Utilization of virtual non-contrast images derived from dual-energy CT in evaluation of biliary stone disease: Virtual non-contrast image can replace true non-contrast image regarding biliary stone detection

Comparison of Muscle and Fat Measurements Between True Noncontrast and Virtual Noncontrast Images From Three Phases of Dual-Energy Dynamic Liver CT

RATIONALE AND OBJECTIVES

To determine whether virtual noncontrast (VNC) images derived from three-phase dynamic dual-energy CT (DECT) imaging can reliably substitute true noncontrast (TNC) images in assessing muscle and fat with automatic segmentation software.

MATERIALS AND METHODS

The data from 476 dynamic liver DECT examinations performed between April 2019 and December 2020 were retrospectively analyzed. VNC images were generated from arterial (VNCa), portal-venous (VNCp), and delayed (VNCd) phase images. Automated software measured muscle, visceral fat (VF), and subcutaneous fat (SF) areas. Sarcopenia was defined using muscle-related indices. Differences in muscle and fat measurements, as well as sarcopenia prevalence, between TNC and VNC images were assessed using paired t tests and McNemar tests, respectively.

RESULTS

The average age of the 476 patients (307 men) was 58.4±12.5years. Muscle density and area differed significantly between the TNC and VNC images; TNC images showed higher mean muscle density and smaller skeletal muscle area (SMA) than all VNC images (P<0.001). VF and SF attenuations were significantly lower on TNC images than on all VNC images (P<0.001). The proportions of sarcopenic patients did not differ significantly between TNC and VNCp or VNCd, regardless of the muscle index used.

CONCLUSION

Despite significant differences in muscle and fat attenuations between TNC and VNC images, VNCp and VNCd may be acceptable alternatives for measuring muscle and fat areas. However, TNC and VNC images should not be used interchangeably for assessing tissue attenuation or specific muscle components such as LAMA or NAMA.

Automated hepatic steatosis assessment on dual-energy CT-derived virtual non-contrast images through fully-automated 3D organ segmentation

PURPOSE

To evaluate the efficacy of volumetric CT attenuation-based parameters obtained through automated 3D organ segmentation on virtual non-contrast (VNC) images from dual-energy CT (DECT) for assessing hepatic steatosis.

MATERIALS AND METHODS

This retrospective study included living liver donor candidates having liver DECT and MRI-determined proton density fat fraction (PDFF) assessments. Employing a 3D deep learning algorithm, the liver and spleen were automatically segmented from VNC images (derived from contrast-enhanced DECT scans) and true non-contrast (TNC) images, respectively. Mean volumetric CT attenuation values of each segmented liver (L) and spleen (S) were measured, allowing for liver attenuation index (LAI) calculation, defined as L minus S. Agreements of VNC and TNC parameters for hepatic steatosis, i.e., L and LAI, were assessed using intraclass correlation coefficients (ICC). Correlations between VNC parameters and MRI-PDFF values were assessed using the Pearson's correlation coefficient. Their performance to identify MRI-PDFF ≥ 5% and ≥ 10% was evaluated using receiver operating characteristic (ROC) curve analysis.

RESULTS

Of 252 participants, 56 (22.2%) and 16 (6.3%) had hepatic steatosis with MRI-PDFF ≥ 5% and ≥ 10%, respectively. LVNC and LAIVNC showed excellent agreement with LTNC and LAITNC (ICC = 0.957 and 0.968) and significant correlations with MRI-PDFF values (r = - 0.585 and - 0.588, Ps < 0.001). LVNC and LAIVNC exhibited areas under the ROC curve of 0.795 and 0.806 for MRI-PDFF ≥ 5%; and 0.916 and 0.932, for MRI-PDFF ≥ 10%, respectively.

CONCLUSION

Volumetric CT attenuation-based parameters from VNC images generated by DECT, via automated 3D segmentation of the liver and spleen, have potential for opportunistic hepatic steatosis screening, as an alternative to TNC images.

Incremental diagnostic value of virtual non-contrast dual-energy CT for the diagnosis of choledocholithiasis over conventional unenhanced CT

PURPOSE

The purpose of this study was to evaluate the incremental diagnostic value of virtual non-contrast (VNC) images derived from unenhanced dual-energy computed tomography (CT) for the diagnosis of choledocholithiasis by comparison with conventional unenhanced CT.

