# Design and characterisation of intervertebral disc mimicking phantoms for photoacoustic imaging

## TL;DR

This paper presents phantoms that mimic intervertebral discs for photoacoustic imaging, enabling better validation and algorithm development.

## Contribution

The study introduces calibrated tissue-mimicking materials with tunable photoacoustic properties for intervertebral disc applications.

## Key findings

- TiO2-doped agarose hydrogels can replicate the photoacoustic properties of soft tissues.
- Empirical laws were derived to tailor the optical and acoustic properties of the phantoms.
- Phantoms accurately mimic healthy intervertebral discs, validated using porcine tissue tests.

## Abstract

Photoacoustics has gained momentum as a new medical imaging technique owing to its ability to benefit from good optical contrast and acoustic resolution. To ease transfer into clinical settings and validate the algorithms, calibrated tissue-mimicking materials (TMM) are required. This paper describes a complete photoacoustic characterisation of a line of titanium dioxide (TiO2) doped agarose hydrogels whose optical absorption (490–835 nm), reduced scattering (590–815 nm), isobaric heat capacity, mass density, speed of sound and acoustic attenuation were quantified for an agarose concentration up to 4% w/w and a TiO2 concentration ranging from 0.25 to 1 mg/mL. Empirical constitutive laws as a function of the concentrations of the components were derived, enabling the creation of TMM with tailored properties. Results showed that these phantoms are suitable candidates to mimic the photoacoustic properties of various soft tissues including intervertebral discs (IVD). Photoacoustic probings performed on an IVD-mimicking phantom and six healthy porcine discs demonstrated the ability of these TMM to accurately replicate healthy IVD properties; this could serve as a first step towards an application of photoacoustic imaging to quantifying disc degeneration.

•The design of soft tissue phantoms with a focus on intervertebral discs is presented.•The photoacoustics characteristics of soft tissue phantoms are determined.•Empirical laws allowing the photoacoustic properties to be varied are proposed.•Photoacoustic tests with excised tissues are carried out to valid the concept.

The design of soft tissue phantoms with a focus on intervertebral discs is presented.

The photoacoustics characteristics of soft tissue phantoms are determined.

Empirical laws allowing the photoacoustic properties to be varied are proposed.

Photoacoustic tests with excised tissues are carried out to valid the concept.