Faculty Bibliography

PURPOSE: To assess two methods of fat and fibroglandular tissue (FGT) segmentation for measuring breast MRI FGT volume and FGT%, the volume percentage of FGT in the breast, in longitudinal studies. MATERIALS AND METHODS: Nine premenopausal women provided one MRI per week for 4 weeks during a natural menstrual cycle for a total of 36 datasets. We compared a fuzzy c-means (FC) and a 3-point Dixon segmentation method for estimation of changes in FGT volume and FGT% across the menstrual cycle. We also assessed whether differences due to changes in positioning each week could be minimized by coregistration, i.e., the application of the breast boundary selected at one visit to images obtained at other visits. RESULTS: FC and Dixon FGT volume were highly correlated (r = 0.93, P < 0.001), as was FC and Dixon FGT% (r = 0.86, P = 0.01), although Dixon measurements were on average 10-20% higher. Although FGT measured by both methods showed the expected pattern of increase during the menstrual cycle, the magnitude, and for one woman the direction, of change varied according to the method used. Measurements of FGT for coregistered images were in close agreement with those for which the boundaries were determined independently. CONCLUSION: The method of segmentation of fat and FGT tissue may have an impact on the results of longitudinal studies of changes in breast MRI FGT. J. Magn. Reson. Imaging 2012;. (c) 2012 Wiley Periodicals, Inc.

Object In patients with tuberous sclerosis complex (TSC), the tuber-to-brain proportion (TBP) is a marker of seizure severity and cognitive function. However, few studies have quantified the TBP. Furthermore, authors of these studies have measured the TBP at only a single time point, despite the fact that tuber cells were found to express proliferation markers, suggesting that they may be dynamic lesions. Authors of the present study used a semi-automated tuber segmentation program to determine whether the TBP changes over time. Methods Axial FLAIR MR images were retrospectively identified for patients with TSC who had undergone imaging at the authors' institution between February 1998 and June 2009. Using FireVoxel software, the TBP was measured for each patient at a minimum interval of 2 years. Results Twelve patients meeting the study inclusion criteria were identified. The mean TBP was 1.88% (range 0.38%-3.70%). Eight patients demonstrated minimal changes and 3 patients demonstrated small increases in TBP. The remaining patient exhibited a decrease of 1.00%, which correlated with a visible decrease in the size of 2 cerebellar lesions. Conclusions Semi-automated brain segmentation is a valuable tool in the longitudinal study of tubers. A subset of patients with TSC, particularly those with cerebellar lesions, may exhibit changes in the TBP over time.

OBJECTIVES: The aim of this study was to assess the impact of oral water and intravenous furosemide challenges on blood oxygenation level-dependent magnetic resonance imaging measurements in the kidney and to examine the contribution of R2 (=1/T2) to changes in R2* (=1/T2*). MATERIALS AND METHODS: This Health Insurance Portability and Accountability Act-compliant study had institutional review board approval, and written informed consent was obtained from all subjects. Nine healthy volunteers were imaged at 3 T on 2 visits. During each visit, a baseline fasting magnetic resonance acquisition was followed by a diuretic challenge: oral water load for the first visit and furosemide for the second. R2* and R2 values in the renal cortex and medulla were measured using multiple gradient echo and multiple spin echo sequences, respectively, and R2' values were computed as R2' = R2* - R2. Timed urinary output was also measured. RESULTS: Averaged across all subjects, the R2* response to furosemide was greater than to water and greater in the medulla than the cortex. The mean R2 responses exhibited the same trends but were uniformly smaller than the mean R2* responses. The peak changes in R2* and R2 appeared, on average, 10 to 14 minutes before peak urinary output. The median percentage contribution of R2 to R2* changes was 16% in the medulla after both challenges. In the cortex, the median contribution was 48% after water load and 58% after furosemide challenge. CONCLUSIONS: The contributions of R2 to R2* changes after water load and furosemide challenge are not negligible, especially in the renal cortex. In routine clinical practice, R2* could be used alone as a rough surrogate for R2' in the medulla. However, in the cortex, both R2 and R2* should be measured to obtain accurate values of R2'.

