Faculty Bibliography

PURPOSE: To assess dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) tracer pharmacokinetic parameters obtained with Generalized Kinetic Model (GKM) and extended Shutter Speed Model (SSM2) in renal tumors stratified by histologic subtypes. MATERIALS AND METHODS: In all, 24 patients with renal tumors were imaged at 1.5 T utilizing DCE-MRI with high temporal resolution (1.2 sec/temporal frame) prior to surgery. Tracer kinetic analysis was performed for the entire tumor using individualized aortic input function. GKM and SSM2 were employed to generate transfer constant (K(trans) ), plasma volume, and interstitial volume. These parameters, and DeltaK(trans) (K(trans) SSM2 - K(trans) GKM) were compared between tumors stratified by histologic subtype. RESULTS: There were 25 renal tumors: 15 clear cell, 4 papillary, 3 chromophobe, and 3 oncocytoma/oncocytic subtype. K(trans) GKM was significantly higher in chromophobe compared to other subtypes (P < 0.01). Using K(trans) GKM > 1.0 min(-1) , chromophobe were diagnosed with 100% sensitivity and 90.9% specificity. K(trans) SSM2 was higher than K(trans) GKM for all renal tumors except for all chromophobe and two clear cell subtype. Using K(trans) GKM > 1.0 min(-1) and Delta K(trans) < 0, chromophobe could be discriminated from other lesions with 100% accuracy. CONCLUSION: K(trans) obtained with GKM and SSM2 analysis can potentially discriminate chromophobe from other renal lesions with high accuracy. J. Magn. Reson. Imaging 2013;. (c) 2013 Wiley Periodicals, Inc.

OBJECTIVES: To evaluate changes in single-kidney glomerular filtration rate (SK-GFR) using low-dose dynamic contrast-enhanced magnetic resonance (MR) renography (MRR) in patients undergoing partial nephrectomy for renal masses. MATERIALS AND METHODS: In this Health Information Patient Protection Act-compliant prospective study, 18 patients with renal masses underwent preoperative MR imaging at 1.5 T for renal mass evaluation and low-dose gadolinium-enhanced MRR. Magnetic resonance renography was repeated approximately 48 to 72 hours and 6 months after partial nephrectomy. Single-kidney glomerular filtration rate was calculated from the MRR images, and the right and left kidney values were summed for total MR-GFR. Postoperative changes in SK-GFR and MR-GFR were compared with changes in estimated glomerular filtration rate calculated using modification of diet in renal disease formula, renal lesion characteristics, ischemia type (warm vs cold), and ischemia time. RESULTS: A decrease in the operated kidney SK-GFR was seen in 15 of the 18 patients, with a mean (SD) loss of 31% (23%), whereas estimated glomerular filtration rate decreased in 13 of the 18 patients with mean (SD) decrease of 19% (14%). Decrease in SK-GFR was greatest in the patients with warm ischemia time greater than 40 minutes and least in the patients with cold ischemia. In the immediate postoperative period, 6 of 7 patients (86%) with preoperative MR-GFR less than 60 mL/min per 1.73 m failed to demonstrate compensatory increase in SK-GFR in the nonoperated kidney, whereas 5 of 11 patients with baseline MR-GFR more than 60 mL/min per 1.73 m showed compensatory increase in nonoperated kidney SK-GFR. CONCLUSIONS: Magnetic resonance renography can demonstrate functional loss in the operated kidney and compensatory increase in the function of the contralateral kidney, thus enabling evaluation of various surgical techniques on kidney function.

OBJECTIVE. The purpose of this article is to evaluate the influence of patient radiation exposure histories on radiologists' imaging decisions. MATERIALS AND METHODS. We conducted a physician survey study in three academic medical centers. Radiologists were asked to make an imaging recommendation for a hypothetical patient with a history of multiple CT scans. We queried radiologists' decision making, evaluating whether they incorporated cancer risks from previous imaging, reported acceptance (or rejection) of the linear no-threshold model, and understood linear no-threshold model implications in this setting. Consistency between radiologists' decisions and their linear no-threshold model beliefs was evaluated; those acting in accordance with the linear no-threshold model were expected to disregard previously incurred cancer risks. A Fisher exact test was used to verify the generalizability of results across institutions and training levels (residents, fellows, and attending physicians). RESULTS. Fifty-six percent (322/578) of radiologists completed the survey. Most (92% [295/322]) incorporated risks from the patient's exposure history during decision making. Most (61% [196/322]) also reported acceptance of the linear no-threshold model. Fewer (25% [79/322]) rejected the linear no-threshold model; 15% (47/322) could not judge. Among radiologists reporting linear no-threshold model acceptance or rejection, the minority (36% [98/275]) made decisions that were consistent with their linear no-threshold model beliefs. This finding was not statistically different across institutions (p = 0.070) or training levels (p = 0.183). Few radiologists (4% [13/322]) had an accurate understanding of linear no-threshold model implications. CONCLUSION. Most radiologists, when faced with patient exposure histories, make decisions that contradict their self-reported acceptance of the linear no-threshold model and the linear no-threshold model itself. These findings underscore a need for educational initiatives.

OBJECTIVE. The purpose of this review is to describe the role of functional renal MRI, or MR renography, in the care of patients with renal masses undergoing partial nephrectomy. CONCLUSION. MR renography can be used to monitor renal functional outcome for patients undergoing partial nephrectomy and may help guide patient selection in this population with elevated risk of chronic kidney disease.

