Protocol analysis of dual-energy CT for optimization of kidney stone detection in virtual non-contrast reconstructions.

OBJECTIVES: Previous studies have shown that split-bolus protocols in virtual non-contrast (VNC) reconstructions of dual-energy computed tomography (DE-CT) significantly decrease radiation dose in patients with urinary stone disease. To evaluate the impact on kidney stone detection rate of stone composition, size, tube voltage, and iodine concentration for VNC reconstructions of DE-CT. METHODS: In this prospective study, 16 kidney stones of different sizes (1.2-4.5 mm) and compositions (struvite, cystine, whewellite, brushite) were placed within a kidney phantom. Seventy-two scans with nine different iodine contrast agents/saline solutions with increasing attenuation (0-1400 HU) and different kilovoltage settings (70 kV/150 kV; 80 kV/150 kV; 90 kV/150 kV; 100 kV/150 kV) were performed. Two experienced radiologists independently rated the images for the presence and absence of stones. Multivariate classification tree analysis and descriptive statistics were used to evaluate the diagnostic performance. RESULTS: Classification tree analysis revealed a higher detection rate of renal calculi > 2 mm in size compared with that of renal calculi < 2 mm (84.7%; 12.7%; p < 0.001). For stones with a diameter > 2 mm, the best results were found at 70 kV/Sn 150 kV and 80 kV/Sn 150 kV in scans with contrast media attenuation of 600 HU or less, with sensitivity of 99.6% and 96.0%, respectively. A higher luminal attenuation (> 600 HU) resulted in a significantly decreased detection rate (91.8%, 0-600 HU; 70.7%, 900-1400 HU; p < 0.001). In our study setup, the detection rates were best for cystine stones. CONCLUSION: Scan protocols in DE-CT with lower tube current and lower contrast medium attenuation show excellent results in VNC for stones larger than 2 mm but have limitations for small stones. KEY POINTS: • The detection rate of virtual non-contrast reconstructions is highly dependent on the surrounding contrast medium attenuation at the renal pelvis and should be kept as low as possible, as at an attenuation higher than 600 HU the VNC reconstructions are susceptible to masking ureteral stones. • Protocols with lower tube voltages (70 kV/Sn 150 kV and 80 kV/Sn 150 kV) improve the detection rate of kidney stones in VNC reconstructions. • The visibility of renal stones in virtual non-contrast of dual-energy CT is highly associated with the size, and results in a significantly lower detection rate in stones below 2 mm.

Dual-energy CT for liver iron quantification in patients with haematological disorders.

OBJECTIVES: To retrospectively quantify liver iron content in haematological patients suspected of transfusional haemosiderosis using dual-energy CT (DECT) and correlate with serum ferritin levels and estimated quantity of transfused iron. METHODS: One hundred forty-seven consecutive dual-source dual-energy non-contrast chest-CTs in 110 haematologic patients intended primarily for exclusion of pulmonary infection between September 2016 and June 2017 were retrospectively evaluated. Image data was post-processed with a software prototype. After material decomposition, an iron enhancement map was created and freehand ROIs were drawn including most of the partially examined liver. The virtual iron content (VIC) was calculated and expressed in milligram/millilitre. VIC was correlated with serum ferritin and estimated amount of transfused iron. Scans of patients who had not received blood products were considered controls. RESULTS: Forty-eight (32.7%) cases (controls) had not received any blood transfusions whereas 67.3% had received one transfusion or more. Median serum ferritin and VIC were 138.0 µg/dl (range, 6.0-2628.0 µg/dl) and 1.33 mg/ml (range, - 0.94-7.56 mg/ml) in the post-transfusional group and 27.0 µg/dl (range, 1.0-248.0 µg/dl) and 0.61 mg/ml (range, - 2.1-2.4) in the control group. Correlation between serum ferritin and VIC was strong (r = 0.623; p < 0.001) as well as that between serum ferritin and estimated quantity of transfused iron (r = 0.681; p < 0.001). CONCLUSIONS: Hepatic VIC obtained via dual-energy chest-CT examinational protocol strongly correlates with serum ferritin levels and estimated amount of transfused iron and could therefore be used in the routine diagnosis for complementary evaluation of transfusional haemosiderosis. KEY POINTS: • Virtual liver iron content was measured in routine chest-CTs of haematological patients suspected of having iron overload. Chest-CTs were primarily intended for exclusion of pulmonary infection. • Measurements correlate strongly with the most widely used blood marker of iron overload serum ferritin (after exclusion of infection) and the amount of transfused iron. • Liver VIC could be used for supplemental evaluation of transfusional haemosiderosis in haematological patients.

