Cecilia Besa

Hepatocellular carcinoma: short-term reproducibility of apparent diffusion coefficient and intravoxel incoherent motion parameters at 3.0T.

To evaluate short‐term test–retest and interobserver reproducibility of IVIM (intravoxel incoherent motion) diffusion parameters and ADC (apparent diffusion coefficient) of hepatocellular carcinoma (HCC) and liver parenchyma at 3.0T.

Imaging Assessment of Hepatocellular Carcinoma Response to Locoregional and Systemic Therapy

OBJECTIVE This article focuses on imaging techniques and imaging findings after locoregional and systemic therapy in patients with hepatocellular carcinoma (HCC). We discuss currently available locoregional and systemic therapies for HCC, imaging modalities and protocols used to assess HCC response, criteria for assessing HCC response, imaging appearances of treated HCC, and future directions. CONCLUSION The evaluation of tumor response after systemic and locoregional therapies is essential in directing management for HCC. An understanding of the various therapeutic strategies and of their posttherapy imaging appearances is essential for accurately assessing treatment response. The evaluation of tumor response should include not only anatomic imaging biomarkers, such as reduction in tumor size, but also tumor enhancement and necrosis.

Abdominal 4D Flow MR Imaging in a Breath Hold: Combination of Spiral Sampling and Dynamic Compressed Sensing for Highly Accelerated Acquisition

PURPOSE To develop a highly accelerated phase-contrast cardiac-gated volume flow measurement (four-dimensional [4D] flow) magnetic resonance (MR) imaging technique based on spiral sampling and dynamic compressed sensing and to compare this technique with established phase-contrast imaging techniques for the quantification of blood flow in abdominal vessels. MATERIALS AND METHODS This single-center prospective study was compliant with HIPAA and approved by the institutional review board. Ten subjects (nine men, one woman; mean age, 51 years; age range, 30-70 years) were enrolled. Seven patients had liver disease. Written informed consent was obtained from all participants. Two 4D flow acquisitions were performed in each subject, one with use of Cartesian sampling with respiratory tracking and the other with use of spiral sampling and a breath hold. Cartesian two-dimensional (2D) cine phase-contrast images were also acquired in the portal vein. Two observers independently assessed vessel conspicuity on phase-contrast three-dimensional angiograms. Quantitative flow parameters were measured by two independent observers in major abdominal vessels. Intertechnique concordance was quantified by using Bland-Altman and logistic regression analyses. RESULTS There was moderate to substantial agreement in vessel conspicuity between 4D flow acquisitions in arteries and veins (κ = 0.71 and 0.61, respectively, for observer 1; κ = 0.71 and 0.44 for observer 2), whereas more artifacts were observed with spiral 4D flow (κ = 0.30 and 0.20). Quantitative measurements in abdominal vessels showed good equivalence between spiral and Cartesian 4D flow techniques (lower bound of the 95% confidence interval: 63%, 77%, 60%, and 64% for flow, area, average velocity, and peak velocity, respectively). For portal venous flow, spiral 4D flow was in better agreement with 2D cine phase-contrast flow (95% limits of agreement: -8.8 and 9.3 mL/sec, respectively) than was Cartesian 4D flow (95% limits of agreement: -10.6 and 14.6 mL/sec). CONCLUSION The combination of highly efficient spiral sampling with dynamic compressed sensing results in major acceleration for 4D flow MR imaging, which allows comprehensive assessment of abdominal vessel hemodynamics in a single breath hold.

Interplatform reproducibility of liver and spleen stiffness measured with MR elastography.

To assess interplatform reproducibility of liver stiffness (LS) and spleen stiffness (SS) measured with magnetic resonance elastography (MRE) based on a 2D gradient echo (GRE) sequence.

Technical Failure of MR Elastography Examinations of the Liver: Experience from a Large Single-Center Study

