Chest CT using spectral filtration: radiation dose, image quality, and spectrum of clinical utility.

OBJECTIVES: To determine the radiation dose, image quality, and clinical utility of non-enhanced chest CT with spectral filtration. METHODS: We retrospectively analysed 25 non-contrast chest CT examinations acquired with spectral filtration (tin-filtered Sn100 kVp spectrum) compared to 25 examinations acquired without spectral filtration (120 kV). Radiation metrics were compared. Image noise was measured. Contrast-to-noise-ratio (CNR) and figure-of-merit (FOM) were calculated. Diagnostic confidence for the assessment of various thoracic pathologies was rated by two independent readers. RESULTS: Effective chest diameters were comparable between groups (P = 0.613). In spectral filtration CT, median CTDIvol, DLP, and size-specific dose estimate (SSDE) were reduced (0.46 vs. 4.3 mGy, 16 vs. 141 mGy*cm, and 0.65 vs. 5.9 mGy, all P < 0.001). Spectral filtration CT had higher image noise (21.3 vs. 13.2 HU, P < 0.001) and lower CNR (47.2 vs. 75.3, P < 0.001), but was more dose-efficient (FOM 10,659 vs. 2,231/mSv, P < 0.001). Diagnostic confidence for parenchymal lung disease and osseous pathologies was lower with spectral filtration CT, but no significant difference was found for pleural pathologies, pulmonary nodules, or pneumonia. CONCLUSIONS: Non-contrast chest CT using spectral filtration appears to be sufficient for the assessment of a considerable spectrum of thoracic pathologies, while providing superior dose efficiency, allowing for substantial radiation dose reduction. KEY POINTS: • Spectral filtration enables non-contrast chest CT with very high dose efficiency. • This approach reduces CTDI vol , DLP, and SSDE (effective chest diameter 28 cm). • Lung nodules, pneumonia, and pleural pathologies can be assessed with uncompromised confidence.

Non-invasive determination of pulmonary hypertension with dynamic contrast-enhanced computed tomography: a pilot study.

OBJECTIVES: In this pilot study we explored whether contrast-material bolus propagation time and speed in the pulmonary arteries (PAs) determined by dynamic contrast-enhanced computed tomography (DCE-CT) can distinguish between patients with and without pulmonary hypertension (PH). METHODS: Twenty-three patients (18 with and 5 without PH) were examined with a DCE-CT sequence following their diagnostic or follow-up right-sided heart catheterisation (RHC). X-ray attenuation over time curves were recorded for regions of interest in the main, right and left PA and fitted with a spline fit. Contrast material bolus propagation speeds and time differences between the peak concentrations were compared with haemodynamic parameters from RHC. RESULTS: Bolus speed correlated (ρ = -0.55) with mean pulmonary arterial pressure (mPAP) and showed a good discriminative power between patients with and without PH (cut-off speed 317 mm/s; sensitivity 100%/specificity 100%). Additionally, time differences between peaks correlated with mPAP (ρ = 0.64 and 0.49 for right and left PA, respectively) and discrimination was achieved with sensitivity 100%/specificity 100% (cut-off time 0.15 s) and sensitivity 93 %/specificity 80% (cut-off time 0.45 s), respectively. CONCLUSIONS: Bolus propagation speed and time differences between contrast material peaks in the PA can identify PH. This method could be used to confirm the indication for RHC in patients screened for pulmonary hypertension. KEY POINTS: • Dynamic contrast-enhanced computed tomography (CT) can identify patients with pulmonary hypertension. • Bolus propagation speed in the pulmonary artery is reduced in pulmonary hypertension. • Peak-contrast propagation times provide a practical surrogate for speed. • This non-invasive technique could serve as a screening method for pulmonary hypertension. • Invasive right-sided heart catheterisations might be restricted to a smaller group of patients.

Dual-energy CT for the evaluation of silicone breast implants.

