Dual-energy CT Scans Research Articles

Dual-Energy Computed Tomography in Thoracic Imaging-Current Practices and Utility: Survey of the Society of Thoracic Radiology.

The purpose of this study was to determine the current practice patterns of utilization of dual-energy computed tomography (DECT) in thoracic imaging. In this IRB-approved study, the URL link for an anonymous 26-question survey was sent by email to all the members of the Society of Thoracic Radiology (STR). Survey questions focused on the practice type, case volume, DECT scanner availability, common indications, image types, and perceived utility of DECT. Study data were collected and managed using SurveyMonkey tools and analyzed with χ tests. The survey response rate was 11% (104/962). DECT was available in 75% of respondents' institutions, with 90% of these having 1 to 5 DECT scanners (P<0.001). Seventy percent performed 1 to 500 DECT chest CTs per month (P<0.001). Dual-source was the most common DECT scanner (81%) (P=0.239). DECT was opted depending on the clinical indication in 89% (P=0.433). The technologist reconstructs the additional DECT images in 75% of instances (P<0.001). Acute pulmonary embolism (PE) was the most common indication of DECT (53%) (P=0.006), while chronic PE was considered the most valuable use of DECT (33%) (P<0.001). Iodine map was the most commonly used DECT image (53%) (P<0.001) followed by low-energy virtual monoenergetic image (VMI) (29%). For VMI, 50 keV was the most commonly used energy level for improving vascular contrast (43%) (P=0.048), whereas 120 keV was the most commonly used energy in VMI for decreasing artifacts (25%) (P=0.027). There is wide variability on the utilization of DECT in thoracic imaging. PE is perceived to be the most valuable utility of DECT, and iodine map is considered the most valuable DECT image.

Optimal energy selection for proton stopping-power-ratio estimation using dual-energy CT-based monoenergetic imaging

The dual-energy computed tomography (DECT)-based approach holds promise in reducing the overall uncertainty in proton stopping-power-ratio (SPR) estimation, but cannot be easily implemented with most commercial proton treatment planning systems (TPS). In this study, we revisited the idea of coupling the stoichiometric calibration method with virtual monoenergetic CT datasets (MonoCT) generated by modern DECT scanners, because of its readiness for implementation with the existing TPS. Our objective was to determine the optimal energy of the MonoCT dataset for stoichiometric calibration and estimate the overall uncertainty in SPR estimation at the optimal energy. We performed stoichiometric calibration for MonoCT datasets across the energy range available on a Siemens Force DECT scanner and a Philips IQon DECT scanner in a 10 keV step. We estimated the uncertainties of different sources (imaging, modeling, and inherent uncertainties) for different tissue types (lung, soft, and bone tissues) associated with each energy; these were then combined into a single composite uncertainty for three tumor sites (head-and-neck (HN), lung, and prostate). The optimal energy was eventually selected based on the composite range uncertainty, which turned out to be 160 keV for both DECT scanners. At 160 keV, the total uncertainties (2σ) in SPR estimation were determined to be 3.2%–4.5%, 0.9%, and 1.4%–1.6% for lung, soft, and bony tissues, respectively. These results were comparable to the corresponding values estimated for the DECT approach evaluated in our previous study: 3.8%, 1.2% and 2.0%, for lung, soft, and bony tissues, respectively. The composite range uncertainties (2σ) were estimated as 1.5%, 1.7%, and 1.5% for prostate, lung, and HN, respectively. Our results demonstrated the potential of MonoCT images for reducing proton SPR uncertainty. Further clinical studies are needed to compare this approach with the DECT approach directly on real patient cases.

Establishment of a novel system for the preoperative prediction of adherent perinephric fat (APF) occurrence based on a multi-mode and multi-parameter analysis of dual-energy CT.

Adherent perinephric fat (APF) is evaluated preoperatively with the Mayo adhesive probability (MAP) scoring system using conventional single-form computed tomography (CT) images. An objective or quantitative indicator for predicting APF is urgently needed for clinical application. A total of 150 patients with renal tumours who underwent laparoscopic partial nephrectomy (LPN) were retrospectively enrolled and divided into the APF group (n=100) and the non-APF group (n=50) according to surgical results. All patients underwent a renal contrast-enhanced dual-energy CT (DECT) scan. The obtained CT DICOM data were transmitted to the DECT post-processing workstation and adopted virtual non-contrast (VNC), Rho/Z Maps, and Monoenergetic Plus (mono+) modes separately to undergo a multi-parameter analysis. A logistic stepwise investigation was utilized to analyse the related risk factors. The cutoff value was determined by the Youden index. Fifty patients were prospectively enrolled to validate the constructed model. The area under the curve (AUC), sensitivity, specificity and accuracy of the model were calculated. The study demonstrated that age, sex, body mass index (BMI), smoking status, tumour diameter, exophytic status, degree of malignancy and posterior perinephric fat thickness were related to the occurrence of APF (P<0.05). Model 1 was selected with the contrast material (CM) parameter (cutoff point 0.5), model 2 was selected with the effective atomic number (Zeff) parameter (cutoff point 6.5), and model 3 was selected with the slope K (K) parameter (cutoff point -0.95). The AUC, sensitivity, specificity and accuracy of model 1 were 0.94, 0.94, 0.93 and 0.94, respectively; for model 2, they were 0.94, 0.93, 0.93 and 0.96, respectively; and for model 3, they were 0.92, 0.92, 0.93 and 0.92, respectively. Multi-mode and multi-parameter models of DECT can effectively be used to predict the occurrence of APF.

