Technical Recommendation on Multi-Driver Multifrequency MR Elastography for Tomographic Mapping of Abdominal Stiffness With a Focus on the Pancreas and Pancreatic Ductal Adenocarcinoma.

Objectives: MR elastography (MRE) offers valuable mechanical tissue characterization for clinical diagnosis. However, conventional single-driver, single-frequency MRE systems are often limited by insufficient coverage of deep-seated organs like the pancreas. This study investigates whether multiplex MRE using multiple drivers and vibration frequencies can overcome these limitations.

Materials and methods: This prospective study used single-shot spin-echo MRE in 18 healthy volunteers (mean age 30±8 y) targeting the liver, pancreas, kidneys, and spleen. Each healthy volunteer underwent 16 MRE examinations with different sets of 4 vibration frequencies in the range of 30 to 60 Hz and 4 driver combinations, and an additional null experiment without vibrations. In addition, a cohort of 14 patients with pancreatic ductal adenocarcinoma (PDAC, mean age 57±15 y) were retrospectively assessed. The quality of shear-wave fields and stiffness maps were assessed in terms of displacement amplitudes and image sharpness.

Results: In healthy volunteers, abdominal coverage with displacement amplitudes above the pre-determined noise level of 4 µm varied among the MRE investigated: 24.2% (0.0% to 56.2%, single-driver at 60 Hz), 66.9% (24.8% to 97.7%, single-driver at 30 to 60 Hz), 70.2% (0.0% to 92.5%, multi-driver at 60 Hz), and 99.9% (89.4% to 100%, multi-driver at 30 to 60 Hz). In the pancreas, more than 60% coverage was achieved in all subjects using 4 drivers and multiple frequencies. This was achieved in only 2 of 18 subjects (11%) using single-driver/single-frequency MRE. Superficial organs were adequately assessed with all configurations. In patients with PDAC, multi-driver MRE at 30 to 60 Hz achieved 99.1% (91.4% to 100%) coverage of the pancreas and 96.3% (63.1% to 100%) abdominal coverage, suggesting that tomographic stiffness mapping is clinically feasible.

Conclusion: MRE with at least 4 drivers and multiple vibration frequencies in the range of 30 to 60 Hz enables tomographic mapping of tissue stiffness across the entire abdomen, including the pancreas. Our results thus indicate that multiplex MRE is a promising approach for generating detailed images of abdominal stiffness that can improve clinical diagnosis of abdominal and pancreatic diseases.