OBJECTIVE: The evaluation of breast implants for rupture is currently the domain of ultrasound and MRI, while mammography is of very limited diagnostic value. Recently, specific visualisation of silicone has become feasible using dual-energy CT. Our objective was to evaluate whether it is feasible to identify silicone in breast implants by dual-energy CT and to reliably diagnose or rule out ruptures. METHODS: Seven silicone breast implant specimens were examined on dual-source CT at 100- and 140-kV tube potential with a 0.8-mm tin filter (collimation 128 × 0.6 mm, current-time products 165 and 140 mAsref with modulation, rotation time 0.28 s, pitch 0.55). Two patients scheduled for implant removal or replacement were examined with identical parameters. RESULTS: The silicone of the implant specimens showed a strong dual-energy signal. In one patient, both implants were intact, while a rupture was identified in the other patient. Ultrasound, MRI, surgical findings and histology confirmed the dual-energy CT diagnosis. CONCLUSION: Dual-energy CT may serve as an alternative technique for speedy evaluation of silicone breast implants. Specific clinical studies are required to determine the diagnostic accuracy and define indications for this technique.

Time-resolved CT angiography for the detection and classification of endoleaks.

PURPOSE: To assess the feasibility and diagnostic performance of time-resolved computed tomographic (CT) angiography in the detection and classification of endoleaks after endovascular aortic aneurysm repair (EVAR) in high-risk patients. MATERIALS AND METHODS: The study was approved by our ethics committee. Written informed consent was obtained from all participating patients. Fifty-four patients (42 male and 12 female patients; mean age, 70.9 years ± 9.3 [standard deviation]) with either thoracic (n = 8) or abdominal (n = 46) aortic aneurysms treated with a stent-graft were prospectively included. The patients were examined with a time-resolved CT angiographic protocol consisting of 12 low-dose phases (80 kVp; 120 mAs [effective]; scan range, 27 cm), with 60 mL of iomeprol. Patients with abdominal aneurysm repair also underwent contrast material-enhanced (CE) ultrasonography (US). The time delay between contrast enhancement within the stent lumen and the endoleak was measured. Effective radiation dose was calculated from the scanner protocols. Measures of diagnostic performance for the detection of endoleaks were calculated for time-resolved CT angiography, with CE US serving as the reference standard. RESULTS: All time-resolved CT angiographic data sets were diagnostic. Mean effective radiation dose was 14.6 mSv. Four thoracic and 19 abdominal endoleaks were identified by using time-resolved CT angiography. Seventeen of 19 abdominal endoleaks were confirmed with CE US. This rate resulted in a sensitivity of 94%, a specificity of 93%, a positive predictive value of 89%, and a negative predictive value of 96% for time-resolved CT angiography after abdominal EVAR. Type I endoleaks showed significantly earlier mean peak contrast enhancement (0.28 second ± 0.83) compared with that for type II endoleaks (9.17 seconds ± 3.59, P < .0001). CONCLUSION: Time-resolved CT angiography with 12 low-dose phases is feasible for patients after thoracic and abdominal EVAR. The protocol approximates the radiation dose of standard triphasic protocols. Its dynamic information differentiates types of endoleaks and shows high diagnostic performance.

Ventilation imaging of the paranasal sinuses using xenon-enhanced dynamic single-energy CT and dual-energy CT: a feasibility study in a nasal cast.

