Su1240 Magnetic Resonance Elastography (MRE) of the Pancreas, a Feasibility Study in Healthy Volunteers

Abstract

Background: MRE is a non-invasive advanced imaging technique utilizing wave propagation to characterize the In Vivo mechanical properties of tissue, including stiffness, in organs such as the liver. MRE of the pancreas has not been thoroughly studied, but could provide a non-invasive tool for assessing pancreatic pathology such as pancreatitis, solid and cystic pancreatic masses. Aims: To determine the feasibility of MRE of the pancreas and establish normal ranges for tissue density of the normal pancreas. Methods: IRB approval was obtained. Stage 1: MRE of the pancreas was performed in 12 healthy volunteers with a 2-D gradientecho (GRE) sequence. An acoustic driver (AD) system delivered 40 HZ vibrations into the abdomen via a plastic drum secured via an elastic belt and powered pneumatically by a speaker located outside of the scan room. In an attempt to optimize wave propagation, the AD was placed over the liver, pancreas and left flank with the patient supine, and over the mid back with patient prone. MR elastograms were generated using an inversion algorithm to yield quantitative images of tissue stiffness in kilopascals (kPa). Stage 2: 3-D MRE was performed in 12 healthy volunteers using a flow-compensated single-shot spin-echo planar imaging (EPI) acquisition with motion encoding performed sequentially in the X, Y, and Z directions. Processing of the measured 3D displacement field was performed by first calculating the 3D vector curl of the displacement field and then using a 3D local frequency estimation (LFE) algorithm to calculate the tissue stiffness from the curl data. The pancreas was manually segmented using the MRE magnitude images and the mean stiffness in kilopascals (kPa) was recorded. Results: Stage 1: With the 2D MRE technique, there was poor pancreatic wave propagation at all AD locations including patient supine and prone for all 12 volunteers. This precluded accurate mean shear pancreatic stiffness calculation. Stage 2: With 3D MRE technique (image 1), 10 of 12 volunteers had adequate pancreatic wave propagation, with calculated mean shear hepatic stiffness of 1.04 ± 0.25 kPa (range 0.861.25 kPa). Of the 2 with poor wave propagation, one had BMI >30 kg/m2, and one had an atrophic pancreas. Conclusions: MRE of the pancreas is feasible, but requires 3D image sequencing to obtain adequate elastograms to calculate tissue stiffness. Further refinements in the technology are required to obtain consistent elastograms, including for patients with obesity or pancreatic atrophy. Ongoing investigations include determining the variation in stiffness within regions of the pancreas and to compare the normal pancreas with the spectrum of pancreatic diseases including pancreatic cancer, pancreatic cysts, acute and chronic pancreatitis.