Second-generation Dual-source CT Scanner Research Articles

Assessing carpal kinematics following scapholunate interosseous ligament injury ex vivo using four-dimensional dynamic computed tomography

BackgroundScapholunate interosseous ligament injuries are prevalent and often challenging to diagnose radiographically. Four-dimensional CT allows visualization of carpal bones during motion. We present a cadaveric model of sequential ligamentous sectionings (“injuries”) to quantify their effects on interosseous proximities at the radioscaphoid joint and scapholunate interval. We hypothesized that injury, wrist position, and their interaction affect carpal arthrokinematics. MethodsEight cadaveric wrists were moved through flexion-extension and radioulnar deviation after injuries. Dynamic CT images of each motion were acquired in each injury condition using a second-generation dual-source CT scanner. Carpal osteokinematics were used to calculate arthrokinematic interosseous proximity distributions during motion. Median interosseous proximities were normalized and categorized by wrist position. Linear mixed-effects models and marginal means tests were used to compare distributions of median interosseous proximities. FindingsThe effect of wrist position was significant for both flexion-extension and radioulnar deviation at the radioscaphoid joint; the effect of injury was significant for flexion-extension at the scapholunate interval; and the effect of their interaction was significant for radioulnar deviation at the scapholunate interval. Across wrist positions, radioscaphoid median interosseous proximities were less able to distinguish injury conditions versus scapholunate proximities. Median interosseous proximities at the scapholunate interval are majoritively able to detect differences between less (Geissler I-III) versus more (Geissler IV) severe injuries when the wrist is flexed, extended, and ulnarly-deviated. InterpretationDynamic CT enhances our understanding of carpal arthrokinematics in a cadaveric model of SLIL injury. Scapholunate median interosseous proximities in flexion, extension, and ulnar deviation best demonstrate ligamentous integrity.

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.

Implementation of Size-Dependent Local Diagnostic Reference Levels for CT Angiography.

Diagnostic reference levels (DRLs) are established for standard-sized patients; however, patient dose in CT depends on patient size. The purpose of this study was to introduce a method for setting size-dependent local diagnostic reference levels (LDRLs) and to evaluate these LDRLs in comparison with size-independent LDRLs and with respect to image quality. One hundred eighty-four aortic CT angiography (CTA) examinations performed on either a second-generation or third-generation dual-source CT scanner were included; we refer to the second-generation dual-source CT scanner as "CT1" and the third-generation dual-source CT scanner as "CT2." The volume CT dose index (CTDIvol) and patient diameter (i.e., the water-equivalent diameter) were retrieved by dose-monitoring software. Size-dependent DRLs based on a linear regression of the CTDIvol versus patient size were set by scanner type. Size-independent DRLs were set by the 5th and 95th percentiles of the CTDIvol values. Objective image quality was assessed using the signal-to-noise ratio (SNR), and subjective image quality was assessed using a 4-point Likert scale. The CTDIvol depended on patient size and scanner type (R2 = 0.72 and 0.78, respectively; slope = 0.05 and 0.02 mGy/mm; p < 0.001). Of the outliers identified by size-independent DRLs, 30% (CT1) and 67% (CT2) were adequately dosed when considering patient size. Alternatively, 30% (CT1) and 70% (CT2) of the outliers found with size-dependent DRLs were not identified using size-independent DRLs. A negative correlation was found between SNR and CTDIvol (R2 = 0.36 for CT1 and 0.45 for CT2). However, all outliers had a subjective image quality score of sufficient or better. We introduce a method for setting size-dependent LDRLs in CTA. Size-dependent LDRLs are relevant for assessing the appropriateness of the radiation dose for an individual patient on a specific CT scanner.

