Magnetic Resonance Imaging (MRI)

OBJECTIVE: To investigate the integrity of hippocampal-prefrontal circuitry during episodic encoding in patients with HIV.
METHODS: Functional MRI was used to observe changes in blood oxygenation level-dependent (BOLD) signal in 14 HIV-positive participants and 14 age- and education-matched control subjects while performing an episodic encoding task. Subjects also completed neuropsychological measures of attention and memory.

Fluent speech comprises sequences that are composed from a finite alphabet of learned words, syllables, and phonemes. The sequencing of discrete motor behaviors has received much attention in the motor control literature, but relatively little has been focused directly on speech production. In this paper, we investigate the cortical and subcortical regions involved in organizing and enacting sequences of simple speech sounds.

PURPOSE: To combine the specific advantages of the generalized autocalibrating partially parallel acquisitions (GRAPPA) technique and sensitivity encoding (SENSE) with two-dimensional (2D) undersampling.

The study protocol was approved by the institutional review board and was in full compliance with HIPAA guidelines. Informed consent was obtained from all patients. The purpose of this study was to prospectively compare intra- and intersubject variability of manual versus automatic magnetic resonance (MR) imaging section prescription. In two examinations, T2-weighted series were acquired with both methods. All intrasubject and three of six intersubject section prescription variances were significantly higher for manual prescription (P

Although the magnetic field of an MR scanner is very stable under little or no load, it can become less stable under heavy-duty cycle conditions, such as in diffusion tensor imaging (DTI). Uncorrected, such field drifts lead to an apparent image shift along the phase-encoding direction and decreasing effectiveness of fat saturation pulses. A method is presented to adjust the center frequency of all RF pulses and the receiver in real time during the acquisition. No data postprocessing or changes to the sequence timing are necessary.

Cortical analysis related to visual object recognition is traditionally thought to propagate serially along a bottom-up hierarchy of ventral areas. Recent proposals gradually promote the role of top-down processing in recognition, but how such facilitation is triggered remains a puzzle. We tested a specific model, proposing that low spatial frequencies facilitate visual object recognition by initiating top-down processes projected from orbitofrontal to visual cortex.

BACKGROUND: Myocardial injury can occur after ischemic stroke in the absence of primary cardiac causes. The neuroanatomic basis of stroke-related myocardial injury is not well understood.
OBJECTIVE: To identify regions of brain infarction associated with myocardial injury using a method free of the bias of an a priori hypothesis as to any specific location.

The purpose of the study was to assess the effects of electrodes and leads on electromagnetic field and specific absorption rate (SAR) distributions during simultaneous electroencephalography (EEG) and 7-T MRI. Two different approaches were evaluated and compared to the case without electrodes: (a) the use of different EEG lead resistivity and (b) the use of a radiofrequency (RF) resistor on the lead near the EEG electrode. These configurations are commonly used in research and clinical settings.

How does the amount of time for which we see an object influence the nature and content of its cortical representation? To address this question, we varied the duration of initial exposure to visual objects and then measured functional magnetic resonance imaging (fMRI) signal and behavioral performance during a subsequent repeated presentation of these objects. We report a novel 'rise-and-fall' pattern relating exposure duration and the corresponding magnitude of fMRI cortical signal.

Two of the most robust markers for "special" face processing are the behavioral face-inversion effect (FIE)-the disproportionate drop in recognition of upside-down (inverted) stimuli relative to upright faces-and the face-selective fMRI response in the fusiform face area (FFA). However, the relationship between these two face-selective markers is unknown. Here we report that the behavioral FIE is closely associated with the fMRI response in the FFA, but not in other face-selective or object-selective regions.