Magnetic Resonance Imaging (MRI)

We evaluate a wavelet-based algorithm to estimate the coil sensitivity modulation from surface coils. This information is used to improve the image homogeneity of magnetic resonance imaging when a surface coil is used for reception, and to increase image encoding speed by reconstructing images from under-sampled (aliased) acquisitions using parallel magnetic resonance imaging (MRI) methods for higher spatiotemporal image resolutions.

Diffusion spectrum imaging (DSI) has been demonstrated to resolve crossing axonal fibers by mapping the probability density function of water molecules diffusion at each voxel. However, the accuracy of DSI in defining individual fiber orientation and the validity of Fourier relation under finite gradient pulse widths are not assessed yet. We developed an ex vivo and an in vivo model to evaluate the error of DSI with gradient pulse widths being relatively short and long, respectively. The ex vivo model was a phantom comprising sheets of parallel capillaries filled with water.

The aim of this study was to gain further insights into how the brain distinguishes between meaning and syntax during language comprehension. Participants read and made plausibility judgments on sentences that were plausible, morphosyntactically anomalous, or pragmatically anomalous. In an event-related potential (ERP) experiment, morphosyntactic and pragmatic violations elicited significant P600 and N400 effects, respectively, replicating previous ERP studies that have established qualitative differences in processing conceptually and syntactic anomalies.

BACKGROUND: Schizophrenia is characterized by small reductions in cortical gray matter volume, particularly in the temporal and prefrontal cortices. The question of whether cortical thickness is reduced in schizophrenia has not been addressed using magnetic resonance imaging (MRI) techniques.

Although many neuroimaging studies of visual mental imagery have revealed activation in early visual cortex (Areas 17 or 18), many others have not. The authors review this literature and compare how well 3 models explain the disparate results. Each study was coded 1 or 0, indicating whether activation in early visual cortex was observed, and sets of variables associated with each model were fit to the observed results using logistic regression analysis. Three variables predicted all of the systematic differences in the probability of activation across studies.

If attention is divided during learning, memory suffers. Nevertheless, individuals can learn information with divided attention. This event-related functional magnetic resonance imaging (fMRI) study (n = 17) investigated what neural processes support (1) learning with divided attention and (2) retrieval of information learned with divided attention. Participants encoded words (Is the word abstract or concrete?) while performing an auditory discrimination task (press a button whenever an auditory pattern changes).

Several current brain imaging techniques rest on the assumption of a tight coupling between neural activity and hemodynamic response. The nature of this neurovascular coupling, however, is not completely understood. There is some evidence for a decoupling of these processes at the onset of neural activity, which manifests itself as a momentary increase in the relative concentration of deoxyhemoglobin (HbR). The existence of this early component of the hemodynamic response function, however, is controversial, as it is inconsistently found.

PURPOSE: The purpose of this work was to compare diffusion-weighted imaging (DWI) with conventional MRI in the detection of shearing injuries in acute closed head injuries.
METHOD: Twenty-five patients (19 male, 6 female) were examined within 48 h of trauma. Conventional MRI included T2-weighted fast spin echo, fluid-attenuated inversion recovery (FLAIR), and T2*-weighted gradient echo sequences. Full tensor DWI with calculation of apparent diffusion coefficient (ADC) maps was also performed. Lesions were identified and compared on all sequences.

RATIONALE AND OBJECTIVES: A cardiac imaging pilot study was performed on 1.5 and 3.0 Tesla (T) whole body magnetic resonance units equipped with identical gradient sets and geometrically equivalent body coils. The goals were to compare the signal-to-noise (SNR) and contrast-to-noise (CNR) ratios on matched studies conducted at both field strengths and demonstrate the potential for functional and morphologic cardiac evaluation at 3.0 T.

The temporal dynamics of fMRI responses can span a broad range, indicating a rich underlying physiology, but also posing a significant challenge for detection. For instance, in human auditory cortex, prolonged sound stimuli ( approximately 30 sec) can evoke responses ranging from sustained to highly phasic (i.e., characterized by prominent peaks just after sound onset and offset).