Yu Nishina1, Satoru Morita1, Tatsuya Kuramoto2, Makoto Suzuki2, Hitoshi Tadenuma2, Yasuhiro Goto2, Masami Yoneyama3, and Shuji Sakai1
1Diagnostic Imaging and Nuclear Medicine, Tokyo Women's Medical University Hospital, Tokyo, Japan, 2Radiological Service, Tokyo Women's Medical University Hospital, Tokyo, Japan, 3Philips Electronics Japan, Tokyo, Japan
Synopsis
We
compared the image quality of single-shot turbo spin-echo
diffusion-weighted imaging (TSE-DWI) with parallel imaging and conventional echo planar
DWI (EPI-DWI) in the pancreas of healthy volunteers. TSE-DWI with a sensitivity
encoding factor (SF) of 2, 4, 6, and EPI-DWI with SF2 (b-values = 0, 500, 1000
s/mm2) were obtained using a 3T MRI scanner. Two radiologists
evaluated overall image quality, susceptibility artifacts, and aliasing
artifacts. TSE-DWI with moderate SF had better image quality than conventional
EPI-DWI for a medium b-value because of less susceptibility artifacts.Purpose
Single-shot
turbo spin-echo (TSE) sequence, which has fewer susceptibility artifacts
compared with echo planar imaging (EPI), can be used for diffusion-weighted
imaging (DWI). A newly developed TSE-DWI sequence can reduce the echo train
length due to short echo space by use of a short radio frequency pulse shape,
resulting in a reduction of blurring. In addition, parallel imaging can be
applied to this sequence, which can further reduce blurring. However, parallel
imaging with a high sensitivity encoding factor (SF) may worsen the
signal-to-noise ratio, especially for DWI with a high b-value. Thus, the
optimal acquisition parameters including SF and b-value are unknown. The
purpose of this study was to compare the image quality of the pancreas in
healthy volunteers using single-shot TSE-DWI with parallel imaging and
conventional EPI-DWI.
Methods
This
prospective single-institution study was approved by the Institutional Review
Board of our facility. TSE-DWI with SF2, 4, 6, and EPI-DWI with SF2 (b-values =
0, 500, 1000 s/mm2) of the pancreas in 10 healthy volunteers were
obtained using a 3T MRI scanner. Two radiologists evaluated overall image
quality, susceptibility artifacts, and aliasing artifacts, of each image in a
blind fashion using the visual analog scale (VAS, 0–10). VAS scores between the
sequences were compared using a Tukey–Kramer test. Interobserver variability was assessed with Kendall
correlation analysis to measure the degree of agreement between the two
observers.
Results
There was good observed agreement for overall image quality, susceptibility
artifacts, and aliasing artifacts, with Kendall tau rank correlation coefficients of 0.57, 0.53, and 0.87 (p < 0.001), respectively. For a b-value of 500 s/mm2, the overall
image quality of TSE-DWI with SF4 (8.7
± 0.2) was significantly higher than that of TSE-DWI with SF2 (7.3 ± 0.2, p < 0.001), SF6 (5.9 ± 0.2, p < 0.001),
and EPI-DWI (6.6 ± 0.3, p < 0.001). For a b-value of
1000 s/mm2, the overall image quality of TSE-DWI with SF4 (6.5 ± 0.6) was significantly higher
than that of TSE-DWI with SF2 (5.6 ±
0.5, p = 0.02) and SF6 (1.8 ± 0.5, p < 0.001), while no significant difference was observed
compared with EPI-DWI (6.4 ± 0.6, p = 0.99). For a b-value of 500
s/mm2, susceptibility artifacts of EPI-DWI (5.1 ± 0.1) were
significantly worse than those of TSE-DWI with SF2 (8.0 ± 0.2, p < 0.001), SF4 (9.0 ± 0.1, p < 0.001), and SF6 (8.0 ± 0.1, p < 0.001). For a b-value of 1000
s/mm2, susceptibility artifacts of EPI-DWI (5.6 ± 0.2) were
significantly worse than those of TSE-DWI with SF2 (7.9 ± 0.4, p < 0.001) and SF4 (8.3 ± 0.1, p < 0.001), while no significant
difference was observed compared with TSE-DWI with SF6 (5.4 ± 0.2, p = 0.90). For b-values of 500 and
1000 s/mm2, TSE-DWI with SF6 had severe aliasing artifacts. For a
b-value of 1000 s/mm2, mild aliasing artifacts were observed in
TSE-DWI with SF4.
Conclusion
TSE-DWI
with moderate SF has better image quality in the pancreas than conventional
EPI-DWI for a medium b-value because of fewer susceptibility artifacts.
However, there are fewer benefits at a high b-value.
Acknowledgements
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