White and gray matter contrast enhancement in MR images of the mouse brain in vivo using IR UTE with a cryo-coil at 9.4 T.

Abstract

The aim of this work was to assess the capability of high field MRI to image brain micro-structures containing various amount of myelin. A cryogenic RF receiver coil (Bruker 'CryoProbe') and an ultra-short echo (UTE) 2D pulse sequence with and without inversion pulse were used for coronal brain MR imaging of a healthy C57BL/6J mouse. A 9.4 T magnet system was used. Signal-to-noise ratio (SNR) within the selected regions was measured. A room temperature volume RF coil was also used for SNR comparison. The inversion recovery IR-UTE 2D pulse sequence was optimized for maximum white matter (WM) and gray matter (GM) contrast-to-noise ratio (CNR). The results showed 3- to 12-fold improvement in SNR for the cryo-coil compared to the volume coil depending on the area. The inversion times providing optimum CNR for WM and GM were found to be 500 ms (negative CNR) and 1000 ms (positive CNR) for the echo time of 350 μs. Presented method provide better SNR and CNR for the brain structures with short T2 than the current techniques. The results indicate that the optimized IR-UTE pulse sequence when used with the cryo-coil allows for over 10-fold enhancement of the CNR for WM and GM as compared to the standard UTE without inversion pulse.