A Copolymer-in-Oil Tissue-Mimicking Material With Tuneable Acoustic and Optical Characteristics for Photoacoustic Imaging Phantoms

Abstract

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.

Performance evaluation of mesoscopic photoacoustic imaging

“…For evaluation of long-term system precision, copolymer-in-oil base material was chosen 25 . The material was prepared according to Hacker et al 24 . Briefly, the phantom was composed of 30 w/v% high molecular weight SEBS (Sigma Aldrich 200557-250G) and 8 w/v% LDPE (Alfa Aesar 43949.30) in mineral oil (Sigma Aldrich-330779-1L), with 0.03 w/v% TiO 2 (Sigma Aldrich 232033-100g) added to provide optical scattering and 0.0007 w/v% Nigrosin (Sigma Aldrich 211680-100G) added to provide optical absorption.…”

“…Briefly, the phantom was composed of 30 w/v% high molecular weight SEBS (Sigma Aldrich 200557-250G) and 8 w/v% LDPE (Alfa Aesar 43949.30) in mineral oil (Sigma Aldrich-330779-1L), with 0.03 w/v% TiO 2 (Sigma Aldrich 232033-100g) added to provide optical scattering and 0.0007 w/v% Nigrosin (Sigma Aldrich 211680-100G) added to provide optical absorption. The acoustic properties were characterised using a through transmission substitution system (available at NPL, London, UK) 24 , yielding a speed of sound of 1483.5 ± 0.17 m·s −1 and an acoustic attenuation of 6.73 ± 0.04 dB·cm −1 at 5 MHz. The optical properties were determined using a custom-built double-integrating sphere (DIS) system 24 , yielding a reduced scattering coefficient of 0.4 mm −1 and an optical absorption coefficient of 0.01 mm −1 at 532 nm.…”

Hyperspectral Imaging for Clinical Applications

“…According to spectral imaging methods, the optical system shows different specifications, such as spatial, spectral, and temporal resolution, which hampers the development of standard HSI systems. Recently, standard tissue-mimicking phantoms have been suggested for the quantitative evaluation of optical systems [1,90]. This will help to overcome issues related to the standardization of the HSI optical system.…”

SIMPA: an open-source toolkit for simulation and image processing for photonics and acoustics

“… 69 In Fig. 8(b) , a cylindrical phantom with two absorbing inclusions, comparable to the one presented by Hacker et al., 74 is generated. A volume containing complex vessel trees can easily be generated similar to the human lung vessel dataset acquired from computed tomography used by Bench et al.…”