OBJECTIVE: To show the feasibility of dual-energy CT (DECT) and dynamic CT for ventilation imaging of the paranasal sinuses in a nasal cast. METHODS: In a first trial, xenon gas was administered to a nasal cast with a laminar flow of 7 L/min. Dynamic CT acquisitions of the nasal cavity and the sinuses were performed. This procedure was repeated with pulsating xenon flow. Local xenon concentrations in the different compartments of the model were determined on the basis of the enhancement levels. In a second trial, DECT measurements were performed both during laminar and pulsating xenon administration and the xenon concentrations were quantified directly. RESULTS: Neither with dynamic CT nor DECT could xenon-related enhancement be detected in the sinuses during laminar airflow. Using pulsating flow, dynamic imaging showed a xenon wash-in and wash-out in the sinuses that followed a mono-exponential function with time constants of a few seconds. Accordingly, DECT revealed xenon enhancement in the sinuses only after pulsating xenon administration. CONCLUSION: The feasibility of xenon-enhanced DECT for ventilation imaging was proven in a nasal cast. The superiority of pulsating gas flow for the administration of gas or aerosolised drugs to the paranasal sinuses was demonstrated. KEY POINTS : • Ventilation of the paranasal sinuses is poorly understood. • Dual-energy CT ventilation imaging has been explored using phantom simulation. • Xenon can be seen in the paranasal sinuses using pulsating xenon flow. • Dual-energy CT uses a lower radiation dose compared with dynamic ventilation CT.

Severity assessment of pulmonary embolism using dual energy CT - correlation of a pulmonary perfusion defect score with clinical and morphological parameters of blood oxygenation and right ventricular failure.

OBJECTIVE: To correlate a Dual Energy (DE)-based visual perfusion defect scoring system with established CT-based and clinical parameters of pulmonary embolism (PE) severity. METHODS: In 63 PE patients, DE perfusion maps were visually scored for perfusion defects (P-score). Vascular obstruction was quantified using the Mastora score. Both scores were correlated with short-axis diameters of the right and left ventricle, their ratio (RV/LV ratio), width of the pulmonary trunk, a number of clinical parameters and each other. Univariate and multivariate analyses were performed. Times to generate both scores were recorded. RESULTS: After univariate and multivariate analysis, a significant (p < 0.05) correlation with the P-score was shown for the Mastora score (r = 0.65), RV/LV ratio (r = 0.47), width of the pulmonary trunk (r = 0.26), troponin I (r = 0.43) and PaO(2) (r = -0.50). For the left ventricular diameter, only univariate analysis showed a significant correlation. Mastora score correlated significantly with RV/LV ratio (r = 0.36), width of the pulmonary trunk (r = 0.27), PaO(2) (r = -0.41) and troponin I (r = 0.37). Mean time for generating the P-score was significantly shorter than for the Mastora score. CONCLUSIONS: A DE-based P-score correlates with a number of parameters of PE severity. It might be easier and faster to perform than some traditional CT scoring methods for vascular obstruction.

Dual-energy CT: general principles.

OBJECTIVE: In dual-energy CT (DECT), two CT datasets are acquired with different x-ray spectra. These spectra are generated using different tube potentials, partially also with additional filtration at 140 kVp. Spectral information can also be resolved by layer detectors or quantum-counting detectors. Several technical approaches-that is, sequential acquisition, rapid voltage switching, dual-source CT (DSCT), layer detector, quantum-counting detector-offer different spectral contrast and dose efficiency. Various postprocessing algorithms readily provide clinically relevant spectral information. CONCLUSION: DECT offers the possibility to exploit spectral information for diagnostic purposes. There are different technical approaches, all of which have inherent advantages and disadvantages, especially regarding spectral contrast and dose efficiency. There are numerous clinical applications of DECT that are easily accessible with specific postprocessing algorithms.

Xenon-Enhanced Dynamic Dual-Energy CT Is Able to Quantify Sinus Ventilation Using Laminar and Pulsating Air-/Gas Flow Before and After Surgery: A Pilot Study in a Cadaver Model.

