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RATIONALE AND OBJECTIVES To evaluate the material decomposition (MD) techniques in rapid kVp switching dual-energy CT (rsDECT) for quantifying liver fat content in rats with nonalcoholic fatty liver. MATERIALS AND METHODS Fifty male Sprague-Dawley (SD) rats were divided into study group (n=37) and control group (n = 13) and underwent rsDECT examination at different intervals. All the data analysis was performed using AW4.7 workstation. The fat contents under the traditional fat(water), fat(blood), and fat(muscle) material decomposition (MD) images and the fat volume fraction (FVF) from the liver fat maps generated using multi-material decomposition (MMD) technique were measured. The pathological grades (grade 0, 1, 2 and 3) of fatty liver were determined after euthanasia. The measurement differences among different grades and the correlation of measurements with different grades was analyzed using ANOVA and Spearman correlation, respectively. A receiver operating characteristics (ROC) curve was used to analyze the diagnostic efficacies of fat contents and FVF. RESULTS There were statistically significant differences in FVF and fat contents under fat(water), fat(blood), fat(muscle) based MD images among different grades. These values correlated well with the pathological grades (R-value: 0.90, 0.75, 0.79, 0.80, all p

Background This study aimed to explore the value of gastric cancer (GC) tumor markers and dual-energy CT（DECT） scans of arterial and venous GC lesions with quantitative iodine concentration (IC) and radiomics, to predict lymph node metastasis (LNM) in patients with GC. Methods This prospective study comprised of 177 patients that underwent dual-energy CT scans before surgery, and were subsequently diagnosed with GC by postoperative pathology. Serum tumor markers and arterial phases (AP) and venous phases (VP) of GC lesion iodine concentration (IC) and normalized iodine concentration (nIC) were analyzed. Patients were divided into either the LNM group or non-LNM group according to pathological results. The Wilcoxon rank-sum test was used to compare the serum tumor markers, IC, and nIC of the 2 groups, and a ROC curve was drawn to evaluate their effectiveness in predicting LNM in patients with GC. After using the Siemens syngo.via Frontier Radiomics software to extract radiomics features , all patients were randomly divided into a train set and a test set with a 7:3 ratio to predict GC LNM. Results Among the 177 patients with GC, 83 were diagnosed with LNM, while 94 did not have LNM. The preoperative serum tumor markers CA125, CA199, and CEA were statistically significant for predicting the presence of LNM (PConclusion Models based on preoperative serum tumor markers (CA125, CA199, and CEA) in patients with GC, quantitative dual-energy CT parameter values of the lesions (AP and VP IC, nIC), and radiomics have a higher diagnosis of LNM. The value of nomogram in combination with multi-parameter analysis is higher diagnosis of LNM, which can provide a reliable basis for preoperative evaluation of LNM.

Background and Purpose: Quantification of hepatic virtual iron content (VIC) by using Multidetector Dual Energy Computed Tomography (DECT) has been recently investigated since this technique could offer a good compromise between accuracy and non-invasiveness for liver iron content quantification. The aim of our study is to investigate differences in VIC at different DECT time points (namely baseline and arterial, venous and tardive phases), identifying the most reliable and also exploring the underlying temporal trend of these values. Materials and Methods: Eleven patients who underwent DECT examination and were characterized by low liver fat content were included in this retrospective study. By using the Syngo.via Frontier–DE IronVNC tool, regions of interest (ROI) were placed on the VIC images at 3 hepatic levels, both in left and right liver lobes, at each DECT time point. Friedman’s test followed by Bonferroni-adjusted Wilcoxon signed-rank test for post-hoc analysis was performed to assess differences between DECT timepoints. Page’s L test was performed to test the temporal trend of VIC across the 4 examined timepoints. Results: For both liver lobes, Friedman’s test followed by Bonferroni-adjusted Wilcoxon signed-rank test revealed that VIC values differed significantly when extracted from ROIs placed at the 4 different timepoints. The Page’s L test for multiple comparison revealed a significant growing trend for VIC, from baseline acquisition to the fourth and last time point post-contrast agent injection. Conclusions: The extraction of hepatic VIC in healthy subjects was found to be significantly influenced by the DECT time point chosen for the extrapolation of the VIC values.