Purpose To assess the determinants of technical failure of magnetic resonance (MR) elastography of the liver in a large single-center study. Materials and Methods This retrospective study was approved by the institutional review board. Seven hundred eighty-one MR elastography examinations performed in 691 consecutive patients (mean age, 58 years; male patients, 434 [62.8%]) in a single center between June 2013 and August 2014 were retrospectively evaluated. MR elastography was performed at 3.0 T (n = 443) or 1.5 T (n = 338) by using a gradient-recalled-echo pulse sequence. MR elastography and anatomic image analysis were performed by two observers. Additional observers measured liver T2* and fat fraction. Technical failure was defined as no pixel value with a confidence index higher than 95% and/or no apparent shear waves imaged. Logistic regression analysis was performed to assess potential predictive factors of technical failure of MR elastography. Results The technical failure rate of MR elastography at 1.5 T was 3.5% (12 of 338), while it was higher, 15.3% (68 of 443), at 3.0 T. On the basis of univariate analysis, body mass index, liver iron deposition, massive ascites, use of 3.0 T, presence of cirrhosis, and alcoholic liver disease were all significantly associated with failure of MR elastography (P < .004); but on the basis of multivariable analysis, only body mass index, liver iron deposition, massive ascites, and use of 3.0 T were significantly associated with failure of MR elastography (P < .004). Conclusion The technical failure rate of MR elastography with a gradient-recalled-echo pulse sequence was low at 1.5 T but substantially higher at 3.0 T. Massive ascites, iron deposition, and high body mass index were additional independent factors associated with failure of MR elastography of the liver with a two-dimensional gradient-recalled-echo pulse sequence.

Magnetic Resonance Elastography of the Liver: Qualitative and Quantitative Comparison of Gradient Echo and Spin Echo Echoplanar Imaging Sequences

ObjectiveThe aim of this study was to compare 2-dimensional (2D) gradient recalled echo (GRE) and 2D spin echo echoplanar imaging (SE-EPI) magnetic resonance elastography (MRE) sequences of the liver in terms of image quality and quantitative liver stiffness (LS) measurement. Materials and MethodsThis prospective study involved 50 consecutive subjects (male/female, 33/17; mean age, 58 years) who underwent liver magnetic resonance imaging at 3.0 T including 2 MRE sequences, 2D GRE, and 2D SE-EPI (acquisition time 56 vs 16 seconds, respectively). Image quality scores were assessed by 2 independent observers based on wave propagation and organ coverage on the confidence map (range, 0–15). A third observer measured LS on stiffness maps (in kilopascal). Mean LS values, regions of interest size (based on confidence map), and image quality scores between SE-EPI and GRE-MRE were compared using paired nonparametric Wilcoxon test. Reproducibility of LS values between the 2 sequences was assessed using intraclass coefficient correlation, coefficient of variation, and Bland-Altman limits of agreement. T2* effect on image quality was assessed using partial Spearman correlation. ResultsThere were 4 cases of failure with GRE-MRE and none with SE-EPI-MRE. Image quality scores and region of interest size were significantly higher using SE-EPI-MRE versus GRE-MRE (P < 0.0001 for both measurements and observers). Liver stiffness measurements were not significantly different between the 2 sequences (3.75 ± 1.87 kPa vs 3.55 ± 1.51 kPa, P = 0.062), were significantly correlated (intraclass coefficient correlation, 0.909), and had excellent reproducibility (coefficient of variation, 10.2%; bias, 0.023; Bland-Altman limits of agreement, −1.19; 1.66 kPa). Image quality scores using GRE-MRE were significantly correlated with T2* while there was no correlation for SE-EPI-MRE. ConclusionsOur data suggest that SE-EPI-MRE may be a better alternative to GRE-MRE. The diagnostic performance of SE-EPI-MRE for detection of liver fibrosis needs to be assessed in a future study.

Intravoxel incoherent motion diffusion-weighted imaging of hepatocellular carcinoma: Is there a correlation with flow and perfusion metrics obtained with dynamic contrast-enhanced MRI?

To assess the correlation between intravoxel incoherent motion diffusion‐weighted imaging (IVIM‐DWI) and dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) metrics in hepatocellular carcinoma (HCC) and liver parenchyma.

3D T1 relaxometry pre and post gadoxetic acid injection for the assessment of liver cirrhosis and liver function