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

BACKGROUND: We 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. METHODS: We 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. RESULTS: Stents 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. CONCLUSION: Both 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.

Multiple Myeloma and Dual-Energy CT: Diagnostic Accuracy of Virtual Noncalcium Technique for Detection of Bone Marrow Infiltration of the Spine and Pelvis.

Purpose To determine the diagnostic performance of dual-energy computed tomography (CT) for detection of bone marrow (BM) infiltration in patients with multiple myeloma by using a virtual noncalcium (VNCa) technique. Materials and Methods In this prospective study, 34 consecutive patients with multiple myeloma or monoclonal gammopathy of unknown significance sequentially underwent dual-energy CT and magnetic resonance (MR) imaging of the axial skeleton. Two independent readers visually evaluated standard CT and color-coded VNCa images for the presence of BM involvement. MR imaging served as the reference standard. Analysis on the basis of the region of interest (ROI) of VNCa CT numbers of infiltrated (n = 75) and normal (n = 170) BM was performed and CT numbers were subjected to receiver operating characteristic analysis to calculate cutoff values. Results In the visual analysis, VNCa images had an overall sensitivity of 91.3% (21 of 23), specificity of 90.9% (10 of 11), accuracy of 91.2% (31 of 34), positive predictive value of 95.5% (21 of 22), and a negative predictive value of 83.3% (10 of 12). ROI-based analysis of VNCa CT numbers showed a significant difference between infiltrated and normal BM (P < .001). Receiver operating characteristic analysis revealed an area under the curve of 0.978. A cutoff of -44.9 HU provided a sensitivity of 93.3% (70 of 75), specificity of 92.4% (157 of 170), accuracy of 92.7% (227 of 245), positive predictive value of 84.3% (70 of 83), and negative predictive value of 96.9% (157 of 162) for the detection of BM infiltration. Conclusion Visual and ROI-based analyses of dual-energy VNCa images had excellent diagnostic performance for assessing BM infiltration in patients with multiple myeloma with precision comparable to that of MR imaging. © RSNA, 2017 Online supplemental material is available for this article.

Dual-energy CT of the bone marrow in multiple myeloma: diagnostic accuracy for quantitative differentiation of infiltration patterns.

OBJECTIVES: Bone marrow imaging patterns in patients with multiple myeloma possess prognostic and potential therapeutic relevance. We aim to evaluate whether different magnetic resonance imaging (MRI) patterns also result in different bone marrow dual-energy computed tomography (DECT) virtual non-calcium (VNCa) attenuation values. METHODS: The institutional review board approved this study. Written informed consent was obtained from all participants. 53 patients with plasma cell disorders (24 with normal imaging pattern, 24 with focal infiltration, 5 with diffuse infiltration) and 21 control subjects sequentially underwent DECT and MRI of the axial skeleton. MRI served as reference standard for imaging pattern assessment. Bone marrow VNCa attenuation numbers were obtained according to pattern allocation. Generalised estimating equations and a receiver operating characteristic (ROC) analysis were performed. RESULTS: Mean VNCa attenuation numbers in patients with normal, focal and diffuse imaging patterns were - 65.8 HU, 3.3 HU and - 13.3 HU, respectively. We found significant differences between diffuse vs. normal (p < 0.001), diffuse vs. focal (p = 0.002) and normal vs. focal (p < 0.001) patterns. A cut-off of - 35.7 HU showed a sensitivity of 100% (24/24) and specificity of 97% (116/120) for the identification of a diffuse pattern vs. normal pattern, with an area under the ROC curve of 0.997. CONCLUSIONS: Bone marrow VNCa attenuation numbers of various imaging patterns in patients with plasma cell disorders differ significantly and a diffuse imaging pattern can be determined confidently using DECT, when ROIs are carefully selected on the basis of MRI findings. KEY POINTS: • DECT allows for imaging pattern allocation similar to MRI. • Bone marrow VNCa attenuation numbers differ significantly depending on the imaging pattern. • A diffuse imaging pattern can be determined confidently using DECT.