Clinicians should be aware of SDCT as a useful tool in the assessment of focal airway lesions. Spectral detector dual-energy computed tomography (SDCT) is a relatively novel imaging technology which has been utilized to aid in the diagnosis of many cardiothoracic conditions. Specifically, the availability of generated iodine density maps, virtual monoenergetic images, and effective atomic number maps allow for better evaluation of thoracic lesions compared to conventional CT. SDCT has previously been shown to be useful in the differentiation of benign vs malignant pulmonary nodules, pleural lesions, and lymph nodes. We describe 3 cases in which a patient presents with an indeterminate tracheal or bronchial lesion on conventional CT and subsequent SDCT reconstructions provided additional information which helped guide diagnosis or management of the patient. The goal is to help clinicians understand the benefit of SDCT in the detection and workup of airway lesions.

To evaluate the predictive value of dual-energy CT (DECT) quantitative parameters and clinical influence factors for intracerebral hemorrhage (ICH) complications after endovascular treatment in patients with acute ischemic stroke (AIS).Seventy-two consecutive patients who underwent brain DECT immediately after endovascular treatment for AIS from November 2017 to October 2019 were included. Retrospectively, the volume of brain parenchymal hyperdensity area (HDA), the maximum iodine concentration, and maximum CT value on DECT images was evaluated and measured by two radiologists blinded to any clinical information independently. Follow-up CT imaging (24-72 h) were used to assess the development of ICH complications. DECT parameters and clinical influence factors were analyzed by Chi-square test or Fisher's exact test and Mann-Whitney U test. Receiver operating characteristic curves were generated for continuous variables.Follow-up CT images confirmed that forty of 72 patients (55.6%) developed ICH. The volume of HDA, median maximum iodine concentration and maximum CT value between ICH group and non-ICH group were significantly different (P 0.001). Combining the DECT quantitative parameters with clinical predictors, receiver operating characteristic analysis revealed an area under the curve of 0.985, for identifying patients developing ICH with sensitivity, specificity, positive predictive value and negative predictive value were 90%, 100%, 100% and 88.9%, respectively.Three quantitative parameters of DECT and clinical predictors showed great predictive performance in identifing ICH complications in patients with brain parenchyma HDA after endovascular therapy, which may contribute to better clinical decision-making.

The aim of this study is to assess whether perifocal bone marrow edema (BME) in patients with osteoid osteoma (OO) can be accurately detected on dual-layer spectral CT (DLCT) with three-material decomposition. To that end, 18 patients with OO (25.33 ± 12.44 years; 7 females) were pairwise-matched with 18 patients (26.72 ± 9.65 years; 9 females) admitted for suspected pathologies other than OO in the same anatomic location but negative imaging findings. All patients were examined with DLCT and MRI. DLCT data was decomposed into hydroxyapatite and water- and fat-equivalent volume fraction maps. Two radiologists assessed DLCT-based volume fraction maps for the presence of perifocal BME, using a Likert scale (1 = no edema; 2 = likely no edema; 3 = likely edema; 4 = edema). Accuracy, sensitivity, and specificity for the detection of BME on DLCT were analyzed using MR findings as standard of reference. For the detection of BME in patients with OO, DLCT showed a sensitivity of 0.92, a specificity of 0.94, and an accuracy of 0.92 for both radiologists. Interreader agreement for the assessment of BME with DLCT was substantial (weighted κ = 0.78; 95% CI, 0.59, 0.94). DLCT with material-specific volume fraction maps allowed accurate detection of BME in patients with OO. This may spare patients additional examinations and facilitate the diagnosis of OO.

