Dual-energy Computed Tomography Protocol Research Articles

Impact of Dual-Energy Computed Tomography (DECT) Postprocessing Protocols on Detection of Monosodium Urate (MSU) Deposits in Foot Tendons of Cadavers.

To evaluate two different dual-energy computed tomography (DECT) post-processing protocols for the detection of MSU deposits in foot tendons of cadavers with verification by polarizing light microscopy as the gold standard. A total of 40 embalmed cadavers (15 male; 25 female; median age, 82 years; mean, 80 years; range, 52-99; SD ± 10.9) underwent DECT to assess MSU deposits in foot tendons. Two postprocessing DECT protocols with different Hounsfield unit (HU) thresholds, 150/500 (=established) versus 120/500 (=modified). HU were applied to dual source acquisition with 80 kV for tube A and 140 kV for tube B. Six fresh cadavers (4 male; 2 female; median age, 78; mean, 78.5; range 61-95) were examined by DECT. Tendon dissection of 2/6 fresh cadavers with positive DECT 120 and negative DECT 150 studies were used to verify MSU deposits by polarizing light microscopy. The tibialis anterior tendon was found positive in 57.5%/100% (DECT 150/120), the peroneus tendon in 35%/100%, the achilles tendon in 25%/90%, the flexor halluces longus tendon in 10%/100%, and the tibialis posterior tendon in 12.5%/97.5%. DECT 120 resulted in increased tendon MSU deposit detection, when DECT 150 was negative, with an overall agreement between DECT 150 and DECT 120 of 80% (p = 0.013). Polarizing light microscope confirmed MSU deposits detected only by DECT 120 in the tibialis anterior, the achilles, the flexor halluces longus, and the peroneal tendons. The DECT 120 protocol showed a higher sensitivity when compared to DECT 150.

Improving visualization of free fibula flap perforators and reducing radiation dose in dual-energy CT angiography.

The precise assessment of the perforators of the fibula free flap (FFF) is crucial for minimizing procedure-related complications when harvesting the FFF in patients with maxillofacial lesions. This study aims to investigate the utility of virtual noncontrast (VNC) images for radiation dose saving and to determine the optimal energy level of virtual monoenergetic imaging (VMI) reconstructions in dual-energy computed tomography (DECT) for visualization of the perforators of the fibula free flap (FFF). Data from 40 patients with maxillofacial lesions who received lower extremity DECT examinations in the noncontrast and arterial phase were collected in this retrospective, cross-sectional study. To compare VNC images from the arterial phase with true non-contrast images in a DECT protocol (M_0.5-TNC) and to compare VMI images with 0.5 linear images blending from the arterial phase (M_0.5-C), the attenuation, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and subjective image quality were assessed in different arteries, muscles, and fat tissues. Two readers evaluated the image quality and visualization of the perforators. The dose-length product (DLP) and CT volume dose index (CTDIvol) were used to determine the radiation dose. Objective and subjective analyses showed no significant difference between the M_0.5-TNC and VNC images in the arteries and muscles (P>0.09 to P>0.99), and VNC imaging could reduce 50% of the radiation dose (P<0.001). Compared with those of the M_0.5-C images, the attenuation and CNR of VMI reconstructions at 40 kiloelectron volt (keV) and 60 keV were higher (P<0.001 to P=0.04). Noise was similar at 60 keV (all P>0.99) and increased at 40 keV (all P<0.001), and the SNR in arteries was increased at 60 keV (P<0.001 to P=0.02) in VMI reconstructions compared with those in the M_0.5-C images. The subjective scores in VMI reconstructions at 40 and 60 keV was higher than those in M_0.5-C images (all P<0.001). The image quality at 60 keV was superior to that at 40 keV (P<0.001), and there was no difference in the visualization of the perforators between 40 and 60 keV (P=0.31). VNC imaging is a reliable technique for replacing M_0.5-TNC and provides radiation dose saving. The image quality of the 40-keV and 60-keV VMI reconstructions was higher than that of the M_0.5-C images, and 60 keV provided the best assessment of perforators in the tibia.

Individualized Scan Protocol Based on Body Mass Index in Dual-Energy Computed Tomography Pulmonary Angiography to Reduce Radiation and Contrast Doses with Improved Image Quality.