Background: Chronic rhinosinusitis is a common disease with a significant impact on the quality of life. Topical drug delivery to the paranasal sinuses is not efficient to prevent sinus surgery or expensive biologic treatment in a lot of cases as the affected mucosa is not reached. More efficient approaches for topical drug delivery are, therefore, necessary. In the current study, dual-energy CT (DECT) imaging was used to examine sinus ventilation before and after sinus surgery using a pulsating xenon gas ventilator in a cadaver head. Methods: Xenon gas was administered to the nasal cavity of a cadaver head with a laminar flow of 7 L/min and with pulsating xenon-flow (45 Hz frequency, 25 mbar amplitude). Nasal cavity and paranasal sinuses were imaged by DECT. This procedure was repeated after functional endoscopic sinus surgery (FESS). Based on the enhancement levels in the different sinuses, regional xenon concentrations were calculated. Results: Xenon-related enhancement could not be detected in most of the sinuses during laminar gas flow. By superimposing laminar flow with pulsation, DECT imaging revealed a xenon wash-in and wash-out in the sinuses. After FESS, xenon enhancement was immediately seen in all sinuses and reached higher concentrations than before surgery. Conclusion: Xenon-enhanced DECT can be used to visualize and quantify sinus ventilation. Pulsating air-/gas flow was superior to laminar flow for the administration of xenon to the paranasal sinuses. FESS leads to successful ventilation of all paranasal sinuses.

Detection of hemodynamically significant coronary artery stenosis: incremental diagnostic value of dynamic CT-based myocardial perfusion imaging.

PURPOSE: To determine the feasibility of computed tomography (CT)-based dynamic myocardial perfusion imaging for the detection of hemodynamically significant coronary artery stenosis, as defined with fractional flow reserve (FFR). MATERIALS AND METHODS: Institutional review board approval and informed patient consent were obtained before patient enrollment in the study. The study was HIPAA compliant. Subjects who were suspected of having or were known to have coronary artery disease underwent electrocardiographically triggered dynamic stress myocardial perfusion imaging. FFR measurement was performed within all main coronary arteries with a luminal narrowing of 50%-85%. Estimated myocardial blood flow (MBF) was derived from CT images by using a model-based parametric deconvolution method for 16 myocardial segments and was related to hemodynamically significant coronary artery stenosis with an FFR of 0.75 or less in a blinded fashion. Conventional measures of diagnostic accuracy were derived, and discriminatory power analysis was performed by using logistic regression analysis. RESULTS: Of 36 enrolled subjects, 33 (mean age, 68.1 years ± 10 [standard deviation]; 25 [76%] men, eight [24%] women) completed the study protocol. An MBF cut point of 75 mL/100 mL/min provided the highest discriminatory power (C statistic, 0.707; P <.001). While the diagnostic accuracy of CT for the detection of anatomically significant coronary artery stenosis (>50%) was high, it was low for the detection of hemodynamically significant stenosis (positive predictive value [PPV] per coronary segment, 49%; 95% confidence interval [CI]: 36%, 60%). With use of estimated MBF to reclassify lesions depicted with CT angiography, 30 of 70 (43%) coronary lesions were graded as not hemodynamically significant, which significantly increased PPV to 78% (95% CI: 61%, 89%; P = .02). The presence of a coronary artery stenosis with a corresponding MBF less than 75 mL/100 mL/min had a high risk for hemodynamic significance (odds ratio, 86.9; 95% CI:17.6, 430.4). CONCLUSION: Dynamic CT-based stress myocardial perfusion imaging may allow detection of hemodynamically significant coronary artery stenosis.

Metal artifact reduction by dual energy computed tomography using monoenergetic extrapolation.

OBJECTIVE: The aim of the study was to assess the performance and diagnostic value of a dual energy CT approach to reduce metal artefacts in subjects with metallic implants. METHODS: 31 patients were examined in the area of their metallic implants using a dual energy CT protocol (filtered 140 kVp and 100 kVp spectrum, tube current relation: 3:1). Specific post-processing was applied to generate energies of standard 120 and 140 kVp spectra as well as a filtered 140 kVp spectrum with mean photon energies of 64, 69 and 88 keV, respectively, and an optimized hard spectrum of 95-150 keV. Image quality and diagnostic value were subjectively and objectively determined. RESULTS: Image quality was rated superior to the standard image in 29/31 high energy reconstructions; the diagnostic value was rated superior in 27 patients. Image quality and diagnostic value scores improved significantly from 3.5 to 2.1 and from 3.6 to 1.9, respectively. In several exams decisive diagnostic features were only discernible in the high energy reconstructions. The density of the artefacts decreased from -882 to -341 HU. CONCLUSIONS: Dual Energy CT with specific postprocessing can reduce metal artefacts and may significantly enhance diagnostic value in the evaluation of metallic implants.