Objectives: To compare radiation dose and image quality of single-energy (SECT) and dual-energy (DECT) head and neck CT examinations performed with second- and third-generation dual-source CT (DSCT) in matched patient cohorts. Methods: 200 patients (mean age 55.1 ± 16.9 years) who underwent venous phase head and neck CT with a vendor-preset protocol were retrospectively divided into four equal groups (n = 50) matched by gender and BMI: second (Group A, SECT, 100-kV; Group B, DECT, 80/Sn140-kV), and third-generation DSCT (Group C, SECT, 100-kV; Group D, DECT, 90/Sn150-kV). Assessment of radiation dose was performed for an average scan length of 27 cm. Contrast-to-noise ratio measurements and dose-independent figure-of-merit calculations of the submandibular gland, thyroid, internal jugular vein, and common carotid artery were analyzed quantitatively. Qualitative image parameters were evaluated regarding overall image quality, artifacts and reader confidence using 5-point Likert scales. Results: Effective radiation dose (ED) was not significantly different between SECT and DECT acquisition for each scanner generation (p = 0.10). Significantly lower effective radiation dose (p < 0.01) values were observed for third-generation DSCT groups C (1.1 ± 0.2 mSv) and D (1.0 ± 0.3 mSv) compared to second-generation DSCT groups A (1.8 ± 0.1 mSv) and B (1.6 ± 0.2 mSv). Figure-of-merit/contrast-to-noise ratio analysis revealed superior results for third-generation DECT Group D compared to all other groups. Qualitative image parameters showed non-significant differences between all groups (p > 0.06). Conclusion: Contrast-enhanced head and neck DECT can be performed with second- and third-generation DSCT systems without radiation penalty or impaired image quality compared with SECT, while third-generation DSCT is the most dose efficient acquisition method. Advances in knowledge: Differences in radiation dose between SECT and DECT of the dose-vulnerable head and neck region using DSCT systems have not been evaluated so far. Therefore, this study directly compares radiation dose and image quality of standard SECT and DECT protocols of second- and third-generation DSCT platforms.

Purpose: Quantification of range uncertainty in proton treatment planning using dual-energy computed tomography (DECT) for direct stopping-power prediction (DirectSPR) and its clinical implementation. Methods and materials: To assess the overall uncertainty in stopping-power ratio (SPR) prediction of a DirectSPR implementation calibrated for different patient geometries, the influencing factors were categorized in imaging, modelling as well as others. The respective SPR uncertainty was quantified for lung, soft tissue and bone and translated into range uncertainty for several tumor entities. The uncertainty assessment was experimentally validated in various phantom geometries and compared to the standard look-up-table (HLUT) approach. Finally, the dosimetric effect of the assessed margins was quantified for a representative brain tumor patient. Results: For bone, soft tissue and lung, an SPR uncertainty (1𝜎) of 1.6%, 1.3% and 1.3% was determined for DirectSPR, respectively. This allowed for a reduction of the clinically applied range uncertainty from currently (3.5%+2mm) to (1.7%+2mm) for brain tumor patients and (2.0%+2mm) for prostate-cancer patients. In all phantom validation setups, DirectSPR outperformed the HLUT approach, with an accuracy in SPR prediction as high as 0.3% in an anthropomorphic head phantom (0.7% using HLUT). In the representative patient case, a dose reduction in organs at risk close-by to the target volume was achieved, with a mean dose reduction of up to 16% in the brainstem. Patient-specific DECT-based treatment planning with reduced safety margins was successfully introduced into clinical routine at our institute in April 2019. Within the first year, 90 brain-tumor and 60 prostate-cancer patients were treated using DirectSPR. Conclusions: A substantial reduction of range uncertainty in clinical proton treatment planning was achieved by patient-specific DECT-based SPR prediction. Thereby, for the first time since the initial introduction of range margins in proton therapy in the 1980s, a relevant reduction of range uncertainty on a 2% level was achieved.

Rationale and Objectives To develop and validate 2 iodine maps based radiomics nomograms for preoperatively predicting cervical lymph node metastasis (LNM) and central lymph node metastasis (CLNM) in papillary thyroid cancer (PTC). Materials and Methods A total of 346 patients with PTC were enrolled and allocated to training (242) and validation (104) sets. Radiomics features were extracted from arterial and venous phase iodine maps, respectively. Aggregated machine-learning strategy was applied for features selection and construction of 2 radiomics scores (LN rad-score; CLN rad-score). Logistic regression model was employed to establish two radiomics nomograms (nomogram 1: predicting LNM; nomogram 2: predicting CLNM) after incorporating LN or CLN rad-score with clinical predictors. Nomograms performance was determined by discrimination, calibration and clinical usefulness. Results Nomogram 1 incorporated LN rad-score, age (categorized by 55) and CT reported LN status; Nomogram 2 incorporated CLN rad-score, capsule contact >25% and CT reported CLN status. 2 nomograms both showed good discrimination and calibration in the training (AUC = 0.847; AUC = 0.837) and validation cohorts (AUC = 0.807; AUC = 0.795). Significant improved AUC, net reclassification index (NRI) and integrated discriminatory improvement (IDI) confirmed additional great predictive value of 2 rad-scores, compared with clinical models without radiomics. Decision curve analysis indicated clinical utility of nomograms. 2 nomograms both demonstrated favorable predictive efficacy in CT reported LN or CLN negative subgroup (AUC = 0.766; AUC = 0.744). Conclusion The presented 2 radiomics nomograms are useful tools for preoperative prediction of LNM and CLNM in PTC