CT angiography to evaluate coronary artery disease and revascularization requirement before trans-catheter aortic valve replacement

BackgroundCoronary artery disease (CAD) and aortic stenosis share pathophysiological mechanisms and risk factors. We evaluated the clinical utility of coronary computed tomography angiography (CTA) to identify CAD and revascularization requirement in patients with severe aortic stenosis considered for transcatheter aortic valve replacement (TAVR). MethodsConsecutive patients without known CAD underwent calcium scoring, CTA and invasive coronary angiography (ICA). A second-generation dual-source CT scanner was used. ICA-quantitative coronary angiography (QCA) served as reference standard. CAD was reported using a lenient threshold of ≥50% and a stricter threshold of ≥70% diameter reduction. Findings of ≥70% diameter reduction and of high-risk CAD were used to predict revascularization. ResultsThe study included 140 patients [68 males; 82.3 (7.7) years]. CAD defined by the 50% threshold on ICA was found in 58/140 (41%) patients. CAD by the 70% threshold was found in 23/140 (16%) patients. High-risk CAD was found in 16/140 (11%) patients. CTA and ICA had similar odd-ratios of 3.22 (1.26–8.23) and 4.62 (1.64–13.05), respectively, in predicting revascularization. Forty-two/140 (30%) patients had <400 Agatston calcium score, 98/140 (70%) patients had ≥400 calcium score. The diagnostic performance of CTA in the low calcium score group was better than the high calcium score group (AUC 0.81 vs. 0.63). ConclusionCTA remained questionable to rule-out CAD as gatekeeper to ICA in TAVR candidates who had severe coronary calcifications. In patients with less severe coronary calcifications, accounting for 30% of participants in this study, CTA may play a clinical role.

Systematic radiation dose optimization of abdominal dual-energy CT on a second-generation dual-source CT scanner: assessment of the accuracy of iodine uptake measurement and image quality in an in vitro and in vivo investigations

To assess the accuracy of iodine quantification in a phantom study at different radiation dose levels with dual-energy dual-source CT and to evaluate image quality and radiation doses in patients undergoing a single-energy and two dual-energy abdominal CT protocols. In a phantom study, the accuracy of iodine quantification (4.5-23.5mgI/mL) was evaluated using the manufacturer-recommended and three dose-optimized dual-energy protocols. In a patient study, 75 abdomino-pelvic CT examinations were acquired as follows: 25 CT scans with the manufacturer-recommended dual-energy protocol (protocol A); 25 CT scans with a dose-optimized dual-energy protocol (protocol B); and 25 CT scans with a single-energy CT protocol (protocol C). CTDIvol and objective noise were measured. Five readers scored each scan according to six subjective image quality parameters (noise, contrast, artifacts, visibility of small structures, sharpness, overall diagnostic confidence). In the phantom study, differences between the real and measured iodine concentrations ranged from -8.8% to 17.0% for the manufacturer-recommended protocol and from -1.6% to 20.5% for three dose-optimized protocols. In the patient study, the CTDIvol of protocol A, B, and C were 12.5±1.9, 7.5±1.2, and 6.5±1.7mGycm, respectively (p<0.001), and the average image noise values were 6.6±1.2, 7.8±1.4, and 9.6±2.2HU, respectively (p<0.001). No significant differences in the six subjective image quality parameters were observed between the dose-optimized dual-energy and the single-energy protocol. A dose reduction of 41% is feasible for the manufacturer-recommended, abdominal dual-energy CT protocol, as it maintained the accuracy of iodine measurements and subjective image quality compared to a single-energy protocol.

Feasibility of Dose Optimization in a Second-Generation Dual-Source CT Scanner for a Manufacturer-Recommended Urolithiasis Protocol for Imaging Renal Stones.

The purpose of this article is to investigate the magnitude of dose optimization for a manufacturer-recommended urolithiasis protocol in a second-generation dual-source CT scanner. Custom renal phantoms with 24 stones were scanned using the manufacturer-provided dual-energy CT protocol (tube A, 100 kVp and 210 reference mAs; tube B, 140 kVp and 162 reference mAs) and seven dose-optimized protocols in which the reference tube current-time product setting of tube A was reduced stepwise by 20 mAs. Detection and characterization of the stones was assessed. In the patient study, 25 patients underwent the manufacturer-provided dual-energy protocol and 25 patients underwent imaging with a dose-optimized protocol (tube A, 100 kVp and 90 reference mAs; tube B, 140 kVp and 70 reference mAs). Dose-length product (DLP), image noise, and contrast-to-noise ratio (CNR) were assessed. Subjective image quality was analyzed by three independent radiologists. In the phantom study, the reference tube current-time product of tube A could be reduced from 210 to 90 mAs without losing the accuracy of detection or characterization of the calculi. In the patient study, the dose-optimized protocol resulted in a significant reduction of the average DLP by 51% compared with the standard protocol (219.4 vs 443.5 mGy·cm, respectively; p = 0.0001). The image noise was higher, and the CNR was lower, in the dose-optimized group than in the standard-dose group (p < 0.05). The subjective overall image quality of the dose-optimized CT examinations was rated as good, and that of the standard-dose CT examinations was rated as excellent (p = 0.001). The in vitro and in vivo assessment revealed a potential for a 51% dose reduction of the manufacturer-recommended dual-energy CT protocol for urolithiasis without compromising the accuracy.

