Faculty Bibliography

OBJECTIVE: The purpose of this study was to validate the utility of dual-source dual-energy MDCT in quantifying iodine concentration in a phantom and in renal masses. MATERIALS AND METHODS: A series of tubes containing solutions of varying iodine concentration were imaged with dual-source dual-energy MDCT. Iodine concentration was calculated and compared with known iodine concentration. Single-phase contrast-enhanced dual-source dual-energy MDCT data on 15 patients with renal lesions then were assessed independently by two readers. Dual-energy postprocessing was used to generate iodine-only images. Regions of interest were placed on the iodine image over the lesion and, as a reference, over the aorta, for recording of iodine concentration in the lesion and in the aorta. Another radiologist determined lesion enhancement by comparing truly unenhanced with contrast-enhanced images. Mixed-model analysis of variance based on ranks was used to compare lesion types (simple cyst, hemorrhagic cyst, enhancing mass) in terms of lesion iodine concentration and lesion-to-aorta iodine ratio. RESULTS: In the phantom study, there was excellent correlation between calculated and true iodine concentration (R(2) = 0.998, p < 0.0001). In the patient study, 13 nonenhancing (10 simple and three hyperdense cysts) and eight enhancing renal masses were evaluated in 15 patients. The lesion iodine concentration and lesion-to-aorta iodine ratio in enhancing masses were significantly higher than in hyperdense and simple cysts (p < 0.0001). CONCLUSION: Iodine quantification with dual-source dual-energy MDCT is accurate in a phantom and can be used to determine the presence and concentration of iodine in a renal lesion. Characterization of renal masses may be possible with a single dual-source dual-energy MDCT acquisition without unenhanced images or reliance on a change in attenuation measurements

OBJECTIVES: : To obtain intravoxel incoherent motion (IVIM) parameters with biexponential analysis of multiple b-value diffusion-weighted imaging (DWI) and compare these parameters to apparent diffusion coefficient (ADC) obtained with monoexponential modeling in their ability to discriminate enhancing from nonenhancing renal lesions. MATERIALS AND METHODS: : Twenty-eight patients were imaged at 1.5 T utilizing contrast-enhanced (CE) magnetic resonance imaging (MRI) and breath-hold DWI using 8 b values (range: 0-800 s/mm). Perfusion fraction (fp), tissue diffusivity (Dt), and pseudo-diffusion coefficient (Dp) were calculated using segmented biexponential analysis. ADCtotal and ADC0-400-800 were calculated with monoexponential fitting of the DWI data. fp, Dt, Dp, ADCtotal, and ADC0-400-800 were compared between enhancing and nonenhancing renal lesions. Receiver operating characteristic analysis was performed for all DWI parameters. fp was correlated with percent enhancement. RESULTS: : There were a total of 31 renal lesions (15 enhancing and 16 nonenhancing) in 28 patients on CE-MRI. fp of enhancing masses was significantly higher (27.9 vs. 6.1) and Dt was significantly lower (1.47 vs. 2.40 x10 mm/s). IVIM parameters fp and Dt demonstrated higher accuracy in differentiating enhancing from nonenhancing renal lesions compared with monoexponential parameters ADC0-400-800 and ADCtotal, with area under the curve of 0.946, 0.896, 0.854, and 0.675, respectively. There was a good correlation between fp and percent enhancement (r = 0.7; P < 0.001). CONCLUSION: : IVIM parameters fp and Dt obtained with biexponential fitting of multi-b value DWI have higher accuracy compared with ADC (obtained with monoexponential fit) in discriminating enhancing from nonenhancing renal lesions. Furthermore, fp demonstrates good correlation with percent enhancement and can provide information regarding lesion vascularity without the use of exogenous contrast agent

PURPOSE: To assess the accuracy of glomerular filtration rate (GFR) measurements obtained with low-contrast agent dose dynamic contrast material-enhanced magnetic resonance (MR) renography in patients with liver cirrhosis who underwent routine liver MR imaging, with urinary clearance of technetium 99m ((99m)Tc) pentetic acid (DTPA) as the reference standard. MATERIALS AND METHODS: This HIPAA-compliant study was institutional review board approved. Written informed patient consent was obtained. Twenty patients with cirrhosis (14 men, six women; age range, 41-70 years; mean age, 54.6 years) who were scheduled for routine 1.5-T liver MR examinations to screen for hepatocellular carcinoma during a 6-month period were prospectively included. Five-minute MR renography with a 3-mL dose of gadoteridol was performed instead of a routine test-dose timing examination. The GFR was estimated at MR imaging with use of two kinetic models. In one model, only the signal intensities in the aorta and kidney parenchyma were considered, and in the other, renal cortical and medullary signal intensities were treated separately. The GFR was also calculated by using serum creatinine levels according to the Cockcroft-Gault and modification of diet in renal disease (MDRD) formulas. All patients underwent a (99m)Tc-DTPA urinary clearance examination on the same day to obtain a reference GFR measurement. The accuracies of all MR- and creatinine-based GFR estimations were compared by using Wilcoxon signed rank tests. RESULTS: The mean reference GFR, based on (99m)Tc-DTPA clearance, was 74.9 mL/min/1.73 m(2) +/- 27.7 (standard deviation) (range, 10.3-120.7 mL/min/1.73 m(2)). With both kinetic models, 95% of MR-based GFRs were within 30% of the reference values, whereas only 40% and 60% of Cockcroft-Gault- and MDRD-based GFRs, respectively, were within this range. MR-based GFR estimates were significantly more accurate than creatinine level-based estimates (P < .001). CONCLUSION: GFR assessment with MR imaging, which outperformed the Cockcroft-Gault and MDRD formulas, adds less than 10 minutes of table time to a clinically indicated liver MR examination without ionizing radiation. Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1

