Histological studies suggest that hippocampal subfields are differently affected by aging and Alzheimer's disease (AD). The aims of this study were: (1) To test if hippocampal subfields can be identified and marked using anatomical landmarks on high resolution MR images obtained on a 4T magnet. (2) To test if age-specific volume changes of subfields can be detected. Forty-two healthy controls (21-85 years) and three AD subjects (76-86 years) were studied with a high resolution T2 weighted fast spin echo sequence. The entorhinal cortex (ERC), subiculum, CA1, CA2 and CA3/4 and dentate were marked. A significant correlation between age and CA1 (r=-0.51, p=0.0002) which was most pronounced in the seventh decade of life was found in healthy controls. In AD subjects, CA1 and subiculum were smaller than in age-matched controls. These preliminary findings suggest that measurement of hippocampal subfields may be helpful to distinguish between normal aging and AD.

SENSitivity Encoding (SENSE) greatly enhances the quality of diffusion-weighted echo-planar imaging (EPI) by reducing blurring and off-resonance artifacts. Such improvement would also be desirable for diffusion tensor imaging (DTI), but measures derived from the diffusion tensor can be extremely sensitive to any kind of image distortion. Whether DTI is feasible in combination with SENSE has not yet been explored, and is the focus of this study. Using a SENSE-reduction factor of 2, DTI scans in eight healthy volunteers were carried out with regular-and high-resolution acquisition matrices. To further improve the stability of the SENSE reconstruction, a new coil-sensitivity estimation technique based on variational calculus and the principles of matrix regularization was applied. With SENSE, maps of the trace of the diffusion tensor and of fractional anisotropy (FA) had improved spatial resolution and less geometric distortion. Overall, the geometric distortions were substantially removed and a significant resolution enhancement was achieved with almost the same scan time as regular EPI. DTI was even possible without the use of quadrature body coil (QBC) reference scans. Geometry-factor-related noise enhancement was only discernible in maps generated with higher-resolu- Key words: magnetic resonance imaging; diffusion tensor imaging; brain; white matter; brain morphology SENSitivity Encoding (SENSE) is a valuable complement to regular gradient encoding in MRI (1). It uses some of the spatial information contained in the individual elements of an RF coil array to more efficiently traverse k-space. SENSE can therefore serve to accelerate virtually any conventional MRI technique without interfering with the numerous different contrast mechanisms used in MRI, such as diffusion weighting. It has been demonstrated that SENSE can help to improve single-shot EPI and FSE scans by reducing artifacts, as well as improving spatial resolution (2,3). In this context, it has been shown that singleshot SENSE EPI considerably increases lesion conspicuity in diffusion-weighted imaging (DWI) of ischemic stroke (4), which currently represents one of the most important fields of application for the DWI technique (5). One tradeoff of SENSE is a lower signal-to-noise ratio (SNR) due to the reduced number of phase-encoding steps (1). This penalty can be minimized, as discussed below.The ability to show the anisotropic diffusion of white matter is another powerful feature of DWI (6,7). White matter anisotropy reflects the anatomic organization of white matter tracts and is characterized best by the diffusion tensor D, which provides a mathematical-physical description of diffusion properties in three dimensions. Damage to the cerebral fiber system, and therefore a reduction of anisotropy, may occur with or be characteristic of various CNS disorders (8 -12). Similarly, measurements of diffusion anisotropy can serve to probe the degree of invasiveness of neoplasms to specific functional tracts (13), and to elucidate functional and anatomic ...

The ability of the asymmetric spin-echo (ASE) pulse sequence to provide different degrees of spin-echo (SE)-type and gradient-echo (GE)-type contrast when imaging media containing magnetic inhomogeneities is investigated. The dependence of the ASE signal on the size of magnetic field perturbers is examined using theory, computer simulations, and experiment. A theoretical prediction of the ASE signal is obtained using the Anderson-Weiss mean field theory, the results of which are qualitatively supported by computer simulations and experimental studies. It is shown that the ASE sequence can be used to tune the range of perturber sizes that provide the largest contributions to susceptibility contrast effects.

The brain continuously influences and perceives the physiological condition of the body. Related cortical representations have been proposed to shape emotional experience and guide behavior. Although previous studies have identified brain regions recruited during autonomic processing, neurological lesion studies have yet to delineate the regions critical for maintaining autonomic outflow. Even greater controversy surrounds hemispheric lateralization along the parasympathetic–sympathetic axis. The behavioral variant of frontotemporal dementia (bvFTD), featuring progressive and often asymmetric degeneration that includes the frontoinsular and cingulate cortices, provides a unique lesion model for elucidating brain structures that control autonomic tone. Here, we show that bvFTD is associated with reduced baseline cardiac vagal tone and that this reduction correlates with left-lateralized functional and structural frontoinsular and cingulate cortex deficits and with reduced agreeableness. Our results suggest that networked brain regions in the dominant hemisphere are critical for maintaining an adaptive level of baseline parasympathetic outflow.