Comparison of image quality and radiation dose between split-filter dual-energy images and single-energy images in single-source abdominal CT.

OBJECTIVES: To compare image quality and radiation dose of abdominal split-filter dual-energy CT (SF-DECT) combined with monoenergetic imaging to single-energy CT (SECT) with automatic tube voltage selection (ATVS). METHODS: Two-hundred single-source abdominal CT scans were performed as SECT with ATVS (n = 100) and SF-DECT (n = 100). SF-DECT scans were reconstructed and subdivided into composed images (SF-CI) and monoenergetic images at 55 keV (SF-MI). Objective and subjective image quality were compared among single-energy images (SEI), SF-CI and SF-MI. CNR and FOM were separately calculated for the liver (e.g. CNRliv) and the portal vein (CNRpv). Radiation dose was compared using size-specific dose estimate (SSDE). Results of the three groups were compared using non-parametric tests. RESULTS: Image noise of SF-CI was 18% lower compared to SEI and 48% lower compared to SF-MI (p < 0.001). Composed images yielded higher CNRliv over single-energy images (23.4 vs. 20.9; p < 0.001), whereas CNRpv was significantly lower (3.5 vs. 5.2; p < 0.001). Monoenergetic images overcame this inferiority in CNRpv and achieved similar results compared to single-energy images (5.1 vs. 5.2; p > 0.628). Subjective sharpness was equal between single-energy and monoenergetic images and diagnostic confidence was equal between single-energy and composed images. FOMliv was highest for SF-CI. FOMpv was equal for SEI and SF-MI (p = 0.78). SSDE was significant lower for SF-DECT compared to SECT (p < 0.022). CONCLUSIONS: The combined use of split-filter dual-energy CT images provides comparable objective and subjective image quality at lower radiation dose compared to single-energy CT with ATVS. KEY POINTS: • Split-filter dual-energy results in 18% lower noise compared to single-energy with ATVS. • Split-filter dual-energy results in 11% lower SSDE compared to single-energy with ATVS. • Spectral shaping of split-filter dual-energy leads to an increased dose-efficiency.

Vertebral Compression Fractures: Third-Generation Dual-Energy CT for Detection of Bone Marrow Edema at Visual and Quantitative Analyses.

Purpose To assess the diagnostic performance of a third-generation dual-energy computed tomographic (CT) virtual noncalcium (VNCa) technique for detection of traumatic bone marrow edema in patients with vertebral compression fractures. Materials and Methods This prospective study was approved by the institutional review board. Informed consent was obtained from all participants. Twenty-two consecutive patients with 37 morphologic vertebral fractures were studied between October 2015 and May 2016. All patients underwent dual-energy CT (90 kV and 150 kV with a tin filter) and 3-T magnetic resonance (MR) imaging. Two independent readers visually evaluated all vertebral bodies (n = 163) for the presence of abnormal bone marrow attenuation on VNCa images by using color-coded maps and performed a quantitative analysis of CT numbers on VNCa images. MR images served as the reference standard. CT numbers were subjected to receiver operating characteristic analysis to calculate cutoff values. Results In the visual analysis, VNCa images had an overall sensitivity of 64.0%, specificity of 99.3%, accuracy of 93.9%, positive predictive value of 94.1%, and negative predictive value of 93.8%. The interobserver agreement was excellent (κ = 0.85). CT numbers obtained from VNCa images were significantly different in vertebral bodies with and without edema (P < .001). Receiver operating characteristic analysis revealed an area under the curve of 0.922. A cutoff value of -47 provided sensitivity of 92.0%, specificity of 82.6%, accuracy of 84.0%, positive predictive value of 48.9%, and negative predictive value of 98.3% for the differentiation of edematous vertebral bodies. Conclusion Visual and quantitative analyses of dual-energy VNCa images showed excellent diagnostic performance for assessing traumatic bone marrow edema in vertebral compression fractures. © RSNA, 2017 Online supplemental material is available for this article.