OBJECTIVE: The purpose of this article is to correlate clinicopathologic and MRI parameters with the presence of microvascular invasion at histopathologic examination in patients with hepatocellular carcinoma (HCC) who are undergoing liver transplantation. MATERIALS AND METHODS: In this retrospective single-center study, we assessed 60 patients (47 men and 13 women; mean age, 58 years) with HCC who underwent liver transplantation and pretransplant MRI (performed within 90 days before liver transplantation). Two observers analyzed the following tumor parameters in consensus: number, size, T1 and T2 signal intensity, margins, presence of capsule or pseudocapsule, distance to closest vessel, distance to liver capsule, and quantitative tumor enhancement. The size and number of HCCs, tumor differentiation, and the presence or absence of microvascular invasion were determined at histopathologic examination. Odds ratios (ORs) were calculated and logistic regression analysis was performed to assess the utility of these clinicopathologic and imaging parameters for predicting microvascular invasion. RESULTS: None of the clinical parameters or morphologic and enhancement MRI features of HCC was predictive of microvascular invasion. Tumor multifocality, on both MRI and pathologic examination, was the only variable that predicted microvascular invasion (OR = 2.43 and p = 0.013 for MRI; OR = 1.94 and p = 0.013 for pathologic examination). The presence of three or more tumors on MRI and four or more tumors at pathologic examination had high specificity (88.2% and 91.2%, respectively) for the prediction of microvascular invasion. CONCLUSION: Tumor multifocality on MRI was the only parameter that correlated significantly with microvascular invasion. All other MRI tumor characteristics failed to predict microvascular invasion

Renal masses increasingly are detected incidentally in asymptomatic individuals. Accurate characterization of these lesions is important for clinical management, planning intervention, and avoiding unnecessary procedures. Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are the mainstays of renal mass detection and characterization. Ultrasonography is useful for distinguishing cystic from solid lesions and can detect lesion vascularity, especially with use of ultrasound contrast agents, but is less sensitive, less specific, and less reproducible than CT and MRI. CT, with and without intravenous contrast, is the primary imaging test for characterization and staging of renal lesions, and is utilized more often than MRI. Current multidetector CT technology provides near isotropic acquisition, with three-dimensional reformatting capabilities. Due to lack of exposure to iodinated contrast and ionizing radiation and superior soft tissue contrast, MRI is being increasingly utilized as a problem-solving tool for diagnosis, staging, and preoperative planning for renal malignancies. Future directions for imaging of primary renal neoplasm include accurate characterization of renal cell cancer subtype, assistance with treatment planning, and evaluation of treatment response

MRI of the liver is an important tool for the detection and characterization of focal liver lesions, for assessment of tumor response to treatment, and for the evaluation of diffuse liver disease. With recent advances in technology, functional MRI methods such as diffusion-weighted (DW) and perfusion-weighted (PW)-MRI are increasingly used in the abdomen with promising results, particularly in the evaluation of diffuse and focal liver diseases. In this review, we will discuss background, technical considerations, acquisition, applications, limitations and future applications of DW-MRI and PW-MRI applied in evaluation of diffuse and focal liver diseases

Functional MRI is a new and exciting tool enabling non-invasive assessment of renal function. Diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), blood oxygen level-dependent (BOLD) MRI, and magnetic resonance elastography (MRE) are some of the techniques under investigation. In this article we review the basic principles of these techniques, their possible applications, and their limitations

OBJECTIVE: The purpose of our study was to assess the utility of the apparent diffusion coefficient (ADC) in distinguishing low-grade and high-grade clear cell renal cell carcinoma (ccRCC). MATERIALS AND METHODS: The cases of 57 patients with pathologically proven ccRCC who underwent preoperative MRI, including diffusion-weighted imaging, were retrospectively assessed. ADC values were obtained from ADC maps calculated using b-value combinations of 0 and 400 s/mm(2) and of 0 and 800 s/mm(2) (hereafter referred to as ADC-400 and ADC-800). Lesions were also evaluated for an array of conventional MRI features. A single expert uropathologist reviewed all slides to determine nuclear grade. The utility of ADC for detecting high-grade ccRCC, alone and in combination with conventional MRI features, was assessed using receiver operating characteristic (ROC) analysis and binary logistic regression. RESULTS: ADC-400 and ADC-800 were significantly lower among high-grade than among low-grade ccRCC (2.24 +/- 0.50 mm(2)/s vs 1.59 +/- 0.57 mm(2)/s for ADC-400, p < 0.001; 1.85 +/- 0.40 mm(2)/s vs 1.28 +/- 0.48 mm(2)/s for ADC-800; p < 0.001). The area under the ROC curve for identifying high-grade ccRCC using ADC-400 and ADC-800 was 0.801 and 0.824 respectively (p = 0.606), with optimal thresholds, sensitivity, and specificity as follows: ADC-400: 2.17 mm(2)/s, 88.5%, 64.5% and ADC-800: 1.20 mm(2)/s, 65.4%, 96.0%. Using multivariate logistic regression, only necrosis (p = 0.0229) and perinephric fat invasion (p = 0.0160) were retained among conventional imaging features as independent risk factors for high-grade ccRCC. The accuracy of the logistic regression model for predicting high-grade ccRCC was significantly improved by inclusion of either ADC-400 (p = 0.0143) or ADC-800 (p = 0.015). CONCLUSION: ADC is significantly lower in high-grade ccRCC compared with low-grade ccRCC and increases the accuracy for detecting high-grade ccRCC compared with conventional MRI features alone