Crowned Dens Syndrome Illustrated by Dual Energy Computed Tomography Scan.

Crowned Dens Syndrome Illustrated by Dual Energy Computed Tomography Scan.

Feasibility of Single Post-Contrast Dual-Energy CT for Pediatric Treatment Planning and Dose Calculation

Standard practice requires a separate non-contrast scan for dose calculation, especially for proton therapy, when iodinated contrast is administered during CT simulation. Based on the observation that the presence of iodine strongly affects the Hounsfield unit (HU) more than electron density (ED), we hypothesized that information derived from post-contrast dual-energy CT (DECT) would alone suffice for accurate dose calculation in both photon and proton therapy. Ten pediatric patients with abdominal tumors received DECT scans before and after iodinated contrast administration for treatment planning. In addition to HU images, ED images were generated for direct photon dose calculation and also combined with effective atomic number images to form stopping power ratio (SPR) images for direct proton dose calculation. Dose distributions of DECT-based methods (i.e., direct calculation) were compared to those of conventional calibration curve methods that map HU to ED and SPR. Both 7-field coplanar photon and 2-field posterior oblique SFUD/MFO treatment plans were simulated for each patient using pre- and post-contrast scans. For photon plans, conventional and DECT approaches based on post-contrast scans underestimated PTV D99 by 0.87±0.70% (p=0.18) and 0.36±0.31% (p=0.34), respectively. Iodine concentration in kidneys was weakly associated with the deviation in D99 for the conventional method (R2=0.10) and DECT (R2=0.02). For proton plans, the errors in CTV D99 were 3.67±2.43% (p=0.0001) and 0.30±0.25% (p=0.40) for conventional and DECT approaches, respectively. Changes to the proton beam range were quite noticeable in the conventional approach. Iodine concentration in kidneys was also highly associated with the D99 deviation for the conventional approach (R2=0.83) while no association existed for DECT (R2=0.007). Compared to true non-contrast plans, the presence of iodine contrast on conventional CT resulted in a large dosimetric error for proton therapy, but to a lesser degree for photon therapy. These errors can be greatly reduced if ED and SPR derived from DECT are used instead, which opens the possibility of using only single post-contrast CT for RT simulation and dose calculation with a lesser imaging dose to younger children.Abstract 3670; Table 1Patient #DiagnosisDisease SiteAge (y)Renal Iodine Uptake (mg/ml)Proton PlanningPhoton PlanningCONV CT ΔD99 (%)DECT ΔD99 (%)CONV CT ΔD99 (%)DECT ΔD99 (%)1NeuroblastomaAdrenal (L)132.391.10.11.40.92NeuroblastomaAdrenal (L)62.462.50.10.20.13NeuroblastomaAdrenal (L)53.101.20.40.40.14NeuroblastomaAdrenal (R)43.312.80.20.50.25NeuroblastomaAdrenal (L)63.371.80.81.50.96NeuroblastomaAdrenal (R)43.392.30.20.60.17NeuroblastomaAdrenal (R)114.564.10.70.20.28Hodgkin LymphomaRetroperitoneal L.N.204.746.50.20.40.59Hodgkin LymphomaPorta Hepatis L.N.114.837.30.11.20.310RhabdomyosarcomaPara-Aortic L.N.185.337.10.22.30.3Avg.N/AN/A9.83.753.70.30.90.4 Open table in a new tab

A Single Enhanced Dual-Energy CT Scan May Distinguish Lung Squamous Cell Carcinoma From Adenocarcinoma During the Venous phase

