Original contributionMagnetic resonance elastography of the pancreas: Measurement reproducibility and relationship with age
Introduction
Advances in non-invasive imaging of the pancreas are needed to address the increasing burden of pancreatic disorders. Pancreatic cancer is the third leading cause of cancer-related death in the United States, and has one of the worst 5-year survival rates of all cancers [1], [2]. One important factor for this poor survival is difficulty detecting cancers early with currently available diagnostic methods [3]. Similarly, the early diagnosis of chronic pancreatitis (CP) is challenging, and patients often develop irreversible pancreatic insufficiency prior to clinical diagnosis [4]. The current imaging modalities for CP do not permit an accurate diagnosis at an early stage, during which interventions can be provided to retard disease progression [5].
There are currently multiple options for pancreatic imaging, however each has limitations [4]. Computed tomography (CT) can provide high spatial resolution, but is unable to detect early CP with high sensitivity [4], [5]. Endoscopic retrograde pancreatography (ERCP) was previously utilized due to sensitive imaging of the pancreatic duct, however due to risks of post-ERCP pancreatitis (along with increased access to MRCP) this test is no longer recommended for diagnostic purposes alone [4], [5]. Similarly, magnetic resonance cholangiopancreatography (MRCP) provides information of the main pancreatic and branch ducts, but does not provide reliable evidence regarding pancreatic fibrosis [4]. Lastly, endoscopic ultrasonography (EUS) provides sensitive imaging of the pancreatic parenchyma and pancreatic ducts, but these findings are subject to inter-observer variability and overlap with changes seen during normal aging and secondary to cigarette smoking and diabetes mellitus [6]. In summary, the current imaging modalities are complimentary for the diagnosis of CP, but the accuracy for early CP remains limited.
Both CP and pancreatic ductal adenocarcinoma (PDAC) cause inflammation and fibrosis leading to an increase in pancreatic stiffness compared to a healthy state [5], [7]. Additionally, stiffness of the pancreas also changes with age due to atrophy [8]. Therefore, it is important to understand mechanical properties of the pancreas that can provide valuable information other than morphological changes in detecting early stage pancreatic diseases.
Magnetic resonance elastography (MRE) is a noninvasive technique to estimate stiffness of soft tissues [9], [10], [11], [12], [13], [14], [15] and is currently a clinical diagnostic tool to stage liver fibrosis [16], [17], [18], [19], [20]. To date there are a few studies to evaluate the feasibility of in-vivo pancreatic MRE [21], [22], [23], [24]. An early study by Shi et al. [22] determined the stiffness of pancreas at multiple frequencies and subsequent studies [21], [23] used small cohorts to determine variation in stiffness between normal and focal pancreatic disease. The aim of the study was to evaluate the short term and midterm reproducibility and age-related variance of MRE-derived pancreatic stiffness in healthy volunteers.
Section snippets
Methods
Pancreatic MRE was performed on 22 healthy subjects (n = 66 repeated measurements; age range of 20–64 years) with a mean body mass index (BMI) of 24.5 kg/m2 and range of 20.6–34.55 kg/m2, after obtaining written informed consent under the approval of the Institutional Review Board. Subjects with no known prior history of pancreatic diseases were included in the study. Only two subjects reported BMI ≥ 30 kg/m2.
Results
Discernible waves were observed in the pancreas at 60 Hz vibrational frequency. Fig. 2 shows magnitude image with red contour delineating pancreas and a snapshot of wave propagation after curl processing in all three spatial encoding directions (i.e., x, y, and z) of the pancreas and the corresponding stiffness map with an overall mean stiffness value of 1.42 kPa. No significant correlation (p > 0.7) was observed between BMI and age and as well as with different anatomical and overall pancreatic
Discussion
This study of healthy volunteers demonstrated excellent short and midterm reproducibility of MRE-derived stiffness estimates of the pancreas. Additionally, the MRE-derived stiffness of the pancreas increased with age when compared as a continuous or categorical variable.
The pancreatic MRE technique in this study is reproducible. It is important to demonstrate robustness of MRE-derived shear stiffness of pancreas, as the pancreas is an elongated organ located deep in the abdomen before its
Conclusion
In summary, this study demonstrated excellent short term and midterm reproducibility of MRE-derived stiffness values of the pancreas. Stiffness of the pancreas positively correlated with increased age. These data provide additional evidence showing potential for the future clinical application of MRE technology for imaging of pancreatic diseases and warrants additional investigations.
Funding source
This manuscript has been supported by Grant sponsor: American Heart Association; Grant number: 13SDG14690027; Grant sponsor: Center for Clinical and Translational Sciences; Grant number: UL1TR000090; Grant Sponsor: NIH – NHLBI; Grant number: NIH-R01HL124096. Research reported in this publication was also supported by NCI and NIDDK of the NIH under award number U01DK108327 (PH and DC).
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