BACKGROUND We evaluated an individualized dual-energy computed tomography (DECT) scan protocol by combining optimal monochromatic images with an appropriate ASIR-V reconstruction strength in computed tomography pulmonary angiography (CTPA) to reduce radiation and iodine doses and superior vena cava (SVC) artifacts. MATERIAL AND METHODS A total of 127 patients who underwent CTPA were prospectively enrolled and randomly divided into a standard (n=63) and individualized group (n=64). The standard group used 120 kVp, 150 mAs, and 60 mL contrast media at an injection rate of 5 mL/s; the individualized group used DECT imaging mode with tube current selected according to patients' BMI (BMI ≤20 kg/m², 200 mA; 20< BMI ≤23 kg/m², 240 mA; 23< BMI ≤25 kg/m², 280 mA; BMI >25 kg/m², 320 mA). Contrast media intake was 130 mgI/kg with an injection time of 7 s. The data in the individualized group was reconstructed to 55-70 keV (5 keV interval) monochromatic images combined with 40-80% ASIR-V (10% interval). Radiation dose, contrast dose, and image quality were compared between the groups. RESULTS There were no significant differences in patient habitus. Compared with the standard group, the individualized group significantly decreased radiation dose by 33.93% (3.31±0.57 mSv vs 5.01±0.34 mSv) and contrast dose by 56.95% (9.04±1.40 gI vs 21.00±0.00 gI). The 60 keV image with 80%ASIR-V in the individualized group provided the best image quality and further reduced SVC beam-hardening artifacts. CONCLUSIONS The use of BMI-dependent DECT protocol in CTPA further reduces radiation dose, contrast agent dose, and SVC artifacts, with the 60 keV images reconstructed using 80%ASiR-V having the best image quality.

Influence of Scan Parameters of Single and Dual-Energy CT Protocols in Combination with Metal Artifact Suppression Algorithms for THA: An ex Vivo Study.

Metal artifacts caused by hip arthroplasty stems limit the diagnostic value of computed tomography (CT) in the evaluation of periprosthetic fractures or implant loosening. The aim of this ex vivo study was to evaluate the influence of different scan parameters and metal artifact algorithms on image quality in the presence of hip stems. Nine femoral stems, 6 uncemented and 3 cemented, that had been implanted in subjects during their lifetimes were exarticulated and investigated after death and anatomical body donation. Twelve CT protocols consisting of single-energy (SE) and single-source consecutive dual-energy (DE) scans with and without an iterative metal artifact reduction algorithm (iMAR; Siemens Healthineers) and/or monoenergetic reconstructions were compared. Streak and blooming artifacts as well as subjective image quality were evaluated for each protocol. Metal artifact reduction with iMAR significantly reduced the streak artifacts in all investigated protocols (p = 0.001 to 0.01). The best subjective image quality was observed for the SE protocol with a tin filter and iMAR. The least streak artifacts were observed for monoenergetic reconstructions of 110, 160, and 190 keV with iMAR (standard deviation of the Hounsfield units: 151.1, 143.7, 144.4) as well as the SE protocol with a tin filter and iMAR (163.5). The smallest virtual growth was seen for the SE with a tin filter and without iMAR (4.40 mm) and the monoenergetic reconstruction of 190 keV without iMAR (4.67 mm). This study strongly suggests that metal artifact reduction algorithms (e.g., iMAR) should be used in clinical practice for imaging of the bone-implant interface of prostheses with either an uncemented or cemented femoral stem. Among the iMAR protocols, the SE protocol with 140 kV and a tin filter produced the best subjective image quality. Furthermore, this protocol and DE monoenergetic reconstructions of 160 and 190 keV with iMAR achieved the lowest levels of streak and blooming artifacts. Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Effect of contrast material injection protocol on first-pass myocardial perfusion assessed by dual-energy dual-layer computed tomography.

Dual-energy dual-layer computed tomography (CT) scanners can provide useful tools, such as iodine maps and virtual monochromatic images (VMI), for the evaluation of myocardial perfusion defects. Data about the influence of acquisition protocols and normal values are still lacking. Clinically indicated coronary CT-angiographies performed between January-October 2018 in a single university hospital with dual-energy dual-layer CT (DE-DLCT) and different injection protocols were retrospectively evaluated. The two protocols were: 35 mL in patients <80 kg and 0.5 mL/kg in patients >80 kg at 2.5 mL/s (group A) or double contrast dose at 5 mL/s (group B). Patients with coronary stenosis >50% were excluded. Regions of interest were manually drawn on 16 myocardial segments and iodine concentration was measured in mg/mL. Signal-to-noise, contrast-to-noise ratios (CNR) and image noise were measured on conventional images and VMI. A total of 30 patients were included for each protocol. With iodine concentrations of 1.38±0.41 mg/mL for protocol A and 2.07±0.73 mg/mL for protocol B, the two groups were significantly different (P<0.001). No significant iodine concentration differences were found between the 16 segments (P=0.47 and P=0.09 for group A and B respectively), between basal, mid and apical segments for group A and B (P=0.28 and P=0.12 for group A and B respectively) and between wall regions for group A (P=0.06 on normalised data). In group B, iodine concentration was significantly different between three wall regions [highest values for the lateral wall, median =2.03 (1.06) mg/mL]. Post-hoc analysis showed highest contrast-to-noise and signal-to-noise in VMI at 40 eV (P<0.05). Iodine concentration in left ventricular myocardium of patients without significant coronary artery stenosis varied depending on the injection protocol and appeared more heterogeneous in different wall regions at faster injection rate and greater iodine load. Signal-to-noise and contrast-to-noise gradually improved when decreasing VMI energy, although at the expenses of higher noise, demonstrating the potential of DE-DLCT to enhance objective image quality.