To investigate whether iodine quantification extracted from enhanced dual energy-computed tomography (DE-CT) is useful for distinguishing lung squamous cell carcinoma from adenocarcinoma and to evaluate whether a single scan evaluated during the venous phase (VP) can be substituted for scans evaluated during other phases. Sixty-two patients with lung cancer (32 squamous cell carcinomas; 30 adenocarcinomas) underwent enhanced dual-phase DE-CT scans, including an arterial phase and VP. The iodine concentration (IC), normalized iodine concentration (NIC), and slope of the curve (K) in lesions were measured during two scanning phases in two different pathological types of lung cancers. The differences in parameters (IC, NIC, and K) between these two types of lung cancers were statistically analyzed. In addition, the receiver operating characteristic curves of these parameters were performed to discriminate squamous cell carcinoma from adenocarcinoma. The mean IC, NIC, and K in adenocarcinomas were all higher than those in squamous cell carcinomas during the two scanning phases. However, the differences in these parameters between the two types of cancers were significant only during the VP, not during the arterial phase. Receiver operating characteristic analysis demonstrated that the optimal thresholds of the IC, NIC, and K for discriminating squamous cell carcinoma from adenocarcinoma were 1.550, 0.227, and 1.608, respectively. In addition, the sensitivity, specificity, and area under the curve were 81.2%, 83.3%, and 0.871 for the IC; 56.2%, 93.3%, and 0.800 for the NIC; and 65.6%, 80%, and 0.720 for the K; 81.3%, 83.3%, and 0.874 for the IC + NIC; 68.8%, 93.3%, and 0.891 for the IC + NIC + K, respectively. The "IC + NIC + K" had the highest diagnostic efficiency for discriminating two types of lung cancers, but with low sensitivity. Whereas, "IC"and "IC + NIC" had the similar lower diagnostic efficiency, but with high sensitivity and specificity. The iodine quantification parameters derived from enhanced DE-CT during the VP may be useful for distinguishing lung squamous cell carcinoma from adenocarcinoma.

Effects of Allopurinol Dose Escalation on Bone Erosion and Urate Volume in Gout: A Dual-Energy Computed Tomography Imaging Study Within a Randomized, Controlled Trial.

To examine whether allopurinol dose escalation to achieve serum urate (SU) target can influence bone erosion or monosodium urate (MSU) crystal deposition, as measured by dual-energy computed tomography (DECT) in patients with gout. We conducted an imaging study of a 2-year randomized clinical trial that compared immediate allopurinol dose escalation to SU target with conventional dosing for 1 year followed by dose escalation to target, in gout patients who were receiving allopurinol and who had an SU level of ≥0.36 mmoles/liter. DECT scans of feet and radiographs of hands and feet were obtained at baseline, year 1, and year 2 visits. DECT scans were scored for bone erosion and urate volume. Paired imaging data were available for 87 patients (42 in the dose-escalation group and 45 in the control group). At year 2, the progression in the CT erosion score was higher in the control group than in the dose-escalation group (+7.8% versus +1.4%; P = 0.015). Changes in plain radiography erosion or narrowing scores did not differ between groups. Reductions in DECT urate volume were observed in both groups. At year 2, patients in the control group who had an SU level of <0.36 mmoles/liter and patients in the dose-escalation group had reduced DECT urate volume (-27.6 to -28.3%), whereas reduction in DECT urate volume was not observed in control group patients with an SU level of ≥0.36 mmoles/liter (+1.5%) (P = 0.023). These findings provide evidence that long-term urate-lowering therapy using a treat-to-SU-target strategy can influence structural damage and reduce urate crystal deposition in gout.

