Anatomical brain imaging at 7T using two-dimensional GRASE.
OBJECTIVE
Specific absorption rate is a serious problem at high field strengths, especially for sequences involving many high power radiofrequency pulses, such as turbo spin echo (TSE). GRASE (gradient and spin echo) may overcome this problem by omitting a certain number of refocusing pulses of a TSE sequence, and replacing them with segmented echo-planar imaging readouts.


METHODS
GRASE and TSE were compared using similar sequence parameters at a field strength of 7T. The signal-to-noise ratio (SNR) per unit time, contrast, and point spread function (PSF) were determined. High-resolution human brain images were acquired and the implementation of an inversion recovery preparation for T(1) weighting was evaluated.


RESULTS
TSE and GRASE images at 7T showed very similar SNR and contrast. The slightly worse PSF for GRASE is balanced by a significant reduction in scan time or increase in spatial coverage compared with TSE. Furthermore, implementing an additional inversion recovery preparation enables the acquisition of T(1)-weighted images with high SNR per unit time.


CONCLUSIONS
GRASE is highly suitable for structural scanning at ultra-high field strengths and is a valid alternative to the commonly used TSE sequence.
Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
Robert
R
Trampel
Enrico
E
Reimer
Laurentius
L
Huber
Dimo
D
Ivanov
Robin M
RM
Heidemann
Andreas
A
Schäfer
Robert
R
Turner
D001931:Brain Mapping / Q000379:methods*; D017352:Echo-Planar Imaging; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio
7 Tesla; GRASE; SAR; brain; high resolution; structural imaging