Non-invasive prediction of hemodynamically significant coronary artery stenoses by contrast density difference in coronary CT angiography

ObjectivesCoronary computed tomography angiography (CTA) allows the detection of obstructive coronary artery disease. However, its ability to predict the hemodynamic significance of stenoses is limited. We assessed differences in plaque characteristics and contrast density difference between hemodynamically significant and non-significant stenoses, as defined by invasive fractional flow reserve (FFR). MethodsLesion characteristics of 59 consecutive patients (72 lesions) in whom invasive FFR was performed in at least one coronary artery with moderate to high-grade stenoses in coronary CTA were evaluated by two experienced readers. Coronary CTA data sets were acquired on a second-generation dual-source CT scanner using retrospectively ECG-gated spiral acquisition or prospectively ECG-triggered axial acquisition mode. Plaque volume and composition (non-calcified, calcified), remodeling index as well as contrast density difference (defined as the percentage decline in luminal CT attenuation/cross-sectional area over the lesion) were assessed using a semi-automatic software tool (Autoplaq). Additionally, the transluminal attenuation gradient (defined as the linear regression coefficient between intraluminal CT attenuation and length from the ostium) was determined. Differences in lesion characteristics between hemodynamically significant (invasively measured FFR ≤0.80) and non-significant lesions (FFR >0.80) were determined. ResultsMean patient age was 64±11 years with 44 males (75%). 21 out of 72 coronary artery lesions (29%) were hemodynamically significant according to invasive FFR. Mean invasive FFR was 0.66±0.12 vs. 0.91±0.05 for hemodynamically significant versus non-significant lesions. Hemodynamically significant lesions showed a significantly greater percentage of non-calcified plaque compared to non-hemodynamically relevant lesions (51.3±15.3% vs. 43.6±16.5%, p=0.021). Contrast density difference was significantly increased in hemodynamically relevant lesions (26.0±20.2% vs. 16.6±10.9% for non-significant lesions; p=0.013). At a threshold of ≥24%, the contrast density difference predicted hemodynamically significant lesions with a specificity of 75%, sensitivity of 33%, PPV of 35% and NPV of 73%. The transluminal attenuation gradient showed no significant difference between hemodynamically significant and non-significant lesions (−1.4±1.4HU/mm vs. −1.1±1.3HU/mm, p=n.s.). ConclusionsQuantitative contrast density difference across coronary lesions in coronary CTA data sets may be applied as a non-invasive tool to identify hemodynamically significant stenoses.

Image quality and radiation dose of a prospectively electrocardiography-triggered high-pitch data acquisition strategy for coronary CT angiography: The multicenter, randomized PROTECTION IV study

BackgroundConcerns have been raised about radiation dose of coronary CT angiography. Although high-pitch acquisition technique yields high potential for radiation dose savings, it is more vulnerable to artifacts, which impair diagnostic image quality. ObjectiveThe purpose of this study was to compare 2 scan strategies for coronary CT angiography: a high-pitch helical scan first or a conventional scan first strategy. MethodsIn this prospective, multicenter trial, we randomized 303 consecutive patients with a low and stable heart rate to either of the aforementioned mentioned strategies. Intravenous β-blockers were administered to achieve target heart rates. All scans were performed on a second-generation dual-source CT scanner. In case of nondiagnostic image quality, coronary CT angiography was allowed to be repeated. The primary end point was to demonstrate noninferior image quality in the high-pitch group. Image quality was assessed on a 4-point scale (1: nondiagnostic, 4: excellent). Secondary end point was total radiation dose. ResultsIn the high-pitch helical first group, repeat scanning was necessary in 21 patients compared with 14 patients in the conventional first scan group (P = .25). Image quality in the high-pitch group was noninferior compared to the conventional scan group (3.81 ± 0.35 vs 3.83 ± 0.37; P for noninferiority <.0001). The total effective radiation dose estimate was 58% lower in the high-pitch group (2.0 ± 2.4 vs 4.7 ± 4.8 mSv; P < .0001). ConclusionsIn patients with a low and stable heart rate diagnostic image quality can be maintained with a high-pitch helical scan first strategy while 58% of radiation dose can be saved.

