Accelerated chemical shift imaging of hyperpolarized (13) C metabolites

PURPOSE

Chemical shift imaging (CSI) has long been considered the gold standard method for in vivo hyperpolarized (13) C metabolite imaging because of its high sensitivity. However, CSI requires a large number of excitations so it is desirable to reduce the number of RF excitations and the total acquisition time.

METHODS

Centric phase encoding and three-dimensional compressed sensing methods were adopted into a CSI acquisition to improve efficiency and reduce the number of excitations required for imaging hyperpolarized metabolites. The new method was implemented on a GE MR750W scanner for routine real time metabolic imaging experiments.

RESULTS

Imaging results from phantoms and in vivo animals using hyperpolarized (13) C tracers demonstrate that when the entire CSI dataset is treated as a single object, compressed sensing can be satisfactorily applied to spectroscopic CSI. Centric k-space trajectory data collection also greatly improves the acquisition efficiency. This combination of compressed sensing CSI and acquisition time reduction was used to perform a hyperpolarized (13) C dynamic study.

CONCLUSION

Compressed sensing can be satisfactorily applied to conventional CSI in hyperpolarized (13) C metabolite MR imaging to reduce the number of RF excitations and accelerate the imaging speed to take advantage of conventional CSI in providing high sensitivity and a large spectral bandwidth. Magn Reson Med 76:1033-1038, 2016. © 2016 Wiley Periodicals, Inc.

DWI and complex brain network analysis predicts vascular cognitive impairment in spontaneous hypertensive rats undergoing executive function tests

The identification of biomarkers of vascular cognitive impairment is urgent for its early diagnosis. The aim of this study was to detect and monitor changes in brain structure and connectivity, and to correlate them with the decline in executive function. We examined the feasibility of early diagnostic magnetic resonance imaging (MRI) to predict cognitive impairment before onset in an animal model of chronic hypertension: Spontaneously Hypertensive Rats. Cognitive performance was tested in an operant conditioning paradigm that evaluated learning, memory, and behavioral flexibility skills. Behavioral tests were coupled with longitudinal diffusion weighted imaging acquired with 126 diffusion gradient directions and 0.3 mm³ isometric resolution at 10, 14, 18, 22, 26, and 40 weeks after birth. Diffusion weighted imaging was analyzed in two different ways, by regional characterization of diffusion tensor imaging (DTI) indices, and by assessing changes in structural brain network organization based on Q-Ball tractography. Already at the first evaluated times, DTI scalar maps revealed significant differences in many regions, suggesting loss of integrity in white and gray matter of spontaneously hypertensive rats when compared to normotensive control rats. In addition, graph theory analysis of the structural brain network demonstrated a significant decrease of hierarchical modularity, global and local efficacy, with predictive value as shown by regional three-fold cross validation study. Moreover, these decreases were significantly correlated with the behavioral performance deficits observed at subsequent time points, suggesting that the diffusion weighted imaging and connectivity studies can unravel neuroimaging alterations even overt signs of cognitive impairment become apparent.