MATERIALS AND METHODS

Eighty-nine patients with gallbladder stones who had undergone both abdominal unenhanced dual-energy CT and magnetic resonance cholangiopancreatography (MRCP) were retrospectively included. There were 53 men and 36 women, with a mean age of 54 ± 13 (standard deviation) years (age range: 41-67 years). VNC and conventional CT images were generated. Two independent radiologists evaluated the presence of choledocholithiasis in three reading sessions (session 1, conventional unenhanced CT images; session 2, VNC images; session 3, conventional unenhanced CT plus VNC images). The reading time to identify choledocholithiasis was recorded. Inter-reader agreement was measured by using the Cohen kappa (κ) test. Incremental diagnostic value of VNC imaging when combined with conventional unenhanced CT was assessed based on discrimination (area under the curve [AUC]) and clinical utility (decision curve analysis). The diagnostic performance of dual-energy CT and that of MRCP were compared using DeLong test.

RESULTS

Using the standard of reference, 39 patients (39/89; 44%) had choledocholithiasis. The diagnosis of choledocholithiasis was improved using VNC images in combination with conventional unenhanced CT (AUC, 0.877; 95% confidence interval [CI]: 0.808, 0.947) by comparison with conventional unenhanced CT alone (AUC, 0.789; 95% CI: 0.718, 0.877) (P = 0.033) and achieved almost perfect inter-reader agreement (κ = 0.88; 95% CI: 0.72, 1.00) for the diagnosis of choledocholithiasis, without lengthening the median reading time (16.2 s for the combination of conventional CT and VNC images vs. 14.7 s for conventional CT alone; P= 0.325). Based on decision curve analysis, adding VNC imaging to conventional unenhanced CT resulted in a higher net benefit among most of decision thresholds. No differences in diagnostic performance were found between the combination of conventional unenhanced CT and VNC imaging (AUC, 0.877; 95% CI: 0.808, 0.947) and MRCP (AUC, 0.913; 95% CI: 0.852, 0.974) (P= 0.458).

CONCLUSIONS

VNC images derived from dual-energy unenhanced CT have incremental diagnostic value for the diagnosis of choledocholithiasis. Unenhanced CT in a dual-energy mode may be a useful tool for the diagnosis of choledocholithiasis.

Gallstones Detection on Dual-Energy Computerized Tomography-Is It Ready for Real-World Use? A Retrospective Observational Study

AIMS

The aims of the study are to evaluate the performance of dual-energy computed tomography (DECT) imaging in the detection of noncalcified gallstones (GSs) and to assess its performance relative to transabdominal ultrasound (US) in identifying cholelithiasis.

METHOD

This study is a retrospective review of radiology records and images to find all patients who had both US and DECT scans within a 6-month period and were found to have GSs. Patients who did not have GSs on US served as the control group. The CT scans were reviewed by 4 radiologists who did not have access to the US results when assessing the presence or absence of GSs on the DECT scans. In case of any discrepancies among the radiologists, the majority opinion was considered. If there was a split opinion, a fifth reviewer was consulted. The data were analyzed to calculate sensitivity, specificity, positive and negative predictive values, as well as overall accuracy and to evaluate interreader variability. The absolute Hounsfield unit (HU) differences of the GSs and bile were compared between polychromatic (PC), virtual noncontrast (VNC), and virtual monochromatic (VMC) images.

RESULTS

Considering at least 3-reader agreement, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were found to be 92%, 96%, 96%, 92%, and 94%, respectively. Individual reader sensitivity varied between 87% and 92%. There was good interobserver agreement with a Fleiss' kappa of 0.76. Quantification of the whole data set showed that no significant difference was observed in the HU values for the stones between the PC images and the VNC images. A significant increase was observed on the 50-keV VMC images compared with the PC and VNC images. In the study group, 17% stones were visualized only on the VNC or/and 50-keV VMC images, and not on the PC images. On quantitative analysis of these cases, there was a significant increase of HU in the VNC images as compared with PC images and a significant decrease of HU in the 50-keV VMC images as compared with PC images.

CONCLUSIONS

Low-keV images increase stone-bile contrast. Evaluation of cholelithiasis using VNC and 50-keV VMC images demonstrated a 14% increase in sensitivity relative to conventional CT.

