Faculty Bibliography

OBJECTIVE. The purpose of this study was to compare the accuracy of the spatial registration of conventional PET/CT with that of hybrid PET/MRI of patients with FDG-avid metastatic lesions. SUBJECTS AND METHODS. Thirteen patients with known metastatic lesions underwent FDG PET/CT followed by PET/MRI with a hybrid whole-body system. The inclusion criterion for tumor analysis was spherical or oval FDG-avid tumor clearly identified with both CT and MRI. The spatial coordinates (x, y, z) of the visually estimated centers of the lesions were determined for PET/CT (PET and CT independently) and PET/MRI (PET, T1-weighted gradient-echo sequence with radial stack-of-stars trajectory, T2-weighted sequence), and the b0 images of an echo-planar imaging (EPI) diffusion-weighted imaging (DWI) acquisition. All MRI sequences were performed in the axial plane with free breathing. The spatial coordinates of the estimated centers of the lesions were determined for PET and CT and PET and MRI sequences. Distance between the isocenter of the lesion on PET images and on the images obtained with the anatomic modalities was measured, and misregistration (in millimeters) was calculated. The degree of misregistration was compared between PET/CT and PET/MRI with a paired Student t test. RESULTS. Nineteen lesions were evaluated. On PET/CT images, the average of the total misregistration in all planes of CT compared with PET was 4.13 +/- 4.24 mm. On PET/MR images, lesion misregistration between PET and T1-weighted gradient-echo images had a shift of 2.41 +/- 1.38 mm and between PET and b0 DW images was 5.97 +/- 2.83 mm. Similar results were calculated for 11 lesions on T2-weighted images. The shift on T2-weighted images compared with PET images was 2.24 +/- 1.12 mm. Paired Student t test calculations for PET/CT compared with PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory, b0 DW images, and T2-weighted images showed significant differences (p < 0.05). Similar results were seen in the analysis of six lung lesions. CONCLUSION. PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory and T2-weighted images had more accurate spatial registration than PET/CT images. This may be because that the whole-body PET/MRI system used can perform simultaneous acquisition, whereas the PET/CT system acquires data sequentially. However, the EPI-based b0 DWI datasets were significantly misregistered compared with the PET/CT datasets, especially in the thorax. Radiologists reading PET/MR images should be aware of the potential for misregistration on images obtained with EPI-based DWI sequences because of inherent spatial distortion associated with this type of MRI acquisition.

OBJECTIVES: To investigate the impact of prostate computed diffusion-weighted imaging (DWI) on image quality and tumour detection. METHODS: Forty-nine patients underwent 3-T magnetic resonance imaging using a pelvic phased-array coil before prostatectomy, including DWI with b values of 50 and 1,000 s/mm(2). Computed DW images with b value 1,500 s/mm(2) were generated from the lower b-value images. Directly acquired b-1,500 DW images were obtained in 39 patients. Two radiologists independently assessed DWI for image quality measures and location of the dominant lesion. A third radiologist measured tumour-to-peripheral-zone (PZ) contrast. Pathological findings from prostatectomy served as the reference standard. RESULTS: Direct and computed b-1,500 DWI showed better suppression of benign prostate tissue than direct b-1,000 DWI for both readers (P /= 0.180). Tumour-to-PZ contrast was greater on computed b-1,500 than on either direct DWI set (P < 0.001). CONCLUSION: Computed DWI of the prostate using b value >/=1,000 s/mm(2) improves image quality and tumour detection compared with acquired standard b-value images. KEY POINTS: * Diffusion weighted MRI is increasingly used for diagnosing and assessing prostate carcinoma. * Prostate computed DWI can extrapolate high b-value images from lower b values. * Computed DWI provides greater suppression of benign tissue than lower b-value images. * Computed DWI provides less distortion and artefacts than images using same b value. * Computed DWI provides better diagnostic performance than lower b-value images.

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.

Purpose:To assess diagnostic sensitivity of radial T1-weighted gradient-echo (radial volumetric interpolated breath-hold examination [VIBE]) magnetic resonance (MR) imaging, positron emission tomography (PET), and combined simultaneous PET and MR imaging with an integrated PET/MR system in the detection of lung nodules, with combined PET and computed tomography (CT) as a reference.Materials and Methods:In this institutional review board-approved HIPAA-compliant prospective study, 32 patients with tumors who underwent clinically warranted fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT followed by PET/MR imaging were included. In all patients, the thorax station was examined with free-breathing radial VIBE MR imaging and simultaneously acquired PET data. Presence and size of nodules and FDG avidity were assessed on PET/CT, radial VIBE, PET, and PET/MR images. Percentage of nodules detected on radial VIBE and PET images was compared with that on PET/MR images by using generalized estimating equations. Maximum standardized uptake value (SUVmax) in pulmonary nodules with a diameter of at least 1 cm was compared between PET/CT and PET/MR imaging with Pearson rank correlation.Results:A total of 69 nodules, including 45 FDG-avid nodules, were detected with PET/CT. The sensitivity of PET/MR imaging was 70.3% for all nodules, 95.6% for FDG-avid nodules, and 88.6% for nodules 0.5 cm in diameter or larger. PET/MR imaging had higher sensitivity than PET for all nodules (70.3% vs 61.6%, P = .002) and higher sensitivity than MR imaging for FDG-avid nodules (95.6% vs 80.0%, P = .008). There was a significantly strong correlation between SUVmax of pulmonary nodules obtained with PET/CT and that obtained with PET/MR imaging (r = 0.96, P < .001).Conclusion:Radial VIBE and PET data acquired simultaneously with PET/MR imaging have high sensitivity in the detection of FDG-avid nodules and nodules 0.5 cm in diameter or larger, with low sensitivity for small non-FDG-avid nodules.(c) RSNA, 2013.

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: 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.

PURPOSE: To assess the utility of diffusion-weighted imaging (DWI) findings as an indirect marker of side-specific risk of extracapsular extension (ECE) of prostate cancer. MATERIALS AND METHODS: Fifty-one patients underwent 3T magnetic resonance imaging (MRI) before prostatectomy. Radiologists 1 and 2 (4 and 1 years experience) assessed each side for ECE using T2-weighted imaging (T2WI) and evaluated apparent diffusion coefficient (ADC) maps for the presence of apparent tumor in each lobe and to measure peripheral zone ADC. A uropathologist measured the extent of any ECE. RESULTS: In all, 28/102 lobes had ECE, of which 12 measured 1 mm and 2 mm. Side-specific accuracies for detection of ECE for readers 1 and 2 were respectively: T2WI 68.6% and 74.5%; presence of apparent tumor on ADC map 66.7% and 60.8%; ADC value 75.5% and 69.6%. For ECE >2 mm, both readers achieved 100% sensitivity based on apparent tumor on ADC map or ADC values and 80% sensitivity using T2WI. For detection of ECE