Dual-energy computed tomography: Survey results on current uses and barriers to further implementation.

To gauge the current availability of dual-energy computed tomography (DECT) scanners in the UK, establish available technologies, look broadly at current clinical uses in adults and paediatrics, and identify barriers to implementation and potential ways to increase use. A survey was distributed amongst 10 radiology departments and shared on two national professional co-operation mail bases; the survey ran from 20th July to 9th December 2020. It explored current DECT utilisation in adults and paediatrics as well as barriers to use and suggestions to overcome those barriers. The survey demonstrated DECT availability on 39 (40%) of the 98 CT scanners, but there was limited clinical use in adults and paediatrics. Eighteen (72%) of the 25 respondents had access to at least one DECT scanner, with 14 (56%) having adult DECT protocols in clinical use; <10% head examinations and <50% for other anatomical areas. Only two (8%) respondents had DECT paediatric protocols in clinical use; <10% examinations for all anatomical areas.The main barriers to implementation identified were lack of experience with DECT (8 (44%) users (adult) and 10 (56%) users (paediatric)) and no clinical protocols available (6 (33%) users (adult and paediatric)).Understanding DECT benefits and establishing suitable protocols were the most popular suggestions for increased implementation (10 (40%) of 25 respondents). DECT scanners are available, but clinical use is limited for both adults and paediatrics. The main barriers identified were lack of experience with DECT and the availability of suitable protocols. Further work identified to help implementation included better education on the benefits of DECT, provision of clinical protocols and ensuring a multidisciplinary approach. Barriers to implementation of clinical DECT protocols were identified, together with potential solutions to overcome these and enable further implementation.

Dual-energy computed tomography: Tube current settings and detection of uric acid tophi

PurposeTo derive optimal scanning parameters for single-source dual-energy computed tomography (DECT) in the detection of urate by analyzing influence of tube current ratio (TCR) and total radiation exposure in a phantom. MethodSpecimens with different urate concentrations in a realistic porcine bio-phantom were repeatedly imaged with sequential single-source DECT scans at 80 kVp (16.5–220 mA s) and 135 kVp (2.75–19.25 mA s). Detection index (DI - true positive minus false positive urate volume) was calculated for every possible tube current combination. Optimal tube current combinations reaching at least 85 % of the highest measured DI of all combinations without exceeding 150 % of equivalent single-energy radiation dose were identified. TCR, DLP and DI were plotted and compared. ResultsCubic regression analysis showed a flattening increase in the DI with increasing tube currents. Five out of the 100 tube current combinations analyzed achieved the detection target: the lowest DLP of 53.9 mGy*cm at 19.25/16.5 mAs (135/80 kVp) achieved a DI of 2.07 mL and the highest DI of 2.11 mL at a dose of 65.3 mGy*cm and 8.25/79.75 mAs. The optimal TCR is between two and four, while both, higher and lower ratios decreased DI. ConclusionsA minimum tube current of the high-energy scans is needed before an acceptable overall sensitivity is achieved and before increases in low-energy exposure result in more urate detection. High TCRs above 10 are not beneficial while the optimal TCR ranges between two and four, indicating that special care has to be taken in designing a suitable DECT protocol.

Quantitative accuracy and dose efficiency of dual-contrast imaging using dual-energy CT: a phantom study.

