Metal artifact reduction by virtual monoenergetic reconstructions from spectral brain CT.

Purpose: Conventional computed tomography (CT) images are severely affected by metal artifacts in patients with intracranial coils. Monoenergetic images have been suggested to reduce metal artifacts.The aim of this study was to assess metal artifacts in virtual monoenergetic images (VMIs) reconstructed from spectral brain CT. Methods: Thirty-two consecutive patients with intracranial coils examined by spectral non contrast brain CT (NCCT) at our center between November 2017 and April 2019 were included. Attenuation and standard deviations were measured in regions of interest (ROIs) at predefined areas in artifact-free and artifact-affected areas. Measurements were performed in conventional polyenergetic images (CIs) and the corresponding data for VMIs were retrieved through spectral diagrams for the each ROI. Subjective analysis was performed by visual grading of CIs and specific VMIs by two neuroradiologists, independently. Results: In artefact-affected image areas distal from the metal objects, the attenuation values decreased with higher energy level VMIs. The same effect was not seen for artefact-affected image areas close to the metal.Subjective rating of the artefact severity was significantly better in VMIs at 50 keV for one of the two reviewers compared to the CIs. Overall image quality and tissue differentiation scores were significantly higher for both reviewers in VMIs at 60 and 70 keV compared to CIs. Conclusion: Our quantitative and qualitative image analysis shown that there is a small significant reduction of intracranial coils artifacts severity by all monoenergetic reconstructions from 50 to 200 keV with preserved or increased overall subjective image quality compared to conventional images.

Imaging biomarkers to stratify lymph node metastases in abdominal CT - Is radiomics superior to dual-energy material decomposition?

Purpose: To assess the potential of radiomic features in comparison to dual-energy CT (DECT) material decomposition to objectively stratify abdominal lymph node metastases. Materials and methods: In this retrospective study, we included 81 patients (m, 57; median age, 65 (interquartile range, 58.7-73.3) years) with either lymph node metastases (n = 36) or benign lymph nodes (n = 45) who underwent contrast-enhanced abdominal DECT between 06/2015-07/2019. All malignant lymph nodes were classified as unequivocal according to RECIST criteria and confirmed by histopathology, PET-CT or follow-up imaging. Three investigators segmented lymph nodes to extract DECT and radiomics features. Intra-class correlation analysis was applied to stratify a robust feature subset with further feature reduction by Pearson correlation analysis and LASSO. Independent training and testing datasets were applied on four different machine learning models. We calculated the performance metrics and permutation-based feature importance values to increase interpretability of the models. DeLong test was used to compare the top performing models. Results: Distance matrices and t-SNE plots revealed clearer clusters using a combination of DECT and radiomic features compared to DECT features only. Feature reduction by LASSO excluded all DECT features of the combined feature cohort. The top performing radiomic features model (AUC = 1.000; F1 = 1.000; precision = 1.000; Random Forest) was significantly superior to the top performing DECT features model (AUC = 0.942; F1 = 0.762; precision = 0.800; Stochastic Gradient Boosting) (DeLong < 0.001). Conclusion: Imaging biomarkers have the potential to stratify unequivocal lymph node metastases. Radiomics models were superior to DECT material decomposition and may serve as a support tool to facilitate stratification of abdominal lymph node metastases.

Associations between paraspinal muscles fatty infiltration and lumbar vertebral bone mineral density - An investigation by fast kVp switching dual-energy CT and QCT.

Purpose: To investigate the relationship between paraspinal muscles fat content and lumbar bone mineral density (BMD). Methods: A total of 119 participants were enrolled in our study (60 males, age: 50.88 ± 17.79 years, BMI: 22.80 ± 3.80 kg·m-2; 59 females, age: 49.41 ± 17.69 years, BMI: 22.22 ± 3.12 kg·m-2). Fat content of paraspinal muscles (erector spinae (ES), multifidus (MS), and psoas (PS)) were measured at (ES L1/2-L4/5; MS L2/3-L5/S1; PS L2/3-L5/S1) levels using dual-energy computed tomography (DECT). Quantitative computed tomography (QCT) was used to assess BMD of L1 and L2. Linear regression analysis was used to assess the relationship between BMD of the lumbar spine and paraspinal muscles fat content with age, sex, and BMI. The variance inflation factor (VIF) was used to detect the degree of multicollinearity among the variables. P < .05 was considered to indicate a statistically significant difference. Results: The paraspinal muscles fat content had a fairly significant inverse association with lumbar BMD after controlling for age, sex, and BMI (adjusted R 2 = 0.584-0.630, all P < .05). Conclusion: Paraspinal muscles fat content was negatively associated with BMD.Paraspinal muscles fatty infiltration may be considered as a potential marker to identify BMD loss.

Persistent respiratory failure after SARS-CoV-2 infection: The role of dual energy computed tomography. A case report.

