A novel MRI compatible Soft Tissue Indentor and Fibre Bragg Grating Force Sensor

Magnetic Resonance Imaging (MRI) is an ideal method for non-invasive determination of soft tissue mechanical properties when combined with inverse Finite Element Analysis (FEA). This requires mechanical excitation of the body’s tissues and measurement of the corresponding boundary conditions and soft tissue deformation in an MRI environment. However, this is technically difficult since the boundary condition measurements require an MRI compatible actuator and load sensor. This paper describes a novel MRI compatible soft tissue indentor and optical force sensor. The high speed (100Hz) and temperature compensated Fibre Bragg Grating (FBG) force sensor was calibrated using uniaxial testing and demonstrated a maximum error of 0.3%. In addition the performance and MRI compatibility of the devices within the MRI environment were verified using indentation tests on a volunteer while MRI methods were used to record tissue geometry and deformation. The computer controlled indentor provided a highly repeatable tissue deformation. Since the indentor and force sensor are composed of non-ferromagnetic materials, they are fully MRI compatible and no artefacts or other influences on the MRI data due to the presence and action of the devices were observed. The device has a broad spectrum of potential applications including MRI guided interventions.