Robust high resolution strain imaging by alternating pulsed field gradient stimulated echo imaging (APGSTEi) at 7 Tesla

[Display omitted] •Efficient APGSTEi probes strains in elastomers and ovine ligaments.•Bipolar spatial encoding and SE refocusing pulses eliminate background fields.•Measured 3D-resolved strains tensors agree quantitatively with results of finite element simulations.•Measured strains in an ovine patellar tendon reflect boundary conditions.•Measured strain tensors are useful for the extraction of material properties, using inverse full field methods. A novel displacement-encoding spin-echo-stimulated-echo MRI sequence (APGSTEi) was used to obtain full-volume 3D strain fields in samples of two soft materials, a silicone elastomer and an ovine ligament. The samples were stretched cyclically and imaged synchronously. The multi-slice imaging sequence employed a combination of hard and soft spin-echos with bipolar gradient pulses for spatial encoding and decoding, combined with rapid multi-slice spin echo readouts. The sequence minimized undesirable signal loss due to T2∗ and T2 decays, which occur in polymeric materials or in the presence of appreciable air-solid susceptibility contrast, a particular concern for irregularly shaped samples in high magnetic fields. The images’ magnitudes were T1-weighted; their phase encoded displacements which occurred during a Δ = 400 ms storage interval separating encoding and decoding pulses. Unwanted residual signals were filtered using a Gaussian filter tailored to attain the desired noise floor. The experiments measured 3D deformation with a nominal resolution of 290 μm × 250 μm × 250 μm in a sample volume of 5.6 cm × 1.6 cm × 1.6 cm, in less than an hour.