Proton-Density Fat Fraction measurement: A Viable Quantitative Biomarker for Differentiating Adrenal Adenomas from Nonadenomas
Xiaoyan Meng1, Xiao Chen1, Yaqi Shen1, Zhen Li1, Xuemei Hu1, Hui Lin2, and Daoyu Hu1

1raidology, Tongji hospital, Tongji medical college, Huazhong university of science and technology, Wuhan,Hubei province, China, People's Republic of, 2GE Healthcare, Wuhan,Hubei, China, People's Republic of

Synopsis

The aim of our study was to compare the accuracy of PDFF measurements and conventional IP/OP images for quantifying the fat content of adrenal gland nodules and for distinguishing adenomas from nonadenomas.Our results showed that PDFF imaging provided almost accuracy compared with IP/OP imaging.PDFF could be a simpler diagnostic tool for discriminating adenomas from nonadenomas, with a high sensitivity and a relatively high specificity, thus avoiding complicated data calculations. This technique is potentially a helpful and a widely applicable method for diagnosing adrenal gland nodules in clinical studies.

Introduction

Adrenal nodules are clinically common and account for approximately 10% of genitourinary system tumors . With the application of abdominal and thoracic computed tomography (CT), adrenal nodules are incidentally discovered in up to 4 to 5% of these patients . Adenomas and metastases are the most common benign and malignant adrenal nodules, respectively. The detection of metastases in adrenal glands is crucial for the clinical therapeutic schedule in patients with tumors , whereas pheochromocytomas generate life-threatening hypertension or cardiac arrhythmias. In addition, 10% of these lesions are malignant . It is crucially important to differentiate adenomas from nonadenomas; thus, pheochromocytomas and metastases (both suspected and incidental) were included in this study. It is also important to distinguish benign nodules from malignant nodules .
In-phase (IP)/OP imaging provides high accuracy for the differentiation of adenomas from nonadenomas.However, the calculation method for IP/OP images was quite complicated and not intuitive. Therefore, it was necessary to identify a new method that can provide high sensitivity and specificity without radiation exposure and contrast agent side-effects. MRI proton-density fat fraction (PDFF) was described as a confounder-corrected chemical shift-encoded MRI sequence (CSE-MRI), and R2*(1/T2*) was performed with a several seconds breath-hold. The fat-fraction images were calculated based on the following formula: triglycerides signal/(water signal+ triglycerides signal). A low flip angle was used to minimize T1 bias. Noise bias and T2* decay was corrected with multi-echoes in this technique compared with the conventional 2- or 3-point Dixon technique . Recently, PDFF calculations were widely used as an MRI biomarker for an accurate and noninvasive quantification of the fat content in numerous tissues, such as hepatic steatosis. These calculations were compared to the golden reference of liver biopsy and osteoporosis. To the best of our knowledge, this precise technique has not been used in adrenal nodules to discriminate between adenomas and nonadenomas.
The aim of our study was to compare the accuracy of PDFF measurements and conventional IP/OP images for quantifying the fat content of adrenal gland nodules and for distinguishing adenomas from nonadenomas.

Abstract

Purpose

This study aims to compare the accuracy of proton-density fat fraction (PDFF) measurements with chemical shift magnetic resonance imaging for quantifying the fat content of adrenal nodules and for differentiating adenomas from nonadenomas.

Materials and Methods

This study was compliant with HIPAA and was approved by the Institutional Review Board. Informed written consent was obtained from each patient. Consecutive research was performed between Aug 2013 and Aug 2014. During this period, 43 patients (22 male, 21 female; mean age 49.4 years; range 15-78 years) with 48 nodules underwent T1 independent volumetric multi-echo gradient-echo imaging with T2* correction chemical shift-encoded magnetic resonance imaging sequence (CSE-MRI) and conventional axial three-dimensional (3D) dual-echo Dixon sequences. All MRI examinations were performed on a 3.0 T MR scanner. Proton-density fat fraction (PDFF) was measured, and the signal intensity (SI) index (SII), SI adrenal-to-liver ratio (ALR) and SI adrenal-to-spleen ratio (ASR) of the adrenal nodules were calculated. All statistical analyses were performed using the SPSS statistical software.

Results

Of the 48 adrenal nodules, 23 were histopathologically proven adenoma, 14 were proven pheochromocytoma and 11 were clinically proven metastasis. The PDFF of adrenal adenoma (22.02±10.05%) was significantly increased compared with that of nonadenoma (2.62±2.90%) (p<0.001). PDFF was an effective tool for distinguishing adenoma from nonadenoma, with an area under the curve (AUC) of 0.98. PDFF values higher than the cut-off value 2.85 % indicated adenoma with a sensitivity of 100% (23/23) and a specificity of 84.0% (21/25). In comparison, the sensitivities and specificities for diagnosing adenoma were 91.3% (21/23) and 100% (25/25) for SII, ALR and ASR on IP/OP images, with an area of the curve (AUC) of 0.94, 0.95 and 0.93, respectively. No significant difference was noted between PDFF imaging and in-phase (IP)/out-of-phase (OP) imaging for the sensitivity and specificity (p>0.05).

Conclusion

PDFF measurements provide an accurate estimation of fat content for discriminating adenoma from nonadenoma compared with IP/OP images, avoiding complicated data calculations and offering a simpler technique for diagnosing adrenal gland nodules in clinical studies.

Acknowledgements

No acknowledgement found.

References

1.Idilman IS, Aniktar H, Idilman R et al (2013) Hepatic steatosis: quantification by proton density fat fraction with MR imaging versus liver biopsy. Radiology 267:767-775

2.Tang A, Tan J, Sun M et al (2013) Nonalcoholic Fatty Liver Disease: MR Imaging of Liver Proton Density Fat Fraction to Assess Hepatic Steatosis. Radiology 267:422-431

3.Meisamy S, Hines CDG, Hamilton G et al (2011) Quantification of Hepatic Steatosis with T1-independent, T2*-corrected MR Imaging with Spectral Modeling of Fat: Blinded Comparison with MR Spectroscopy. Radiology 258:767-775

4.Schindera ST, Soher BJ, Delong DM et al (2008) Effect of echo time pair selection on quantitative analysis for adrenal tumor characterization with in-phase and opposed-phase MR imaging: initial experience. Radiology 248:140-147

Figures

Figure 1: Study population selection flow chart and characteristics in all patients.


Figure 2: Box and whisker plot illustrates the PDFF (a), SII (b), ALR (c) and ASR (d) of adenomas and nonadenomas.

Figure 3: Right adrenal adenoma in a 58-year-old woman, indicated by white arrows. a) PDFF image with a PDFF of 32.5% indicates a lipid-rich adenoma. b) T2WI propeller image revealed the nodule (indicated by the white arrow) .c, d) IP/OP images indicates signal loss on OP images. The formulas mentioned above (SII, ALR and ASR) were 0.68, 0.33 and 0.33, respectively.



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