Evaluation of the inner ear by 3D fast asymmetric spin echo (FASE) MR imaging: Phantom and volunteer studies

The 3D fast asymmetric spin echo (FASE) method combines the half-Fourier te chnique and 3D fast spin echo (FSE) sequence. The advantage of this method is that it maintains the same spatial resolution as FSE while markedly redu cing the imaging time, The purpose of the present study was to evaluate the usefulness of the 3D FASE technique in displaying the inner ear structure using phantom and volunteer studies. 3D PSE sequence images were obtained f or comparison, and the optimum 3D FASE sequence was investigated on a 1.5T MR scanner. The results of phantom experiments showed increased signal-to-n oise ratio (SNR) with prolonging repetition time (TR) on both 3D FASE and 3 D FSE sequences. Although the SNR of 3D FASE images was 20-25% lower than t hat of 3D FSE images with the same TR, the SNR per minute with 3D FASE was about twice that with 3D FSE. On 3D FASE images, a higher spatial resolutio n was obtained with 2- or 4-shot images than with single-shot images. Howev er, no significant difference was observed between 2-shot and 4-shot images . In the volunteer study, 3D FASE images using a TR of 5000 ms and an effec tive echo time (TEeff) of 250 ms showed a high SNR and spatial resolution a nd provided excellent contrast between cerebrospinal fluid and nerves in th e internal auditory canal. The highest contrast was achieved in the 2-shot/ 2 number of excitations sequence. 3D FASE provides the same image quality a s 3D FSE with a significant reducing in imaging time, and gives strong T2-w eighted images. This method enables detailed visualization of the tiny stru ctures of the inner ear. (C) 1999 Elsevier Science Inc.