Magnetic Resonance Imaging (MRI)

A spectroscopic imaging sequence incorporating a two-shot lactate editing method was used in two human brain studies to image lactate and NAA. The subtractive editing method allows separate images of lactate, NAA, and lipids to be collected during a single study with no SNR penalty. The sequence uses a spectral-spatial excitation for slice selection and water suppression, and employs inversion recovery and an echo time of 136 ms for additional lipid suppression.

Spiral-based k-space trajectories were applied in a spectroscopic imaging sequence with time-varying readout gradients to collect volumetric chemical shift information. In addition to spectroscopic imaging of low signal-to-noise ratio (SNR) brain metabolites, the spiral trajectories were used to rapidly collect reference signals from the high SNR water signal to automatically phase the spectra and to aid the reconstruction of metabolite maps. Spectral-spatial pulses were used for excitation and water suppression.

Iron deposition increases in normal aging, has its greatest presence in structures of the extrapyramidal system, and may contribute to functional decline. MR imaging provides a method for indexing iron deposition in brain structures because of iron's ferromagnetic properties, which interact with the MRI environment to cause signal intensity attenuation that is quantifiable by comparing images collected at 1.5 and 3.0 T.

In patients with Alzheimer's disease, but not in health controls, longitudinal magnetic resonance spectroscopy shows a striking decline in the neuronal marker, N-acetyl aspartate, despite little decline in underlying grey-matter volume.

OBJECTIVE: To apply in vivo proton magnetic resonance spectroscopy imaging estimates of N-acetylaspartate (NAA), a neuronal marker, to clarify the relative contribution of neuronal and glial changes to the widespread volume deficit of cortical gray matter seen in patients with schizophrenia with magnetic resonance images.

BACKGROUND: Postmortem studies report degradation of brain white matter microstructure in chronic alcoholism, but until recently, in vivo neuroimaging could provide measurement only at a macrostructural level. The development of magnetic resonance diffusion tensor imaging (DTI) for clinical use offers a method for depicting and quantifying the diffusion properties of white matter expressed as intravoxel and intervoxel coherence of tracts and fibers.

To perceive the vast array of stimuli in the world around us, the visual system employs parallel processing mechanisms that ensure efficiency in perceiving multiple objects in a scene. A way to test this efficiency is to measure reaction time (RT) to pairs of identical stimuli, presented singly or as doublets; typically, the resulting phenomenon is the redundant targets effect (RTE), which manifests as faster RTs to paired than singly presented stimuli.

The corpus callosum, the principal white matter structure enabling interhemispheric information transfer, is heterogeneous in its microstructural composition, heterotopic in its anteroposterior cortical connectivity, and differentially susceptible to aging. In vivo characterization of callosal features is possible with diffusion tensor imaging (DTI), a magnetic resonance imaging method sensitive to the detection of white matter's linear structure.

Diffusion tensor imaging was used to measure regional differences in brain white matter microstructure (intravoxel coherence) and macrostructure (intervoxel coherence) and age-related differences between men and women. Neuropsychiatrically healthy men and women, spanning the adult age range, showed the same pattern of variation in regional white matter coherence.

Nonrigid registration and atlas-based parcellation methods were used to compare the volume of the ventricular system and the cross-sectional area of the midsagittal corpus callosum on brain MRIs from 272 subjects in four groups: patients with HIV infection, with and without alcoholism comorbidity, alcoholics, and controls. Prior to testing group differences in regional brain metrics, each measure was corrected by regression analysis for significant correlations with supratentorial cranial volume and age, observed in 121 normal control men and women, whose age spanned six decades.