Systolic acquisition of coronary dual-source computed tomography angiography: feasibility in an unselected patient population.

OBJECTIVE: To determine the practicability and potential dose saving of an imaging algorithm incorporating a pulsing scheme applying systolic data acquisition at heart rates >75 beats per minute (bpm). METHODS: Patients clinically referred for coronary computed tomography angiography (CTA) underwent cardiac CTA using either a diastolic pulsing window (30-70%) or a narrow systolic pulsing window (150 ms at 300 ms). Independent investigators retrospectively determined image quality (1, excellent, to 5, unreadable) and derived effective radiation exposure. RESULTS: Among all 101 subjects (62 +/- 2 years, 59% male) the predicted decrease in the best reconstruction interval for diastolic phases was 12 ms per 1 bpm [95% confidence interval (CI): -13.5 to -11.2] and -1.9 ms for systolic phases (95% CI: -3.2 to -0.62, p = 0.004), independent of age, gender and body mass index (BMI). The systolic pulsing strategy in 47 subjects (23 subjects >75 bpm) resulted in significantly lower radiation exposure (4.97 +/- 2.3 vs 9.38 +/- 5.5 mSv, p < 0.001 for systolic versus diastolic, respectively), whereas there was no difference with respect to image quality or heart rate (p = 0.65 and p = 0.74, respectively). CONCLUSIONS: Our results suggest that a systolic window for tube current modulation in subjects with higher heart rates represents a reliable tool to ensure high image quality at significantly lower dose in patients undergoing routine cardiac CTA.

Pulmonary ventilation and perfusion imaging with dual-energy CT.

OBJECTIVE: To evaluate the feasibility of dual-energy CT (DECT) ventilation imaging in combination with DE perfusion mapping for a comprehensive assessment of ventilation, perfusion, morphology and structure of the pulmonary parenchyma. METHODS: Two dual-energy CT acquisitions for xenon-enhanced ventilation and iodine-enhanced perfusion mapping were performed in patients under artificial respiration. Parenchymal xenon and iodine distribution were mapped and correlated with structural or vascular abnormalities. RESULTS: In all datasets, image quality was sufficient for a comprehensive image reading of the pulmonary CTA images, lung window images and pulmonary functional parameter maps and led to expedient results in each patient. CONCLUSION: With dual-source CT systems, DECT of the lung with iodine or xenon administration is technically feasible and makes it possible to depict the regional iodine or xenon distribution representing the local perfusion and ventilation.

Image quality of virtual noncontrast images derived from dual-energy CT angiography after endovascular aneurysm repair.