PURPOSE To assess the diagnostic value of a 3D dual-flip-angle (DFA) T1 mapping technique with whole liver coverage before and after gadoxetic acid injection for assessment of cirrhosis and liver function, compared to blood tests (APRI: aspartate aminotransferase-to-platelet ratio index). MATERIALS AND METHODS A total of 133 patients who underwent gadoxetic acid-enhanced liver MRI including a 3D FLASH DFA-T1 mapping sequence before and 20min post-contrast (hepatobiliary phase, HBP) were included in this retrospective IRB approved study. T1 values (msec) were measured on pre-contrast and during HBP in liver parenchyma, ΔT1 (%) was calculated as [(T1 pre-T1 post)/T1 pre]×100. T1 and ΔT1 values were compared between cirrhotic and non-cirrhotic patients and between patients stratified using Child-Pugh and Model for End-Stage Liver Disease (MELD) scores using Mann-Whitney U test. Diagnostic performance of T1 mapping parameters vs. APRI for diagnosing cirrhosis and for assessing degree of liver dysfunction was evaluated using ROC analysis. RESULTS Fifty non-cirrhotic and 83 cirrhotic patients [Child-Pugh A (n=41), B (n=31) and C (n=11)] were included. There was no significant difference in pre-contrast T1 values between cirrhotic and non-cirrhotic patients. T1-HBP and ΔT1 values were significantly different in patients with cirrhosis (p<0.0001) and higher MELD scores (>17) (p=0.003). ΔT1 showed significant strong correlations with Child-Pugh and MELD scores (r=-0.7, p<0.0001; r=-0.56, p<0.001 respectively). Similar AUCs (p=0.9) for detection of liver cirrhosis were observed for T1 HBP (0.83), ΔT1 (0.86) and APRI (0.85); however APRI showed limited sensitivity (≤55%) in comparison with ΔT1 (74.7%) and T1 HBP (80.7%). CONCLUSION 3D DFA-T1 mapping sequence used before and after gadoxetic acid injection is useful for the diagnosis of cirrhosis and for the assessment of liver function.

IVIM diffusion-weighted imaging of the liver at 3.0 T: Comparison with 1.5 T

Purpose To compare intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) of the liver between 1.5 T and 3.0 T in terms of parameter quantification and inter-platform reproducibility. Materials and methods In this IRB approved prospective study, 19 subjects (17 patients with chronic liver disease and 2 healthy volunteers) underwent two repeat scans at 1.5 T and 3.0 T. Each scan included IVIM DWI using 16 b values from 0 to 800 s/mm2. A single observer measured IVIM parameters for each platform and estimated signal to noise ratio (eSNR) at b0, 200, 400 and 800 s/mm2. Wilcoxon paired tests were used to compare liver eSNR and IVIM parameters. Inter-platform reproducibility was assessed by calculating within-subject coefficient of variation (CV) and Bland–Altman limits of agreement. An ice water phantom was used to test ADC variability between the two MRI systems. Results The mean invitro difference in ADC between the two platforms was 6.8%. eSNR was significantly higher at 3.0T for all selected b values (p = 0.006–0.020), except for b0 (p = 0.239). Liver IVIM parameters were significantly different between 1.5 T and 3.0 T (p = 0.005–0.044), except for ADC (p = 0.748). The inter-platform reproducibility of true diffusion coefficient (D) and ADC were good, with mean CV of 10.9% and 11.1%, respectively. Perfusion fraction (PF) and pseudodiffusion coefficient (D*) showed more limited inter-platform reproducibility (mean CV of 22.6% for PF and 46.9% for D*). Conclusion Liver D and ADC values showed good reproducibility between 1.5 T and 3.0 T platforms; while there was more variability in PF, and large variability in D* parameters between the two platforms. These findings may have implications for drug trials assessing the role of IVIM DWI in tumor response and liver fibrosis.

Quantification of hepatocellular carcinoma heterogeneity with multiparametric magnetic resonance imaging

Tumour heterogeneity poses a significant challenge for treatment stratification. The goals of this study were to quantify heterogeneity in hepatocellular carcinoma (HCC) using multiparametric magnetic resonance imaging (mpMRI), and to report preliminary data correlating quantitative MRI parameters with advanced histopathology and gene expression in a patient subset. Thirty-two HCC patients with 39 HCC lesions underwent mpMRI including diffusion-weighted imaging (DWI), blood-oxygenation-level-dependent (BOLD), tissue-oxygenation-level-dependent (TOLD) and dynamic contrast-enhanced (DCE)-MRI. Histogram characteristics [central tendency (mean, median) and heterogeneity (standard deviation, kurtosis, skewness) MRI parameters] in HCC and liver parenchyma were compared using Wilcoxon signed-rank tests. Histogram data was correlated between MRI methods in all patients and with histopathology and gene expression in 14 patients. HCCs exhibited significantly higher intra-tissue heterogeneity vs. liver with all MRI methods (P < 0.030). Although central tendency parameters showed significant correlations between MRI methods and with each of histopathology and gene expression, heterogeneity parameters exhibited additional complementary correlations between BOLD and DCE-MRI and with histopathologic hypoxia marker HIF1α and gene expression of Wnt target GLUL, pharmacological target FGFR4, stemness markers EPCAM and KRT19 and immune checkpoint PDCD1. Histogram analysis combining central tendency and heterogeneity mpMRI features is promising for non-invasive HCC characterization on the imaging, histologic and genomics levels.