[Accuracy of Virtual Non-contrast Image Reconstruction Using Material Decomposition for Fast kV-switching Dual-energy CT]

PURPOSE

Dual-energy computed tomography (DECT) system can generate virtual non-contrast (VNC) images. Although several reconstruction algorithms are defined, there are not many researches using deep learning image reconstruction (DLIR) algorithm. In this study, we evaluated the accuracy of the VNC image reconstruction under various conditions using DLIR algorithm.

METHODS

At first, each iodine insert with variable concentrations (2.0, 5.0, 10.0, 15.0 mg/ml) or diameters (2.0, 5.0, 10.0, 28.5 mm), or mixed insert including blood-mimicking material with iodine (iodine concentrations: 2.0, 4.0 mg/ml) was put in the center of the multi-energy CT phantom (Gammex, USA). This phantom was placed in the isocenter of DECT, and it scanned and reconstructed the VNC images. In addition, the VNC images were reconstructed with various display field of view (DFOV) sizes (240, 350 mm) or reconstruction algorithms (filtered back projection, advanced statistical iterative reconstruction, deep learning image reconstruction) for each iodine diameter. Attenuation values of these images (CT_VNC) were measured and assessed by placing a circular region of interest (ROI) on each insert.

RESULTS

CT_VNC form iodine inserts increased with iodine concentration became lower, whereas CT_VNC form blood plus iodine inserts were stable regardless of low iodine concentration. As iodine diameter became smaller, CT_VNC increased remarkably. CT_VNC remained steady even though reconstruction parameters were varied.

CONCLUSION

In our study, the VNC image reconstruction using DLIR algorithm was affected by various conditions such as iodine concentration and size. In particular, its accuracy was reduced by the size of target.

Dual-energy CT: Technical considerations and clinical applications

Although dual-energy CT was initially described by Hounsfield in 1973, it remains underused in clinical practice. It is therefore important to emphasize the clinical benefits and limitations of this technique. Iodine mapping makes it possible to quantify the uptake of iodine, which is very important in characterizing tumors, lung perfusion, pulmonary nodules, and the tumor response to new treatments. Dual-energy CT also makes it possible to obtain virtual single-energy images and virtual images without iodinated contrast or without calcium, as well as to separate materials such as uric acid or fat and to elaborate hepatic iron overload maps. In this article, we review some of the clinical benefits and technical limitations to improve understanding of dual-energy CT and expand its use in clinical practice.

Beyond acute cholecystitis-gallstone-related complications and what the emergency radiologist should know

The purpose of this study is to emphasize the imaging features of complications of gallstones beyond the cystic duct on ultrasound (US), enhanced and nonenhanced computed tomography (CECT and NECT), magnetic resonance imaging (MRI), magnetic resonance cholangiopancreatography (MRCP), and endoscopic retrograde cholangiopancreatography (ERCP). This article includes a brief overview of gallstone imaging and emerging trends in the detection of gallstones. This review article will highlight complications of gallstones, including choledocholithiasis, gallstone pancreatitis, acute cholangitis, Mirizzi syndrome, cholecystobiliary and cholecystoenteric fistulas, and gallstone ileus. Imaging findings and limitations of US, CT, MRI, and ERCP will be discussed. The review article will also briefly discuss the management of each disease. The presence of gallstones beyond the level of the cystic duct can lead to a spectrum of diseases, and emergency radiologists play a critical role in disease management by providing a timely diagnosis. Documenting the location of a gallstone within the common bile duct (CBD) in symptomatic cholelithiasis and the presence of acute interstitial edematous pancreatitis and/or ascending cholangitis plays a pivotal role in disease management. Establishing the presence of ectopic gallstones and biliary-enteric fistulae has a significant role in directing patient management.

Quantitative benchmarking of iodine imaging for two CT spectral imaging technologies: a phantom study

BACKGROUND

The aim of this study was to quantitatively benchmark iodine imaging across specific virtual monoenergetic energy levels, iodine maps and virtual non-contrast images with different phantom sizes and iodine concentrations, using a rapid switching dual-energy CT (DECT) and a dual source DECT, in order to investigate accuracy and potential differences between the technologies.