A comparison of relative proton stopping power measurements across patient size using dual- and single-energy CT.

PURPOSE: To evaluate the accuracy and precision across phantom size of a dual-energy computed tomography (DECT) technique used to calculate relative proton stopping power (SPR) in tissue-simulating materials and a silicone implant relative to conventional single-energy CT (SECT). MATERIAL AND METHODS: A 32 cm lateral diameter (CIRS model 062M, Norfolk, Virginia) electron density phantom containing inserts which simulated the chemical composition of eight tissues in a solid-water background was scanned using SECT and DECT. A liquid water insert was included to confirm CT number accuracy. All materials were also placed in four water tanks, ranging from 15 to 45 cm in lateral width and scanned using DECT and SECT. A silicone breast implant was scanned in the same water phantoms. SPR values were calculated based on commercial software (syngo CT Dual Energy, Siemens Healthcare GmbH) and compared to reference values derived from proton beam measurements. Accuracy and precision were quantified across phantom size using percent error and standard deviation. Graphical and regression analysis were used to determine whether SECT or DECT was superior in estimating SPR across phantom size. RESULTS: Both DECT and SECT SPR data resulted in good agreement with the reference values. Percent error was ±3% for both DECT and SECT in all materials except lung and dense bone. The coefficient of variation (CV) across materials and phantom sizes was 1.12% for SECT and 0.96% for DECT. Material-specific regression and graphical analysis did not reveal size dependence for either technique but did show reduced systematic bias with DECT for dense bone and liver. Mean percent error in SPR for the implant was reduced from 11.46% for SECT to 0.49% for DECT. CONCLUSIONS: We demonstrate the superior ability of DECT to mitigate systematic bias in bones and liver and estimate SPR in a silicone breast implant.

Advanced virtual monochromatic reconstruction of dual-energy unenhanced brain computed tomography in children: comparison of image quality against standard mono-energetic images and conventional polychromatic computed tomography.

BACKGROUND: Advanced virtual monochromatic reconstruction from dual-energy brain CT has not been evaluated in children. OBJECTIVE: To determine the most effective advanced virtual monochromatic imaging energy level for maximizing pediatric brain parenchymal image quality in dual-energy unenhanced brain CT and to compare this technique with conventional monochromatic reconstruction and polychromatic scanning. MATERIALS AND METHODS: Using both conventional (Mono) and advanced monochromatic reconstruction (Mono+) techniques, we retrospectively reconstructed 13 virtual monochromatic imaging energy levels from 40 keV to 100 keV in 5-keV increments from dual-source, dual-energy unenhanced brain CT scans obtained in 23 children. We analyzed gray and white matter noise ratios, signal-to-noise ratios and contrast-to-noise ratio, and posterior fossa artifact. We chose the optimal mono-energetic levels and compared them with conventional CT. RESULTS: For Mono+maximum optima were observed at 60 keV, and minimum posterior fossa artifact at 70 keV. For Mono, optima were at 65-70 keV, with minimum posterior fossa artifact at 75 keV. Mono+ was superior to Mono and to polychromatic CT for image-quality measures. Subjective analysis rated Mono+superior to other image sets. CONCLUSION: Optimal virtual monochromatic imaging using Mono+ algorithm demonstrated better image quality for gray-white matter differentiation and reduction of the artifact in the posterior fossa.

Correlation between Dual-Energy and Perfusion CT in Patients with Hepatocellular Carcinoma.

