Existing model-free approaches to determine cerebral blood flow by external residue detection show a marked dependence of flow estimates on tracer arrival delays and dispersion. In theory, this dependence can be circumvented by applying a specific model of vascular transport and tissue flow heterogeneity. The authors present a method to determine flow heterogeneity by magnetic resonance residue detection of a plasma marker.
The aim of this study was to assess the potential of high-speed interleaved echo-planar imaging (EPI) to achieve diagnostic image quality comparable to T2-weighted imaging in patients with brain tumors. Seventeen patients with intra-axial, supratentorial tumors (10 untreated gliomas, 7 radiated gliomas) were investigated on a 1. 5-T scanner. The conventional scan (SE, TR/TE = 2200/80 ms, 18 slices) was acquired in 8 min, 4 s, and EPI (TR/TE = 3000/80 ms, 18 slices) was completed in 25 s. The films were compared in a blinded trail by three radiologists.
BACKGROUND AND PURPOSE: The heterogeneity of microvascular flows is known to be an important determinant of the efficacy of oxygen delivery to tissue. Studies in animals have demonstrated decreased flow heterogeneity (FH) in states of decreased perfusion pressure. The purpose of the present study was to assess microvascular FH changes in acute stroke with use of a novel perfusion-weighted MRI technique and to evaluate the ability of combined diffusion-weighted MRI and FH measurements to predict final infarct size.
Functional neuroimaging experiments have revealed an organization of frequency-dependent responses in human auditory cortex suggestive of multiple tonotopically organized areas. Numerous studies have sampled cortical responses to isolated narrow-band stimuli, revealing multiple locations in auditory cortex at which the position of response varies systematically with frequency content. Because appropriate anatomical or functional grouping of these distinct frequency-dependent responses is uncertain, the number and location of tonotopic mappings within human auditory cortex remains unclear.
There is increasing interest in using algorithms combining multiple magnetic resonance imaging (MRI) modalities to predict tissue infarction in acute human stroke. We developed and tested a voxel-based generalized linear model (GLM) algorithm to predict tissue infarction in an animal stroke model in order to directly compare predicted outcome with the tissue's histologic outcome, and to evaluate the potential for assessing therapeutic efficacy using these multiparametric algorithms.
Delivery of diagnostic agents to the central nervous system (CNS) poses several challenges as a result of the special features of CNS blood vessels and tissue fluids. Diffusion barriers exist between blood and neural tissue, in the endothelium of parenchymal vessels (blood-brain barrier, BBB), and in the epithelia of the choroid plexuses and arachnoid membrane (blood-CSF barriers), which severely restrict penetration of several diagnostic imaging agents.
To understand the relationship between brainstem lesions and auditory neurology in patients with multiple sclerosis, we compared behavioural, electrophysiological and imaging data in 38 patients with probable or definite multiple sclerosis and normal or near normal hearing. Behavioural measures included (i) general hearing tests (audiogram, speech discrimination) and (ii) hearing tests likely to be critically dependent upon brainstem processing (masking level difference, interaural time and level discrimination). Brainstem auditory evoked potentials provided the electrophysiological data.
Recordings in experimental animals have detailed the tonotopic organization of auditory cortex, including the presence of multiple tonotopic maps. In contrast, relatively little is known about tonotopy within human auditory cortex, for which even the number and location of tonotopic maps remains unclear. The present study begins to develop a more complete picture of cortical tonotopic organization in humans using functional magnetic resonance imaging, a technique that enables the non-invasive localization of neural activity in the brain.
OBJECTIVE: To examine alterations in patterns of brain activation seen in normal aging and in mild Alzheimer's disease by functional magnetic resonance imaging (fMRI) during an associative encoding task.
METHODS: 10 young controls, 10 elderly controls, and seven patients with mild Alzheimer's disease were studied using fMRI during a face-name association encoding task. The fMRI paradigm used a block design with three conditions: novel face-name pairs, repeated face-name pairs, and visual fixation.
Magnetic resonance (MR) imaging, brainstem auditory evoked potentials (BAEPs), and tests of interaural time and level discrimination were performed on sixteen subjects with multiple sclerosis (MS). Objective criteria were used to define MR lesions. Of the eleven subjects in whom no pontine lesions were detected and the one subject who had pontine lesions that did not encroach upon the auditory pathways, all had normal BAEPs and interaural level discrimination, although a few had abnormal interaural time discrimination.