Dual-Energy CT and Radiation Dose

As dual-energy CT scanners become more common, it is worth revisiting their benefits over conventional CT. The promises to increase the conspicuity of pathology and assist in differentiating tissue are much touted, but how can we realize the benefits of radiation dose reduction [1Grajo J.R. Sahani D.V. Dual-energy CT of the abdomen and pelvis: radiation dose considerations.J Am Coll Radiol. 2018; 15: 1128-1132Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar]? This article will briefly discuss the technology of dual-energy CT scanners, review some of the practical applications, and discuss the potential benefits and shortcomings of dose reduction. The principle behind dual-energy CT is that scanning at two different kilovoltage peaks allows determination of attenuation curves of tissue. This can be accomplished through several different methods, including fast kilovoltage switching with single-source and single-detector, dual-layer detectors with one source, or dual detectors with dual-source, or dual-detector offset 90° from each other. The spectral information can be used to generate standard CT images in addition to mono-energetic reformats (often chosen slightly higher than the k-edge of iodine to increase conspicuity of enhancement; Fig. 1), virtual noncontrast images (Fig. 2), perfusion-like imaging (iodine-only images) [2Weidman E.K. Plodkowski A.J. Halpenny D.F. et al.Dual-energy CT angiography for detection of pulmonary emboli: incremental benefit of iodine maps.Radiology. 2018; 289: 546-553Crossref PubMed Scopus (53) Google Scholar], as well as other niche benefits to identify elements by k-edge and z-effective techniques (such as uric acid in gout) [3Glazebrook K.N. Guimaraes L.S. Murthy N.S. et al.Identification of intraarticular and periarticular uric acid crystals with dual-energy CT: initial evaluation.Radiology. 2011; 261: 516-524Crossref PubMed Scopus (189) Google Scholar]. Further applications of mono-energetic selection at higher kilovoltage may allow for reduced streak artifact from beam hardening in the case of orthopedic prostheses or other hardware [4Bamberg F. Dierks A. Nikolaou K. Reiser M.F. Becker C.R. Johnson T.R. Metal artifact reduction by dual energy computed tomography using monoenergetic extrapolation.Eur Radiol. 2011; 21: 1424-1429Crossref PubMed Scopus (423) Google Scholar].Fig 2Traditional (A), virtual noncontrast (B), and iodine-only (C) reformats of a CT abdomen/pelvis with intravenous contrast. Indeterminate density right renal lesion (arrows). Circle region of interest on lesion with measurements of Area (A/Ar), Perimeter (P/Perim), Mean attenuation (M/Av), and Standard Deviation of attenuation (SD). Virtual noncontrast image shows similar density to traditional scan and iodine-only image shows no enhancement, confirming benign cyst.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Some of these benefits translate well into radiation dose reduction. The virtual noncontrast imaging at times permits removing a whole phase of imaging, as with renal or angiographic imaging. This could cut the dose in half for some studies. Furthermore, if the mono-energetic imaging is sufficient to salvage a poorly timed contrast bolus, this may spare a patient from needing to return for repeat imaging, reducing dose to the patient and delay in care. Yet, in other ways, the dual-energy CT scanner is similar to a traditional scanner. Simply substituting a dual-energy CT scanner for a conventional scanner will not reduce dose. Automatic exposure compensation works in the same way as on a traditional scanner, and though there are additional tools at the radiologist’s disposal as described previously, the intrinsic radiation exposure will be similar. The responsibility remains with the radiologist to act as steward of diagnostic medical radiation and determine if the advantages of dual-energy CT permit a dose reduction. If protocols are not adapted to remove the noncontrast phase, optimal dose savings will not be realized. If practices do not elect to reduce dose to offset the other benefits of dual-energy imaging, dose will remain the same. The responsibility falls to the radiologist to decide conscientiously how to reduce radiation dose in keeping with the principles of “as low as reasonably allowable” and the efforts of groups like Image Wisely and Image Gently. Dual-energy CT empowers us to re-assess imaging protocols in a new light and optimize patient care.

Noise reduction in dual-energy computed tomography virtual monoenergetic imaging.

PurposeVirtual monoenergetic images (VMIs) derived from dual‐energy computed tomography (DECT) have been explored for several clinical applications in recent years. However, VMIs at low and high keVs have high levels of noise. The aim of this study was to reduce image noise in VMIs by using a two‐step noise reduction technique.MethodsVMI was first denoised using a modified highly constrained backprojection (HYPR) method. After the first‐step denoising, a general‐threshold filtering method was performed. Two sets of anthropomorphic phantoms were scanned with a clinical dual‐source DECT system. DECT data (80/140Sn kV) were reconstructed as VMI series at 12 different energy levels (range, 40‐150 keV, interval, 10 keV). For comparison, the averaged VMIs obtained from 10 repeated DECT scans were used as the reference standard. The signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR) and root‐mean‐square error (RMSE) were used to evaluate the quality of VMIs.ResultsCompared to the original HYPR method, the proposed two‐step image denoising method could provide better performance in terms of SNR, CNR, and RMSE. In addition, the proposed method could achieve effective noise reduction while preserving edges and small structures, especially for low‐keV VMIs.ConclusionThe proposed two‐step image denoising method is a feasible method for reducing noise in VMIs obtained from a clinical DECT scanner. The proposed method can also reduce edge blurring and the loss of intensity in small lesions.

Application value of dual-energy computed tomography spectrum curve combined with clinical risk factors in predicting adherent perinephric fat.

Adherent perinephric fat (APF) is evaluated preoperatively with the Mayo adhesive probability (MAP) scoring system using conventional single form computed tomography (CT) images. An objective or quantitative indicator for predicting APF is urgently needed for clinical application. Data obtained from 150 renal tumor patients with partial nephrectomy (PN) were used in the present study. Patients were divided into two groups based on the surgical results: an APF group (n=100) and a non-APF group (n=50). All patients had renal contrast-enhanced dual-energy CT (DECT) scan, and the data were brought into a post-processing workstation. Monoenergetic plus mode was adopted to analyze the spectrum curve of the region of interest (ROI). Logistic stepwise relapse investigation was utilized to analyze the related risk factors. The maximum Youden index was taken as the cut-off value. The sensitivity, specificity, accuracy, and 95% CI of the model were calculated. APF is related to patients' clinical characteristics of age, gender, BMI, smoking, tumor diameter, exophytic, and benign or malignant nature of the renal masses (P<0.05). The shape of the curve of ROI1 in the APF group was different from that of the ROI4 in the non-APF group, and the curve slope of K1 (-0.21±0.47) was different from that of K4 (-1.30±0.14) (P<0.001). Statistical analysis showed that the slope K was solely retained in the model index. The best cut-off point for the K value was -0.95. The AUC of the cut-off point was 0.97 (95% CI: 0.96-0.99). The DECT spectrum curve performed well in predicting APF, and the curve slope K can be used as an objective quantitative indicator.