Purpose To develop a dual-energy contrast media-enhanced computed tomographic (CT) protocol by using time-attenuation curves from previously acquired perfusion CT data and to evaluate prospectively the relationship between iodine enhancement metrics at dual-energy CT and perfusion CT parameters in patients with hepatocellular carcinoma (HCC). Materials and Methods Institutional review board and local ethics committee approval and written informed consent were obtained. The retrospective part of this study included the development of a dual-energy CT contrast-enhanced protocol to evaluate peak arterial enhancement of HCC in the liver on the basis of time-attenuation curves from previously acquired perfusion CT data in 20 patients. The prospective part of the study consisted of an intraindividual comparison of dual-energy CT and perfusion CT data in another 20 consecutive patients with HCC. Iodine density and iodine ratio (iodine attenuation of the lesion divided by iodine attenuation in the aorta) from dual-energy CT and arterial perfusion (AP), portal venous perfusion, and total perfusion (TP) from perfusion CT were compared. Pearson R and linear correlation coefficients were calculated for AP and iodine density, AP and iodine ratio, TP and iodine density, and TP and iodine ratio. Results The dual-energy CT protocol consisted of bolus tracking in the abdominal aorta (threshold, 150 HU; scan delay, 9 seconds). The strongest intraindividual correlations in HCCs were found between iodine density and AP (r = 0.75, P = .0001). Moderate correlations were found between iodine ratio and AP (r = 0.50, P = .023) and between iodine density and TP (r = 0.56, P = .011). No further significant correlations were found. The volume CT dose index (11.4 mGy) and dose-length product (228.0 mGy · cm) of dual-energy CT was lower than those of the arterial phase of perfusion CT (36.1 mGy and 682.3 mGy · cm, respectively). Conclusion A contrast-enhanced dual-energy CT protocol developed by using time-attenuation curves from previously acquired perfusion CT data sets in patients with HCC could show good correlation between iodine density from dual-energy CT with AP from perfusion CT. (©) RSNA, 2016.

Noise-optimized virtual monoenergetic images and iodine maps for the detection of venous thrombosis in second-generation dual-energy CT (DECT): an ex vivo phantom study.

AIMS AND OBJECTIVES: Deep venous thrombosis (DVT) can be difficult to detect using CT due to poor and heterogeneous contrast. Dual-energy CT (DECT) allows iodine contrast optimization using noise-optimized monoenergetic extrapolations (MEIs) and iodine maps (IMs). Our aim was to assess whether MEI and IM could improve the delineation of thrombotic material within iodine-enhanced blood compared to single-energy CT (SECT). MATERIALS AND METHODS: Six vessel phantoms, including human thrombus and contrast media-enhanced blood and one phantom without contrast, were placed in an attenuation phantom and scanned with DECT 100/140 kV and SECT 120 kV. IM, virtual non-contrast images (VNC), mixed images, and MEI were calculated. Attenuation of thrombi and blood were measured. Contrast and contrast-to-noise-ratios (CNRs) were calculated and compared among IM, VNC, mixed images, MEI, and SECT using paired t tests. RESULTS: MEI40keV and IM showed significantly higher contrast and CNR than SE120kV from high to intermediate iodine concentrations (contrast:pMEI40keV < 0.002,pIM < 0.005;CNR:pMEI40keV < 0.002,pIM < 0.004). At low iodine concentrations, MEI190keV and VNC images showed significantly higher contrast and CNR than SE120kV with inverted contrasts (contrast:pMEI190keV < 0.008,pVNC < 0.002;CNR:pMEI190keV < 0.003,pVNC < 0.002). CONCLUSIONS: Noise-optimized MEI and IM provide significantly higher contrast and CNR in the delineation of thrombosis compared to SECT, which may facilitate the detection of DVT in difficult cases. KEY POINTS: • Poor contrast makes it difficult to detect thrombosis in CT. • Dual-energy-CT allows contrast optimization using monoenergetic extrapolations (MEI) and iodine maps (IM). • Noise-optimized-MEI and IM are significantly superior to single-energy-CT in delineation of thrombosis. • Noise-optimized-MEI and IM may facilitate the detection of deep vein thrombosis.

Dual-energy CT: virtual calcium subtraction for assessment of bone marrow involvement of the spine in multiple myeloma.