Background: A great deal of current research is aiming to better understand what happens to brains affected by Alzheimer's disease, both structurally and metabolically. However, little is known about how the brain ages in the cognitively normal adult population. There is also a limited understanding as to how glucose metabolism and brain atrophy interact in the normal human brain. To our knowledge, this study is the first to longitudinally analyze measures of atrophy and metabolism in both MRI and FDG-PET in cognitively normal subjects. Methods: 45 cognitively normal subjects were studied longitudinally over a span of at least 1.5 years (average = 5.99 years). Each had at least two structural MRIs and 2 FDG-PET scans. Free Surfer was used to analyze ventricle and intracranial volume. This was turned into an intracranial volume ratio to get a normalized picture of brain atrophy. A hippocampal masking technique (HipMask) was used to analyze the FDG-PET scans for changes in metabolic rates in regions normally affected by Alzheimer's disease (precuneus/posterior cingulate, hippocampus, inferior parietal lobe), as well as regions affected by normal aging (prefrontal cortex and cerebellum). Results: Mixed model analysis indicates that ventricle enlargement occurs in the cognitively normal adult brain as early as adult middle age (t = 7.050, p < .001), with a particular acceleration after the age of 65 (t = 2.878, p = .004). However, the mixed model results did not show any evidence of a concomitant decrease in rate with age, nor any acceleration, in regional metabolism after controlling for brain atrophy. Conclusions: Our results show that brain atrophy increases over the adult lifespan. These changes appear to accelerate over time. However, metabolically, we did not find any significant results with regard to change over time. This is in contrast to Alzheimer's disease, where literature has shown metabolic decreases in frontal and parietal regions, particularly in precuneus/posterior cingulate. Our !

Surface morphology is an important indicator of malignant potential for solid-type lung nodules detected at CT, but is difficult to assess subjectively. Automated methods for morphology assessment have previously been described using a common measure of nodule shape, representative of the broad class of existing methods, termed area-to-perimeter-length ratio (APR). APR is static 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 morphology detection scheme. SO measures the degree of change of nodule masks upon Gaussian blurring. We hypothesized that this new metric would afford equally high accuracy and superior precision than APR. Application of the two methods to a set of 119 patient lung nodules and a set of simulation nodules showed our approach to be slightly more accurate and on the order of ten times as precise, respectively. The dynamic quality of this new automated metric renders it less sensitive to image noise and artifacts than APR, and as such, SO is a potentially useful measure of cancer risk for solid-type lung nodules detected on CT.

To test the hypotheses that global decreased neuro-axonal integrity reflected by decreased N-acetylaspartate (NAA) and increased glial activation reflected by an elevation in its marker, the myo-inositol (mI), present in a CD8-depleted rhesus macaque model of HIV-associated neurocognitive disorders. To this end, we performed quantitative MRI and 16 x 16 x 4 multivoxel proton MRS imaging (TE/TR = 33/1400 ms) in five macaques pre- and 4-6 weeks post-simian immunodeficiency virus infection. Absolute NAA, creatine, choline (Cho), and mI concentrations, gray and white matter (GM and WM) and cerebrospinal fluid fractions were obtained. Global GM and WM concentrations were estimated from 224 voxels (at 0.125 cm(3) spatial resolution over ~35% of the brain) using linear regression. Pre- to post-infection global WM NAA declined 8%: 6.6 +/- 0.4 to 6.0 +/- 0.5 mM (p = 0.05); GM Cho declined 20%: 1.3 +/- 0.2 to 1.0 +/- 0.1 mM (p < 0.003); global mI increased 11%: 5.7 +/- 0.4 to 6.5 +/- 0.5 mM (p < 0.03). Global GM and WM brain volume fraction changes were statistically insignificant. These metabolic changes are consistent with global WM (axonal) injury and glial activation, and suggest a possible GM host immune response

Renal function is characterized by different physiologic aspects, including perfusion, glomerular filtration, interstitial diffusion, and tissue oxygenation. Magnetic resonance imaging (MRI) shows great promise in assessing these renal tissue characteristics noninvasively. The last decade has witnessed a dramatic progress in MRI techniques for renal function assessment. This article briefly describes relevant renal anatomy and physiology, reviews the applications of functional MRI techniques for the diagnosis of renal diseases, and lists unresolved issues that will require future work. J. Magn. Reson. Imaging 2013;37:282-293. (c) 2012 Wiley Periodicals, Inc.

OBJECTIVES: We conducted a pilot study to identify whether MRI parameters are sensitive to hormone-induced changes in the breast during the natural menstrual cycle and whether changes could also be observed during an oral contraceptive (OC) cycle. MATERIALS AND METHODS: The New York University Langone Medical Center Institutional Review Board approved this HIPAA-compliant prospective study. All participants provided written informed consent. Participants were aged 24-31 years.We measured several non-contrast breast MRI parameters during each week of a single menstrual cycle (among 9 women) and OC cycle (among 8 women). Hormones were measured to confirm ovulation and classify menstrual cycle phase among naturally cycling women and to monitor OC compliance among OC users. We investigated how the non-contrast MRI parameters of breast fibroglandular tissue (FGT), apparent diffusion coefficient (ADC), magnetization transfer ratio (MTR), and transverse relaxation time (T2) varied over the natural and the OC cycles. RESULTS: We observed significant increases in MRI FGT% and ADC in FGT, and longer T2 in FGT in the luteal vs. follicular phase of the menstrual cycle. We did not observe any consistent pattern of change for any of the MRI parameters among women using OCs. CONCLUSIONS: MRI is sensitive to hormone-induced breast tissue changes during the menstrual cycle. Larger studies are needed to assess whether MRI is also sensitive to the effects of exogenous hormones, such as various OC formulations, on the breast tissue of young premenopausal women.