High-resolution MR cisternography of the cerebellopontine angle: 2D versus3D fast spin-echo sequences

BACKGROUND AND PURPOSE: The clinical usefulness of MR cisternography of the cerebellopontine angle, applying 2D or 3D fast spin-echo sequences, has be en reported recently. Our purpose was to investigate the cause of signal lo ss in CSF in the prepontine or cerebellopontine angle cistern on 2D FSE MR images and to compare the cisternographic effects of 2D and 3D FSE sequence s, METHODS: Preliminary experiments were performed in four volunteers to asses s the causes of signal loss. Initially, using a 2D cardiac-gated cine phase -contrast method with a velocity encoding value of 6 cm/s, we measured the velocity and flow pattern of CSF, Comparisons were made to assess the effec ts of intravoxel dephasing, amplitude of the section-selecting gradient, ec ho time (TE), and section thickness. Four healthy subjects and 13 patients with ear symptoms were examined, and multisection 3-mm-thick 2D images and 30-mm-slab, 1-mm-section 3D images were compared qualitatively and quantita tively. Then, 3D MR cisternography was performed in 400 patients with ear s ymptoms, and qualitative evaluation was performed. RESULTS: In volunteers, the average peak velocity of CSF was 1.2 cm/s, With TE = 250, CSF may move an average of 3 mm, and can be washed out of a 3-mm -thick 2D section volume. The CSF signal relative to that of a water phanto m decreased gradually as TE increased on single-section S-mm-thick 2D image s, The CSF signal relative to that of the water phantom increased gradually as section thickness increased. No significant differences were noted in i ntravoxel dephasing and amplitude of the section-selecting gradient. The co ntrast-to-noise ratio (CNR) between CSF and the cerebellar peduncle, and th e visibility of the cranial nerves and vertebrobasilar artery were signific antly improved on 3D images in 17 subjects, In images from 400 patients, no significant signal loss in the cistern was observed using 3D FSE. CONCLUSION: CSF signal loss in thin-section 2D MR cisternography is mainly attributable to the wash-out phenomenon. 3D acquisition can reduce this phe nomenon and provide thinner sections. The scan time for 3D acquisition is n ot excessive when a long echo train length and half-Fourier imaging are use d. MR cisternography should be performed using a 3D acquisition.