PURPOSE: To compare true and "virtual" noncontrast images derived from dual-energy CT examinations in patients after endovascular repair of aortic aneurysms. MATERIALS AND METHODS: Seventy dual-energy CT examinations were performed on a dual-source CT scanner with a single-energy noncontrast scan and a dual-energy acquisition in venous phase. True and virtual noncontrast images were compared regarding image quality, calcifications in true noncontrast images, subtraction of calcification in virtual noncontrast images, and acceptance levels by two radiologists. Presence of endoleaks was assessed on venous-phase images and on virtual or true noncontrast images. In addition, the acceptance of color-coded images, in which iodine information is colored, was assessed. Possible dose reduction of a single-phase dual-energy examination protocol was compared with a standard biphasic examination protocol. RESULTS: Twenty-four endoleaks were detected and correctly classified with both approaches. Mean image quality was rated good for virtual noncontrast images (1.97 +/- 0.99) and excellent for true noncontrast images (1.16 +/- 0.37; P< .0001). Ninety-four percent of virtual noncontrast images were rated as diagnostic, and 80% of all true noncontrast images showed calcifications within the aneurysm. Subtraction of calcification in virtual noncontrast images was classified as none (30%), minimal (40%), moderate (24%), or severe (6%). Eighty-three percent of color-coded images were rated as fully diagnostic, 11% were accepted with restrictions, and 6% were nondiagnostic. Possible dose reduction of a single-phase dual-energy protocol, compared with a standard biphasic protocol, was 44%. CONCLUSIONS: Dual-energy CT makes a reliable detection of endoleaks feasible in a single acquisition. This provides a potential dose reduction for patients who have to undergo lifelong follow-up examinations after endovascular aneurysm repair.

Feasibility and radiation dose of high-pitch acquisition protocols in patients undergoing dual-source cardiac CT.

OBJECTIVE: The objective of this study was to compare image quality and radiation dose between high-pitch and established retrospectively and prospectively gated cardiac CT protocols using an Alderson-Rando phantom and a set of patients. MATERIALS AND METHODS: An anthropomorphic Alderson-Rando phantom equipped with thermoluminiscent detectors and a set of clinical patients underwent the following cardiac CT protocols: high-pitch acquisition (pitch 3.4), prospectively triggered acquisition, and retrospectively gated acquisition (pitch 0.2). For patients with sinus rhythm below 65 beats per minute (bpm), high-pitch protocol was used, whereas for patients in sinus rhythm between 65 and 100 bpm, prospective triggering was used. Patients with irregular heart rates or heart rates of ≥ 100 bpm, were examined using retrospectively gated acquisition. Evaluability of coronary artery segments was determined, and effective radiation dose was derived from the phantom study. RESULTS: In the phantom study, the effective radiation dose as determined with thermoluminescent detector (TLD) measurements was lowest in the high-pitch acquisition (1.21, 3.12, and 11.81 mSv, for the high-pitch, the prospectively triggered, and the retrospectively gated acquisition, respectively). There was a significant difference with respect to the percentage of motion-free coronary artery segments (99%, 87%, and 92% for high-pitch, prospectively triggered, and retrospectively gated, respectively (p < 0.001), whereas image noise was lowest for the high-pitch protocol (p < 0.05). CONCLUSION: High-pitch scans have the potential to reduce radiation dose up to 61.2% and 89.8% compared with prospectively triggered and retrospectively gated scans. High-pitch protocols lead to excellent image quality when used in patients with stable heart rates below 65 bpm.

Dual-energy lung perfusion computed tomography: a novel pulmonary functional imaging method.

Dual-energy computed tomography (DECT) can be used for visualization of pulmonary microvascular contrast material distribution, representing regional perfusion. It is performed as DECT angiography and allows for the reconstruction of morphologic images as well as of "perfusion maps." The authors of previous studies have shown its potential to reliably depict perfusion defects, mainly in the context of pulmonary embolism. Also in the diagnostic work-up of other pulmonary diseases, there might be additional functional information provided by dual-energy acquisition techniques. This review focuses on the physical and technical background and the potential clinical value of pulmonary DECT. Technical improvements of a second-generation dual-source CT system are elucidated.

Dual-energy CT in patients suspected of having renal masses: can virtual nonenhanced images replace true nonenhanced images?