Iodine-based Dual-Energy CT of Traumatic Hemorrhagic Contusions: Relationship to In-Hospital Mortality and Short-term Outcome.

BackgroundTraumatic hemorrhagic contusions are associated with iodine leak; however, quantification of leakage and its importance to outcome is unclear.PurposeTo identify iodine-based dual-energy CT variables that correlate with in-hospital mortality and short-term outcomes for contusions at hospital discharge.Materials and MethodsIn this retrospective study, consecutive patients with contusions from May 2016 through January 2017 were analyzed. Two radiologists evaluated CT variables from unenhanced admission head CT and follow-up head dual-energy CT scans obtained after contrast material-enhanced whole-body CT. The outcomes evaluated were in-hospital mortality, Rancho Los Amigos scale (RLAS) score, and disability rating scale (DRS) score. Logistic regression and linear regression were used to develop prediction models for categorical and continuous outcomes, respectively.ResultsThe study included 65 patients (median age, 48 years; interquartile range, 25-65.5 years); 50 were men. Dual-energy CT variables that correlated with mortality, RLAS score, and DRS score were iodine concentration, pseudohematoma volume, iodine quantity in pseudohematoma, and iodine quantity in contusion. The single-energy CT variable that correlated with mortality, RLAS score, and DRS score was hematoma volume at follow-up CT. Multiple logistic regression analysis after inclusion of clinical variables identified two predictors that enabled determination of mortality: postresuscitation Glasgow coma scale (P-GCS) (adjusted odds ratio, 0.42; 95% confidence interval [CI]: 0.2, 0.86; P = 0.01) and iodine quantity in pseudohematoma (adjusted odds ratio, 1.4 per milligram; 95% CI: 1.02 per milligram, 1.9 per milligram; P = 0.03), with a mean area under the receiver operating characteristic curve of 0.96 ± 0.05 (standard error). For RLAS, the predictors were P-GCS (mean coefficient, 0.32 ± 0.06; P < .001) and iodine quantity in contusion (mean coefficient, -0.04 per milligram ± 0.02; P = 0.01). Predictors for DRS were P-GCS (mean coefficient, -1.15 ± 0.27; P < .001), age (mean coefficient, 0.13 per year ± 0.04; P = .002), and iodine quantity in contusion (mean coefficient, 0.19 per milligram ± 0.07; P = .02).ConclusionIodine-based dual-energy CT variables correlate with in-hospital mortality and short-term outcomes for contusions at hospital discharge.© RSNA, 2019Online supplemental material is available for this article.See also the editorial by Talbott and Hess in this issue.

Development and validation of a quantitative method for estimation of the urate burden in patients with gouty arthritis using dual-energy computed tomography.

To develop a method that allows approximating the mass of monosodium uric acid (MSU) in a gouty tophus using phantom measurements and including tophus density into the calculation of the dual-energy computed tomography (DECT) tophus volumetry. We prepared specimens of different concentrations of MSU placed in an epoxy-based phantom and an excised porcine foreleg. Density and volumetric measurements were performed in sequential single-source DECT scans acquired with increasingly higher tube currents. We developed a method for estimating the tophus mass by multiplying the detected tophus volume with its mean density and adding a specific gravimetric coefficient k. k was derived from the DECT scans by comparing the approximated MSU masses in the epoxy phantom with the known true MSU masses of the specimens. Comparison of the approximated MSU masses in the porcine foreleg scans with the true MSU masses of the syringe contents showed similar performance to sole volume measurement while providing additional information on the true uric acid burden: Over 70% of the true urate masses have been detected in MSU concentrations ≥ 45%, while the detection rate was much lower for MSU concentrations ≤ 40%. Retrospective analysis of patients with proven gouty arthritis confirmed the diagnostic potential of the mass approximation technique. We successfully established a method to include tophus density measurement for estimation of the uric acid burden in milligrams (instead of ml) in a phantom setting for MSU concentrations above 40%. Future studies should validate its use for follow-up in clinical practice. • Including tophus density measurement in dual-energy computed tomography scans in a phantom setting can be used for estimating the urate burden in milligrams, which might be useful for imaging follow-up. • The mass [mg] of the uric acid burden in a patient with gouty arthritis can be calculated by multiplying volume [ml] with mean density [HU] using a specific gravimetric coefficient. • Retrospective analysis of two patients with gouty tophi showed the relevance of measuring urate mass in addition to urate volume alone.