METHODS

Solutions of iodine contrast (10, 20, 30, 50, and 100 mg/mL), sterile water and saline were scanned in a phantom on a rapid switching single-source and dual-source DECT scanners from two different vendors. The phantom was equipped with polyurethane rings simulating three body sizes. The datasets were reconstructed in virtual monoenergetic energy levels (70, 80, 90, 100, 110, 120, 130, and 140 keV), virtual non-contrast images and iodine maps. HU and iodine concentrations were measured by placing ROIs in the iodine solutions.

RESULTS

The iodine concentrations were reproduced with a high degree of accuracy for the single-source DECT (1.8-9.0%), showing a slight dependence on phantom size. The dual source DECT technique showed deviant values (error -33.8 to 12.0%) for high concentrations. In relation to the virtual non-contrast measurements, the images from both vendors were affected by the iodine concentration and phantom size (-127.8 to 539.1 HU). Phantom size did not affect the calculated monoenergetic attenuation values, but the attenuation values varied between the scanners.

CONCLUSIONS

Quantitative measurements of post-processed images are dependent on the concentration of iodine, the phantom size and different technologies. However, our study indicates that the iodine maps are reliable for quantification of iodine.

Challenges in Diagnosis and Management of Hemobilia

Hemobilia, or hemorrhage within the biliary system, is an uncommon form of upper gastrointestinal (GI) bleeding that presents unique diagnostic and therapeutic challenges. Most cases are the result of iatrogenic trauma, although accidental trauma and a variety of inflammatory, infectious, and neoplastic processes have also been implicated. Timely diagnosis can often be difficult, as the classic triad of upper GI hemorrhage, biliary colic, and jaundice is present in a minority of cases, and there may be considerable delay in the onset of bleeding after the initial injury. Therefore, the radiologist must maintain a high index of suspicion for this condition and be attuned to its imaging characteristics across a variety of modalities. CT is the first-line diagnostic modality in evaluation of hemobilia, while catheter angiography and endoscopy play vital and complementary roles in both diagnosis and treatment. The authors review the clinical manifestations and multimodality imaging features of hemobilia, describe the wide variety of underlying causes, and highlight key management considerations.^©RSNA, 2021.

Dual-energy CT of the liver: True noncontrast vs. virtual noncontrast images derived from multiple phases for the diagnosis of fatty liver

PURPOSE

To evaluate the difference in liver density and to compare the performance to diagnose fatty liver between true noncontrast (TNC) images and virtual noncontrast (VNC) images generated from dual-energy CT (DECT).

MATERIALS AND METHODS

Patients who underwent liver dynamic DECT and MRI were included (n = 49). Two observers measured the liver and spleen densities on TNC images and three VNC images from the arterial, portal and delayed phases of DECT (VNCa, VNCp and VNCd, respectively). The liver-minus-spleen density (density L-S) and liver-to-spleen ratio (density L/S) were calculated. The CT parameters were compared between normal liver patients and fatty liver patients by using the independent t-test. Differences and agreements between measurements on TNC images and VNC images were evaluated by using the paired t-test and Bland-Altman analysis. Receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic performance of CT parameters for diagnosing fatty liver.

RESULTS

All CT parameters measured on TNC and VNC images were significantly higher in normal liver patients than in fatty liver patients. Although the mean liver densities on VNC images were significantly lower than those on TNC images, all CT parameters showed good agreement between TNC images and VNC images. The diagnostic performances of CT parameters on VNC images were not significantly different from those on TNC images.

CONCLUSION

Although the liver and spleen density on VNC images was significantly lower than that on TNC images, the diagnostic performances of CT parameters on three VNC images from multiple phases were similar to those on TNC images for diagnosing fatty liver.

Could both intrinsic and extrinsic iodine be successfully suppressed on virtual non-contrast CT images for detecting thyroid calcification?

PURPOSE

Although virtual non-contrast (VNC) successfully removes iodinated contrast, uncertainty exists regarding the feasibility of VNC to suppress iodine for detecting thyroid calcification. Therefore, we evaluated whether both intrinsic and extrinsic iodine attenuation were suppressed on VNC images.

