Achille Mileto

State of the Art: Dual-Energy CT of the Abdomen

Recent technologic advances in computed tomography (CT)--enabling the nearly simultaneous acquisition of clinical images using two different x-ray energy spectra--have sparked renewed interest in dual-energy CT. By interrogating the unique characteristics of different materials at different x-ray energies, dual-energy CT can be used to provide quantitative information about tissue composition, overcoming the limitations of attenuation-based conventional single-energy CT imaging. In the past few years, intensive research efforts have been devoted to exploiting the unique and powerful opportunities of dual-energy CT for a variety of clinical applications. This has led to CT protocol modifications for radiation dose reduction, improved diagnostic performance for detection and characterization of diseases, as well as image quality optimization. In this review, the authors discuss the basic principles, instrumentation and design, examples of current clinical applications in the abdomen and pelvis, and future opportunities of dual-energy CT.

Muscle Fat Fraction in Neuromuscular Disorders: Dual-Echo Dual-Flip-Angle Spoiled Gradient-Recalled MR Imaging Technique for Quantification—A Feasibility Study

PURPOSE To prospectively evaluate the muscle fat fraction (MFF) measured with dual-echo dual-flip-angle spoiled gradient-recalled acquisition in the steady state (SPGR) magnetic resonance (MR) imaging technique by using muscle biopsy as the reference standard. MATERIALS AND METHODS After ethics approval, written informed consent from all patients was obtained. Twenty-seven consecutive patients, evaluated at the Neuromuscular Disorders Center with a possible diagnosis of neuromuscular disorder, were prospectively studied with MR imaging of the lower extremities to quantify muscle fatty infiltration by means of MFF calculation. Spin-density- and T1-weighted fast SPGR in-phase and opposed-phase dual-echo sequences were performed, respectively, with 20° and 80° flip angles. Round regions of interest were drawn by consensus on selected MR sections corresponding to anticipated biopsy sites. These were marked on the patients skin with a pen by using the infrared spider light of the system, and subsequent muscle biopsy was performed. MR images with regions of interest were stored on a secondary console where the MFF calculation was performed by another radiologist blinded to the biopsy results. MFFs calculated with dual-echo dual-flip-angle SPGR MR imaging and biopsy were compared by using a paired t test, Pearson correlation coefficient, and Bland-Altman plots. P value of < .05 was considered to indicate a statistically significant difference. RESULTS The mean MFFs obtained with dual-echo dual-flip-angle SPGR MR imaging and biopsy were 20.3% (range, 1.7%-45.1%) and 20.6% (range, 3%-46.1%), respectively. The mean difference, standard deviation of the difference, and t value were -0.3, 1.3, and -1.3 (P > .2), respectively. The Pearson correlation coefficient was 0.995; with the Bland-Altman method, all data points were within the ± 2 SDs limits of agreement. CONCLUSION The results show that dual-echo dual-flip-angle SPGR MR imaging technique provides reliable calculation of MFF, consistent with biopsy measurements.

Diagnostic Performance of an Advanced Modeled Iterative Reconstruction Algorithm for Low-Contrast Detectability with a Third-Generation Dual-Source Multidetector CT Scanner: Potential for Radiation Dose Reduction in a Multireader Study

PURPOSE To assess the effect of radiation dose reduction on low-contrast detectability by using an advanced modeled iterative reconstruction (ADMIRE; Siemens Healthcare, Forchheim, Germany) algorithm in a contrast-detail phantom with a third-generation dual-source multidetector computed tomography (CT) scanner. MATERIALS AND METHODS A proprietary phantom with a range of low-contrast cylindrical objects, representing five contrast levels (range, 5-20 HU) and three sizes (range, 2-6 mm) was fabricated with a three-dimensional printer and imaged with a third-generation dual-source CT scanner at various radiation dose index levels (range, 0.74-5.8 mGy). Image data sets were reconstructed by using different section thicknesses (range, 0.6-5.0 mm) and reconstruction algorithms (filtered back projection [FBP] and ADMIRE with a strength range of three to five). Eleven independent readers blinded to technique and reconstruction method assessed all data sets in two reading sessions by measuring detection accuracy with a two-alternative forced choice approach (first session) and by scoring the total number of visible object groups (second session). Dose reduction potentials based on both reading sessions were estimated. Results between FBP and ADMIRE were compared by using both paired t tests and analysis of variance tests at the 95% significance level. RESULTS During the first session, detection accuracy increased with increasing contrast, size, and dose index (diagnostic accuracy range, 50%-87%; interobserver variability, ±7%). When compared with FBP, ADMIRE improved detection accuracy by 5.2% on average across the investigated variables (P < .001). During the second session, a significantly increased number of visible objects was noted with increasing radiation dose index, section thickness, and ADMIRE strength over FBP (up to 80% more visible objects, P < .001). Radiation dose reduction potential ranged from 56% to 60% and from 4% to 80% during the two sessions, respectively. CONCLUSION Low-contrast detectability performance increased with increasing object size, object contrast, dose index, section thickness, and ADMIRE strength. Compared with FBP, ADMIRE allows a substantial radiation dose reduction while preserving low-contrast detectability. Online supplemental material is available for this article.

