Peter Bannas

Hepatobiliary MR contrast agents in hypovascular hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) develops via multistep hepatocarcinogenesis, during which hypovascular/early HCC precedes the typical hypervascular HCC. The hypovascular HCC lacks the typical hallmark imaging features of HCC, such as late arterial phase enhancement and portal venous washout, limiting early detection using conventional extracellular contrast agents for dynamic magnetic resonance imaging (MRI) or computed tomography (CT) imaging. In recent years, gadolinium‐based contrast agents with hepatobiliary uptake have garnered interest from radiologists and hepatologists due to their potential for improved detection of HCC during hepatobiliary phase MRI. Lesions with reduced or absent hepatocyte function appear hypointense in the hepatobiliary phase of gadoxetic acid‐enhanced MRI. This behavior can be exploited for earlier detection of hypovascular HCC. This review describes the general characteristics and advantages of gadoxetic acid for the diagnosis of HCC with a particular focus on hypovascular/early HCC. J. Magn. Reson. Imaging 2015;41:251–265.© 2013 Wiley Periodicals, Inc.

MRI-based quantitative susceptibility mapping (QSM) and R2* mapping of liver iron overload: Comparison with SQUID-based biomagnetic liver susceptometry.

We aimed to determine the agreement between quantitative susceptibility mapping (QSM)‐based biomagnetic liver susceptometry (BLS) and confounder‐corrected R2* mapping with superconducting quantum interference device (SQUID)‐based biomagnetic liver susceptometry in patients with liver iron overload.

Quantification of liver fat with respiratory-gated quantitative chemical shift encoded MRI

To evaluate free‐breathing chemical shift‐encoded (CSE) magnetic resonance imaging (MRI) for quantification of hepatic proton density fat‐fraction (PDFF). A secondary purpose was to evaluate hepatic R2* values measured using free‐breathing quantitative CSE‐MRI.

Combined gadoxetic acid and gadofosveset enhanced liver MRI: A feasibility and parameter optimization study

Demonstration of feasibility and protocol optimization for the combined use of gadofosveset trisodium with gadoxetic acid for delayed T1‐weighted liver MRI.

Combined dynamic contrast‐enhanced liver MRI and MRA using interleaved variable density sampling

To develop and evaluate a method for volumetric contrast‐enhanced MRI of the liver, with high spatial and temporal resolutions, for combined dynamic imaging and MR angiography (MRA) using a single injection of contrast agent.

MR Evaluation of the Nontraumatic Acute Abdomen with CT Correlation

Cross-sectional imaging plays a crucial role in the triage of patients with acute abdominal pain. Ionizing radiation exposure is a recognized drawback of computed tomography (CT), the primary imaging technique. MR imaging is a promising alternative to CT; it provides excellent image quality with high-contrast resolution without the disadvantages of ionizing radiation and iodinated contrast. This article provides a basic overview of the typical MR findings of the most frequent disease entities encountered in the setting of the nontraumatic acute abdomen, including direct comparison with CT findings to familiarize the readers with these same findings on MR.

Quantitative MR Imaging of Hepatic Steatosis: Validation in Ex Vivo Human Livers

Emerging magnetic resonance imaging (MRI) biomarkers of hepatic steatosis have demonstrated tremendous promise for accurate quantification of hepatic triglyceride concentration. These methods quantify the proton density fat‐fraction (PDFF), which reflects the concentration of triglycerides in tissue. Previous in vivo studies have compared MRI‐PDFF with histologic steatosis grading for assessment of hepatic steatosis. However, the correlation of MRI‐PDFF with the underlying hepatic triglyceride content remained unknown. The aim of this ex vivo study was to validate the accuracy of MRI‐PDFF as an imaging biomarker of hepatic steatosis. Using ex vivo human livers, we compared MRI‐PDFF with magnetic resonance spectroscopy‐PDFF (MRS‐PDFF), biochemical triglyceride extraction, and histology as three independent reference standards. A secondary aim was to compare the precision of MRI‐PDFF relative to biopsy for the quantification of hepatic steatosis. MRI‐PDFF was prospectively performed at 1.5 Tesla in 13 explanted human livers. We performed colocalized paired evaluation of liver fat content in all nine Couinaud segments using single‐voxel MRS‐PDFF (n = 117) and tissue wedges for biochemical triglyceride extraction (n = 117), and five core biopsies performed in each segment for histologic grading (n = 585). Accuracy of MRI‐PDFF was assessed through linear regression with MRS‐PDFF, triglyceride extraction, and histology. Intraobserver agreement, interobserver agreement, and repeatability of MRI‐PDFF and histologic grading were assessed through Bland‐Altman analyses. MRI‐PDFF showed an excellent correlation with MRS‐PDFF (r = 0.984, confidence interval 0.978‐0.989) and strong correlation with histology (r = 0.850, confidence interval 0.791‐0.894) and triglyceride extraction (r = 0.871, confidence interval 0.818‐0.909). Intraobserver agreement, interobserver agreement, and repeatability showed a significantly smaller variance for MRI‐PDFF than for histologic steatosis grading (all P < 0.001). Conclusion: MRI‐PDFF is an accurate, precise, and reader‐independent noninvasive imaging biomarker of liver triglyceride content, capable of steatosis quantification over the entire liver. (Hepatology 2015;62:1444–1455)

Intraindividual Crossover Comparison of Gadoxetic Acid Dose for Liver MRI in Normal Volunteers.

