Faculty Bibliography

Purpose: To assess prospectively the ability of quantitative low-dose three-dimensional magnetic resonance (MR) renography to help identify the cause of acute graft dysfunction. Materials and Methods: This HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained. Between December 2001 and May 2009, sixty patients with transplanted kidneys (41 men and 19 women; mean age, 49 years; age range, 22-71 years) were included. Thirty-one patients had normal function and 29 had acute dysfunction due to acute rejection (n = 12), acute tubular necrosis (ATN) (n = 8), chronic rejection (n = 6), or drug toxicity (n = 3). MR renography was performed at 1.5 T with three-dimensional gradient-echo imaging. With use of a multicompartment renal model, the glomerular filtration rate (GFR) and the mean transit time (MTT) of the tracer for the vascular compartment (MTT(A)), the tubular compartment (MTT(T)), and the collecting system compartment (MTT(C)) were calculated. Also derived was MTT for the whole kidney (MTT(K) = MTT(A) + MTT(T) + MTT(C)) and fractional MTT of each compartment (MTT(A/K) = MTT(A)/MTT(K), MTT(T/K) = MTT(T)/MTT(K), MTT(C/K) = MTT(C)/MTT(K)). These parameters were compared in patients in the different study groups. Statistical analysis was performed by using analysis of covariance. Results: There were significant differences in GFR and MTT(K) between the acute dysfunction group (36.4 mL/min +/- 20.8 [standard deviation] and 177.1 seconds +/- 46.8, respectively) and the normal function group (65.9 mL/min +/- 27.6 and 140.5 seconds +/- 51.8, respectively) (P < .001 and P = .004). The MTT(A/K) was significantly higher in the acute rejection group (mean, 12.7% +/- 2.9) than in the normal function group (mean, 8.3% +/- 2.2; P < .001) or in the ATN group (mean, 7.1% +/- 1.4; P < .001). The MTT(T/K) was significantly higher in the ATN group (mean, 83.2% +/- 9.2) than in the normal function group (mean, 72.4% +/- 10.2; P = .031) or in the acute rejection group (mean, 69.2% +/- 6.1; P = .003). Conclusion: Low-dose MR renography analyzed by using a multicompartmental tracer kinetic renal model may help to differentiate noninvasively between acute rejection and ATN after kidney transplantation. (c) RSNA, 2011

Polycystic kidney disease (PKD) is a disorder characterized by the growth of numerous fluid filled cysts in the kidneys. Measuring cystic kidney volume is thus crucial to monitoring the evolution of the disease. While T2-weighted MRI delineates the organ, automatic segmentation is very difficult due to highly variable shape and image contrast. The interactive stereology methods used currently involve a compromise between segmentation accuracy and time. We have investigated semi-automated methods: active contours and a sub-voxel morphology based algorithm. Coronal T2-weighted images of 17 patients were acquired in four breath-holds using the HASTE sequence on a 1.5 Tesla MRI unit. The segmentation results were compared to ground truth kidney masks obtained as a consensus of experts. Automatic active contour algorithm yielded an average 22% +/- 8.6% volume error. A recently developed method (Bridge Burner) based on thresholding and constrained morphology failed to separate PKD from the spleen, yielding 37.4% +/- 8.7% volume error. Manual post-editing reduced the volume error to 3.2% +/- 0.8% for active contours and 3.2% +/- 0.6% for Bridge Burner. The total time (automated algorithm plus editing) was 15 min +/- 5 min for active contours and 19 min +/- 11 min for Bridge Burner. The average volume errors for stereology method were 5.9%, 6.2%, 5.4% for mesh size 6.6, 11, 16.5 mm. The average processing times were 17, 7, 4 min. These results show that nearly two-fold improvement in PKD segmentation accuracy over stereology technique can be achieved with a combination of active contours and post-editing.

