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Quantitative assessment of pancreatic proton density fat fraction (PDFF) and R2* with preoperative T2* corrected multi-echo chemical-shift-encoded MRI in patients undergoing pancreatic resection: comparison with single-voxel 1H-MRS
Yali Qu1, Mou Li1, Zhen Zhang1, Zixing Huang1, Chunchao Xia1, and Bin Song1

1Radiology, West China Hospital, Sichuan University, Chengdu, China

Synopsis

Many studies have shown multi-echo chemical-shift-encoded magnetic resonance imaging (CSE-MRI) has good performance for the evaluation of fat and iron in liver. However, the relevant studies in pancreas are fewer. We found that pancreatic PDFF and R2* estimated by T2* corrected multi-echo CSE-MRI showed a moderate correlation with 1H-MRS results in patients undergoing pancreatic resection. In addition, our study showed that pancreatic PDFF was not to be significantly associated with clinically relevant postoperative pancreatic fistula.

Introduction

Ectopic fat and iron deposition in the pancreas are supposed to be associated with endocrine and exocrine abnormalities, such as type 2 diabetes and pancreatitis1-3. Histopathological test remains the gold standard for the assessment of pancreatic fat and iron. However, the invasiveness, sampling variability and complications of biopsy hamper its widespread use. Therefore, noninvasive alternatives to biopsy are desirable. Multi-echo chemical-shift-encoded magnetic resonance imaging (CSE-MRI) addressing all potential confounders (eg, T1 bias, T2*decay, spectral complexity of fat) is able to measure proton density fat fraction (PDFF) and R2* value simultaneously4-6. Many studies have shown multi-echo CSE-MRI has good performance for the evaluation of fat and iron in liver 7-9. However, the relevant studies in pancreas are fewer.

Postoperative pancreatic fistula (POPF) is one of the major complications after pancreatic resection10-12. The risk of mortality is doubled in the patients with POPF 11,12. Pancreatic steatosis has been reported to be one of the factors associated with POPF 13,14. To the best of our knowledge, only a few studies focused on the role of pancreatic MRI fat fraction in the prediction of POPF and their results are not in agreement15,16.

The aim of this study was to (a) evaluate the accuracy of pancreatic PDFF and R2* measured by multi-echo CSE-MRI, with single-voxel 1H-MRS as the reference standard, (b) assess the correlation between PDFF and R2* in pancreas and liver respectively, (c)evaluate the correlation of PDFF and R2* between pancreas and liver, and (d) explore the relationship between pancreatic PDFF and POPF.

Methods

The prospective study was approved by West China Hospital of Sichuan University Biomedical Research Ethics Committee. Informed consent was obtained from all subjects. A total of 40 patients with pancreatic tumor undergoing pancreatic resection were enrolled from September 2016 to August 2017. All subjects underwent preoperative 3-T MR scanning including complex-based low flip angle six-echo CSE-MR sequence with T2* correction and multifrequency fat modeling and single-voxel high-speed T2*-corrected multi-echo 1H-MRS. The incidence of POPF was estimated after the pancreatic resection. Spearman correlation coefficients were obtained for each pair for clinical and MR parameters. The Chi-square test was used for categorical variables comparison and Mann-Whitney test was performed to compare continuous variables between two groups.

Results

Pancreatic PDFF and R2* by CSE-MRI showed a moderate correlation with pancreatic fat fraction and R2* by 1H-MRS respectively (rfat fraction=0.668, p<0.001; rR2*=0.663, p<0.001). A strong correlation was found between hepatic CSE-MRI and 1H-MRS fat fractions (r=0.817, p<0.001), and moderate correlation was found between hepatic CSE-MRI and 1H-MRS R2* values (r=0.622, p<0.001). There was a moderate correlation between pancreatic CSE-MRI PDFF and CSE-MRI R2* value (r=0.513, p=0.001), and the corresponding correlation in liver was weak (r=0.319, p=0.045). Pancreatic CSE-MRI PDFF showed a weak correlation with hepatic CSE-MRI PDFF (r=0.464, p=0.003). There was no significant correlation between pancreatic and hepatic CSE-MRI R2* values. Clinically relevant POPF developed in 7 (18%) of 39 patients. Sex, age, pancreatic fat fraction by CSE-MRI and 1H-MRS were not significantly associated with clinically relevant POPF (all p values>0.05).

Discussion

In this study, we found that pancreatic PDFF and R2* estimated by T2* corrected multi-echo CSE-MRI showed a moderate correlation with 1H-MRS results. One previous study showed there was significant correlation between pancreatic MRI and MRS fat fraction (r2=0.51)17 , which is in accordance with our results. Therefore, our study provided further supporting evidence for the capability of T2* corrected multi-echo CSE-MRI to evaluate the fat and iron of pancreas. However, the correlation between CSE-MRI and 1H-MRS in pancreas was poorer than that in liver. The possible reason might be the size of pancreas is much smaller than that of liver. Thus drawing region of interests in pancreas was more difficult than that in liver, which might more easily introduce bias. In accordance with a previous study16, our study showed pancreatic fat fraction was not significantly associated with clinically relevant POPF. However, one study found the pancreatic fat fraction measured by dual-echo MRI was associated with POPF15. The possible reason might be that dual-echo MRI will estimate fat fraction inaccurately since without T2* correction. In our study, no relationship between MRI PDFF and POPF might be attributed to the not strong correlation between the pancreatic MRI PDFF and reference standard. Therefore, further studies are needed.

Conclusion

T2* corrected multi-echo CSE-MRI measuring pancreatic PDFF and R2* may yield quantitative information regarding the fat and iron in pancreas. Pancreatic PDFF was shown not to be significantly associated with clinically relevant POPF.

Acknowledgements

We thank Guanjian Liu(West China Hospital, Sichuan University) for his support on the statistical analysis.

References

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Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)
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