Noor Jehan Kabani

Automated 3-D Extraction of Inner and Outer Surfaces of Cerebral Cortex from MRI

Automatic computer processing of large multidimensional images such as those produced by magnetic resonance imaging (MRI) is greatly aided by deformable models, which are used to extract, identify, and quantify specific neuroanatomic structures. A general method of deforming polyhedra is presented here, with two novel features. First, explicit prevention of self-intersecting surface geometries is provided, unlike conventional deformable models, which use regularization constraints to discourage but not necessarily prevent such behavior. Second, deformation of multiple surfaces with intersurface proximity constraints allows each surface to help guide other surfaces into place using model-based constraints such as expected thickness of an anatomic surface. These two features are used advantageously to identify automatically the total surface of the outer and inner boundaries of cerebral cortical gray matter from normal human MR images, accurately locating the depths of the sulci, even where noise and partial volume artifacts in the image obscure the visibility of sulci. The extracted surfaces are enforced to be simple two-dimensional manifolds (having the topology of a sphere), even though the data may have topological holes. This automatic 3-D cortex segmentation technique has been applied to 150 normal subjects, simultaneously extracting both the gray/white and gray/cerebrospinal fluid interface from each individual. The collection of surfaces has been used to create a spatial map of the mean and standard deviation for the location and the thickness of cortical gray matter. Three alternative criteria for defining cortical thickness at each cortical location were developed and compared. These results are shown to corroborate published postmortem and in vivo measurements of cortical thickness.

Three-Dimensional MRI Atlas of the Human Cerebellum in Proportional Stereotaxic Space

We have prepared an atlas of the human cerebellum using high-resolution magnetic resonance-derived images warped into the proportional stereotaxic space of Talairach and Tournoux. Software that permits simultaneous visualization of the three cardinal planes facilitated the identification of the cerebellar fissures and lobules. A revised version of the Larsell nomenclature facilitated a simple description of the cerebellum. This atlas derived from a single individual was instrumental in addressing longstanding debates about the gross morphologic organization of the cerebellum. It may serve as the template for more precise identification of cerebellar topography in functional imaging studies in normals, for investigating clinical-pathologic correlations in patients, and for the development of future probabilistic maps of the human cerebellum.

Measurement of cortical thickness using an automated 3-D algorithm: a validation study.

A validation study was conducted to assess the accuracy of the algorithm developed by MacDonald et al. (1999) for measuring cortical thickness. This algorithm automatically determines the cortical thickness by 3-D extraction of the inner and outer surfaces of the cerebral cortex from an MRI scan. A manual method of tagging the grey-csf and grey-white interface was used on 20 regions (10 cortical areas found in each hemisphere) in 40 MRIs of the brain to validate the algorithm. The regions were chosen throughout the cortex to get broad assessment of the algorithms performance. Accuracy was determined by an anatomist tagging the csf-grey and grey-white borders of selected gyri and by allowing the algorithm to determine the csf-grey and grey-white borders and the corresponding cortical thickness of the same region. Results from the manual and automatic methods were statistically compared using overall ANOVA and paired t tests for each region. The manual and automatic methods were in agreement for all but 4 of the 20 regions tested. The four regions where there were significant differences between the two methods were the insula left and right, the right cuneus, and the right parahippocampus. We conclude that the automatic algorithm is valid for most of the cortex and provides a viable alternative to manual methods of determining cortical thickness in vivo. However, caution should be taken when measuring the regions mentioned previously where the results of the algorithm can be biased by surrounding grey structures.

Identification of Genetically Mediated Cortical Networks: A Multivariate Study of Pediatric Twins and Siblings

Structural magnetic resonance imaging data from 308 twins, 64 singleton siblings of twins, and 228 singletons were analyzed using structural equation modeling and selected multivariate methods to identify genetically mediated intracortical associations. Principal components analyses (PCA) of the genetic correlation matrix indicated a single factor accounting for over 60% of the genetic variability in cortical thickness. When covaried for mean global cortical thickness, PCA, cluster analyses, and graph models identified genetically mediated fronto-parietal and occipital networks. Graph theoretical models suggest that the observed genetically mediated relationships follow small world architectural rules. These findings are largely concordant with other multivariate studies of brain structure and function, the twin literature, and current understanding on the role of genes in cortical neurodevelopment.

