Faculty Bibliography

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

OBJECTIVE: The purpose of this study is to compare the diagnostic accuracy of liver apparent diffusion coefficient (ADC) versus normalized liver ADC using the spleen as a reference organ for the diagnosis of liver fibrosis and cirrhosis. MATERIALS AND METHODS: Fifty-six patients, 34 with liver disease and 22 control subjects, were assessed with breath-hold single-shot echo-planar diffusion-weighted imaging using b values of 0, 50, and 500 s/mm(2). Liver ADC and normalized liver ADC (defined as the ratio of liver ADC to spleen ADC) were compared between patients stratified by fibrosis stage. Receiver operating characteristic (ROC) analysis was used to determine the performance of ADC and normalized liver ADC for prediction of liver fibrosis and cirrhosis. Reproducibility was assessed by measuring coefficient of variation (n = 7). RESULTS: Liver ADC failed to distinguish individual stages of fibrosis, except between stages 0 and 4. There were significant differences in normalized liver ADC between control livers and intermediate stages of fibrosis (stages 2-3) and cirrhosis (stage 4) and between stages 1 and 4, and there was a trend toward significance between stages 0 and 1 (p = 0.051) and stages 1 and 3 (p = 0.06). ROC analysis showed that normalized liver ADC was superior to liver ADC for detection of stage >/= 2 (area under the ROC curve, 0.864 vs 0.655; p = 0.013) and stage >/=3 (0.805 vs 0.689; p = 0.015), without a difference for diagnosing cirrhosis (0.935 vs 0.720; p = 0.185). Normalized liver ADC had higher reproducibility than ADC (mean coefficient of variation, 3.5% vs 12.6%). CONCLUSION: Our results suggest that normalizing liver ADC with spleen ADC improves diagnostic accuracy for detection of liver fibrosis and cirrhosis when using breath-hold diffusion-weighted imaging, with better reproducibility

Endovascular repair is increasingly considered a less-invasive alternative to open repair of abdominal aortic aneurysm. However, there are still many potential complications of endovascular repair, including endoleaks, graft migration, thrombosis, and fistula formation. Endoleak is the most common complication for which these patients undergo long-term imaging surveillance. Most centers acquire computed tomographic (CT) data before contrast administration and during an arterial and delayed phase of aortic enhancement after the administration of intravenous contrast material to optimize detection of endoleaks. Although this technique works well, the downside is significant patient radiation exposure. Although the carcinogenic risk of ionizing radiation because of CT exposure is low, it has been linked to an increase in the lifelong risk of developing fatal cancers. Furthermore, this risk is cumulative and increases with multiple radiation exposure, as is true in surveillance after endovascular repair. As a result, considerable research is being performed to optimize CT protocols in an effort to decrease radiation dose. One such approach is to image these patients with recently introduced dual source dual-energy CT system. Using this technique, virtual noncontrast data may be generated from a postcontrast acquisition which may obviate the routine acquisition of noncontrast acquisition, thus decreasing radiation dose. In this article, we discuss the role of dual energy CT imaging in evaluation of patients after endovascular repair of abdominal aortic aneurysm

Liver metastases are the most frequently encountered malignant liver lesions in the Western countries. Accurate diagnosis of liver metastases is essential for appropriate management of these patients. Multiple imaging modalities, including ultrasound, CT, positron emission tomography, and MRI, are available for the evaluation of patients with suspected or known liver metastases. Contrast-enhanced MRI has a high accuracy for detection and characterization of liver lesions. Additionally, diffusion-weighted MRI (DWI) has been gaining increasing attention. It is a noncontrast technique that is easy to perform, could be incorporated in routine clinical protocols, and has the potential to provide tissue characterization. This article discusses the basic principles of DWI and discusses its emerging role in the detection of liver metastases in patients with extrahepatic malignancies

PURPOSE: To determine whether liver metastases conspicuity is improved at 80 kVp when compared with weighted average (WA) simulated 120 kVp data using dual source dual energy CT. METHODS: A total of 11 patients with 44 hypo-vascular liver metastases underwent contrast enhanced Dual Energy CT (DECT). In all cases the subject's abdominal diameter measured <or=35 cm. Data were reconstructed as a WA of the 140 kVp and 80 kVp acquisitions (simulating 120 kVp) and as a pure 80 kVp data set. A region of interest cursor was placed within the metastasis and adjacent normal parenchyma and attenuation differences and contrast to noise ratios (CNR) were calculated for the metastases at 80 kVp and on the WA acquisition. A mixed model 2-way analysis of variance was used to test whether the attenuation difference between metastases and normal liver was higher at 80 kVp than 120 kVp. An exact Wilcoxon matched-pairs signed rank test was used to test whether CNR was higher at 80 kVp. Cases were retrospectively reviewed to determine whether lesions could be seen on only one or both data sets. As the 80 kVp tube has a smaller detector than the 140 kVp tube, we also noted whether any of the liver lesions were not included on the 80 kVp dataset. Two radiologists in consensus evaluated the 80 kVp data and WA data and subjectively rated hepatic metastases conspicuity on a 4 point scale; with 1 being excellent, 2 good, 3 poor, and 4 not seen. RESULTS: The mean size of the metastases was 2.6 cm. The mean +/- SD of the attenuation difference between the metastases and the normal liver was 78.37 +/- 24.6 at 80 kVp and 56.89 +/- 17.9 at 120 kVp. The mean difference in attenuation was significantly higher at 80 kVp (P < 0.001). In 2 cases, a metastases was only seen at 80 kVp. The difference between 80 and 120 kVp in terms of CNR was statistically significant (P = 0.042). In one patient, 11 lesions were not included in the smaller field of view of the 80 kVp detector. The conspicuity scores were rated as significantly better at 80 kv than at 120 kVp (P < 0.0001). CONCLUSION: When compared with 120 kVp data, pure 80 kVp data acquired from a dual source dual energy MDCT scanner demonstrates greater attenuation differences and improved contrast to noise between metastatic disease and normal liver

Cardiac computed tomography angiography (CCTA) has emerged as a powerful noninvasive technique for anatomic evaluation of the coronary arteries. Multiple studies have demonstrated very good diagnostic accuracy for detection of coronary artery disease, particularly with 64-slice systems. CCTA allows for accurate assessment of myocardial structure, perfusion, and function comparable to established techniques. CCTA has the potential to be a ''one-stop shop'' because it can be used to assess coronary artery anatomy and myocardial structure, perfusion, and function. In this article, established and emerging CCTA techniques for the evaluation of myocardial structure, perfusion, and function are reviewed