Evaluation of the chemical composition of nephrolithiasis using dual-energy CT in Southern Chinese gout patients

BackgroundA study to evaluate the prevalence of uric acid (UA) nephrolithiasis with dual-energy CT (DECT) and explore the risk factors for kidney stones in primary gout patients.MethodsEighty-four consecutive gout patients underwent urinary tract ultrasonography or DECT to confirm the existence of kidney stones. Urine and blood samples were also taken for laboratory analysis.ResultsForty-one subjects (48.8%) had nephrolithiasis diagnosed; 38 had a kidney stone. Thirty-two of the 38 patients underwent a DECT scan, and 27 patients had nephrolithiasis in DECT. Among them, 63.0% (17/27) and 14.8% (4/21) of the patients had pure UA and UA-based mixed stone, respectively, and 22.2% (6/27) had a non-UA stone. Those with nephrolithiasis suffered from more frequent acute attacks and had longer disease durations of gout. At least one urine biochemical abnormality was found in 81% of patients. Forty-four (55.0%) patients presented hypomagnesuria. Forty-three (51.8%) patients had low urine volume. Unduly acidic urine (UAU) was present in 36 patients (44.4%). Hyperuricosuria was only found in ten (12.2%) patients. In comparison to the non-lithiasic group, the lithiasic group was more likely to have a UAU. Binary logistic regression showed that female gender was a protective factor, while disease duration of gout and low urine pH were risk factors for nephrolithiasis.ConclusionOur results indicated that nephrolithiasis, especially UA stones, were more common than previous reports in gout patients indicated, and that disease duration of gout, and low urine pH, were risk factors for nephrolithiasis.

Dual-Energy Computed Tomography to Assess Intra- and Inter-Patient Tissue Variability for Proton Treatment Planning of Patients With Brain Tumor

Range prediction in particle therapy is associated with an uncertainty originating from calculating the stopping-power ratio (SPR) based on x-ray computed tomography (CT). Here, we assessed the intra- and inter-patient variability of tissue properties in patients with primary brain tumor using dual-energy CT (DECT) and quantified its influence on current SPR prediction. For 102 patients' DECT scans, SPR distributions were derived from a patient-specific DECT-based approach (DirectSPR). The impact of soft tissue diversity and age-related variations in bone composition on SPR were assessed. Tissue-specific and global deviations between this method and the state-of-the-art CT-number-to-SPR conversion applying a Hounsfield look-up table (HLUT) were quantified. To isolate systematic deviations between the two, the HLUT was also optimized using DECT information. An intra-patient ± inter-patient soft tissue diversity of 5.6% ± 0.7% in SPR (width of 95% confidence interval) was obtained including imaging- and model-related variations of up to 2.9%. This intra-patient SPR variability is associated with a mean absolute SPR deviation of 1.2% between the patient-specific DirectSPR approach and an optimal HLUT. Between adults and children younger than 6 years, age-related variations in bone composition resulted in a median SPR difference of approximately 5%. Accurate patient-specific DECT-based stopping-power prediction allows for improved handling of tissue mixtures and can intrinsically incorporate most of theSPR variability arising from tissue mixtures as well as inter-patient and intra-tissue variations. Since the state-of-the-art HLUT-even after cohort-specific optimization-cannot fully consider the broad tissue variability, patient-specific DECT-based stopping-power prediction is advisable in particle therapy.

Concurrent validity of provisional remission criteria for gout: a dual-energy CT study

BackgroundProvisional gout remission criteria including five domains (serum urate, tophus, flares, pain due to gout, and patient global assessment) have been proposed. The aim of this study was to test the concurrent validity of the provisional gout remission criteria by comparing the criteria with dual-energy CT (DECT) findings.MethodsPatients with gout on allopurinol ≥ 300 mg daily were prospectively recruited into a multicenter DECT study. Participants attended a standardized study visit which recorded gout flare frequency in the preceding 12 months, physical examination for tophus, serum urate, and patient questionnaires. DECT scans of both hands/wrists, feet/ankles/Achilles, and knees were analyzed by two DECT radiologists. The relationship between the DECT urate crystal volume and deposition with individual domains as well as the provisional remission criteria set was analyzed.ResultsThe provisional remission criteria were fulfilled in 23 (15.1%) participants. DECT urate crystal deposition was observed less frequently in those fulfilling the provisional remission criteria (44%), compared with those not fulfilling the criteria (73.6%, odds ratio 0.28, P = 0.004). The median (range) DECT urate crystal volume was 0.00 (0.00–0.46) cm3 for those fulfilling the remission criteria, compared with 0.08 (0.00–19.53) cm3 for those not fulfilling the criteria (P = 0.002). In multivariate regression analysis, the serum urate and tophus domains were most strongly associated with DECT urate crystal deposition.ConclusionsIn people with gout established on allopurinol, a state of remission as defined by the provisional remission criteria is associated with less DECT urate crystal deposition. While this study provides support for the validity of the provisional gout remission criteria, it also demonstrates that some crystal deposition may be present in people achieving these criteria.

