Faculty Bibliography

Background: In hypertension (HTN), cerebral blood flow (CBF) regulation limits are changed and the blood pressure (BP) threshold at which CBF is safely maintained is higher. This shift may increase the brain's vulnerability to hypoperfusion at lower BP. Despite growing recognition of the link between hypoperfusion and neurodegeneration little is known about whether blood pressure reductions can induce deficient perfusion and promote expression of cerebrospinal fluid (CSF) biomarkers of amyloid and neurofibrillary pathology. We investigated the relationship between longitudinal changes in mean arterial pressure (MAP) and CSF biomarkers of Alzheimer's disease in a group of cognitively healthy elderly with and without HTN. Methods: Longitudinal assessments of blood pressure (MAP), CSF ptau181 (phosphorylated tau), total tau, amyloid beta 1-42 (Abeta42), cognition and whole brain volume were conducted on average 2.060.6 years apart in a group of 77 cognitively healthy elderly (age 63.469.4, range 44-86 years; education 16.962.1, range 10-22 years; 60% women). MAP was calculated as: 1/3 systolic blood pressure + 2/3 of diastolic blood pressure. Results: At baseline HTN was found in 23 individuals (30%). When longitudinal change (y) in p-tau181 was predicted with theyMAP, HTN, and the HTNxyMAP interaction, both the total model (F 3,73=3.9, p=.01), and the interaction term (p=.01) were significant. These data indicate that the relationship between yMAP and yp-tau181 was strongly dependent on the presence or absence of HTN. Only in the HTN group was a decrease in MAP from baseline to follow-up related to an increase in p-tau181 (r=-0.5 p=.01). In addition, only among subjects with HTN, was a reduction in MAP related to the worsening of verbal episodic memory (r=0.46 p=.03). Finally in the entire group the increase in p-tau181 was associated with reduction in the verbal episodic memory score (beta=-.223, p=.048). No relationship was observed between changes in MAP and whole brain volume. Conclusions: In subjects with HTN, MAP reduction is associated with increased CSF p-tau181 and deterioration of episodic memory, possibly resulting from suboptimal perfusion and subsequent accumulation of neurofibrillary tangles. Prior experimental work has demonstrated a relationship between perfusion, energetic reductions and tauopathy

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

Early detection of cartilage degeneration in the hip may help prevent onset and progression of osteoarthritis in young patients with femoroacetabular impingement. Delayed gadolinium-enhanced MRI of cartilage is sensitive to cartilage glycosaminoglycan loss and could serve as a diagnostic tool for early cartilage degeneration. We propose a new high resolution 2D T(1) mapping saturation-recovery pulse sequence with fast spin echo readout for delayed gadolinium-enhanced magnetic resonance imaging of cartilage of the hip at 3 T. The proposed sequence was validated in a phantom and in 10 hips, using radial imaging planes, against a rigorous multipoint saturation-recovery pulse sequence with fast spin echo readout. T(1) measurements by the two pulse sequences were strongly correlated (R(2) > 0.95) and in excellent agreement (mean difference = -8.7 ms; upper and lower 95% limits of agreement = 64.5 and -81.9 ms, respectively). T(1) measurements were insensitive to B(1+) variation as large as 20%, making the proposed T(1) mapping technique suitable for 3 T. Magn Reson Med, 2011. (c) 2011 Wiley-Liss, Inc

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

Vascular risk factors affect cerebral blood flow (CBF) and cerebral vascular reactivity, contributing to cognitive decline. Hippocampus is vulnerable to both Alzheimer's disease (AD) pathology and ischemia; nonetheless, the information about the impact of vascular risk on hippocampal perfusion is minimal. Cognitively, healthy elderly (NL=18, 69.9+/-6.7 years) and subjects with mild cognitive impairment (MCI=15, 74.9+/-8.1 years) were evaluated for the Framingham cardiovascular risk profile (FCRP). All underwent structural imaging and resting CBF assessment with arterial spin labeling (ASL) at 3T magnetic resonance imaging (MRI). In 24 subjects (NL=17, MCI=7), CBF was measured after a carbon dioxide rebreathing challenge. Across all subjects, FCRP negatively correlated with hippocampal (rho=-0.41, P=0.049) and global cortical (rho=-0.46, P=0.02) vasoreactivity to hypercapnia (VR(h)). The FCRP-VR(h) relationships were most pronounced in the MCI group: hippocampus (rho=-0.77, P=0.04); global cortex (rho=-0.83, P=0.02). The FCRP did not correlate with either volume or resting CBF. The hippocampal VR(h) was lower in MCI than in NL subjects (Z=-2.0, P=0.047). This difference persisted after age and FCRP correction (F([3,20])=4.6, P=0.05). An elevated risk for vascular pathology is associated with a reduced response to hypercapnia in both hippocampal and cortical tissue. The VR(h) is more sensitive to vascular burden than either resting CBF or brain volume

