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High-Resolution MR Cisternography of the Cerebellopontine Angle, Obtained with a Three-Dimensional Fast Asymmetric Spin-Echo Sequencein a 0.35-T Open MR Imaging UnitGo

Shinji NaganawaGo,a, Tokiko Itoa, Eriko Iwayamaa, Hiroshi Fukatsua and Takeo Ishigakia

a From the Department of Radiology, Nagoya University School of Medicine, Nagoya, Japan.



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  		FIG 1. Comparisons of the images obtained in different numbers of shots. The images obtained in one shot (A) showed contrast-to-noise ratio values that were comparable with those obtained in two shots (B); however, they showed more blur. The images obtained in four shots showed the lowest contrast-to-noise ratio values with the least degree of blur (C).

A, One shot; echo train length, 140; number of excitations, 4.

B, Two shots; echo train length, 76; number of excitations, 2.

C, Four shots, echo train length, 44; 4000/240/1 (TR/TE/excitations); field of view, 15 cm; matrix, 256 x 256 x 40; section thickness, 1 mm; echo spacing, 20 milliseconds; and imaging time, 10 minutes 44 seconds.

FIG 2. Comparisons of the images with different TRs. Images with 4000/2 (TR/excitations) (A) and 8000/1 (B) showed comparable contrast-to-noise ratio values. Images with 8000/1 showed some ghost artifacts (arrow). Other parameters are the same for both TRs: two shots; echo train length, 76; 240 (TE); field of view, 15 cm; matrix, 256 x 256 x 40; section thickness, 1 mm; echo spacing, 20 milliseconds; and imaging time, 10 minutes 44 seconds.FIG 3. Comparisons of the images with 120 (TE) (A), 180 (B), and 240 (C). Images with 240 showed the best contrast-to-noise ratio values. Other parameters were the same for all TEs: two shots; 4000 (TR); field of view, 15 cm; matrix, 256 x 256 x 40; section thickness, 1 mm; echo spacing, 20 milliseconds; and imaging time, 10 minutes 44 seconds.FIG 4. Images without zero-fill interpolation showed more blur on both source images (A) and maximum intensity projection images (C) of the labyrinth than on those with ZIP1 (B and D). The imaging parameters were as follows: field of view, 15 cm; section thickness, 1 mm; 4000/240/2 (TR/TE/excitations); two shots; echo train length, 76; matrix, 256 x 256 x 40, which zero-filled to 512 x 512 x 80; and imaging time, 10 minutes 44 seconds



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  		FIG 5. Images obtained at 1.5 T (imaging time, 3 minutes) (A) and 0.35 T (imaging time, 11 minutes) (B) provided comparable anatomic information.

A, The imaging parameters at 1.5 T were as follows: field of view, 15 cm; section thickness, 1 mm; 5000/250/1 (TR/TE/excitations); one shot; echo train length, 148; matrix, 256 x 256 x 30, which zero-filled to 512 x 512 x 60; echo spacing, 12.5 milliseconds; and imaging time, 2 minutes 45 seconds.

B, The imaging parameters for 0.35 T were as follows: field of view, 15 cm; section thickness, 1 mm; 4000/240/2; two shots, echo train length, 76; matrix, 256 x 256 x 40, which zero-filled to 512 x 512 x 80; and imaging time, 10 minutes 44 seconds.



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  		FIG 6. A case of a 2-mm intracanalicular acoustic schwannoma. A small filling defect in the CSF of the left internal auditory canal was depicted on both 1.5-T images (imaging time, 12 minutes) (A) and 0.35-T images (imaging time, 11 minutes) (B) (arrows).

A, The imaging parameters at 1.5 T were as follows: field of view, 16 cm; section thickness, 0.8 mm; 4000/240 (TR/TE); four shots; echo train length, 79; matrix, 512 x 512 x 40; echo spacing, 15.0 milliseconds; and imaging time, 11 minutes 48 seconds.

B, The imaging parameters for 0.35 T were the same as those presented in the legend to figure 5B. Our protocol for "the screening brain and internal auditory canal" included T2-weighted images for whole-brain and MR cisternography with 3D fast asymmetry spin-echo images obtained in 2 minutes 45 seconds. The protocol for "screening internal auditory canal only" for the patients who had finished their whole-brain study was MR cisternography with 3D fast asymmetric spin-echo images obtained in 12 minutes. For this image, the latter protocol was applied to compare the image quality between the 0.35- and 1.5-T images obtained during comparable imaging time. Note the considerable difference in the image quality between the 0.35- and 1.5-T images when obtained during comparable imaging time, although the pathologic findings can be appreciated on either image.





Copyright © 2009 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X