Task Switching Performance Reveals Heterogeneity Amongst Patients With Mild Cognitive Impairment

OBJECTIVE To assess executive function in patients with mild cognitive impairment (MCI) and to determine whether task switching ability is associated with transition to Alzheimers disease. METHODS Twenty-seven MCI patients and 19 older controls were tested using a cued letter-digit classification switching task. Sixteen patients could perform the task (MCI-able), 6 could not (MCI-unable), and 5 were able only with cognitive support (MCI-cue). Demographic, neuropsychological, event-related potential (ERP), MRI, and genetic data were also collected. RESULTS The four groups did not differ on age, gender, and APO E4 frequency. Compared to the controls, the MCI-unable group had significantly poorer performance on the Trail Making task (η2 = .430), lower education (η2 = .234), and smaller cortical volume (η2 = .245). Most MCI patients exhibited task-switching deficits but to vastly different degrees and with varying outcomes. The combined pattern of neuropsychological and task switching performance indicates that the MCI-able patients displayed memory retrieval difficulties (F(2,39) = 3.6, p = .036, MSE = 1.44), generally preserved task switching abilities, and had a high probability of remaining dementia-free at follow-up. The MCI-cue patients had increased mixing costs, F(2,39) = 11.0, p < .001, MSE = .07; the MCI-unable patients showed episodic memory deficits, and both groups had a high probability of poor outcome (i.e., developing AD or dying within four years). CONCLUSION This study demonstrates that variability in performance on measures of task-switching can highlight important heterogeneity in the MCI population.

Neuroanatomical correlates of familial language impairment: A preliminary report

Language impairment is not always associated with other cognitive and neurological disorders. Individuals identified with Specific Language Impairment (SLI) but normal cognition/intellect and an associated family history are classified as subjects with familial language impairment (FLI). In this preliminary report, we identified five families with FLI and selected six children (FLI-children) and five adults (FLI-adults) for magnetic resonance imaging (MRI) scan of brain volumes. Four out of five adults from these families had generalized cortical atrophy, mostly in the anterior region. Using a tissue-classification method, the volume occupied by grey matter, white matter and cerebro-spinal fluid (CSF) was calculated. The results indicated that compared to the controls, the CSF/grey and CSF (grey+white) ratios were significantly high in FLI-adults, being P < 0.003 and P < 0.02, respectively, whereas the grey/ white ratio was significantly low (P < 0.06) in FLI-adults. The only significant difference observed between FLI-children and controls was in the grey/white ratio (P < 0.0001) with this ratio being higher in affected children. These initial findings suggest that FLI in adults may be associated with cortical atrophy. In future studies, we plan to acquire additional morphological data and perform localized analyses for various brain regions especially those associated with language in order to better understand the neuroanatomical correlates of FLI in both children and adults.

IC-101-02: Role of magnetization transfer imaging in early diagnosis of Alzheimer’s disease

mation based morphometry [1] and investigated the relationship between brain structure at baseline and future cognitive decline. Baseline deformation maps were dependent variables in regression analyses, and independent variables included annualized cognitive change, cognitive score at baseline, head size, age, and group. Separate regressions were computed for change in MMSE, CDR, and for the following California Verbal Learning Test subtests: short and long delay cued recall (SDCR and LDCR), and immediate and short delay free recall (IDFR and SDFR). Results: The figure (right brain is image left) shows T-statistic maps overlaid on the group average spatially normalized MRI. A negative association between structure and cognitive change on SDCR is shown in (a), where reduced tissue volumes in the left ERC at baseline are associated with greater performance decline. Smaller tissue volumes in the hippocampus at baseline were also related to greater declines in SDCR, as shown in (b). Associations between structure and LCDR were similar. Panel (c) shows reduced tissue volume in the posterior cingulate cortex at baseline is associated with greater decline in SDFR; adjacent white matter and left ERC were also implicated. These regions were less significantly associated with decline on IDFR. Smaller volumes of frontal and parietal white matter at baseline were associated with MMSE decline. Future declines in CDR were related to smaller baseline volumes of frontal and parietal lobes, particularly in the precuneus region (d). Conclusions: Deformation morphometry reveals focal brain atrophy on MRI that predicts future cognitive decline, and may allow earlier and more precise separation of normal aging from early Alzheimer’s disease. [1] C. Studholme et al, NeuroImage, Vol 21 (2004), pp 1387-1398.