Determination of proton stopping power ratio with dual-energy CT in 3D-printed tissue/air cavity surrogates.

To study the accuracy with which proton stopping power ratio (SPR) can be determined with dual-energy computed tomography (DECT) for small structures and bone-tissue-air interfaces like those found in the head or in the neck. Hollow cylindrical polylactic acid (PLA) plugs (3cm diameter, 5cm height) were 3D printed containing either one or three septa with thicknesses tsepta =0.8, 1.6, 3.2, and 6.4mm running along the length of the plug. The cylinders were inserted individually into a tissue-equivalent head phantom (16cm diameter, 5cm height). First, DECT scans were obtained using a Siemens SOMATOM Definition Edge CT scanner. Effective atomic number (Zeff ) and electron density (ρe ) images were reconstructed from the DECT to produce SPR-CT images of each plug. Second, independent elemental composition analysis of the PLA plastic was used to determine the Zeff and ρe for calculating the theoretical SPR (SPR-TH) using the Bethe-Bloch equation. Finally, for each plug, a direct measurement of SPR (SPR-DM) was obtained in a clinical proton beam. The values of SPR-CT, SPR-TH, and SPR-DM were compared. The SPR-CT for PLA agreed with SPR-DM for tsepta ≥3mm (for CT slice thicknesses of 0.5, 1.0, and 3.0mm). The density of PLA was found to decrease with thickness when tsepta <3mm. As tsepta (and density) decreased, the SPR-CT values also decreased, in good agreement with SPR-DM and SPR-TH. Overall, the DECT-based SPR-CT was within 3% of SPR-TH and SPR-DM in the high-density gradient regions of the 3D-printed plugs for septa greater than~3mm in thickness.

Evaluation of metal artefacts reduction by application of monoenergetic extrapolation of dual-energy CT: A phantom study with different metal implants

The aim of this study was to evaluate the application of monoenergetic (ME) extrapolation technique of dual-energy computed tomography (DECT) for metal artefact reduction using phantom study. This study involved phantom study with a customized phantom consisting different types of metal implant such as titanium and stainless steel. The phantom was scanned using a single-source DECT scanner (SOMATOM Definition AS+, Siemens Healthcare, Germany) with dual-energy mode of 140/80 kV spectrum. The commercially available post-processing software (Syngo DE, Siemens) was applied to generate ME image datasets with different extrapolated energies ranged from 55 to 160 keV. The reduction of artefacts was measured qualitatively and quantitatively using region of interests (ROIs) statistical analysis. The results show 60% of metal streak regions were reduced significantly at higher extrapolated energy which is 160 keV. Quantitative analysis also resulted in lower HU readings within the region of artefact for 160 keV. However, higher extrapolated energy resulted in higher noise and lower signal-to-noise (SNR) value. ME images at 160 keV appear noisier while ME images at 64, 70 and 80 keV appear smoother. Metal artefacts induced by both metal implants were reduced significantly using DECT ME extrapolation and diagnostic quality of CT images also improved. It can be achieved by using higher ME of DECT. However, image noise is higher, and SNR is reduced with higher ME extrapolated energy.

Quality evaluation of monoenergetic images generated by dual-energy computed tomography for radiotherapy: A phantom study

PurposeQuantification analysis for monoenergetic computed tomography (CT) images obtained from dual-energy CT scanning was performed in the light of their potential use for structures delineation during radiotherapy. MethodsParameters that describe the quality of the images are: linearity, low and high contrast resolution, uniformity, noise and signal to noise ratio (SNR). To evaluate these parameters, a Catphan phantom was scanned using a dual-energy mode at Somatom Definition AS. Based on the polyenergetic CT images, sixteen monoenergetic series (ranged from 40 keV to 190 keV) were created by CT scanner software and automatically analyzed using Artiscan software. ResultsAnalysis of linearity shows that a potential use of any monoenergetic images in radiotherapy planning requires that individual calibration curves are implemented for each of them. While the results of the high contrast resolution analysis were comparable for each energy (5 lp/cm), the results of the analyses for uniformity, low contrast resolution, noise and SNR allowed us to select the best imaging energies. The highest relative uniformity was detected for images reconstructed for energies of 60 keV and 70 keV (98.54% and 98.61%). Similar results were observed for low contrast resolution, where the largest number of disks was detected for these energies, and the noise values (0.42% for 60 keV, 0.44% for 70 keV). The best SNR was observed for images reconstructed for energy of 60 keV. ConclusionsTaking into account these results, the energy of 70 keV was selected as potentially the best for reconstruction of monoenergetic images used for structures delineation during radiotherapy.