Dual-Source Dual-Energy CT Evaluation of Complex Cystic Renal Masses

OBJECTIVE The purpose of this study was to assess the value of dual-source dual-energy CT in the evaluation of complex cystic renal masses. SUBJECTS AND METHODS Seventy patients underwent contrast-enhanced dual-energy CT that included true unenhanced images acquired in single-energy mode, corticomedullary phase images acquired in dual-energy mode, and nephrographic phase images acquired in single-energy mode. Virtual unenhanced, blended weighted-average, and color-coded iodine overlay images were reconstructed. The acceptance level and image quality of virtual and true unenhanced images were evaluated. Contrast enhancement on both true unenhanced or blended weighted-average images and color-coded iodine overlay images was evaluated with both calculation in regions of interest and use of confidence level scales. Radiation dose parameters were estimated. RESULTS Virtual unenhanced images of 70 lesions (97.2%) and true unenhanced images of 72 lesions (100%) were judged acceptable (p = 0.5). The mean quality score of virtual unenhanced images was 2.0 ± 0.7 and of true unenhanced images was 1.5 ± 0.5 (p < 0.001). Mean contrast enhancement measured on true unenhanced and blended weighted-average images was 45.9 ± 15.9 HU (range, 21-78 HU) and on color-coded iodine overlay images was 47.3 ± 16.8 HU (range, 22-75 HU) with no significant differences. Enhancement was excluded on color-coded iodine overlay images with a significantly (p < 0.03) higher level of confidence than it was on true unenhanced and blended weighted-average images. The mean dose reduction with use of a combined dual- and single-energy dual-phase CT protocol was 29.1% ± 11.9% (p < 0.001). CONCLUSION Dual-source dual-energy CT is a reliable imaging technique in the evaluation of complex cystic renal masses. True unenhanced images can be replaced by virtual unenhanced images with considerable radiation dose reduction. The color-coded iodine overlay technique is a useful tool for both excluding and identifying endocystic enhancement.

Iodine quantification to distinguish clear cell from papillary renal cell carcinoma at dual-energy multidetector CT: a multireader diagnostic performance study.