OBJECTIVE. Dual-energy CT (DECT) enables subtraction of calcium, facilitating the visualization of bone marrow (BM) in the axial skeleton. The purpose of this study was to assess whether DECT BM images have the potential to improve the detection of multifocal and diffuse BM infiltration in multiple myeloma (MM) in comparison with regular CT with MRI as the reference standard. SUBJECTS AND METHODS. This study included 32 consecutive patients who had known MM or presented with monoclonal gammopathy of unknown significance and underwent DECT and MRI of the axial skeleton. The degrees (none, n = 14; moderate, n = 10; and high, n = 8) and patterns (diffuse, n = 10 or multifocal, n = 8) of infiltration were assessed on MR images. Attenuation in BM and CT images in known uninvolved and involved areas was measured. Cutoff values of attenuation in BM images for infiltration in lytic and nonlytic lesions were established by ROC analysis. At least 120 days later, sensitivity and specificity for reading CT images alone and when using additional BM images were evaluated. RESULTS. ROC analysis revealed larger AUC in BM images than in CT images; cutoff values for marrow invasion in BM images were 4 and -3 HU in lytic and nonlytic lesions, respectively. In the blinded reading session, BM images improved the sensitivity for the detection of diffuse infiltration from 0 to as much as 75% for cases with high-grade infiltration. In multifocal patterns, BM images did not significantly change the detection rate. CONCLUSION. BM images have the potential to improve the sensitivity for detection of diffuse BM involvement in comparison with regular CT.

Feasibility of discriminating uric acid from non-uric acid renal stones using consecutive spatially registered low- and high-energy scans obtained on a conventional CT scanner.

OBJECTIVE: The objective of our study was to show the feasibility of distinguishing between uric acid (UA) and non-UA renal stones using two consecutive spatially registered low- and high-energy scans acquired on a conventional CT system. SUBJECTS AND METHODS: A total of 33 patients undergoing clinically indicated dual-source dual-energy CT examinations to differentiate UA from non-UA renal stones were enrolled in this study. Immediately after patients underwent clinically indicated dual-source dual-energy CT, two consecutive scans (one at 80 kV and one at 140 kV) were obtained on a conventional CT scanner over the region limited to the stones identified on the dual-source scans. After 3D deformable registration of the 80- and 140-kV images, UA and non-UA stones were identified using commercial software. The sensitivity, specificity, and accuracy of stone classification were calculated using the dual-source results as the reference standard. RESULTS: A total of 469 stones were identified in the dual-source examinations (26 UA and 443 non-UA stones). The average in-plane stone diameter was 4.4 ± 2.5 (SD) mm (range, 2.0-18.9 mm). The overall sensitivity, specificity, and accuracy for identifying UA stones were 73.1%, 90.1%, and 89.1%, respectively. The sensitivity, specificity, and accuracy were 94.7%, 96.9%, and 96.8% for stones 3 mm or larger (n = 341 [19 UA and 322 non-UA]). CONCLUSION: Accurate differentiation of UA from non-UA renal stones is feasible using two consecutively acquired and spatially registered conventional CT scans.

Dual energy computerized tomography with a split bolus-a 1-stop shop for patients with suspected urinary stones?

PURPOSE: We evaluated a dual energy, split bolus computerized tomography protocol that provides virtual noncontrast, parenchymal and urographic phases in a single scan. We assessed the sensitivity of the virtual noncontrast phase using this protocol to detect urinary stones compared to the gold standard of the true noncontrast phase. MATERIALS AND METHODS: We prospectively enrolled in the study 81 patients who underwent unenhanced single energy computerized tomography at 120 kV/200 mA as well as contrast enhanced dual energy computerized tomography on a Somatom® Definition Flash-CT (tube A 80 kV/233 mA and tube B SN 140 kV/180 mA with 1/0.8 mm slice thickness). For the split bolus protocol 400 mg/ml Iomeron® were injected at 2 time points, that is 15 ml 10 minutes before the scan and 80 ml 65 seconds before the scan. In a consensus reading 2 readers evaluated the presence and diameter of stones on the true and virtual noncontrast phases. RESULTS: Of the 350 stones noted on the true noncontrast phase we found 289 on the virtual noncontrast phase as well as 13 false-positive and 66 false-negative stones. Sensitivity was 98.4%, 89.8% and 82.6% per patient, segment and stone, respectively. The diameter measured on the virtual noncontrast phase corresponded to a mean ± SD 92.5% ± 31.6% of the diameter on the true noncontrast phase. The mean effective dose was 4.8 ± 1.8 and 10.5 ± 3.7 mSv for the true and virtual noncontrast phases, respectively. CONCLUSIONS: The proposed protocol allows for combining 3 phases in a single scan while still enabling the detection of urinary stones at high sensitivity. This technique halves the radiation dose and provides the surgeon with better anatomical information on the calyceal system. Therefore, it is a valuable diagnostic tool for kidney stone treatment planning and followup.

