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High resolution GRASE MRI of the brain and spine: 512 and 1024 matrix imaging
D A Feinberg1, B Kiefer, A W Litt
1Department of Radiology, New York University Medical Center, New York 10016.
Objective:
Our goal was to implement 512 and 1024 matrix MRI of the brain in clinically acceptable imaging times.
Materials And Methods:
With use of the GRASE (gradient-SE) imaging technique, 3 signals are refocused from each of 16 SEs, giving a total of 48 echoes per echo train, for a speed advantage of 1/48 over conventional SE imaging. Images in 1024 matrices are acquired in 2D Fourier transform (FT) multisectional MRI. In related experiments, multislab 3D FT GRASE imaging is performed using 16 partitions/slab, providing thinner 1 to 2 mm sections. In all imaging experiments, higher spatial resolution is obtained with stronger and faster gradients, 24 mT/m in 625 microseconds rise time, on a standard commercial MRI system.
Results:
The 2D FT 1024 matrix images of the head were acquired in 4:20 min, with 20 sections and TR/TE 7040/115 ms in a rectangular FOV to obtain .28 x .27 mm2 spatial resolution. Small anatomic structures, including cochlea of inner ear, cranial nerves, and vascular detail, are readily demonstrated. The 512 matrix images were obtained in 4:40 min, with 16 sections and TR/TE 3,500/104 ms in a 24 cm FOV. The 3D FT technique substantially increased slice coverage as well as image signal-to-noise ratio.
Conclusion:
The results show that 1024 matrix MRI is technically feasible in clinically acceptable imaging time and offers advantage for high resolution imaging. Optimization of 1024 matrix and 3D FT GRASE imaging should improve the delineation of anatomic regions of interest.