OBJECTIVE. The purpose of this study was to develop and evaluate a dual-energy CT (DECT)-based nomogram for noninvasive identification of the status of human epidermal growth factor receptor 2 (HER2; also known as ERBB2) expression in gastric cancer (GC). MATERIALS AND METHODS. A total of 206 patients with histologically proven GC who underwent pretreatment DECT were retrospectively recruited and randomly allocated to a training cohort (n = 144) or a test cohort (n = 62). Information on clinical characteristics, qualitative imaging features, and quantitative DECT parameters was collected. Univariate analysis and multivariate logistic regression were implemented to screen independent predictors of HER2 status. An individualized nomogram was built, and its discrimination, calibration, and clinical usefulness were assessed. RESULTS. Tumor location, the iodine concentration of the tumor in the venous phase, and the normalized iodine concentration of the tumor in the venous phase were significant factors predictive of HER2 status (all p .05 by the Hosmer-Lemeshow test) and would offer more net benefits than simple default strategies within a wide range of threshold probabilities in both cohorts. CONCLUSION. The DECT-based nomogram has great application potential in terms of detecting HER2 status in GC, and can serve as a novel substitute for invasive testing.

Purpose To evaluate the performance of a dual-energy (DE) calcium removal software based on a modified three-material decomposition algorithm in assessing the stenosis of the internal carotid artery (ICA) in comparison with mixed images using digital subtraction angiography (DSA) as the reference standard. Methods Forty-six patients (38 men; 67 ± 8 years old), including 154 calcified ICA segments C1–C2 (59), C3–C5 (63), C6 (24), and C7 (8), were recruited in this retrospective study. Mixed images and virtual non-calcium (VNCa) images using the modified dual-energy computed tomography (DECT) algorithm were reconstructed. The differences between VNCa and DSA images vs. mixed and DSA images of degree of stenosis were compared. The intraclass correlation coefficient (ICC) was used for assessing the agreement between VNCa, mixed images, and DSA. Results The degree of stenosis differed significantly between mixed and DSA images in the C3–C5 (30% ± 17.9% vs. 23.0% ± 16.9%, p = 0.026) and C6 (38.3% ± 15.4% vs. 28.5% ± 13.3%, p = 0.023) segments. The stenosis of VNCa images showed no significant difference with DSA images in all segments (all p > 0.05). The ICCs between VNCa and DSA images (0.86–0.97) were higher than those between the mixed and DSA images (0.68–0.96) in all segments. Conclusion The performance of a modified three-material decomposition DECT algorithm for calcium removal in ICA stenosis evaluation, particularly for the C3–C5 and C6 ICA segments, was promising.

To investigate the diagnostic performance of dual-layer dual-energy CT (dlDECT) in the evaluation of adrenal nodules. In this retrospective study, 66 patients with triphasic dlDECT (unenhanced, venous phase (VP), delayed phase (DP)) for suspected adrenal lesions were included. Virtual unenhanced images (VUE) were derived from VP acquisitions. Reference diagnoses were established with true unenhanced (TUE) attenuation, absolute washout, follow-up imaging and pathological data. Attenuation for adrenal lesions and abdominal tissues was acquired on TUE, VUE, VP and DP images. VUE and TUE attenuation were compared in all included tissues. Characterization of adrenal nodules based on TUE and VUE attenuation was investigated. ROC analysis was used to determine an adjusted threshold for diagnosing lipid-rich adenomas. Seventy-three adrenal nodules (mean size: 18.9 ± 8.9 mm) were identified in 66 patients (38 females, 28 males; age: 61 ± 13 years) including adenoma (n = 65), metastases (n = 2), pheochromocytoma (n = 3), adrenocortical carcinoma (n = 1) and myelolipoma (n = 2). Mean attenuation of all included tissues except for the abdominal aorta (p = 0.11) was significantly higher in VUE compared to TUE images, including the attenuation of adrenal nodules (20.0 ± 17.2 vs. 7.1 ± 19.8; p