PURPOSE To investigate whether dual-energy multidetector row computed tomographic (CT) imaging with iodine quantification is able to distinguish between clear cell and papillary renal cell carcinoma ( RCC renal cell carcinoma ) subtypes. MATERIALS AND METHODS In this retrospective, HIPAA-compliant, institutional review board-approved study, 88 patients (57 men, 31 women) with diagnosis of either clear cell or papillary RCC renal cell carcinoma at pathologic analysis, who underwent contrast material-enhanced dual-energy nephrographic phase study between December 2007 and June 2013, were included. Five readers, blinded to pathologic diagnosis, independently evaluated all cases by determining the lesion iodine concentration on color-coded iodine maps. The receiving operating characteristic curve analysis was adopted to estimate the optimal threshold for discriminating between clear cell and papillary RCC renal cell carcinoma , and results were validated by using a leave-one-out cross-validation. Interobserver agreement was assessed by using an intraclass correlation coefficient. The correlation between tumor iodine concentration and tumor grade was investigated. RESULTS A tumor iodine concentration of 0.9 mg/mL represented the optimal threshold to discriminate between clear cell and papillary RCC renal cell carcinoma , and it yielded the following: sensitivity, 98.2% (987 of 1005 [95% confidence interval: 97.7%, 98.7%]); specificity, 86.3% (272 of 315 [95% confidence interval: 85.0%, 87.7%]); positive predictive value, 95.8% (987 of 1030 [95% confidence interval: 95.0%, 96.6%]); negative predictive value, 93.7% (272 of 290 [95% confidence interval: 92.8%, 94.7%]); overall accuracy of 95.3% (1259 of 1320 [95% confidence interval: 94.6%, 96.2%]), with an area under the curve of 0.923 (95% confidence interval: 0.913, 0.933). An excellent agreement was found among the five readers in measured tumor iodine concentration (intraclass correlation coefficient, 0.9990 [95% confidence interval: 0. 9987, 0.9993). A significant correlation was found between tumor iodine concentration and tumor grade for both clear cell (τ = 0.85; P < .001) and papillary RCC renal cell carcinoma (τ = 0.53; P < .001). CONCLUSION Dual-energy multidetector CT with iodine quantification can be used to distinguish between clear cell and papillary RCC renal cell carcinoma , and it provides insights regarding the tumor grade.

Impact of Dual-Energy Multi–Detector Row CT with Virtual Monochromatic Imaging on Renal Cyst Pseudoenhancement: In Vitro and in Vivo Study

PURPOSE To investigate whether dual-energy multi-detector row computed tomography (CT) with virtual monochromatic imaging can overcome renal cyst pseudoenhancement in a phantom experiment and a clinical study. MATERIALS AND METHODS This retrospective single-center HIPAA-compliant study was approved by the institutional review board, with waiver of informed consent. Four renal compartments inserted into torso phantoms were filled with saline to simulate the unenhanced state and with iodinated solutions to simulate the three levels of renal parenchyma enhancement (140, 180, and 240 HU). Saline-filled spheres simulating renal cysts (15 and 18 mm in diameter) were serially suspended in the renal compartments and imaged with dual-energy and single-energy multi-detector row CT at four different energy levels (80, 100, 120, and 140 kVp). In addition, 28 patients (mean age, 66 years ± 10; mean body mass index, 31.3 kg/m(2) ± 6.2) with 34 intrarenal cysts were included. Virtual monochromatic images were reconstructed in 10-keV increments at energy levels ranging from 40 to 140 keV. Phantom and clinical data were analyzed by using multivariate regression analysis. RESULTS In the phantom experiment, all polychromatic image data sets showed pseudoenhancement (postcontrast attenuation increase >10 HU) in all investigated conditions, with a significant effect on cyst size (P <.001), location (P <.001), and renal background attenuation level (P <.001). Virtual monochromatic images at energy levels ranging from 80 to 140 keV did not show pseudoenhancement, with the minimum attenuation increase (mean, 6.1 HU ± 1.6; range, 1.6-7.7 HU) on 80-keV images. In patients, pseudoenhancement never occurred on virtual monochromatic images at energy levels ranging from 90 to 140 keV. Patient body size had a significant effect (P = .007) on selection of the optimal monochromatic energy level. CONCLUSION Dual-energy multi-detector row CT with reconstruction of virtual monochromatic images at an optimal energy level can overcome renal cyst pseudoenhancement.

Dual-energy CT for detection of endoleaks after endovascular abdominal aneurysm repair: usefulness of colored iodine overlay.

