Rodent Abdominal Adipose Tissue Imaging by MR.

Rodents including rats and mice are important models to study obesity, diabetes, and metabolic syndrome in a preclinical setting. Translational and longitudinal imaging of these rodents permit investigation of metabolic diseases and identification of imaging biomarkers suitable for clinical translation. Here we describe the imaging protocols for achieving quantitative abdominal imaging in small animals followed by segmentation and quantification of fat volumes.

Noninvasive evaluation of the regional variations of GABA using magnetic resonance spectroscopy at 3 Tesla.

PURPOSE: Rapid regional fluctuations in GABA may result in inhomogeneous concentrations throughout the brain parenchyma. The goal of this study is to provide further insight into the natural distribution of GABA throughout the brain and thus determine if a surrogate site may be used for spectroscopy when evaluating motor diseases, neurological disorders, or psychiatric dysfunction. MATERIALS AND METHODS: In this prospective study, eight healthy volunteers underwent spectroscopic evaluation of the frontal lobe, occipital lobe, lateral temporal lobe, basal ganglia, and both hippocampi using a spin echo variant of a J-difference editing method. Knowledge of the relative peak intensities of the macromolecule peaks at 3ppm and 0.9ppm was used to correct the contribution of co-edited macromolecules to the GABA peak at 3ppm. The GABA values were internally referenced to NAA. Linear regression was used to normalize the effect of regional tissue-fraction variation on the GABA/NAA values. A one-way ANOVA was performed with Tukey's multiple comparison test to compare the normalized GABA/NAA values in each pair of locations. RESULTS: After accounting for the macromolecule contribution to the GABA signal and correction for tissue fraction variation, the normalized GABA/NAA ratios differ significantly between the six brain locations (p<0.001). Pairwise comparisons of the corrected normalized GABA/NAA ratios show statistically significant variation between the frontal lobe and the basal ganglia, frontal and lateral temporal lobes, and frontal lobe and right hippocampus. Variations in the normalized GABA/NAA ratios trend toward significance between the frontal lobe and left hippocampus, occipital lobe and the frontal lobe, occipital lobe and basal ganglia, and occipital lobe and right hippocampus. CONCLUSION: Our study suggests that GABA concentration is inhomogeneous throughout the parenchyma. Studies evaluating the role of GABA must carefully consider voxel placement when incorporating spectroscopy.

Slow relaxation of longitudinal multispin orders in weakly and strongly coupled two-spin systems.

Longitudinal multispin order (LOMO) corresponds to a nonequilibrium population distribution in spin systems that exhibit scalar (J), dipolar, or quadrupolar coupling. We investigated the relaxation of longitudinal two-spin order (2-LOMO) in systems that had either weakly or strongly J-coupled spins. Our results indicated longer relaxation times for the 2-LOMO state compared with the corresponding longitudinal single-spin state (1-LOMO). Accessing nuclear spin states that have relaxation times longer than T(1), without the use of external contrast agents, is potentially useful for in vivo imaging and also for studying systems using dynamically hyperpolarized nuclear spins where longer life times are sought to increase the time available to study (bio)chemical events.

MR imaging with phase encoding of intermolecular multiple quantum coherences.

Novel 2D and 3D pulse sequences producing images through the phase encoding of intermolecular multiple quantum coherences (i-MQCs) are presented. The signal acquired with these sequences is free from intermolecular zero quantum coherences (i-ZQCs) which are not phase encoded and additional phase cycling eliminates artifacts. Phase encoding during the n-quantum evolution period provides n times the resolution expected from equivalent phase encoding of the reconverted single quantum coherences. These sequences have potential applications for producing i-MQC images of biological tissues as well as nonbiological materials with substantial amounts of water.