To evaluate the quantitative accuracy and dose efficiency of simultaneous imaging of two contrast agents using dual-energy computed tomography (DECT), two imaging tasks each representing one potential clinical application were investigated in a phantom study: biphasic liver imaging with iodine and gadolinium, and small bowel imaging with iodine and bismuth. To separate and quantify mixtures of two contrast agents using a single DECT scan, mixed iodine and gadolinium samples were prepared with the contrast enhancement values corresponding to the late arterial (iodine) and the portal-venous (gadolinium) phase for biphasic liver imaging. Mixed iodine and bismuth samples were prepared mimicking the arterial (iodine) and the enteric (bismuth) enhancement for small bowel imaging. For comparison to the reference condition of performing two single-energy CT (SECT) scans, contrast samples were preparedseparately to mimic separate scans in the arterial/venous phase and arterial/enteric enhancement. Samples were placed in a 35cm wide water tank and scanned using a third-generation dual-source DECT scanner with three tube potential pairs: 80/Sn150, 90/Sn150, and 100/Sn150kV, all with default dose partitioning between two x-ray beams to acquire DECT data. The same scanner operated in a single-energy mode acquired SECT data (120kV). Total radiation dose (CTDIvol) was matched for the single-scan DECT and the two-scan SECT protocols. The DECT protocol was followed by a generic image-based three-material decomposition method to determine the material-specific images, based on which concentrations of each basis material were quantified and noise levels were measured. To compare with the SECT images directly acquired with the SECT protocol, the concentration values in each contrast-specific image were converted to CT numbers at 120kV (i.e., virtual SECT (vSECT) images). The noise level and noise power spectra differences between the SECT and vSECT images were compared to evaluate the dose efficiency of the single-scan DECT protocol. The impact of dose partitioning in the DECT protocol on quantitative dual-contrast imaging performance was also studied. For each imaging task, contrast materials were accurately quantified against the nominal concentrations using the DECT data with strong correlation (R2 ≥0.98 for both imaging tasks). Compared to the SECT protocol, the DECT protocol was not dose efficient.With the optimal x-ray tube potential pair 80/Sn150kV, thenoise level in vSECT images increased by 401%/488%(arterial/portal-venous) for the biphasic liver imaging task and by 10%/41%(arterial/enteric) for the small bowel imaging task compared to that in SECT images. The corresponding radiation dose increase is2410%/3357% for the biphasic liver imaging taskand 21%/99% for the small bowel imaging task, respectively, to achieve the same noise as that in SECT images. This could be improved by adjusting the dose partitioning in DECT. DECT can be used to simultaneously separate and quantify two contrast materials. However, compared to a two-scan SECT protocol, much higher radiation dose is needed in a single-scan DECT protocol to achieve the same image noise, especially for tasks involving the dual contrast of iodineand gadolinium.

P015] Contrast of dual energy CT in carotid artery analysis, a phantom study

Purpose Dual Energy Computed Tomography (DECT) has high tissue characterization properties compared to traditional computed tomography (CT). In CT angiography (CTA), this property is important for analyzing the stage of atherosclerosis. The goal of this project was to study the significance of DECT technology in CTA especially for atherosclerosis diagnosis. Methods A self-made phantom was designed to model the neck area and carotid arteries. Main organs in the neck area were built by using various materials. Agar was used to mimic soft tissue, cattle bone to spine, empty plastic bottle to trachea, oil to lipid, and two small plastic tubes to mimic left and right carotid arteries. A human tooth was placed in the phantom to study the artefacts. The artery tubes contained water and diluted iodine as contrast agent. A 300 mg/ml iodine concentration was diluted to 6 mg/ml to meet the image contrast obtained in arteries of the patients using SECT CTA procedure. The phantom was then scanned with CTA SECT and DECT protocols. Images were analyzed using image processing tool. Results Image resulted from DECT show changes in material contrast compared to SECT. The contrast agent, bone, air and tooth have lower HU when scanned with DECT, while water, oil and agar show increased HU values. Improvement in oil contrast is highly visible on DECT image. The artefact from beam hardening effect caused by tooth and bone was reduced significantly by the DECT technology. Conclusions DECT seems to produce better image quality for studying carotid arteries than SECT. DECT images have higher material contrast and lower artefact from beam hardening effect. Both properties are important in atherosclerosis analysis.

Potential of gadolinium as contrast material in second generation dual energy computed tomography – An ex vivo phantom study

PurposeTo evaluate the potential of gadolinium (Gd) as contrast material (CM) in second generation dual energy computed tomography (DECT). Material and methodsIn a phantom model, DECT post-processing was used to increase Gd attenuation using advanced monoenergetic extrapolation (MEI), to create virtual non-contrast images (Gd-VNC) and Gd maps and to quantify Gd content. Dilutions of Gd and iodinated CM (7–296 HU) were filled in syringes, placed in an attenuation phantom and scanned with standard DECT protocols (80 &100/Sn140 kV). MEI (40–190 keV) and VNC images as well as Gd maps were computed. The amount of Gd was quantified and the accuracy was compared to iodine images. Linear regression models were calculated to evaluate Gd attenuation of equivolume CM doses and clinical MRI doses. ResultsApplying monoenergetic reconstructions and using Gd as contrast agent (Gd MEI 40 keV) doubled Hounsfield-Units (HU) and 90% of the SNR (averaged: 225 HU, SNR3.1) are achievable, as compared to iodinated CM at 120 kV (averaged:110 HU, SNR3.5), at Gd doses of 1.0mmol/kg BW. The accuracies of Gd-VNC (deviation, 6±12 HU) images and Gd quantification (measurement error, 17%) were not significantly different to those of iodine enhanced images (VNC:deviation, 2±11 HU; measurement error,14%). ConclusionUsing monoenergetic extrapolation at 40keV, it is possible to increase Gd-CM attenuation significantly. Thus, equivalent HU and half the SNR in comparison to a standard dose of ICM at 120kV can be expected at a Gd-CM dose of 0.5mmol/kg BW. Post-processing features of iodine based DECT like monoenergetic or VNC images, iodine maps or quantification of CM are feasible with the use of Gd-CM.

