Broadband selective excitation radiofrequency pulses for optimized localization in vivo.

Purpose: The aim of the study is to optimize the performance of localized H MRS sequences at 3T, using the entire spin system of N-acetyl aspartate (NAA) as an example of the large chemical shift spread of all the metabolites routinely detected in vivo, including the amide region. We specifically focus on the design of the suitable broadband excitation radiofrequency (RF) pulses to minimize chemical shift artifacts.

Methods: The performance of the excitation and refocusing pulse shapes is evaluated with respect to NAA localization.

An MRI protocol for anatomical and functional evaluation of the California sea lion brain.

Background: Domoic acid (DOM) is a neurotoxin produced by some harmful algae blooms in coastal waters. California sea lions (Zalophus californianus) exposed to DOM often strand on beaches where they exhibit a variety of symptoms, including seizures. These animals typically show hippocampal atrophy on MRI scans.

Methylsulfonylmethane (MSM): A chemical shift reference for H MRS of human brain.

Purpose: We investigate the potential of a common dietary supplement, methylsulfonylmethane (MSM), to act as a chemical shift reference for in vivo H MR spectroscopy (MRS). The scope of the investigation is 2-fold: (1) We use high-resolution nuclear MR (NMR) measurements of the chemical shift values of MSM to establish the stability of MSM resonance across the ranges of pH and temperature, and (2) we demonstrate MR properties of MSM in the healthy human brain.

Methods: The relationship of chemical shift with temperature and pH is examined using high-resolution H NMR (14.

Pyrolytic graphite foam: a passive magnetic susceptibility matching material.

Purpose: To evaluate a novel soft, lightweight cushion that can match the magnetic susceptibility of human tissue. The magnetic susceptibility difference between air and tissue produces field inhomogeneities in the B(0) field, which leads to susceptibility artifacts in magnetic resonance imaging (MRI) studies.

Materials And Methods: Pyrolytic graphite (PG) microparticles were uniformly embedded into a foam cushion to reduce or eliminate field inhomogeneities at accessible air and tissue interfaces.

Analysis of oxygen metabolism implies a neural origin for the negative BOLD response in human visual cortex.

The sustained negative blood oxygenation level-dependent (BOLD) response in functional MRI is observed universally, but its interpretation is controversial. The origin of the negative response is of fundamental importance because it could provide a measurement of neural deactivation. However, a substantial component of the negative response may be due to a non-neural hemodynamic artifact.

Reducing vascular variability of fMRI data across aging populations using a breathholding task.

The magnitude and shape of blood oxygen level-dependent (BOLD) responses in functional MRI (fMRI) studies vary across brain regions, subjects, and populations. This variability may be secondary to neural activity or vasculature differences, thus complicating interpretations of BOLD signal changes in fMRI experiments. We compare the BOLD responses to neural activity and a vascular challenge and test a method to dissociate these influences in 26 younger subjects (ages 18-36) and 24 older subjects (ages 51-78).