Background: COVID-19 disease is often complicated by respiratory failure, developing through multiple pathophysiological mechanisms, with pulmonary embolism (PE) and microvascular thrombosis as key and frequent components. Newer imaging modalities such as dual-energy computed tomography (DECT) can represent a turning point in the diagnosis and follow-up of suspected PE during COVID-19. Case presentation: A 78-year-old female presented to our internal medicine 3 weeks after initial hospitalization for COVID-19 disease, for recrudescent respiratory failure needing oxygen therapy. A computed tomography (CT) lungs scan showed a typical SARSCoV-2 pneumonia. Over the following 15 days, respiratory function gradually improved. Unexpectedly, after 21 days from symptom onset, the patient started complaining of breath shortening with remarkable desaturation requiring high-flow oxygen ventilation. CT pulmonary angiography and transthoracic echocardiography were negative for signs of PE. Thereby, Dual-energy CT angiography of the lungs (DECT) was performed and detected diffuse peripheral microembolism. After 2 weeks, a second DECT was performed, showing a good response to the anticoagulation regimen, with reduced extent of microembolism and some of the remaining emboli partially recanalized. Discussion: DECT is an emerging diagnostic technique providing both functional and anatomical information. DECT has been reported to produce a much sharper delineation of perfusion defects than pulmonary scintigraphy, using a significantly lower equivalent dose of mSv. We highlight that DECT is particularly useful in SARS-Cov-2 infection, in order to determine the predominant underlying pathophysiology, particularly when respiratory failure prolongs despite improved lung parenchymal radiological findings.

Dual energy imaging in cardiothoracic pathologies: A primer for radiologists and clinicians.

Recent advances in dual-energy imaging techniques, dual-energy subtraction radiography (DESR) and dual-energy CT (DECT), offer new and useful additional information to conventional imaging, thus improving assessment of cardiothoracic abnormalities. DESR facilitates detection and characterization of pulmonary nodules. Other advantages of DESR include better depiction of pleural, lung parenchymal, airway and chest wall abnormalities, detection of foreign bodies and indwelling devices, improved visualization of cardiac and coronary artery calcifications helping in risk stratification of coronary artery disease, and diagnosing conditions like constrictive pericarditis and valvular stenosis. Commercially available DECT approaches are classified into emission based (dual rotation/spin, dual source, rapid kilovoltage switching and split beam) and detector-based (dual layer) systems. DECT provide several specialized image reconstructions. Virtual non-contrast images (VNC) allow for radiation dose reduction by obviating need for true non contrast images, low energy virtual mono-energetic images (VMI) boost contrast enhancement and help in salvaging otherwise non-diagnostic vascular studies, high energy VMI reduce beam hardening artifacts from metallic hardware or dense contrast material, and iodine density images allow quantitative and qualitative assessment of enhancement/iodine distribution. The large amount of data generated by DECT can affect interpreting physician efficiency but also limit clinical adoption of the technology. Optimization of the existing workflow and streamlining the integration between post-processing software and picture archiving and communication system (PACS) is therefore warranted.

Iterative metal artifact reduction in aortic CTA after Onyx®-embolization.

PURPOSE: Onyx® embolization causes severe artifacts on subsequent CT-examinations, thereby seriously limiting the diagnostic quality.The purpose of this work was to compare the diagnostic quality of the tailored metal artifact reducing algorithms iMAR to standard reconstructions of CTA in patients treated with Onyx® embolization. METHOD: Twelve consecutive patients examined with Dual Energy CTA after Onyx® embolization were included. One standard image dataset without iMAR, and eight image datasets with different iMAR algorithms were reconstructed. Mean attenuation and noise were measured in the aorta or iliac arteries close to the Onyx® glue-cast and compared to the reference level in the diaphragmatic aorta. Mean attenuation and noise were also measured in the psoas muscle close to the Onyx®-glue and compared to the reference level in the psoas muscle at the level of the diaphragm.Subjective image quality and severity of artifacts was assessed by two experienced interventional radiologists blinded to reconstruction details. RESULTS: All iMAR reconstructions had less distortion of the attenuation than the standard reconstructions and were also rated significantly better than the standard reconstructions by both interventional radiologists. CONCLUSION: The iMAR algorithms can significantly reduce metal artifacts and improve the diagnostic quality in CTA in patients treated with Onyx® embolization, in many cases restoring non-diagnostic examinations to acceptable diagnostic quality.

Quantitative attenuation accuracy of virtual non-enhanced imaging compared to that of true non-enhanced imaging on dual-source dual-energy CT.