Clinical Implementation of Dual-energy CT for Proton Treatment Planning on Pseudo-monoenergetic CT scans

To determine whether a standardized clinical application of dual-energy computed tomography (DECT) for proton treatment planning based on pseudomonoenergetic CT scans (MonoCTs) is feasible and increases the precision of proton therapy in comparison with single-energy CT (SECT). To define an optimized DECT protocol, CT scan settings were analyzed experimentally concerning beam hardening, image quality, and influence on the heuristic conversion of CT numbers into stopping-power ratios (SPRs) and were compared with SECT scans with identical CT dose. Differences in range prediction and dose distribution between SECT and MonoCT were quantified for phantoms and a patient. Dose distributions planned on SECT and MonoCT datasets revealed mean range deviations of 0.3mm, γ passing rates (1%, 1mm) greater than 99.9%, and no clinically relevant changes in dose-volume histograms. However, image noise and CT-related uncertainties could be reduced by MonoCT compared with SECT, which resulted in a slightly decreased dependence of SPR prediction on beam hardening. Consequently, DECT was clinically implemented at the University Proton Therapy Dresden in 2015. Until October 2016, 150 patients were treated based on MonoCTs, and morethan 950 DECT scans of 351 patients were acquired during radiationtherapy. A standardized clinical use of MonoCT for treatment planning is feasible, leads to improved image quality and SPR prediction, extends diagnostic variety, and enables a stepwise clinical implementation of DECT toward a physics-based, patient-specific, nonheuristic SPR determination. Further reductions of CT-related uncertainties, as expected from such SPR approaches, can be evaluated on the resulting DECT patient database.

Dual-Energy Computed Tomography for the Characterization of Intracranial Hemorrhage and Calcification: A Systematic Approach in a Phantom System.

The aim of this study was to develop a diagnostic framework for distinguishing calcific from hemorrhagic cerebral lesions using dual-energy computed tomography (DECT) in an anthropomorphic phantom system. An anthropomorphic phantom was designed to mimic the CT imaging characteristics of the human head. Cylindrical lesion models containing either calcium or iron, mimicking calcification or hemorrhage, respectively, were developed to exhibit matching, and therefore indistinguishable, single-energy CT (SECT) attenuation values from 40 to 100 HU. These lesion models were fabricated at 0.5, 1, and 1.5 cm in diameter and positioned in simulated cerebrum and skull base locations within the anthropomorphic phantom. All lesion sizes were modeled in the cerebrum, while only 1.5-cm lesions were modeled in the skull base. Images were acquired using a GE 750HD CT scanner and an expansive dual-energy protocol that covered variations in dose (36.7-132.6 mGy CTDIvol, n = 12), image thickness (0.625-5 mm, n = 4), and reconstruction filter (soft, standard, detail, n = 3) for a total of 144 unique technique combinations. Images representing each technique combination were reconstructed into water and calcium material density images, as well as a monoenergetic image chosen to mimic the attenuation of a 120-kVp SECT scan. A true single-energy routine brain protocol was also included for verification of lesion SECT attenuation. Points representing the 3 dual-energy reconstructions were plotted into a 3-dimensional space (water [milligram/milliliter], calcium [milligram/milliliter], monoenergetic Hounsfield unit as x, y, and z axes, respectively), and the distribution of points analyzed using 2 approaches: support vector machines and a simple geometric bisector (GB). Each analysis yielded a plane of optimal differentiation between the calcification and hemorrhage lesion model distributions. By comparing the predicted lesion composition to the known lesion composition, we identified the optimal combination of CTDIvol, image thickness, and reconstruction filter to maximize differentiation between the lesion model types. To validate these results, a new set of hemorrhage and calcification lesion models were created, scanned in a blinded fashion, and prospectively classified using the planes of differentiation derived from support vector machine and GB methods. Accuracy of differentiation improved with increasing dose (CTDIvol) and image thickness. Reconstruction filter had no effect on the accuracy of differentiation. Using an optimized protocol consisting of the maximum CTDIvol of 132.6 mGy, 5-mm-thick images, and a standard filter, hemorrhagic and calcific lesion models with equal SECT attenuation (Hounsfield unit) were differentiated with over 90% accuracy down to 70 HU for skull base lesions of 1.5 cm, and down to 100 HU, 60 HU, and 60 HU for cerebrum lesions of 0.5, 1.0, and 1.5 cm, respectively. The analytic method that yielded the best results was a simple GB plane through the 3-dimensional DECT space. In the validation study, 96% of unknown lesions were correctly classified across all lesion sizes and locations investigated. We define the optimal scan parameters and expected limitations for the accurate classification of hemorrhagic versus calcific cerebral lesions in an anthropomorphic phantom with DECT. Although our proposed DECT protocol represents an increase in dose compared with routine brain CT, this method is intended as a specialized evaluation of potential brain hemorrhage and is thus counterbalanced by increased diagnostic benefit. This work provides justification for the application of this technique in human clinical trials.

