Design of a combined optical and structural bone phantom

Design of a combined optical and structural bone phantom: Concept validation and design tool

van Pelt, Tess (TU Delft Mechanical, Maritime and Materials Engineering)

Dankelman, J. (mentor)
Hendriks, B.H.W. (graduation committee)
Losch, M.S. (graduation committee)

Delft University of Technology

Mechanical Engineering | BioMechanical Design

2022-01-25

Introduction: Although being the most advanced spinal stabilization method, pedicle screw fixation has an increased number of complications compared to other surgical procedures, due to the complex spinal anatomy, large inter-patient anatomical variability, and the highly vulnerable surrounding tissue of the spine. Screw fixation strength can be increased by anchoring a flexible screw in a hole following the curved trajectory of the more dense cortical shell of the vertebral body, instead of the porous core. The curved trajectory can be determined by local diffuse reflectance spectroscopy (DRS) guiding. Currently, there is no commercial phantom or phantom recipe known that provides the correct optical and structural material characteristics for testing DRS guiding and curved trajectory drilling on, comparing it to similar devices, and perform surgical training sessions on. The research goal is to design and validate an integrated phantom that closes this gap. Preliminary test results: Preliminary optical and structural tests were performed separately on hybrid optical filler samples and structural matrix samples, respectively. The hybrid optical filler samples made out of water, fat (30%, 40% and 50% fat fraction) and silicone (95%, 80%, and 50%) were inspected visually, and spectra were obtained by means of a DRS device in week 0 as well as in week 10. The most promising optical filler sample consisted of 50% of silicone and 50% of water+fat, with a fat fraction of 40%. The measured DRS signals showed a clear correlation between the fitted and actual water+fat content, which, can thus be used as a tissue differentiation parameter. The stability and preservability of phantoms that were enhanced with silicone and resulted in homogeneous mixtures, was increased compared to samples without any silicone. For the structural matrix, different 3D printers, materials, and infill densities were evaluated on drill characteristics and compression characteristics. The best bone mimicking structural phantom consisted of an FDM printed part made out of ABS with a gyroid infill structure with an infill density of 50%. Integrated phantom validation: The combination of the optical filler and the structural matrix was validated by infusing the optical filler in the structural matrix with a vacuum chamber and measuring the drill characteristics and DRS spectra at various depths inside the phantom. A gradual increase in axial drilling force and a gradual change in spectral shape was noticed as a function of depth from the cancellous zone, to the pre-cortical zone and cortical zone. Discussion: The ABS material and the actual optical filler constituents (such as peanut oil and specific silicone types) should be implemented inviii the fitting algorithm. Nevertheless, the results of this research show not only great potential phantom design for a wide variety of bone types because of the structure and shape design flexibility of 3D printing, but also for soft tissues by using only the optical filler with a much better stability and preservability than traditional soft tissue phantoms.

Bone phantom
diffuse reflectance spectroscopy
Bone Drilling

http://resolver.tudelft.nl/uuid:1e97d61a-9abc-4342-b902-9409e521c9bf

2023-01-25

Student theses

master thesis

© 2022 Tess van Pelt