MATERIAL AND METHODS

We enrolled 128 patients (male: female 17:111; age 48.0 ± 10.4 years) who underwent dual-layer dual-energy CT (DL-DECT) examination before their thyroid cancer surgeries. Two additional sets of VNC (VNCu, VNCc) images were retrospectively generated from their true unenhanced (TUE) and true contrast-enhanced (TCE) series. We compared CT attenuation values measured on the VNCu and VNCc images by drawing identical regions of interest encompassing thyroid parenchyma, then subjectively determined the concordance of calcification.

RESULTS

Although CT attenuation discrepancies between the VNCu and VNCc were significant (2.0 ± 5.7HU, p < 0.001),61.7%, 89.1%, and 100.0% of all measurements were < 5HU, < 10HU, and < 15HU. Based on Bland-Altman analysis, the limits of agreement were - 9.2HU and 13.2HU, whereas the proportional differences were small for VNC images generated from both TUE and TCE images. There was no discordance between two VNC image sets in detecting thyroid calcification.

CONCLUSIONS

VNC technique could be a feasible method to suppress both intrinsic and extrinsically administered iodine for detecting thyroid calcification.

Dual-layer spectral detector computed tomography versus magnetic resonance cholangiopancreatography for biliary stones

OBJECTIVE

Dual-layer spectral detector computed tomography (DLCT) can detect noncalcified biliary stones. The diagnostic ability of DLCT for detecting biliary stones may be comparable to that of magnetic resonance cholangiopancreatography (MRCP). This study seeks to compare the diagnostic ability for biliary stones between these two imaging modalities.

METHODS

This retrospective study included 102 cases with a diagnosis of biliary stones including gallstones (n = 66) and common bile duct (CBD) stones (n = 25) or spontaneously passing CBD stones (n = 11). The reference standard used was operative findings, endoscopic retrograde cholangiopancreatography or follow-up over 6 months. In DLCT, 120-kVp images, 40-keV virtual monoenergetic images and material decomposition images were created. We compared the diagnostic ability of DLCT and MRCP for biliary stones using the McNemar's test.

RESULTS

The sensitivity and specificity of DLCT versus MRCP for biliary stones were 91.2% versus 95.6% and 90.9% versus 90.9%. Thus, the sensitivity and specificity were not significantly different (P = 0.25 and P = 1.0). Although in small stones (<9 mm) the sensitivity of calcified stones was not different between DLCT and MRCP (100% versus 92.5%), the sensitivity of noncalcified stones in DLCT was lower than that in MRCP (38.5% versus 100%).

CONCLUSION

The diagnostic ability of biliary stones in DLCT appears comparable to that of MRCP in overall cases. However, detecting noncalcified stones less than 9 mm in size is limited in DLCT.

Phantomless assessment of volumetric bone mineral density using virtual non-contrast images from spectral detector computed tomography

OBJECTIVE

To evaluate phantomless assessment of volumetric bone mineral density (vBMD) based on virtual non-contrast images of arterial (VNC_a) and venous phase (VNC_v) derived from spectral detector CT in comparison to true non-contrast (TNC) images and adjusted venous phase conventional images (CI_V(adjusted)).

METHODS

104 consecutive patients who underwent triphasic spectral detector CT between January 2018 and April 2019 were retrospectively included. TNC, VNC_a, VNC_v and venous phase images (CI_V) were reconstructed. vBMD was obtained by two radiologists using an FDA/CE-cleared software. Average vBMD of the first three lumbar vertebrae was determined in each reconstruction; vBMD of CI_V was adjusted for contrast enhancement as suggested earlier.

RESULTS

vBMD values obtained from CI_V(adjusted) are comparable to vBMD values derived from TNC images (91.79 ± 36.52 vs 90.16 ± 41.71 mg/cm³, p = 1.00); however, vBMD values derived from VNC_a and VNC_v (42.20 ± 22.50 and 41.98 ± 23.3 mg/cm³ respectively) were significantly lower as compared to vBMD values from TNC and CI_V(adjusted) (all p ≤ 0.01).

CONCLUSION

Spectral detector CT-derived virtual non-contrast images systematically underestimate vBMD and therefore should not be used without appropriate adjustments. Adjusted venous phase images provide reliable results and may be utilized for an opportunistic BMD screening in CT examinations.

ADVANCES IN KNOWLEDGE

Adjustments of venous phase images facilitate opportunistic assessment of vBMD, while spectral detector CT-derived VNC images systematically underestimate vBMD.