Objectives: Studies show insufficient sensitivity of virtual non-contrast (VNC) reconstructions for stone detection in dual-energy CT urography (DE-CTU). The aim of this study was to investigate if side-by-side-evaluation of both VNC and post-contrast images could increase the sensitivity of single-phase split bolus DE-CTU. Methods: Consecutive patients with haematuria who underwent split bolus DE-CTU on the same dual-source DE-CT scanner were retrospectively enrolled in the study. Intravenous furosemide and oral hydration were employed. Two readers, independently and then jointly in two separate sessions, recorded the location and the longest axial stone diameter on three randomised sets of images: separate VNC and post-contrast images, and side-by-side-reconstructions. True non-contrast (TNC) images served as the standard of reference. Results: A total of 83 urinary stones were detected on TNC images. Independent reader side-by-side-evaluation of VNC and post-contrast images yielded higher stone detection sensitivity (76 and 84%, respectively) compared to evaluation of only VNC (71 and 81%, respectively) or post-contrast images (64 and 80%, respectively). The sensitivity of joint reader evaluation of side-by-side-images reached almost 86% and was not significantly different from TNC images (p = 0.77). All stones larger than 3 mm were correctly detected by side-by-side-evaluation. Dose reduction of 55% could be achieved by omitting TNC scans. Conclusion: Side-by-side-VNC and post-contrast image evaluation enable detection of clinically significant urolithiasis on single-phase split bolus DE-CTU with significant dose reduction. Advances in knowledge: This study shows that single-phase DE-CTU is feasible if VNC imaging is simultaneously utilised with post-contrast images.

International audience; Purpose: To assess myocardial extracellular volume fraction (ECV) measurement provided by a single-source dual-energy computed tomography (SSDE-CT) acquisition added at the end of a routine CT examination before transcatether aortic valve implantation (TAVI) compared to cardiac magnetic resonance imaging (MRI).Materials and methods: Twenty-one patients (10 men, 11 women; mean age, 86±4.9 years [SD]; age range: 71-92 years) with severe aortic stenosis underwent standard pre-TAVI CT with additional cardiac SSDE-CT acquisition 7minutes after intravenous administration of iodinated contrast material and myocardial MRI including pre- and post-contrast T1-maps. Myocardial ECV and standard deviation (σECV) were calculated in the 16-segments model. ECV provided by SSDE-CT was compared to ECV provided by MRI, which served as the reference. Analyses were performed on a per-segment basis and on a per-patient involving the mean value of the 16-segments.Results: ECV was slightly overestimated by SSDE-CT (29.9±4.6 [SD] %; range: 20.9%-48.3%) compared to MRI (29.1±3.9 [SD] %; range: 22.0%-50.7%) (P

Background Due to their easy accessibility, CT scans have been increasingly used for investigation of gastrointestinal (GI) bleeding. Purpose To estimate the performance of a dual-phase, dual-energy (DE) GI bleed CT protocol in patients with overt GI bleeding in clinical practice and examine the added value of portal phase and DE images. Materials and Methods Consecutive patients with GI bleeding underwent a two-phase DE GI bleed CT protocol. Two gastroenterologists established the reference standard. Performance was estimated using clinical CT reports. Three GI radiologists rated confidence in GI bleeding in a subset of 62 examinations, evaluating first mixed kV arterial images, then after examining additional portal venous phase images, and finally after additional DE images (virtual non-contrast and virtual monoenergetic 50 keV images). Results 52 of 176 patients (29.5%) had GI bleeding by the reference standard. The overall sensitivity, specificity, and positive and negative predictive values of the CT GI bleed protocol for detecting GI bleeding were 65.4%, 89.5%, 72.3%, and 86.0%, respectively. In patients with GI bleeding, diagnostic confidence of readers increased after adding portal phase images to arterial phase images ( p = 0.002), without additional benefit from dual energy images. In patients without GI bleeding, confidence in luminal extravasation appropriately decreased after adding portal phase, and subsequently DE images ( p = 0.006, p = 0.018). Conclusion A two-phase DE GI bleed CT protocol had high specificity and negative predictive value in clinical practice. Portal venous phase images improved diagnostic confidence in comparison to arterial phase images alone. Dual-energy images further improved radiologist confidence in the absence of bleeding.

