Synopsis

Keywords: New Devices, Diffusion/other diffusion imaging techniques

Reduced field-of-view (rFOV) technique is a feasible approach to counter the constraints of conventional DWI. Most recently, the 5.0 T whole-body MRI system was developed, which provides an alternative choice for high field abdominal DWI. This research aims to evaluate the image quality of 5.0 T rFOV-DWI with the 3.0 T rFOV-DWI as the reference. The results indicated that 5.0 T rFOV-DWI had better overall image quality and improved SNR compared to 3.0 T rFOV-DWI, which holds clinical potential for identifying the abdominal abnormalities in routine practice.

Introduction

Reduced field-of-view (rFOV) technique is a feasible approach to counter the constraints of conventional DWI. Utilizing a spatially selective localized radiofrequency (RF) excitation pulses or/and an outer-volume suppression (OVS), the sampling density of K-Space is reduced, which results in a smaller dataset size for given resolution. Therefore, the acquisition time, motion artifacts, susceptibility effects and distortion will be diminished.(1, 2) Previous findings unveiled that the combination of rFOV and high-field DWI allows ultra-high-resolution imaging for human brain.(3, 4)
Most recently, the 5.0 T whole-body MRI system was developed, which provides an alternative choice for high-field abdominal DWI. Besides, it was hypothesized by us that: 1) The 5.0 T DWI may be feasible and valuable for abdominal imaging. 2) The combination of 5.0 T high field DWI and rFOV technique is beneficial for providing a relatively good image quality. 3) The image quality of 5.0 T rFOV-DWI is better than 3.0 T rFOV-DWI for abdominal applications. Therefore, this research aims to evaluate the image quality of 5.0 T rFOV-DWI with the 3.0 T rFOV-DWI as the reference. To the best of our knowledge, hardly has the high field abdominal DWI been performed.

Methods

In total, 15 volunteers were included. All subjects underwent the 3.0 T- and 5.0 T-MRI examinations. The 5.0 T MRI examinations were performed with a prototype whole-body MRI scanner (uMR Jupiter, United Imaging Healthcare). Free-breathing (FB), respiratory-triggered (RT) and navigator-triggered (NT) spin-echo echo-planner imaging (SE-EPI) based three imaging protocols were performed subsequently. Except the difference in the strategies of countering the breathing motion, three sequences (5.0 T-FB-DWI (FB_{5.0 T}), 5.0 T-RT-DWI (RT_{5.0 T}) and 5.0 T-NT-DWI (NT_{5.0 T})) were configured to as the same imaging parameters as possible. The detailed imaging protocols were as follows: repetition time (TR): ~4500 ms (Influenced by the respiratory cycle), echo Time (TE): 50.5 ms, flip angle (FA): 90°, field of view (FOV): 120×280 mm², matrix: 96×224, slice thickness: 6 mm, b values: 0 s/mm² (two averages) and 800 s/mm² (8 averages). The 3.0 T MRI examinations were performed with a commercial MRI scanner (uMR 790, United Imaging Healthcare, Shanghai, China). Similar to 5.0 T examinations, FB, NT and RT SE-EPI based three DWI acquisitions (3.0 T-FB-DWI (FB_{3.0 T}), 3.0 T-RT-DWI (RT_{3.0 T}) and 3.0 T-NT-DWI (NT_{3.0 T})) were performed subsequently. The SNR of DWI images were independently measured and compared. The image quality of each DWI acquisition was evaluated based on the overall quality of DWI images (b = 0 and 800 s/mm2) and ADC maps in terms of sharpness, distortion and artifacts. Specifically, the sharpness, distortion and artifact were scored based on the 5-point scaling criteria.

Results

The representative DWI images of six acquisition approaches were displayed in Figure 1-3. For four upper abdominal organs (liver, pancreas, spleen and kidney) in DWI images of b = 0 s/mm² and b = 800 s/mm², there existed the significant differences among the SNRs of six DWI examinations (p < 0.05) (Table 1, Figure 4). The SNRs of liver were relatively low compared to those of pancreas, spleen and kidney. The post-hoc multiple comparisons suggested that the SNRs of any 5.0 T DWI images were significantly higher than those of any 3.0 T DWI images for same anatomic location in DWI images of b = 0 s/mm² and 800 s/mm². The results regarding the image quality analysis were displayed in Figure 5. 5.0 T DWI examinations yielded the significantly higher sharpness scores than their counterparts at 3.0 T. With respect to geometric distortion, six imaging protocols have the similar distortion scores (min: 2.9±0.4, max: 3.7±0.4). The severest artifacts were observed in FB_{3.0 T} and FB_{5.0 T} followed by NT_{3.0 T}, NT_{5.0 T}, RT_{3.0 T} and RT_{5.0 T} (FB_{3.0 T} = 2.3±0.8, FB_{5.0 T} = 2.5±0.5, NT_{3.0 T} = 3.2±0.9, NT_{5.0 T} = 3.3±0.5, RT_{3.0 T} = 3.3±0.7 and RT_{5.0 T} = 3.4±0.5, p < 0.001). Finally, the RT_{5.0 T} displayed the best overall IQ followed by NT_{5.0 T}, FB_{5.0 T}, RT_{3.0 T}, NT_{3.0 T} and FB_{3.0 T} (RT_{5.0 T} = 3.9±0.3, NT_{5.0 T} = 3.8±0.3, FB_{5.0 T} = 3.4±0.3, RT_{3.0 T} = 3.2±0.4, NT_{3.0 T} = 3.1±0.4 and FB_{3.0 T} = 2.7±0.4, p < 0.001).

Discussion

In this study, the results involving the SNR comparison showed that the increase in B0 field strength provided a remarkable SNR gain. For four upper abdomen organs containing the liver, pancreas, spleen and kidney, the SNRs of both b0 and b800 DWI images at 5.0 T were significantly higher than those at 3.0 T. the overall IQs of six sequences were quantified based on the sharpness, distortion and artifacts. Our results showed that the RT_{5.0 T} yielded the best image quality score followed by NT_{5.0 T}, FB_{5.0 T}, RT_{3.0 T}, NT_{3.0 T} and FB_{3.0 T}. Besides, no significant difference was observed between the IQ of RT_{5.0 T} and NT_{5.0 T}, demonstrating that the RT_{5.0 T} and NT_{5.0 T} were recommended for abdominal DWI imaging.

Conclusion

In view of the results that 5.0 T rFOV-DWI showed an improved image quality for upper abdomen compared to 3.0 T rFOV-DWI, 5.0 T rFOV-DWI holds clinical potential for visualizing the abdominal abnormalities.

Acknowledgements

None

References

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