Tissue mimicking materials (TMMs), typically contained within phantoms, have been used for many decades in both imaging and therapeutic applications. This review investigates the specifications that are typically being used in development of the latest TMMs. The imaging modalities that have been investigated focus around CT, mammography, SPECT, PET, MRI and ultrasound. Therapeutic applications discussed within the review include radiotherapy, thermal therapy and surgical applications. A number of modalities were not reviewed including optical spectroscopy, optical imaging and planar x-rays. The emergence of image guided interventions and multimodality imaging have placed an increasing demand on the number of specifications on the latest TMMs. Material specification standards are available in some imaging areas such as ultrasound. It is recommended that this should be replicated for other imaging and therapeutic modalities. Materials used within phantoms have been reviewed for a series of imaging and therapeutic applications with the potential to become a testbed for cross-fertilization of materials across modalities. Deformation, texture, multimodality imaging and perfusion are common themes that are currently under development.

Photoacoustic imaging (PAI) standardisation demands a stable, highly reproducible physical phantom to enable routine quality control and robust performance evaluation. To address this need, we have optimised a lowcost copolymer-in-oil tissue-mimicking material formulation. The base material consists of mineral oil, copolymer and stabiliser with defined Chemical Abstract Service numbers. Speed of sound c(f) and acoustic attenuation coefficient α(f) were characterised over 2-10 MHz; optical absorption µa(ʎ) and reduced scattering µs'(ʎ) coefficients over 450-900 nm. Acoustic properties were optimised by modifying base component ratios and optical properties were adjusted using additives. The temporal, thermomechanical-and photo-stability were studied, along with intra-laboratory fabrication and field-testing. c(f) could be tuned up to (1516±0.6)m•s -1 and α(f) to (17.4±0.3)dB•cm -1 at 5MHz. The base material exhibited negligible µa(ʎ) and µs'(ʎ), which could be independently tuned by addition of Nigrosin or TiO2 respectively. These properties were stable over almost a year and were minimally affected by recasting. The material showed high intra-laboratory reproducibility (coefficient of variation <4% for c(f), α(f), optical transmittance and reflectance), and good photoand mechanical-stability in the relevant working range. The optimised copolymer-in-oil material represents an excellent candidate for widespread application in PAI phantoms, with properties suitable for broader use in biophotonics and ultrasound imaging standardisation efforts.

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Photoacoustic thermometry is a rapidly emerging technique for non-invasive temperature monitoring. The temperature dependence of the Grüneisen parameter of tissues leads to changes in the recorded photoacoustic signal amplitude with temperature. In order to assess the material's suitability for a photoacoustic thermometry phantom, its temperature-dependent speed of sound and Grüneisen parameter must be known. Agarbased phantoms, copolymer-in-oil, gel wax, PVCP, silicone and water were thus characterised in a newly developed photoacoustic thermometry setup and the results presented for temperatures between 22 and 50°C. This information provides a valuable resource for the future development of tissue-mimicking materials with properties suitable for applications in photoacoustic thermometry.