A volumetric graphics model of deformable human tissue with layers of varying stiffness was developed. The model uses spring-mass-damper to calculate haptic force feedback from various layers of tissue. A haptic epidural needle insertion simulation is developed with real-time tissue deformation when external forces are exerted. Voxelization is used to fill surface meshes with grids of spring-mass-damper assemblies. The modeled tissues include all the layers traversed during an epidural procedure, including skin, subcutaneous fat, Supraspinous and interspinous ligaments, ligamentum flavum and the epidural space. Tissue is modeled with volumetric information describing the stiffness and density of each layer. Spring-mass-damper modeling enables the calculation of compression and extension of springs between tissue masses, to simulate tissue stretching and relaxation movement. A haptic force feedback device is used to interact with the tissue model with a virtual needle. The resulting simulation gives a different feeling for each tissue layer. The haptic device allows the user to insert a needle though the modeled tissue layers feeling the various physical properties of each tissue layer during needle insertion. Tissues can be viewed in cross-section to see the progress and depth of the needle. Force feedback graphs were produced to compare the force from the operator’s thumb to the resultant force feedback from the device.

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