PURPOSE: To evaluate the quantitative attenuation and reliability of virtual non-contrast (VNC) images of the abdomen acquired from multiphasic scans with a dual-energy computed tomography (DECT) system and compare it with that of true non-enhanced images (TNC) on second- (Flash) and third- (Force) generation DECT scanners. METHODS: This retrospective study was approved by the institutional review board and included 123 patients with pancreatic cancer who had undergone routine clinical multiphasic DECT examinations at our institution using Flash and Force scanners between March and August 2017. VNC images of the abdomen were reconstructed from late arterial phase images. For every patient, regions-of-interest were defined in the aorta, fluid-containing structures (gallbladder, pleural effusion, and renal cysts > 10 mm), paravertebral muscles, subcutaneous fat, spleen, pancreas, renal cortex, and liver (eight locations) on TNC and VNC images. The mean attenuation of VNC was compared with TNC by organ for each CT scanner using an equivalence test and the Bland-Altman plot. The mean attenuations for TNC or VNC were compared between the Force and Flash CT scanners using a two-sample t test. RESULTS: The VNC attenuation of organs on the Force scanner was lower than was that on the Flash, and the mean attenuation difference in different organs on the Force was closer to 0. The estimated means of TNC and VNC were equivalent for an equivalence margin of 10 on the Force scanner. CONCLUSION: VNC images in DECT are a promising alternative to TNC images. In clinical scenarios in which non-enhanced CT images are required but are not available for accurate diagnosis, VNC images can potentially serve as an alternative to TNC images without the radiation exposure risks.

Feasibility of Macrophage Plaque Imaging Using Novel Ultrasmall Superparamagnetic Iron Oxide in Dual Energy CT.

PURPOSE: While ultrasmall superparamagnetic iron oxide (USPIO) is useful for identifying atherosclerotic lesions as an MRI contrast medium, there are limitations in its power to quantitatively evaluate and resolve USPIO in atherosclerotic lesions of the heart. Computed tomography (CT) has a higher resolution than MRI, and Dual Energy CT is capable of visualizing iron atoms, the main component of USPIO. More recently, a new USPIO capable of achieving longer retention times in blood circulation compared to the previous USPIO has been developed. The objective of this study was to investigate the feasibility of visualizing and quantifying the new USPIO by dual energy CT. MATERIALS AND METHODS: USPIO with iron concentrations adjusted in 5 steps from 2.5 to 50 mg/mL was visualized by dual energy CT to measure the contrast on virtual monochromatic imaging (40 and 70 keV). In parallel experiments, iodine contrast medium was diluted to the same concentrations and visualized by dual energy CT to measure the contrast at 70 keV. The linearity of the contrast against the iron and iodine concentrations was measured for the quantitative evaluation. Further, a vascular phantom simulating clinical cases (divided into 4 layers: meat alone, meat + USPIO, vascular lumen, and with or without calcification) was prepared. The iron density image was overlaid on the image at 70 keV to evaluate the visualization of the USPIO medium. RESULTS: In the imaging of the medium with an iron concentration of 25 mg/mL, the CT numberat 70 keV was 117.0 HU, or about 17% of that of iodine (664.4 HU). The CT number rose to 319.9 HU at 40 keV, or to about 48% of that of iodine. The linearity of the contrast against the iron concentration in USPIO was R2 = 0.9996, indicating a strong correlation. In the simulated vascular phantom, the iron concentration significantly increased in the region containing USPIO, and the quantity could be visualized by overlaying the iron density image displayed with a color scale on the 70-keV image. CONCLUSION: Our results suggested that macrophages could be both quantified and visualized by USPIO on dual energy CT.

Role of dual energy spectral computed tomography in characterization of hepatocellular carcinoma: Initial experience from a tertiary liver care institute.

OBJECTIVE: To investigate dual-energy spectral CT in characterization of hepatocellular Carcinoma (HCC) in patients with chronic liver disease. METHODS: Dynamic computed tomography (CT) was performed in 3600 patients (2879 males; 721 females, mean age 50.9 ± 11.9 years) with working clinical diagnosis of liver cirrhosis for hepatocellular carcinoma screening and other clinical indications. The study was conducted over a period of 3 years. During dynamic CT scanning, spectral (monochromatic) and routine (polychromatic) CT acquisitions were obtained on a single tube, dual energy, 64 slice multi-detector CT scanner. Imaging findings were studied on routine CT. On the basis of routine CT findings, indeterminate lesions (lesions not showing characteristic hypervascularity followed by washout on dynamic routine CT scan) that were referred for biopsy or surgery were segregated. A retrospective blinded review of the lesions, acquired by the spectral CT acquisitions was done with the help of gem stone imaging (GSI) software to characterize these lesions. All the above lesions were analyzed qualitatively in the arterial phase for lesion conspicuity as well as quantitatively using the monochromatic data sets and nodule Iodine concentration on material density maps, respectively. This data was studied with respect to predictability of HCC using the spectral CT technique. Iodine density of the lesion, surrounding liver parenchyma, and lesion to liver parenchyma ratio (LLR) were derived and statistically analyzed. Histopathology of the lesion in question was treated as gold standard for analysis. RESULTS: It was observed via statistical analysis that the value of iodine density of the lesion on material density sets of ≥29.5 mg/dl, enabled a discriminatory power of 86.5%, sensitivity of 90.5% with 95% confidence Interval (CI) (69.2-98.8%) and specificity of 81.2% with 95% Confidence Interval (54.4-95.9%) in predicting HCC. Qualitative assessment also showed higher lesion conspicuity with spectral CT image sets as compared to routine CT data. CONCLUSION: This study reveals that spectral imaging is an excellent qualitative as well as a quantitative tool for assessing and predicting hepatocellular carcinoma in cirrhotic patients.