PURPOSE: To qualitatively and quantitatively compare virtual nonenhanced (VNE) data sets derived from dual-energy (DE) computed tomography (CT) with true nonenhanced (TNE) data sets in the same patients and to calculate potential radiation dose reductions for a dual-phase renal multidetector CT compared with a standard triple-phase protocol. MATERIALS AND METHODS: This prospective study was approved by the institutional review board; all patients provided written informed consent. Seventy one men (age range, 30-88 years) and 39 women (age range, 22-87 years) underwent preoperative DE CT that included unenhanced, DE nephrographic, and delayed phases. DE CT parameters were 80 and 140 kV, 96 mAs (effective). Collimation was 14 x 1.2 mm. CT numbers were measured in renal parenchyma and tumor, liver, aorta, and psoas muscle. Image noise was measured on TNE and VNE images. Exclusion of relevant anatomy with the 26-cm field of view detector was quantified with a five-point scale (0 = none, 4 = >75%). Image quality and noise (1 = none, 5 = severe) and acceptability for VNE and TNE images were rated. Effective radiation doses for DE CT and TNE images were calculated. Differences were tested with a Student t test for paired samples. RESULTS: Mean CT numbers (+/- standard deviation) on TNE and VNE images, respectively, for renal parenchyma were 30.8 HU +/- 4.0 and 31.6 HU +/- 7.1, P = .29; liver, 55.8 HU +/- 8.6 and 57.8 HU +/- 10.1, P = .11; aorta, 42.1 HU +/- 4.1 and 43.0 HU +/- 8.8, P = .16; psoas, 47.3 HU +/- 5.6 and 48.1 HU +/- 9.3 HU, P = .38. No exclusion of the contralateral kidney was seen in 50 patients, less than 25% was seen in 43, 25%-50% was seen in 13, and 50%-75% was seen in four. Mean image noise was 1.71 +/- 0.71 for VNE and 1.22 +/- 0.45 for TNE (P < .001); image quality was 1.70 HU +/- 0.72 for VNE and 1.15 HU +/- 0.36 for TNE (P < .0001). In all but three patients radiologists accepted VNE images as replacement for TNE images. Mean effective dose for DE CT scans of the abdomen was 5.21 mSv +/- 1.86 and that for nonenhanced scans was 4.97 mSv +/- 1.43. Mean dose reduction by omitting the TNE scan was 35.05%. CONCLUSION: In patients with renal masses, DE CT can provide high-quality VNE data sets, which are a reasonable approximation of TNE data sets. Integration of DE scanning into a renal mass protocol will lower radiation exposure by 35%.

Dual energy CT: preliminary observations and potential clinical applications in the abdomen.

Dual energy CT (DECT) is a new technique that allows differentiation of materials and tissues based on CT density values derived from two synchronous CT acquisitions at different tube potentials. With the introduction of a new dual source CT system, this technique can now be used routinely in abdominal imaging. Potential clinical applications include evaluation of renal masses, liver lesions, urinary calculi, small bowel, pancreas, and adrenal glands. In CT angiography of abdominal aortic aneurysms, dual energy CT techniques can be used to remove bones from the datasets, and virtual unenhanced images allow differentiation of contrast agent from calcifying thrombus in patients with endovascular stents. This review describes potential applications, practical guidelines, and limitations of dual energy CT in the abdomen.

Adequate image quality with reduced radiation dose in prospectively triggered coronary CTA compared with retrospective techniques.

The goal of our study was to compare a prospective triggering (PT) CT technique with retrospectively gated (RG) CT techniques in coronary computed tomographic angiograms (CCTA) with respect to image quality and radiation dose. Sixty consecutive patients were enrolled. CCTAs using the RG technique were obtained with a dual-source 64-slice CT system in 40 patients, using ECG-triggered tube current modulation, with either a broad pulsing window at 30-80% of the RR interval (group RGb, 20 patients, heart rate > 70 bpm) or a small pulsing window at 70% (group RGs, 20 patients, heart rate < 70 bpm). The other 20 patients underwent CCTA using the PT technique on a 128-slice CT system (group PT, heart rate < 70 bpm). All images were evaluated by two observers for quality on a three-point scale, with 1 being excellent and 3 being insufficient. The effective radiation dose was calculated for each patient. The average image quality score was 1.5 +/- 0.6 for PT, 1.35 +/- 0.5 for RGs and 1.65 +/- 0.5 for RGb. The mean effective dose for RGb was 9 +/- 4 mSv, for RGs 7 +/- 3 mSv and for PT 3 +/- 1 mSv. This represents a 57% dose reduction for PT compared with RGs and a 67% dose reduction for PT compared with RGb. In conclusion, in selected patients CCTA with the PT technique offers adequate image quality with a significantly lower radiation dose compared with CCTA using RG techniques.

