective IQ parameters can be significantly improved for venous-phase chest CT examinations with reduced contrast doses by utilization of low-keV MonoE reconstructions. All MonoE images provided sufficient overall CE and therefore reduced contrast doses might be considered in a wider range of DLCT examinations and patients.

Ultrasound-guided lymphangiography and interventional embolization of chylous leaks following esophagectomy.

OBJECTIVES: Postoperative chylothorax is a serious complication after transthoracic esophagectomy, and is associated with major morbidity due to dehydration and malnutrition. For patients with high-output fistula, re-thoracotomy with ligation of the thoracic duct is the treatment of choice. Radiologic interventional management is an innovative procedure that has the potential to replace surgery in the treatment algorithm. METHODS: Four patients with high-output chylous leaks following esophagectomy are presented. Ultrasound-guided lymphangiography with embolization of the thoracic duct and/or disruption of the cisterna chyli was performed to occlude the leakage site. Radiologic interventions and procedure-related outcomes are described in detail. RESULTS: In all four patients, ultrasound-guided lymphangiography of the groin with injection of Lipiodol was able to detect and visualize the leakage site in the lower mediastinum. In three patients, the leak could be successfully occluded by Lipiodol embolization. In one patient, embolization failed and the disruption technique was successfully performed. No procedure-related complications were observed. CONCLUSIONS: In case of a postoperative chylothorax, radiologic intervention is feasible and safe. The procedure is indicated for high-output chylous fistulas after esophagectomy, and should be applied early after the diagnosis of this postoperative complication.

Computed tomography pulmonary angiograms using a novel dual-layer spectral detector: Adjusted window settings are essential for diagnostic image quality.

OBJECTIVE: The aim of this study was to determine optimal window settings for conventional polyenergetic and virtual monoenergetic images derived from computed tomography pulmonary angiogram (CTPA) examinations of a novel dual-layer spectral detector computed tomography system (DLCT). METHODS: Monoenergetic (40 keV) and polyenergetic images of 50 CTPA examinations were calculated and the best individual window width and level (W/L) values were manually assessed. Optimized values were obtained afterwards based on regression analysis. Diameters of standardized pulmonary artery segments and subjective image quality parameters were evaluated and compared. RESULTS: Attenuation and contrast-to-noise values were higher in monoenergetic than in polyenergetic images (P≤.001). Averaged best individual W/L for polyenergetic and monoenergetic were 1020/170 and 2070/480 HU, respectively.All adjusted W/L-settings varied significantly compared to standard settings (700/100 HU) and obtained higher subjective image quality scores. A systematic overestimation of artery diameters for standard window settings in monoenergetic images was observed. CONCLUSIONS: Appropriate W/L-settings are required to assess polyenergetic and monoenergetic CTPA images of a novel DLCT. W/L-settings of 1020/170 HU and 2070/480 HU were found to be the best averaged values for polyenergetic and monoenergetic CTPA images, respectively.

Knowledge-based iterative reconstructions for imaging of coronary artery stents: first in-vitro experience and comparison of different radiation dose levels and kernel settings.

BACKGROUND: Advanced knowledge-based iterative model reconstructions (IMR) became recently available for routine computed tomography (CT). Using more realistic physical models it promises improved image quality and potential radiation dose reductions, both possibly beneficial for non-invasive assessment of coronary stents. PURPOSE: To evaluate the influence of different IMR settings at different radiation doses on stent lumen visualization in comparison to filtered back projection (FBP) and first-generation (hybrid) iterative reconstruction (HIR). MATERIAL AND METHODS: Ten coronary stents in a coronary phantom were examined at four different dose settings (120 kV/125 mAs, 120 kV/75 mAs, 100 kV/125 mAs, 100 kV/75 mAs). Images were reconstructed with stent-specific FBP and HIR kernels and with IMR using CardiacRoutine (CR) and CardiacSharp (CS) settings at three different iteration levels. Image quality was evaluated using established parameters: image noise; in-stent attenuation difference; and visible lumen diameter. RESULTS: Image noise was significantly lower in IMR than in corresponding HIR and FBP images. At lower radiation doses, image noise increased significantly except with IMR CR3 and IMR CS3. Visible lumen diameters were significantly larger with IMR CS than with FBP, HIR, and IMR CR. IMR CR showed the smallest attenuation difference, while attenuation was artificially decreased extensively with IMR CS. FBP and HIR showed moderately increased in-stent attenuations. No relevant influence of used radiation doses on visible lumen diameters or attenuation differences was found. CONCLUSION: IMR CR reduces image noise significantly while offering comparable stent-specific image quality in comparison to FBP and HIR and therefore potentially facilitates stent lumen delineation. Utilization of IMR CS for stent evaluation seems unfavorable due to artificial image alterations.

Photon Counting Computed Tomography With Dedicated Sharp Convolution Kernels: Tapping the Potential of a New Technology for Stent Imaging.