Dual-Energy CT: Spectrum of Thoracic Abnormalities.

Recent studies have demonstrated that dual-energy computed tomography (CT) can provide useful information in several chest-related clinical indications. Compared with single-energy CT, dual-energy CT of the chest is feasible with the use of a radiation-dose-neutral scanning protocol. This article highlights the different types of images that can be generated by using dual-energy CT protocols such as virtual monochromatic, virtual unenhanced (ie, water), and pulmonary blood volume (ie, iodine) images. The physical basis of dual-energy CT and material decomposition are explained. The advantages of the use of virtual low-monochromatic images include reduced volume of intravenous contrast material and improved contrast resolution of images. The use of virtual high-monochromatic images can reduce beam hardening and contrast streak artifacts. The pulmonary blood volume images can help differentiate various parenchymal abnormalities, such as infarcts, atelectasis, and pneumonias, as well as airway abnormalities. The pulmonary blood volume images allow quantitative and qualitative assessment of iodine distribution. The estimation of iodine concentration (quantitative assessment) provides objective analysis of enhancement. The advantages of virtual unenhanced images include differentiation of calcifications, talc, and enhanced thoracic structures. Dual-energy CT has applications in oncologic imaging, including diagnosis of thoracic masses, treatment planning, and assessment of response to treatment. Understanding the concept of dual-energy CT and its clinical application in the chest are the goals of this article.

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We thank for these pleasant comments and are happy that the idea of dose-reduced computed tomography (CT) and CT-based compositional analysis of urinary stones is of importance for the editors of Urology. 1 Slater R.C. Jackman S.V. Focused dual-energy CT maintains diagnostic and compositional accuracy for urolithiasis using ultralow-dose noncontrast CT [Editorial Comment]. Urology. 2015; 86: 1097-1103 Abstract Full Text Full Text PDF PubMed Google Scholar New developments of imaging modalities have influenced different fields of medicine sustainably, including urolithiasis management. In many urology departments, CT has replaced radiography of kidney, ureter, and bladder as well as intravenous pyelogram almost completely in primary evaluation of renal colic patients. Over the years, the CT technology could be improved significantly due to bringing innovations such as dose-reduced protocols, shorter examination times, high-definition imaging, and in situ compositional analysis of the targeted stones. Our study was performed on 61 patients revealing high sensitivity and specificity in detection of clinically relevant uric acid- and non–uric acid-containing fragments. 1.We believe that similar results for sensitivity and specificity rates can be reproduced in other institutions using the highly dose-reduced noncontrast CT (NCCT) protocol including compositional analysis. The methods applied have been described in detail. We would be very pleased if other groups, wishing to decrease radiation exposure of urolithiasis patients, would join our efforts and work on related topics in collaborative projects. 2.In the German health care system, the radiologist is involved in the evaluation process of the CT results and decision making whether the dual-energy (DE) technology is applied. Because of this organization model, a significant decrease in radiation can be achieved. We are aware that this is not the case in many countries worldwide. As a consequence, this might be the crucial limitation in the acceptance of this approach in differently organized health care systems, where CT scans are not interpreted directly by a radiologist and the image acquisition is performed independently by excellently trained radiology technicians. We believe that diagnosing urolithiasis might be feasible for such personnel after professional training. Furthermore, these measures would make radiology technicians more familiar with the DE technology and novel CT protocols. In our opinion, the decision whether to use a targeted DE mode scan can also be taken by a radiology technician. In countries where legal issues prohibit such course of action, efforts should be undertaken to rearrange the workflow in radiology departments and establish a timely involvement of a radiologist in the CT scan evaluation in stone patients. 3.Conventional NCCT might provide reliable information regarding stone composition based on Hounsfield unit characteristics of a visualized fragment. However, this might not be accurate in many cases and leads to substantially higher patient radiation exposure. To our knowledge, it is not possible to determine the stone composition correctly while performing an NCCT according to an ultralow energy dose protocol. Therefore, an additional DE technology–based analysis has to be implemented. Applying our novel protocol, low-dose NCCT plus DE mode–based analysis of stone composition results in significantly lower cumulative radiation exposure and provides superior results at the same time. “Primum non nocere” (first, do no harm): We believe that this justifies potentially higher financial expenses and time. Editorial CommentUrologyVol. 86Issue 6PreviewThe authors provide a timely demonstration of an innovative low-dose noncontrast computed tomography (NCCT) plus dual-energy CT (DECT) protocol in reducing radiation exposure in the evaluation of patients presenting with urolithiasis while simultaneously maintaining accurate compositional analysis of such calculi.1 This protocol calls for patients to undergo an ultralow-dose NCCT followed by a focused dose-reduced noncontrast DECT. It was evaluated in 61 patients whose stones were available for chemical analysis. Full-Text PDF