Purpose To investigate whether multiple dual-energy computed tomography (DECT) parameters can noninvasively predict the Ki-67 expression (associated with survival and prognosis) in laryngeal squamous cell carcinoma (LSCC). Methods Eighty-eight patients with histologically proven LSCC were retrospectively reviewed. Multiple DECT-derived parameters were measured and correlated with Ki-67 expression by Spearman correlation analysis. Comparisons of the DECT-derived parameters between tumors with low- and high-level expression of Ki-67 were made with the t-tests. Results The iodine concentration (IC), normalized IC (NIC), effective atomic number (Zeff), 40−80 keV, and slope (k) values were positively correlated with Ki-67 expression (all p Conclusions Multiple DECT-derived parameters (IC, NIC, Zeff, 40−80 keV, and slope (k)) can be used as predictors of survival and prognosis in LSCC, among which the NIC value is the strongest.

Extrapleural space (EPS) is a potential space between the outer layer of the parietal pleura and the inner layer of the chest wall and the diaphragm. Many different pathologies including chronic inflammatory conditions, infections, trauma, neoplastic disease (both benign and malignant) as well as many infiltrative disorders can involve the EPS. It is one of the frequently overlooked entity on imaging due to relative lack of understanding of the anatomy and the imaging appearances of the diseases localized to this space. The knowledge of the EPS is essential for the radiologists as the pathologies which involve the EPS may require different treatment approach compared to pleural or parenchymal lung disease. Additionally, the EPS involvement may influence the staging and treatment planning for chest malignancies. In this review, we give an overview of the anatomy and various pathologies involving EPS, utility of different imaging modalities in the evaluation of EPS lesions with emphasis on cross sectional imaging and emerging technologies like spectral CT and its role in recognizing the imaging features which enable specific diagnosis of various pathologies.

Dual-energy CT (DECT) is an exciting innovation in CT technology with profound capabilities to improve diagnosis and add value to patient care. Significant advances in this technology over the past decade have improved our ability to successfully adopt DECT into the clinical routine. To enable effective use of DECT, one must be aware of the pitfalls and artifacts related to this technology. Understanding the underlying technical basis of artifacts and the strategies to mitigate them requires optimization of scan protocols and parameters. The ability of radiologists and technologists to anticipate their occurrence and provide recommendations for proper selection of patients, intravenous and oral contrast media, and scan acquisition parameters is key to obtaining good-quality DECT images. In addition, choosing appropriate reconstruction algorithms such as image kernel, postprocessing parameters, and appropriate display settings is critical for preventing quantitative and qualitative interpretive errors. Therefore, knowledge of the appearances of these artifacts is essential to prevent errors and allows maximization of the potential of DECT. In this review article, the authors aim to provide a comprehensive and practical overview of possible artifacts that may be encountered at DECT across all currently available commercial clinical platforms. They also provide a pictorial overview of the diagnostic pitfalls and outline strategies for mitigating or preventing the occurrence of artifacts, when possible. The broadening scope of DECT applications necessitates up-to-date familiarity with these technologies to realize their full diagnostic potential. An invited commentary by Szczykutowicz is available online. (©)RSNA, 2021 An earlier incorrect version of this article appeared online and in print. This article was corrected on March 1st, 2021.

MRI-only treatment planning is highly desirable in the current proton radiation therapy workflow due to its appealing advantages such as bypassing MR-CT co-registration, avoiding x-ray CT exposure dose and reduced medical cost. However, MRI alone cannot provide stopping power ratio (SPR) information for dose calculations. Given that dual energy CT (DECT) can estimate SPR with higher accuracy than conventional single energy CT, we propose a deep learning-based method in this study to generate synthetic DECT (sDECT) from MRI to calculate SPR. Since the contrast difference between high-energy and low-energy CT (LECT) is important, and in order to accurately model this difference, we propose a novel label generative adversarial network-based model which can not only discriminate the realism of sDECT but also differentiate high-energy CT (HECT) and LECT from DECT. A cohort of 57 head-and-neck cancer patients with DECT and MRI pairs were used to validate the performance of the proposed framework. The results of sDECT and its derived SPR maps were compared with clinical DECT and the corresponding SPR, respectively. The mean absolute error for synthetic LECT and HECT were 79.98 ± 18.11 HU and 80.15 ± 16.27 HU, respectively. The corresponding SPR maps generated from sDECT showed a normalized mean absolute error as 5.22% ± 1.23%. By comparing with the traditional Cycle GANs, our proposed method significantly improves the accuracy of sDECT. The results indicate that on our dataset, the sDECT image form MRI is close to planning DECT, and thus shows promising potential for generating SPR maps for proton therapy.