OBJECTIVES: The aims of this study were to assess the value of a dedicated sharp convolution kernel for photon counting detector (PCD) computed tomography (CT) for coronary stent imaging and to evaluate to which extent iterative reconstructions can compensate for potential increases in image noise. MATERIALS AND METHODS: For this in vitro study, a phantom simulating coronary artery stenting was prepared. Eighteen different coronary stents were expanded in plastic tubes of 3 mm diameter. Tubes were filled with diluted contrast agent, sealed, and immersed in oil calibrated to an attenuation of -100 HU simulating epicardial fat. The phantom was scanned in a modified second generation 128-slice dual-source CT scanner (SOMATOM Definition Flash, Siemens Healthcare, Erlangen, Germany) equipped with both a conventional energy integrating detector and PCD. Image data were acquired using the PCD part of the scanner with 48 × 0.25 mm slices, a tube voltage of 100 kVp, and tube current-time product of 100 mAs. Images were reconstructed using a conventional convolution kernel for stent imaging with filtered back-projection (B46) and with sinogram-affirmed iterative reconstruction (SAFIRE) at level 3 (I463). For comparison, a dedicated sharp convolution kernel with filtered back-projection (D70) and SAFIRE level 3 (Q703) and level 5 (Q705) was used. The D70 and Q70 kernels were specifically designed for coronary stent imaging with PCD CT by optimizing the image modulation transfer function and the separation of contrast edges. Two independent, blinded readers evaluated subjective image quality (Likert scale 0-3, where 3 = excellent), in-stent diameter difference, in-stent attenuation difference, mathematically defined image sharpness, and noise of each reconstruction. Interreader reliability was calculated using Goodman and Kruskal's γ and intraclass correlation coefficients (ICCs). Differences in image quality were evaluated using a Wilcoxon signed-rank test. Differences in in-stent diameter difference, in-stent attenuation difference, image sharpness, and image noise were tested using a paired-sample t test corrected for multiple comparisons. RESULTS: Interreader and intrareader reliability were excellent (γ = 0.953, ICCs = 0.891-0.999, and γ = 0.996, ICCs = 0.918-0.999, respectively). Reconstructions using the dedicated sharp convolution kernel yielded significantly better results regarding image quality (B46: 0.4 ± 0.5 vs D70: 2.9 ± 0.3; P < 0.001), in-stent diameter difference (1.5 ± 0.3 vs 1.0 ± 0.3 mm; P < 0.001), and image sharpness (728 ± 246 vs 2069 ± 411 CT numbers/voxel; P < 0.001). Regarding in-stent attenuation difference, no significant difference was observed between the 2 kernels (151 ± 76 vs 158 ± 92 CT numbers; P = 0.627). Noise was significantly higher in all sharp convolution kernel images but was reduced by 41% and 59% by applying SAFIRE levels 3 and 5, respectively (B46: 16 ± 1, D70: 111 ± 3, Q703: 65 ± 2, Q705: 46 ± 2 CT numbers; P < 0.001 for all comparisons). CONCLUSIONS: A dedicated sharp convolution kernel for PCD CT imaging of coronary stents yields superior qualitative and quantitative image characteristics compared with conventional reconstruction kernels. Resulting higher noise levels in sharp kernel PCD imaging can be partially compensated with iterative image reconstruction techniques.

Whole-body computed tomography in trauma patients: optimization of the patient scanning position significantly shortens examination time while maintaining diagnostic image quality.

BACKGROUND: The study was conducted to compare examination time and artifact vulnerability of whole-body computed tomographies (wbCTs) for trauma patients using conventional or optimized patient positioning. PATIENTS AND METHODS: Examination time was measured in 100 patients scanned with conventional protocol (Group A: arms positioned alongside the body for head and neck imaging and over the head for trunk imaging) and 100 patients scanned with optimized protocol (Group B: arms flexed on a chest pillow without repositioning). Additionally, influence of two different scanning protocols on image quality in the most relevant body regions was assessed by two blinded readers. RESULTS: Total wbCT duration was about 35% or 3:46 min shorter in B than in A. Artifacts in aorta (27 vs 6%), liver (40 vs 8%) and spleen (27 vs 5%) occurred significantly more often in B than in A. No incident of non-diagnostic image quality was reported, and no significant differences for lungs and spine were found. CONCLUSION: An optimized wbCT positioning protocol for trauma patients allows a significant reduction of examination time while still maintaining diagnostic image quality.

Virtual Monoenergetic Images From a Novel Dual-Layer Spectral Detector Computed Tomography Scanner in Portal Venous Phase: Adjusted Window Settings Depending on Assessment Focus Are Essential for Image Interpretation.

OBJECTIVE: We aimed to determine optimal window settings for conventional polyenergetic (PolyE) and virtual monoenergetic images (MonoE) derived from abdominal portal venous phase computed tomography (CT) examinations on a novel dual-layer spectral-detector CT (SDCT). METHODS: From 50 patients, SDCT data sets MonoE at 40 kiloelectron volt as well as PolyE were reconstructed and best individual window width and level values manually were assessed separately for evaluation of abdominal arteries as well as for liver lesions. Via regression analysis, optimized individual values were mathematically calculated. Subjective image quality parameters, vessel, and liver lesion diameters were measured to determine influences of different W/L settings. RESULTS: Attenuation and contrast-to-noise values were significantly higher in MonoE compared with PolyE. Compared with standard settings, almost all adjusted W/L settings varied significantly and yielded higher subjective scoring. No differences were found between manually adjusted and mathematically calculated W/L settings. CONCLUSIONS: PolyE and MonoE from abdominal portal venous phase SDCT examinations require appropriate W/L settings depending on reconstruction technique and assessment focus.