OBJECTIVE The purpose of our study was to evaluate the value of dual-source dual-energy CT with colored iodine overlay for detection of endoleaks after endovascular abdominal aortic aneurysm repair. We also calculated the potential dose reduction by using a dual-energy CT single-phase protocol. SUBJECTS AND METHODS From November 2007 to November 2009, 74 patients underwent CT angiography 2-7 days after endovascular repair during single-energy unenhanced and dual-energy venous phases. By using dual-energy software, the iodine overlay was superimposed on venous phase images with different percentages ranging between 0 (virtual unenhanced images) and 50-75% to show the iodine in an orange color. Two blinded readers evaluated the data for diagnosis of endoleaks during standard unenhanced and venous phase images (session 1, standard of reference) and virtual unenhanced and venous phase images with colored iodine overlay images (session 2). We compared the effective dose radiation of a single-energy biphasic protocol with that of a single-phase dual-energy protocol. The diagnostic accuracy of session 2 was calculated. RESULTS The mean dual-energy effective dose was 7.27 mSv. By using a dual-energy single-phase protocol, we obtained a mean dose reduction of 28% with respect to a single-energy biphasic protocol. The diagnostic accuracy of session 2 was: 100% sensitivity, 100% specificity, 100% negative predictive value, and 100% positive predictive value. Statistically significant differences in the level of confidence for endoleak detection between the two sessions were found by reviewers for scores 3-5. CONCLUSION Dual-energy CT with colored iodine overlay is a useful diagnostic tool in endoleak detection. The use of a dual-energy single-phase study protocol will lower radiation exposure to patients.

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 Multidetector CT for the Characterization of Incidental Adrenal Nodules: Diagnostic Performance of Contrast-enhanced Material Density Analysis

PURPOSE To determine whether contrast material-enhanced dual-energy multidetector computed tomography (CT) with material decomposition analysis allows differentiation of adrenal adenomas from nonadenomatous lesions and to compare findings with those of nonenhanced multidetector CT. MATERIALS AND METHODS This retrospective HIPAA-compliant study was approved by the institutional review board of Duke University, with waiver of informed consent. Thirty-eight nonconsecutive patients (22 men and 16 women; mean age, 65 years) with 47 adrenal nodules underwent nonenhanced and contrast-enhanced dual-energy multidetector CT of the abdomen. For each adrenal nodule, nonenhanced attenuation values were recorded; dual-energy density measurements were obtained by using fat-iodine and fat-water material density basis pairs. Mean and median values of nonenhanced attenuation and material densities were compared between adenomas and nonadenomas by using the two-sample t test and Wilcoxon rank sum test, respectively. The diagnostic performance of nonenhanced multidetector CT and dual-energy material densities was assessed by setting the specificity for diagnosis of adenomas at 100%. RESULTS Adenomas (lipid rich and lipid poor) displayed significantly different mean density values (in milligrams per cubic centimeter) than those of nonadenomas on fat-iodine (970.4 ± 17.2 vs 1012.3 ± 9.3), iodine-fat (2.5 ± 0.3 vs 4.5 ± 1.5), fat-water (-666.7 ± 154.8 vs -2141.8 ± 953.2), and water-fat (1628.4 ± 177.3 vs 3225 ± 986.1) images, respectively (P < .0001). For diagnosis of adenomas, dual-energy material density analysis showed a sensitivity of 96% (23 of 24 lesions) at a specificity of 100% (23 of 23 lesions), yielding significantly improved diagnostic performance compared with nonenhanced multidetector CT attenuation (sensitivity of 67% [16 of 24 lesions] at a specificity of 100% [23 of 23 lesions]) (P = .035). CONCLUSION Contrast-enhanced dual-energy multidetector CT with material density analysis allows differentiation between adrenal adenomas and nonadenomas, reflecting an improved ability over nonenhanced multidetector CT for diagnosis of lipid-poor adenoma.

Dual energy MDCT assessment of renal lesions: an overview.

AbstractWith the expansion of cross-sectional imaging, the number of renal lesions that are incidentally discovered has increased. Multidetector CT (MDCT) is the investigation of choice for characterising and staging renal lesions. Although a definitive diagnosis can be confidently posed for most of them, a number of renal lesions remain indeterminate following MDCT. Further imaging tests are therefore needed, with subsequent increase of healthcare costs, radiation exposure, and patient anxiety. By addressing most of the issues with conventional MDCT imaging, dual-energy MDCT can improve the diagnosis of renal lesions and, potentially, may represent a paradigm shift from a merely attenuation-based to a material-specific spectral imaging investigation. The purpose of this review is to provide an overview of current clinical applications of dual-energy CT in the evaluation of renal lesions. Key Points • As MDCT expands, an increasing number of renal lesions are serendipitously discovered. • With conventional MDCT, technical issues affect the diagnosis of renal lesions. • Dual-energy CT addresses some of the drawbacks of conventional MDCT. • Dual-energy CT may represent a paradigm shift for renal lesions imaging.