Dual-energy computed tomography in calcium pyrophosphate deposition: initial clinical experience

To determine the dual-energy computed tomography (DECT) attenuation properties of meniscal calcifications in calcium pyrophosphate deposition (CPPD) invivo, and assess whether DECT was able to discriminate meniscal CPP deposits from calcium hydroxyapatite (HA) in subchondral and trabecular bone. Patients with clinical suspicion of crystal-related arthropathy (gout and/or CPPD) and knee DECT scans were retrospectively assigned to CPPD (n=19) or control (n=21) groups depending on the presence/absence of chondrocalcinosis on DECT. Two observers drew standardized regions of interest (ROI) in meniscal calcifications, non-calcified menisci, as well as subchondral and trabecular bone. Five DECT parameters were obtained: CT numbers (HU) at 80 and 140kV, dual-energy index (DEI), electron density (ρe), and effective atomic number (Zeff). The four different knee structures were compared within/between patients and controls using linear mixed models, adjusting for confounders. Meniscal calcifications (n=89) in CPPD patients had mean±SD CT numbers at 80 and 140kV of 257±64 and 201±48 HU, respectively; with a DEI of 0.023±0.007, and ρe and Zeff of 140±35 and 8.8±0.3, respectively. Meniscal CPP deposits were readily distinguished from calcium HA in subchondral and trabecular bone (p≤0.001), except at 80kV separately (p=0.74). Zeff and ρe both significantly differed between CPP deposits and calcium HA in subchondral and trabecular bone (p<0.0001). This proof-of-concept study shows that DECT has the potential to discriminate meniscal CPP deposits from calcium HA in subchondral and trabecular bone invivo, paving the way for the non-invasive biochemical signature assessment of intra- and juxta-articular calcium crystal deposits.

Low-keV and Low-kVp CT for Positive Oral Contrast Media in Patients with Cancer: A Randomized Clinical Trial.

Background Substantial gain in the attenuation of iodine on low-kVp and dual-energy CT processed low-keV virtual monochromatic images provides an opportunity for customization of positive oral contrast media administration. Purpose To perform an intrapatient comparison of bowel labeling, opacification, and taste preference with iodinated oral contrast medium (ICM) in standard (sICM) and 25%-reduced (rICM) concentrations at low tube voltage (100 kVp) or on low-energy (50-70 keV) virtual monochromatic images compared with barium-based oral contrast medium (BCM) at 120 kVp. Materials and Methods In this prospective clinical trial, 200 adults (97 men, 103 women; mean age, 63 years ± 13 [standard deviation]) who weighed less than 113 kg and who were undergoing oncologic surveillance (from April 2017 to July 2018) and who had previously undergone 120-kVp abdominopelvic CT with BCM randomly received sICM (7.2 g iodine) or rICM (5.4 g iodine) and underwent 100-kVp CT or dual-energy CT (80/140 kVp) scans to be in one of four groups (n = 50 each): sICM/100 kVp, rICM/100 kVp, sICM/dual-energy CT, and rICM/dual-energy CT. Qualitative analysis was performed for image quality (with a five-point scale), extent of bowel labeling, and homogeneity of opacification (with a four-point scale). Intraluminal attenuation of opacified small bowel was measured. A post-CT patient survey was performed to indicate contrast medium preference, taste of ICM (with a five-point scale), and adverse effects. Data were analyzed with analogs of analysis of variance. Results All CT studies were of diagnostic image quality (3.4 ± 0.3), with no difference in the degree of bowel opacification between sICM and rICM (P > .05). Compared with BCM/120 kVp (282 HU ± 73), mean attenuation was 78% higher with sICM/100 kVp (459 HU ± 282) and 26%-121% higher at sICM/50-65 keV (50 keV = 626 HU ± 285; 65 keV = 356 HU ± 171). With rICM, attenuation was 46% higher for 100 kVp (385 HU ± 215) and 19%-108% higher for 50-65 keV (50 keV = 567 HU ± 270; 65 keV = 325 HU ± 156) compared with BCM (P < .05). A total of 171 of 200 study participants preferred ICM to BCM, with no taste differences between sICM and rICM (3.9 ± 0.6). Fifteen participants had diarrhea with BCM, but none had diarrhea with ICM. Conclusion A 25%-reduced concentration of iodinated oral contrast medium resulted in acceptable bowel labeling while yielding substantially higher luminal attenuation at low-kVp and low-keV CT examinations with improved preference in patients undergoing treatment for cancer. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Laghi in this issue.