Development of an Ex Vivo, Beating Heart Model for CT Myocardial Perfusion.

Objective. To test the feasibility of a CT-compatible, ex vivo, perfused porcine heart model for myocardial perfusion CT imaging. Methods. One porcine heart was perfused according to Langendorff. Dynamic perfusion scanning was performed with a second-generation dual source CT scanner. Circulatory parameters like blood flow, aortic pressure, and heart rate were monitored throughout the experiment. Stenosis was induced in the circumflex artery, controlled by a fractional flow reserve (FFR) pressure wire. CT-derived myocardial perfusion parameters were analysed at FFR of 1 to 0.10/0.0. Results. CT images did not show major artefacts due to interference of the model setup. The pacemaker-induced heart rhythm was generally stable at 70 beats per minute. During most of the experiment, blood flow was 0.9–1.0 L/min, and arterial pressure varied between 80 and 95 mm/Hg. Blood flow decreased and arterial pressure increased by approximately 10% after inducing a stenosis with FFR ≤ 0.50. Dynamic perfusion scanning was possible across the range of stenosis grades. Perfusion parameters of circumflex-perfused myocardial segments were affected at increasing stenosis grades. Conclusion. An adapted Langendorff porcine heart model is feasible in a CT environment. This model provides control over physiological parameters and may allow in-depth validation of quantitative CT perfusion techniques.

Optimized low-kV spectrum of dual-energy CT equipped with high-kV tin filtration for electron density measurements

This paper describes the low-kV spectral optimization of dual-energy CT (DECT) equipped with high-kV tin filtration for the quantitative acquisition of electron density information, which is essential for treatment planning in radiotherapy. In addition, an analytical DECT image simulation was preliminarily performed to demonstrate the effectiveness of the optimized DECT with respect to the beam-hardening reduction. To optimize the low-kV spectrum of DECT, the author calculated the beam-hardening error, CT dose index, and tube loadings for a 50-cm diameter cylindrical water phantom with various combinations of filter materials, a range of thicknesses, and low-kV tube potentials. In addition, a single tube potential of 140 kV filtered by 0.4 mm tin (Sn) was employed for high-kV scanning, as is similar to the commercial implementation of the second-generation dual-source CT scanner. The optimized spectral parameters were then applied to the analytical DECT image simulation using two-dimensional fan-beam geometry for a virtual solid water phantom with 16 bodylike tissue inserts. The author predicts that an optimal low-kV filtration would be 0.144-mm tungsten (W) at 90 kV, as it yields a minimal beam-hardening error with lower tube loadings and dose. The high-kV tube loading and dose obtained using the W filtration were 99 mAs and 2.2 mGy, respectively. These values are nearly equal to those obtained in the case of 2.5 mm Al at 100 kV (100 mAs and 2.3 mGy), which was regarded in this study as a reference filtration; however, the W filtration significantly reduced the beam-hardening error, from 9.5 to 1.4%. The corresponding low-kV tube loading (112 mAs) was five times greater than that of the reference case (21 mAs), but it was maintained at a certain practical level since the low-kV tube loading was comparable to the high-kV tube loading of the reference (100 mAs). The superiority of the beam-hardening reduction is reflected in the simulated images; for example, by the use of the W filter, the beam-hardening-induced deviation between the simulated and theoretical electron density values of cortical bone was reduced from 7.4 to 1.2% as compared with the reference filtration, even though no correction for beam hardening was performed. In terms of beam hardening reduction, the DECT with the low-kV W filtration is more effective for the quantitative measurement of electron density within a practical limit of tube loadings and without additional dose.