Optimization of Single-shot Turbo Spin-echo Diffusion-weighted Imaging with Parallel Imaging in Healthy Pancreas
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

No acknowledgement found.

References

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Figures

Average visual analog scores of overall image quality, susceptibility artifacts, and aliasing artifacts of TSE-DWI and EPI-DWI.

*Values are mean ± standard deviation on a score of the visual analog scale. TSE = turbo spin-echo, DWI = diffusion-weighted imaging, SF = sensitivity encoding factor, EPI = echo planar imaging


Examples of TSE-DWI with a b-value of 500 s/mm2 and SF2, 4, and 6 and EPI-DWI of the pancreas. The image quality of TSE-DWI with SF4 is excellent. Susceptibility artifacts are observed on EPI-DWI (arrow), but are not observed on TSE-DWI. Severe aliasing artifacts are observed on TSE-DWI with SF6 (arrowheads).

Examples of TSE-DWI with a b-value of 1000 s/mm2 and SF2, 4, and 6 and EPI-DWI of the pancreas (same volunteer as Figure 1). Susceptibility artifacts are observed on EPI-DWI (arrow), but are not observed on TSE-DWI. Severe aliasing artifacts are observed on TSE-DWI with SF6 (arrowheads), and mild aliasing artifacts are observed on TSE-DWI with SF4 (arrowheads).



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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