Case Study: Multimodal Analysis of Tissue Phantom Material
The mechanical and imaging properties of polyvinyl chloride (PVC) can be adjusted to meet the needs of researchers as a tissue-mimicking material. Examples include adjusting the hardness my changing the ratio of a softener to the PVC polymer, adding mineral oil for lubrication for needle insertion experiments, and mixing in glass beads to scatter acoustic energy similar to biological materials. Below are several techniques used to characterize the properties appropriate to various investigations including mechanical (hardness, elastic modulus, needle insertion friction) and medical imaging (optical clarity, ultrasound, magnetic resonance, and x-ray).
Example samples of PVC material with different compositions and geometries.
Mechanical Properties
Hardness test using microstages (~1 µm precision) to place a Shore durometer atop samples.
To determine the elastic moduli of the samples, an aluminum plate mounted to a linear actuator compressed samples while force exerted was measured by a piezoelectric dynamometer.
A fixture to hold a biopsy needle was attached to linear stages to gauge the cutting, insertion, friction, and retraction forces.
Medical Imaging Properties
Optical clarity was measured by cutting samples to shape and placing them in cuvettes. Transmittance of visible light was measured by a spectrophotometer (380 nm to 750 nm in 1 nm increments) .
Acoustic properties (such as speed of sound and attenuation) were determined by placing a sample in a degassed water tank between an unfocused ultrasound transducer and a hydrophone and comparing the transmitted signal to the received signal.
Ultrasound images of PVC samples without (left) and with (right) glass beads additives to enable scatter similar to that found in biological materials.
Representative T1 (inversion time) and T2 (echo time) images and resulting time constants indicating parameters appropriate for magnetic resonance imaging.