Dual-energy CT for the assessment of contrast material distribution in the pulmonary parenchyma.

OBJECTIVE: The purpose of this study was to assess the feasibility and diagnostic value of dual-energy CT iodine mapping at pulmonary CT angiography. SUBJECTS AND METHODS: Ninety-three patients underwent CT angiography with the dual-energy technique on a dual-source CT scanner. Postprocessing was used to map iodine in the lung parenchyma on the basis of its spectral behavior, and image quality was assessed by two readers. Iodine distribution patterns were rated as homogeneous, patchy, or circumscribed defects. Conventional CT angiographic images reconstructed from the same data sets were reviewed for the presence and localization of pulmonary embolism, whether embolic occlusion was partial or complete, and the presence of changes in the lung parenchyma. Dual-energy perfusion findings were correlated with the CT angiographic and lung-window CT findings in per-patient and per-segment analyses. RESULTS: Iodine distribution was homogeneous in 49 patients, of whom CT angiography showed no pulmonary embolism in 46 patients and nonocclusive pulmonary emboli in three patients. Images of 29 patients showed a patchy pattern; 24 of these patients had no pulmonary embolism, and five had nonocclusive pulmonary emboli with solely nonocclusive intravascular clots. Images of 15 patients showed segmental or subsegmental defects; four of these patients had evidence of pulmonary embolism, and 11 had occlusive pulmonary emboli with at least one occlusive clot in the pulmonary vasculature. CONCLUSION: Dual-energy CT is reliable in the detection of defects in pulmonary parenchymal iodine distribution that correspond to embolic vessel occlusion.

Dual energy CT characterization of urinary calculi: initial in vitro and clinical experience.

OBJECTIVE: The purpose of this study is to assess the accuracy of dual energy CT (DECT) in the characterization of renal and ureteral stones. MATERIAL AND METHODS: Twenty-four renal calculi of known variable composition were scanned on a dual-source CT scanner (Somatom Definition; Siemens Medical Solutions, Forchheim, Germany) in dual energy (DECT) mode. Scan parameters for DECT were: tube potentials, 80 and 140 kV; tube current, 342 and 76 mA.s; collimation, 14 x 1.2 mm2. Dual energy properties of calculi were used to differentiate between uric acid (UA) and other calculi. Differentiation was based on a 3-material decomposition implemented in the dual energy software (Syngo VA 11; Siemens Medical Solutions). Color coding was used to display different types of stones and their DECT properties were characterized with density measurements at both photon energies. Subsequently, 20 consecutive patients with known or suspected uroliths were scanned using identical scan parameters. Stone size and material were assessed in DECT and compared with the chemical analyses of stones after mechanical extraction. RESULTS: With DECT characterization, differentiation of UA from other calculi was possible. Additionally, differentiation between cystine and struvite stones was shown to be feasible in vitro. In the patient cohort, DECT correctly characterized 4 UA calculi, 4 mixed, multiple calcified, and 1 cystine stone. The calculi were displayed in specific colors, ie, UA stones in red and calcified stones in blue. CONCLUSION: With dual energy CT techniques, the UA, cystine, struvite, and mixed renal calculi can be differentiated from other types of stones in vitro and in vivo. This is of clinical relevance as UA uroliths may be treated pharmacologically rather than with surgical extraction or extracorporal shockwave lithotripsy.