Coupling computed tomography with positron emission tomography (PET/CT) supplements tracer uptake with anatomical information for localization and improves PET quantification by using CT images for attenuation correction. Iodinated contrast agents in CT scans are used to enhance vascularity, organs, and abnormalities and for characterize lesions. However, current attenuation correction methodologies generate overestimates in standardized uptake values (SUV) in the presence of materials with high atomic numbers such as iodinated contrast agents. Utilizing electron density (ED) from dual energy CT (DECT) may result in less biased attenuation correction as ED is proportional to attenuation at PET emission energy of 511 keV. To evaluate different methods of attenuation correction, five phantom configurations with varying iodine concentrations and constant concentrations of Fluorine-18 were scanned using PET/CT and DECT at similar scanning parameters. Phantom configurations were scanned at CTDIvol 2, 4, 6, and 8 mGy with DECT to evaluate the effect of dose on ED and SUV. For attenuation correction, ED was transformed into attenuation at 511 keV through reported material compositions and ED. SUV demonstrated less biased behavior in the presence of iodinated contrast media with ED-based correction (-1.3% to 1.4%, p=0.271) compared to nominal correction (1.5% to 8.6%, p=0.000). No interaction effect between dose and phantom configuration or effect of dose on SUV was present, which was also reflected in ED stability in different tissue mimics. Use of ED-based attenuation correction from DECT allowed for less biased SUV when increasing concentrations of iodinated contrast agents, indicating quantitative advantages of DECT coupled with PET.

CT colonography (CTC) uses abdominal CT scans to examine the colon for cancers and polyps. To visualize the complete region of the colon without the obstructing residual materials inside the colon, an orally administered contrast agent is used to opacify the residual fecal materials on CT images, followed by virtual cleansing of the opacified materials from the images. We developed a self-supervised 3D generative adversarial network model based on residual blocks (ResBlocks), called 3D-ResNet-GAN, for performing electronic cleansing (EC) in CTC. In this model, the convolution layers of the generator network are implemented with ResBlocks for enhancing the EC performance of the generator network over that of our previously developed U-net-based 3D-GAN EC model. We compared the performance of the proposed selfsupervised 3D-ResNet-GAN EC scheme with that of the previous 3D-GAN EC scheme by the use of an anthropomorphic phantom and a clinical CTC case with submerged polyps in single-energy CTC and dual-energy CTC. Our preliminary quantitative evaluation based on the phantom indicated that the proposed 3D-ResNet-GAN EC scheme can yield a statistically significant improvement over the EC performance of our previous 3D-GAN EC scheme in both single-energy and dual-energy CTC. Our preliminary visual evaluation based on the clinical CTC case indicated that the use of ResBlocks and dual-energy CTC yields the best EC result.

Pediatric imaging utilizes the quantitative capabilities of CT to guide clinical decision making and treatment, but image quality is heavily affected by variation in patient sizes and the need for lower dose scans. Dual energy CT generates spectral results such as virtual monoenergetic images (VMI), electron density (ED), and effective atomic number (Zeff) that enhance material characterization and quantification. Though it has not been extensively explored, application of DECT to pediatric imaging may allow increased stability in quantitative measures with varying patient size, dose, and tube voltage. To examine the dependency of size, dose, and tube voltage, a phantom with tissue-mimicking inserts was scanned with dual-layer spectral detector CT with different extension rings to simulate different pediatric patient sizes. Each size configuration was subsequently scanned at CTDIvol of 9, 6, and 3 mGy with 100 and 120 kVp to obtain conventional CT and spectral results. Overall, both VMI and ED values were accurately quantified. VMI at 70 keV and 9 mGy demonstrated smaller differences among patient size and kVp compared to conventional images. Low dose dependency relative to 9 mGy was also present for VMI. Similarly, ED and Zeff showed low dependency on patient size, dose, and kVp and maintained material differentiability. Stability of these spectral results with different patient sizes, doses, and tube voltages illustrates the potential application of spectral detector CT to pediatric patients not only to improve the consistency of quantitative measures across patient sizes but also to allow lower doses without impairing quantification.