PURPOSE We performed a quantitative intraindividual comparison of the performance of 0.025- and 0.05-mmol/kg doses for gadoxetic acid-enhanced liver magnetic resonance (MR) imaging. MATERIALS AND METHODS Eleven healthy volunteers underwent liver MR imaging twice, once with a 0.025- and once with a 0.05-mmol/kg dose of gadoxetic acid. MR spectroscopy and 3-dimensional gradient-echo T1-weighted images (3D-GRE) were obtained before and 3, 10, and 20 min after injection of the contrast medium to measure T1 and T2 values and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) performance. During the dynamic phase, highly time-resolved 3D-GRE was used to estimate the relative CNR (CNRrel) of the hepatic artery and portal vein (PV) to the liver. We used paired t-tests to compare the results of different doses. RESULTS During the hepatobiliary phase, we observed shorter T1 values and higher SNRs of the liver (P < 0.001) and higher liver-to-PV and liver-to-muscle CNRs (P < 0.002) using 0.05 mmol/kg compared to 0.025 mmol/kg. Increasing the dose to 0.05 mmol/kg yielded a greater T1-shortening effect at 10 min delay even compared with 0.025 mmol/kg at 20 min (P < 0.001). During the dynamic phase, the peak CNRrel for the hepatic artery and portal vein were higher using 0.05 mmol/kg (P = 0.007 to 0.035). CONCLUSION Use of gadoxetic acid at a dose of 0.05 mmol/kg leads to significantly higher SNR and CNR performance than with 0.025 mmol/kg. Quantitatively, a 10-min delay may be feasible for hepatobiliary-phase imaging when using 0.05 mmol/kg of gadoxetic acid.

Prior Image Constrained Compressed Sensing Metal Artifact Reduction (PICCS-MAR): 2D and 3D Image Quality Improvement with Hip Prostheses at CT Colonography

AbstractPurposeTo assess the effect of the prior-image-constrained-compressed-sensing-based metal-artefact-reduction (PICCS-MAR) algorithm on streak artefact reduction and 2D and 3D-image quality improvement in patients with total hip arthroplasty (THA) undergoing CT colonography (CTC).Materials and methodsPICCS-MAR was applied to filtered-back-projection (FBP)-reconstructed DICOM CTC-images in 52 patients with THA (unilateral, n = 30; bilateral, n = 22). For FBP and PICCS-MAR series, ROI-measurements of CT-numbers were obtained at predefined levels for fat, muscle, air, and the most severe artefact. Two radiologists independently reviewed 2D and 3D CTC-images and graded artefacts and image quality using a five-point-scale (1 = severe streak/no-diagnostic confidence, 5 = no streak/excellent image-quality, high-confidence). Results were compared using paired and unpaired t-tests and Wilcoxon signed-rank and Mann-Whitney-tests.ResultsStreak artefacts and image quality scores for FBP versus PICCS-MAR 2D-images (median: 1 vs. 3 and 2 vs. 3, respectively) and 3D images (median: 2 vs. 4 and 3 vs. 4, respectively) showed significant improvement after PICCS-MAR (all P < 0.001). PICCS-MAR significantly improved the accuracy of mean CT numbers for fat, muscle and the area with the most severe artefact (all P < 0.001).ConclusionsPICCS-MAR substantially reduces streak artefacts related to THA on DICOM images, thereby enhancing visualization of anatomy on 2D and 3D CTC images and increasing diagnostic confidence.Key Points• PICCS-MAR significantly reduces streak artefacts associated with total hip arthroplasty on 2D and 3D CTC. • PICCS-MAR significantly improves 2D and 3D CTC image quality and diagnostic confidence. • PICCS-MAR can be applied retrospectively to DICOM images from single-kVp CT.

Intra-individual comparison of magnesium citrate and sodium phosphate for bowel preparation at CT colonography: Automated volumetric analysis of residual fluid for quality assessment

AIM To perform an objective, intra-individual comparison of residual colonic fluid volume and attenuation associated with the current front-line laxative magnesium citrate (MgC) versus the former front-line laxative sodium phosphate (NaP) at CT colonography (CTC). MATERIALS AND METHODS This retrospective Health Insurance and Portability and Accountability Act-compliant study had institutional review board approval; informed consent was waived. The study cohort included 250 asymptomatic adults (mean age at index 56.1 years; 124 male/126 female) who underwent CTC screening twice over a 5 year interval. Colon catharsis at initial and follow-up screening employed single-dose NaP and double-dose MgC, respectively, allowing for intra-patient comparison. Automated volumetric analysis of residual colonic fluid volume and attenuation was performed on all 500 CTC studies. Colonic fluid volume <200 ml and mean attenuation between 300-900 HU were considered optimal. Paired t-test and McNemars test were used to compare differences. RESULTS Residual fluid volumes <200 ml were recorded in 192 examinations (76.8%) following MgC and in 204 examinations (81.6%) following NaP (p = 0.23). The mean total residual fluid volume was 155 ± 114 ml for MgC and 143 ± 100 ml for NaP (p = 0.01). The attenuation range of 300-900 HU was significantly more frequent for MgC (n = 220, 88%) than for NaP (n = 127, 50.8%; p < 0.001). Mean fluid attenuation was significantly lower for MgC (700 ± 165 HU) than for NaP (878 ± 155 HU; p < 0.001). Concomitant presence of both optimal fluid volume and attenuation was significantly more frequent for MgC 65.2% than for NaP (38%; p < 0.001). CONCLUSIONS Objective intra-individual comparison using automated volumetric analysis suggests that the replacement of NaP by MgC as the front-line laxative for CTC has not compromised overall examination quality.