Innovative CT acquisition technique for the detection of hepatic nodules: What is the dose delivered to the patient?

Introduction A Fast-kVp Switching (FKS) dual-energy and a routine adaptative iterative reconstruction (Adaptative Statistical Iterative Reconstruction, ASIR, GE Healthcare®) single-energy abdominal Computed Tomography (CT) protocols have been designed for hepatocellular carcinomas detection. Previous studies have shown that FKS exams can deliver a higher dose than standard exam with comparable image quality. This study aims to evaluate the dose delivered to patient exposed to these CT protocols. Material and methods Ten patients with 31 hepatocellular carcinomas underwent FKS dual-energy (80–140 kV; 630 mA, rotation time: 0.5 s pitch: 1.375) and single-energy abdominal contrast materialenhanced (120 kV, 150–650 mA, rotation time: 0.7 s pitch: 1.375, ASIR 50%, FBP 50%) CT exams with liver-arterial and portal venous phases. For each exam, image quality was judged qualitatively and quantitatively on arterial phase by radiologists. Radiation dose, based on Volume CT Index (CTDIVOL) and Dose Length Product (DLP) was reported using a Dose Archiving and Communication System (DACS) (DoseWatch, GE HealthCare®). Since only single energy abdominal protocol uses Automatic Exposure Control (AEC), all the results were classified according to patients Body Mass Index (BMI). Results Image quality, allowed the identification of 94% (29/31) of HCC nodules with adaptative iterative reconstruction single-energy exam and 97% (30/31) with FKS dual-energy protocol. A CTDIVOL of 13 mGy and a mean DLP of 393 mGy.cm were determined for the dual energy protocol whathever BMI. Whereas, for the routine exam, mean CTDIVOL and DLP were 7 mGy, 215 mGy cm; 14 mGy, 454 mGy cm and 18 mGy, 783 mGy cm for BMIs less than 20, of 20–25 and greater than 25 BMI, respectively. Conclusion FKS dual-energy and adaptative iterative reconstruction single-energy abdominal CT protocols can be optimized so as to deliver a radiation dose lower than swiss dose reference level (15 mGy, 500 mGy cm) without neglecting image quality. Current FKS dual energy protocol could be optimized since it now uses adaptive iterative reconstruction. Moreover, it could be adapted to low BMI patients.

Evaluation of Silent Thrombus after the Fontan Operation

Thromboembolic complications have been noted after the Fontan operation. However, the prevalence of silent events among an adult contemporary population is not known. Noninvasive screening by any method including computed tomography (CT) has been technically limited to date. The objective of this study was to evaluate a novel dual-energy CT (DECT) protocol in determining the prevalence of "silent" intracardiac thrombus and thrombus in the Fontan and pulmonary circulations among adults after the Fontan operation. All post-Fontan patients attending the Pacific Adult Congenital Heart Clinic were approached for study participation. Those agreeable underwent a full clinical assessment, cardiopulmonary stress testing, transthoracic echocardiogram, and DECT low kilovoltage imaging protocol. Twenty-three patients were included in the study (30 ± 10 years, 26% women). Three (13%) patients had evidence of silent thrombi detected on DECT. All three of these patients had an extracardiac conduit and mural thrombus was found within the conduit. Older age at the time of the Fontan operation was associated with the presence of thrombus (21 ± 14 vs. 11 ± 6 years, P =.05). Thirteen percent of adult patients post-Fontan procedure have clinically silent thrombi. These were all found among patients with an extracardiac conduit traditionally thought to be at low risk for thromboembolism. Given the significant risk of thromboembolic complications, large randomized prospective studies looking at anticoagulation therapy in all Fontan patients are urgently needed. In the meanwhile, given the important rate of silent thrombi, a systematic robust screening protocol that includes noninvasive low radiation methods such as DECT methods should be considered.