Accuracy of contrast-enhanced dual-energy MDCT for the assessment of iodine uptake in renal lesions.

OBJECTIVE: The objective of our study was to assess the accuracy of iodine-related attenuation and iodine quantification as imaging biomarkers of iodine uptake in renal lesions on a single-phase nephrographic image with dual-energy MDCT. MATERIALS AND METHODS: Fifty-nine patients (41 men, 18 women; age range, 28-84 years) with 80 renal lesions underwent contrast-enhanced dual-energy CT during the nephrographic phase of enhancement. Renal lesions were characterized as enhancing or nonenhancing on color-coded iodine overlay maps using iodine-related attenuation (in Hounsfield units) and iodine quantification (in milligrams per milliliter). For iodine-related attenuation the iodine uptake thresholds of 15 and 20 HU were tested; a threshold of 0.5 mg/mL was used for iodine quantification. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of iodine-related attenuation and iodine quantification were calculated from chi-square tests of contingency with histopathology or imaging follow-up as the reference standard. The 95% CIs were calculated from binomial expression. Differences in sensitivity and specificity were assessed by means of McNemar analysis. RESULTS: A significant difference in sensitivity and specificity was found between iodine-related attenuation with the thresholds of 15 HU (sensitivity, 91.4%; specificity, 93.3%; PPV, 91.4%; NPV, 93.3%) and 20 HU (sensitivity, 77.1%; specificity, 100%; PPV, 100%; NPV, 84.9%) (p = 0.008) and between iodine quantification (sensitivity, 100%; specificity, 97.7%; PPV, 97.2%; NPV, 100%) and iodine-related attenuation with a threshold of 20 HU (p = 0.004). No significant difference in sensitivity and specificity was found between iodine quantification and iodine-related attenuation with a threshold of 15 HU. CONCLUSION: Contrast-enhanced dual-energy MDCT with iodine-related attenuation and iodine quantification allows accurate evaluation of iodine uptake in renal lesions on a single-phase nephrographic image.

Dual-energy computed tomographic virtual noncalcium algorithm for detection of bone marrow edema in acute fractures: early experiences.

Computed tomography (CT) is often used to assess the presence of occult fractures when plain radiographs are equivocal in the acute traumatic setting. While providing increased spatial resolution, conventional computed tomography is limited in the assessment of bone marrow edema, a finding that is readily detectable on magnetic resonance imaging (MRI).Dual-energy CT has recently been shown to demonstrate patterns of bone marrow edema similar to corresponding MRI studies. Dual-energy CT may therefore provide a convenient modality for further characterizing acute bony injury when MRI is not readily available. We report our initial experiences of 4 cases with imaging and clinical correlation.

Distinguishing enhancing from nonenhancing renal masses with dual-source dual-energy CT: iodine quantification versus standard enhancement measurements.

PURPOSE: To compare the diagnostic accuracy of iodine quantification and standard enhancement measurements in distinguishing enhancing from nonenhancing renal masses. MATERIALS AND METHODS: The Institutional Review Board approved this retrospective study conducted from data found in institutional patient databases and archives. Seventy-two renal masses were characterised as enhancing or nonenhancing using standard enhancement measurements (in HU) and iodine quantification (in mg/ml). Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of standard enhancement measurements and iodine quantification were calculated from χ (2) tests of contingency with histopathology or imaging follow-up as the reference standard. Difference in accuracy was assessed by means of McNemar analysis. RESULTS: Sensitivity, specificity, PPV, NPV and diagnostic accuracy for standard enhancement measurements and iodine quantification were 77.7 %, 100 %, 100 %, 81.8 %, 89 % and 100 %, 94.4 %, 94.7, 100 % and 97 %, respectively. The McNemar analysis showed that the accuracy of iodine quantification was significantly better (P < 0.001) than that of standard enhancement measurements. CONCLUSION: Compared with standard enhancement measurements, whole-tumour iodine quantification is more accurate in distinguishing enhancing from nonenhancing renal masses. KEY POINTS: • Enhancement of renal lesions is important when differentiating benign from malignant tumours. • Dual-energy CT offers measurement of iodine uptake rather than mere enhancement values. • Whole-tumour iodine quantification seems more accurate than standard CT enhancement measurements.