PURPOSE: The aim of this study was to use intravoxel incoherent motion diffusion-weighted imaging to discriminate subtypes of renal neoplasms and to assess agreement between intravoxel incoherent motion (perfusion fraction, fp) and dynamic contrast-enhanced magnetic resonance imaging (MRI) metrics of tumor vascularity. SUBJECTS AND METHODS: In this Health Insurance Portability and Accountability Act-compliant, institutional review board-approved prospective study, 26 patients were imaged at 1.5-T MRI using dynamic contrast-enhanced MRI with high temporal resolution and diffusion-weighted imaging using 8 b values (range, 0-800 s/mm). Perfusion fraction (fp), tissue diffusivity (Dt), and pseudodiffusivity (Dp) were calculated using biexponential fitting of the diffusion data. Apparent diffusion coefficient (ADC) was calculated with monoexponential fit using 3 b values of 0, 400, and 800 s/mm. Dynamic contrast-enhanced data were processed with a semiquantitative method to generate model-free parameter cumulative initial area under the curve of gadolinium concentration at 60 seconds (CIAUC60). Perfusion fraction, Dt, Dp, ADC, and CIAUC60 were compared between different subtypes of renal lesions. Perfusion fraction was correlated with CIAUC60. RESULTS: We examined 14 clear cell, 4 papillary, 5 chromophobe, and 3 cystic renal cell carcinomas (RCCs). Although fp had higher accuracy (area under the curve, 0.74) for a diagnosis of clear cell RCC compared with Dt or ADC, the combination of fp and Dt had the highest accuracy (area under the curve, 0.78). The combination of fp and Dt diagnosed papillary RCC and cystic RCC with 100% accuracy, and clear cell RCC and chromophobe RCC, with 86.5% accuracy. There was significant strong correlation between fp and CIAUC60 (r = 0.82; P < 0.001). CONCLUSION: Intravoxel incoherent motion parameters fp and Dt can discriminate renal tumor subtypes. Perfusion fraction demonstrates good correlation with CIAUC60 and can assess degree of tumor vascularity without the use of exogenous contrast agent.

Contemporary imaging techniques for renal mass evaluation are essential to clinical management and surgical planning. Ultrasonography can be used to distinguish cystic from solid lesions but is less sensitive and accurate in renal mass characterization than computed tomography (CT) and magnetic resonance imaging (MRI). Multiphase CT imaging before and after administration of contrast is the primary imaging modality for characterization and staging of renal lesions. MRI is increasingly used as a problem solving tool. Advanced MRI techniques such as diffusion-weighted imaging and perfusion-weighted imaging are being explored in assessment of renal lesions. These techniques are discussed in this article.

Computed tomography (CT) is considered the imaging modality of choice in evaluation of renal lesions. The advantages of magnetic resonance imaging (MRI) compared to CT include superior soft tissue contrast, avoidance of ionizing radiation and iodinated contrast media, and the possibility of performing functional and advanced imaging techniques such as diffusion-weighted (DWI) and perfusion-weighted imaging (PWI). Although the traditional role of MRI in the evaluation of renal mass is primarily that of a problem-solving tool, DWI and PWI are expanding the role of MRI in management of renal cell cancers. DWI and PWI have shown considerable promise not only in renal lesion detection and characterization as benign or malignant, but also in assessment of renal cell cancer subtype and nuclear grade. Furthermore, these techniques have the potential to assist with tailoring patient- and disease-specific management by providing surgical planning in patients with localized renal cell cancer and assessing treatment response in patients with advanced renal cell cancer undergoing targeted chemotherapy

PURPOSE: To determine if pretreatment apparent diffusion coefficient (ADC) of leiomyomas could predict volumetric response (VR) following uterine artery embolization (UAE). MATERIALS AND METHODS: We retrospectively studied 11 women who underwent pelvic MRI before and >120 days following UAE. MRI included conventional and diffusion weighted imaging sequences. Percentage change in leiomyoma volume was determined by multiplanar T2-weighted imaging. A Pearson correlation coefficient was calculated between leiomyoma VR following UAE and the following pre-embolization parameters: initial volume, relative enhancement, relative T2 signal intensity (SI) and ADC. Receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity and specificity of ADC for predicting volumetric response. RESULTS: Twenty-eight leiomyomas were included with a mean interval from UAE to follow-up MRI of 207 days. The preprocedural volume of the leiomyomas ranged from 18 to 182 cm(3) (median 47 cm(3)). and ADC ranged from 0.37 to 1.71 mm(2)/s (mean 0.80 mm(2)/s). All leiomyomas were 100% necrotic following UAE. Leiomyoma VR following UAE was 48% +/- 3.5%. with significant correlation between VR and ADC (r = 0.41; P = 0.017) but no correlation with initial leiomyoma volume, relative T2 SI, or relative enhancement. Using a threshold of 0.875 x 10(-3) mm(2)/s, ADC could predict > 50% VR with sensitivity and specificity of 70% and 83%, respectively. CONCLUSION: Pre-UAE ADC of leiomyomas correlated significantly with percent VR following UAE. In contrast, no correlation was seen between VR post-UAE and conventional imaging findings. This suggests that VR following UAE depends on leiomyoma histology reflected in DWI rather than features revealed by conventional MRI