Urinary Calculi Composed of Uric Acid, Cysteine, and Mineral Salts: Differentiation with Dual-energy CT at a Radiation Dose Comparable to that of Intravenous Pyelography

Low-dose unenhanced computed tomography (CT) is usually the modality of choice when evaluating for the presence of nephrolithiasis. Although CT can provide information regarding the size of a stone, its location, and potential complications such as hydronephrosis, there is no way to evaluate the composition of the stone. This retrospective study from Germany evaluated the use of a low-dose dual-energy CT protocol combined with commercially available software to distinguish the composition of various stones (uric acid, calcium, struvite, or cysteine).

Dual-Energy Computed Tomography to Assess Tumor Response to Hepatic Radiofrequency Ablation

to determine the value of dual-energy (DE) scanning with virtual noncontrast (VNC) images and iodine maps in the evaluation of therapeutic response to radiofrequency ablation (RFA) for hepatic tumors. a total of 75 patients with hepatic tumors and who underwent DE computed tomography (CT) after RFA, were enrolled in this study. Our DE CT protocol included precontrast, arterial, and portal phase scans. VNC images and iodine maps were created from 80 to 140 kVp images during the arterial and portal phases. VNC images were then compared with true, noncontrast (TNC) images, and iodine maps were compared with linearly blended images, both qualitatively and quantitatively. For the former comparison, image quality and acceptability of the VNC images as a replacement for TNC images were both rated. The CT numbers of the hepatic parenchyma, ablation zone, and image noise were measured. For the latter comparison, lesion conspicuity of the ablation zone and the additional benefit of integrating the iodine map into the routine protocol, were assessed. Contrast-to-noise ratios (CNR) of the ablation zone-to-liver and aorta-to-liver as well as the CT number differences between the center and the periphery of the ablation zone were calculated. The image quality of the VNC images was rated as good (mean grading score, 1.88) and the level of acceptance was 90% (68/75). The mean CT numbers of the hepatic parenchyma and ablation zone did not differ significantly between the TNC and the VNC images (P > 0.05). The lesion conspicuity of the ablation zone was rated as excellent or good in 97% of the iodine map (73/75), and the additional benefits of the iodine maps were positively rated as better to the same (mean 1.5). The CNR of the aorta-to-liver parenchyma was significantly higher on the iodine map (P = 0.002), and the CT number differences between the center and the periphery of the ablation zone were significantly lower on the iodine map (P < 0.001). with DE CT scanning, VNC images can be an alternative to TNC images for evaluating the ablation zone after RFA in patients who had no a previous transcatheter arterial chemoembolization history. The iodine map improves the conspicuity of the ablation zone more than linearly blended images because of its excellent internal homogeneity and sharp ablative margin. Higher lesion-to-liver CNR on an iodine map than on standard images can be helpful for detecting residual tumors.

Urinary Calculi Composed of Uric Acid, Cystine, and Mineral Salts: Differentiation with Dual-Energy CT at a Radiation Dose Comparable to That of Intravenous Pyelography

To retrospectively evaluate radiation dose, image quality, and the ability to differentiate urinary calculi of differing compositions by using low-dose dual-energy computed tomography (CT). The institutional review board approved this retrospective study; informed consent was waived. A low-dose dual-energy CT protocol (tube voltage and reference effective tube current-time product, 140 kV and 23 mAs and 80 kV and 105 mAs; collimation, 64 × 0.6 mm; pitch, 0.7) for the detection of urinary calculi was implemented into routine clinical care. All patients (n = 112) who were examined with this protocol from July 2008 to August 2009 were included. The composition of urinary calculi was assessed by using commercially available postprocessing software and was compared with results of the reference standard (ex vivo infrared spectroscopy) in 40 patients for whom the reference standard was available. Effective doses were calculated. Image quality was rated subjectively and objectively and was correlated with patient size expressed as body cross-sectional area at the level of acquisition by using Spearman correlation coefficients. One calcified concrement in the distal ureter of an obese patient was mistakenly interpreted as mixed calcified and uric acid. One struvite calculus was falsely interpreted as cystine. All other uric acid, cystine, and calcium-containing calculi were correctly identified by using dual-energy CT. The mean radiation dose was 2.7 mSv. The average image quality was rated as acceptable, with a decrease in image quality in larger patients. Low-dose unenhanced dual-source dual-energy CT can help differentiate between calcified, uric acid, and cystine calculi at a radiation dose comparable to that of conventional intravenous pyelography. Because of decreased image quality in obese patients, only nonobese patients should be examined with this protocol.