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.

Imaging of ventilation with dual-energy CT during breath hold after single vital-capacity inspiration of stable xenon.

PURPOSE: To assess single-breath-hold technique for ventilation mapping by using dual-energy computed tomography (CT) in phantom experiments and volunteers. MATERIALS AND METHODS: Institutional review board approved this study, and written informed consent was obtained from all volunteers. A rubber bag filled with a mixture of xenon (0%-35.4%) and oxygen was scanned with dual-source dual-energy CT (80 kV and 140 kV with tin [Sn] filter [Sn/140 kV] and 100 kV and Sn/140 kV). A cylinder containing six tubes of identical sizes with different apertures was ventilated once with a mixture of 35% xenon and 65% oxygen and was scanned in dual-energy mode (80 kV and Sn/140 kV). Xenon-enhanced images were derived by using three-material decomposition technique. Four volunteers were scanned twice in dual-energy mode (80 kV and Sn/140 kV) during breath hold after a single vital-capacity inspiration of air (nonenhanced) and of 35% xenon. Xenon-enhanced images were obtained by using two methods: three-material decomposition and subtraction of nonenhanced from xenon-enhanced images. Regression analysis with t and F tests was applied to the data of the rubber bag scans, with the significance level set at .05. RESULTS: Mean pixel values of gas in the bag were linearly related to xenon concentration for all x-ray tube voltages (r(2) = 1.00, P < .00001). Pixel values of the xenon-enhanced images of the tubes were related to their aperture size. Nearly homogeneous (coefficient of variation: 0.22, 0.23, and 0.34) pixel values were found in the lungs of healthy volunteers, with higher pixel values in the trachea and lower pixel values in the bullae. Xenon-enhanced images calculated by using three-material decomposition had better image quality on visual comparison than those calculated by using subtraction. CONCLUSION: Xenon-enhanced dual-energy CT with the single-breath-hold technique could depict ventilation in phantoms and in four volunteers.

Diagnostic performance of dual-energy CT for the detection of traumatic bone marrow lesions in the ankle: comparison with MR imaging.

PURPOSE: To evaluate prospectively the performance of noncalcium images reconstructed from dual-energy (DE) computed tomography (CT) for the diagnosis of bone marrow lesions in patients with acute ankle joint trauma in comparison with magnetic resonance (MR) images. MATERIALS AND METHODS: The study had local ethics board approval, and written informed consent was obtained. Thirty consecutive patients (15 women; mean age, 34 years±11.8 [standard deviation]) underwent dual-source DE CT (80 kVp and 140 kVp with tin filter) and MR imaging within 1 day following acute ankle trauma. DE CT data were postprocessed by using a three-material decomposition algorithm for generating noncalcium images. MR and noncalcium images were graded by two blinded, independent readers using a four-point system (1=distinct bone marrow lesion, 4=no lesion); CT numbers in noncalcium images were calculated by a third reader. MR imaging interpretations served as the reference standard. RESULTS: Interreader agreement for qualitative grading of DE CT images was substantial (κ=0.66). The respective sensitivity, specificity, positive predictive value, and negative predictive value of DE CT for depicting distinct bone marrow lesions for both readers were 90.0% each, 80.5% and 81.6%, 25.4% and 26.5%, and 99.1% each. In regions without abnormality, CT numbers in noncalcium images gradually increased from proximal to distal location (P<.001). Significant differences in CT numbers were found in regions positive for bone marrow lesions compared with those that were negative (P<.001). CT numbers for the diagnosis of distinct bone marrow lesions according to MR imaging revealed areas under the receiver operating characteristic curve of 0.973, 0.813, and 0.758 for ankle mortise, talar dome, and talar body/head, respectively. CONCLUSION: Compared with MR images, distinct traumatic bone marrow lesions of the ankle joint can be diagnosed on noncalcium images reconstructed from DE CT with high sensitivity and excellent negative predictive value, but with moderate specificity and low positive predictive value.