Due to methodological difficulties related to the small size, variable distribution of hippocampal arteries, and the location of the hippocampus in the proximity of middle cranial fossa, little is known about hippocampal blood flow (HBF). We have tested the utility of a pulsed arterial spin labeling sequence based on multi-shot true fast imaging in steady precession to measure HBF in 34 normal volunteers (17 women, 17 men, 26-92 years old). Flow sensitivity to a mild hypercapnic challenge was also examined. Coregistered 3D MPRAGE sequence was used to eliminate from hippocampal and cortical regions of interest all voxel with <75% of gray matter. Large blood vessels were also excluded. HBF in normal volunteers averaged 61.2 +/- 9.0 mL/(100 g min). There was no statistically significant age or gender effect. Under a mild hypercapnia challenge (end tidal CO(2) pressure increase of 6.8 +/- 1.9 mmHg over the baseline), HBF response was 14.1 +/- 10.8 mL/(100 g min), whereas cortical gray matter flow increased by 18.0 +/- 12.2 mL/(100 g min). Flow response among women was significantly larger than in the men. The average absolute difference between two successive HBF measures was 3.6 mL/(100 g min) or 5.4%. The 3T true fast imaging in steady precession arterial spin labeling method offers a HBF measurement strategy that combines good spatial resolution, sensitivity, and minimal image distortions. Magn Reson Med, 2010. (c) 2010 Wiley-Liss, Inc

Purpose: Many potential lung cancers start out as small pulmonary nodules showing up as incidental findings on chest radiograph or computed tomography (CT) scans. Diagnosis is confirmed via biopsy, usually involving broncoscopy or CT-guided biopsy. However, these are invasive procedures that expose patients to additional risks. An alternative mode of tumor detection lies in administering successive chest CT scans. This has the advantage of avoiding those risks associated with biopsy. Overall, there is growing evidence for the effectiveness of low-dose CT for lung cancer screening. Morphology is an important indicator of malignant potential for lung nodules detected at CT. Automated methods for morphology assessment have previously been described for breast cancer visualized on mammography [1]. The most common measure of nodule shape is area-to-perimeter-length ratio (APR), low APR values being associated with spiculated or lobulated shape. APR is a static measure and thus highly susceptible to alterations by random noise and artifacts in image acquisition. We introduce and analyze the self-overlap (SO) method as a dynamic automated morphological detection scheme. SO measures the rate of change of nodule masks as a function of the radius of the blurring kernel. In other words, SO measures the degree to which a nodule's shape changes or stays intact upon successive pixel averaging that blurs the original image. Irregularities at the surface mean that a significant number of high-attenuation pixels (representing solid nodular tissue) are surrounded by low-attenuation pixels (representing air). Averaging each pixel with its neighboring pixels thus serves to trim back lobulations and spiculations from a nodule image. Hence, comparedto smooth nodules, lobulated and spiculated nodules are subject to more of this trimming upon successive averaging, so that their shape changes more, resulting in lower SO values. Due to its dynamical nature, we hypothesized that SO is more resilient to random image noise than APR. Methods: In experiment 1 we compare our algorithm with APR for nodules simulated using a spherical harmonic model (degree = 0-7) rasterized and contaminated with random noise. In experiment 2 we compare the new measure with a consensus of two expert morphology ratings of 119 nodules from clinical CT exams. Results: Experiment 1 shows that both methods display the desired trend in that APR and SO both decrease with increasing spherical harmonic degree-meaning more lobulations. As such both methods serve as measures of surface smoothness. However, SO displays significantly greater robustness to CT image noise; for both methods, we calculate variability as standard deviation over mean. We find that APR's variability in the face of random noise is on the order of ten times that of SO. This finding suggests that SO is much more robust than APR to the effects of random noise. Using a logistic regression model, in experiment 2 we achieved 89.9% agreement with the consensus assessment of two expert radiologists, versus 87.4% for APR. Conclusion: Simulation nodules show that both our dynamic method (SO) and a representative static method (APR) for automated lung nodule surface morphology determination yield clear trends as functions of surface smoothness. Hence both methods can, with proper fitting and cutoff selection, yield faithful predictions that have over 80% agreement with expert assessment. However, when the simulation nodules are subjected to random noise, SO yields much more consistent and reproducible results than APR. Overall, we conclude that our method, due to its robustness to the random noise and CT artifacts that can plague nodule images, is well suited for clinical application