Dynamic contrast-enhanced 3D images of the kidneys, or 3D MR renography, has the potential for broad clinical applications, but suffers from respiratory motion that limits analysis and interpretation. Manual registration is prohibitively labor-intensive. In this paper, a fully automated technique, Wavelet Representation and the Fourier Transform (WRFT) method, that corrects for translation and rotation motion in 3D MR renography is presented. The method was composed by anisotropic denoising, wavelet-based feature extraction, and Fourier-based registration. This was first evaluated on a set of simulated MR renography images with defined degrees of kidney motion. The method was then tested on 24 clinical patient MR renography data sets. Results of clinical testing were compared with the results obtained using a mutual information registration method. Based on intrarenal time-intensity curves, our method showed robust and consistent agreement with the results of manually coregistered data sets. (C) 2009 Elsevier Inc. All rights reserved

PURPOSE:: To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced (DCE)-MRI alone and in combination for the diagnosis of liver cirrhosis. MATERIALS AND METHODS:: Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW-MRI (n = 27) and DCE-MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model-free DCE-MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE-MR parameters were compared using a generalized estimating equations model. RESULTS:: PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056-0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006-0.0154). There was no correlation between IVIM- and DCE-MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP-DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis. CONCLUSION:: The combination of DW-MRI and DCE-MRI provides an accurate diagnosis of cirrhosis. J. Magn. Reson. Imaging 2010;31:589-600. (c) 2010 Wiley-Liss, Inc

Purpose: To investigate whether variability in reported renal apparent diffusion coefficient (ADC) values in literature can be explained by the use of different diffusion weightings (b values) and the use of a monoexponential model to calculate ADC. Materials and Methods: This prospective study was approved by institutional review board and was HIPAA-compliant, and all subjects gave written informed consent. Diffusion-weighted (DW) imaging of the kidneys was performed in three healthy volunteers to generate reference diffusion decay curves. In a literature meta-analysis, the authors resampled the reference curves at the various b values used in 19 published studies of normal kidneys (reported ADC = [2.0-4.1] x 10(-3) mm(2) / sec for cortex and [1.9-5.1] x 10(-3) mm(2) / sec for medulla) and then fitted the resampled signals by monoexponential model to produce 'predicted' ADC. Correlation plots were used to compare the predicted ADC values with the published values obtained with the same b values. Results: Significant correlation was found between the reported and predicted ADC values for whole renal parenchyma (R(2) = 0.50, P = .002), cortex (R(2) = 0.87, P = .0002), and medulla (R(2) = 0.61, P = .0129), indicating that most of the variability in reported ADC values arises from limitations of a monoexponential model and use of different b values. Conclusion: The use of a monoexponential function for DW imaging analysis and variably sampled diffusion weighting plays a substantial role in causing the variability in ADC of healthy kidneys. For maximum reliability in renal apparent diffusion coefficient quantification, data for monoexponential analysis should be acquired at a fixed set of b values or a biexponential model should be used. (c) RSNA, 2010

OBJECTIVE: To examine the utility of single-photon emission computed tomography (SPECT) to predict conversion from mild cognitive impairment (MCI) to Alzheimer disease (AD). DESIGN: Longitudinal, prospective study. SETTING: University-based memory disorders clinic. PARTICIPANTS: One hundred twenty seven patients with MCI and 59 healthy comparison subjects followed up for 1-9 years. MEASUREMENTS: Diagnostic evaluation, neuropsychological tests, social/cognitive function, olfactory identification, apolipoprotein E genotype, magnetic resonance imaging, and brain Tc hexamethyl-propylene-aminoxime SPECT scan with visual ratings, and region of interest (ROI) analyses were done. RESULTS: Visual ratings of SPECT temporal and parietal blood flow did not distinguish eventual MCI converters to AD (N = 31) from nonconverters (N = 96), but the global rating predicted conversion (41.9% sensitivity and 82.3% specificity, Fisher's exact test p = 0.013). Blood flow in each ROI was not predictive, but when dichotomized at the median value of the patients with MCI, low flow increased the hazard of conversion to AD for parietal (hazard ratio: 2.96, 95% confidence interval: 1.16-7.53, p = 0.023) and medial temporal regions (hazard ratio: 3.12, 95% confidence interval: 1.14-8.56, p = 0.027). In the 3-year follow-up sample, low parietal (p <0.05) and medial temporal (p <0.01) flow predicted conversion to AD, with or without controlling for age, Mini-Mental State Examination, and apolipoprotein E epsilon4 genotype. These measures lost significance when other strong predictors were included in logistic regression analyses: verbal memory, social/cognitive functioning, olfactory identification deficits, hippocampal, and entorhinal cortex volumes. CONCLUSIONS: SPECT visual ratings showed limited utility in predicting MCI conversion to AD. The modest predictive utility of quantified low parietal and medial temporal flow using SPECT may decrease when other stronger predictors are available

This study aims to assess the feasibility of a protocol to diagnose renovascular disease using dual MR renography (MRR) acquisitions: before and after administration of angiotensin converting enzyme inhibitor (ACEi). Results of our simulation study aimed at testing the reproducibility of glomerular filtration rate (GFR) and renal plasma flow (RPF) demonstrate that for a fixed overall dose of 12 ml gadolinium-based contrast material (500 mmol/L), the second dose should be approximately twice as large as the first dose. A three-compartment model for analyzing the second-injection data was shown to appropriately handle the tracer residue from the first injection. The optimized protocol was applied to 18 hypertensive patients without renovascular disease, showing minimal systematic difference in GFR measurements before and after ACEi of 0.8+/-4.4 ml/min or 2.7%+/-14.9%. For 10 kidneys with significant renal artery stenosis, GFR decreased significantly after ACEi (P < 0.001, T-value = 3.79), and the difference in GFR measurements before and after ACEi averaged 8.3+/-6.9 ml/min or 26.2%+/-43.9%. Dual-injection MRI with optimized dose distribution appears promising for ACEi renography by offering measures of GFR changes with clinically acceptable precision and accuracy. Key words: angiotensin converting enzyme inhibitor, glomerular filtration rate, renovascular disease, compartmental modeling

Little is known of combined utility of magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) biomarkers for prediction of Alzheimer's disease (AD) and longitudinal data is scarce. We examined these biomarkers at baseline and longitudinally in incipient AD. Forty-five subjects [21 controls (NL-NL), 16 stable MCI (MCI-MCI), 8 MCI who declined to AD (MCI-AD)] received MRI and lumbar puncture at baseline and after 2 years. CSF measures included total and phosphorylated tau (T-tau, P-tau<formula>_{231}</formula>), amyloid-beta (Abeta<formula>_{42}</formula>/Abeta<formula>_{40}</formula>) and isoprostane. Voxel-based morphometry identified gray matter concentration (GMC) differences best distinguishing study groups and individual GMC values were calculated. Rate of medial temporal lobe (MTL) atrophy was examined using regional boundary shift (rBS) method. At baseline, for MRI, MCI-AD showed reduced GMC-MTL, and for CSF higher CSF T-tau, P-tau<formula>_{231}</formula>, IP and lower Abeta<formula>_{42}</formula>/Abeta<formula>_{40}</formula> as compared with MCI-MCI or NL-NL. Longitudinally, rBS-MTL atrophy was higher in MCI-AD than in either MCI-MCI or NL-NL, particularly in the left hemisphere. CSF data showed longitudinally greater increases of isoprostane in MCI-AD as compared with NL-NL. Combining baseline CSF-P-tau<formula>_{231}</formula> and GMC-MTL significantly increased overall prediction of AD from 74% to 84% (p<formula>_{step}</formula> < 0.05). These results provide support for including multiple modalities of biomarkers in the identification of memory clinic patients at increased risk for dementia

For time-resolved acquisitions with k-space undersampling, a simulation method was developed for selecting imaging parameters based on minimization of errors in signal intensity versus time and physiologic parameters derived from tracer kinetic analysis. Optimization was performed for time-resolved angiography with stochastic trajectories (TWIST) algorithm applied to contrast-enhanced MR renography. A realistic 4D phantom comprised of aorta and two kidneys, one healthy and one diseased, was created with ideal tissue time-enhancement pattern generated using a three-compartment model with fixed parameters, including glomerular filtration rate (GFR) and renal plasma flow (RPF). TWIST acquisitions with different combinations of sampled central and peripheral k-space portions were applied to this phantom. Acquisition performance was assessed by the difference between simulated signal intensity (SI) and calculated GFR and RPF and their ideal values. Sampling of the 20% of the center and 1/5 of the periphery of k-space in phase-encoding plane and data-sharing of the remaining 4/5 minimized the errors in SI (<5%), RPF, and GFR (both <10% for both healthy and diseased kidneys). High-quality dynamic human images were acquired with optimal TWIST parameters and 2.4 sec temporal resolution. The proposed method can be generalized to other dynamic contrast-enhanced MRI applications, e.g., MR angiography or cancer imaging. Magn Reson Med, 2009. (c) 2009 Wiley-Liss, Inc