Glycerol-in-SEBS gel as a material to manufacture stable wall-less vascular phantom for ultrasound and photoacoustic imaging.

Styrene-ethylene/butylene-styrene (SEBS) copolymer-in-mineral oil gel is an appropriate tissue-mimicking material to manufacture stable phantoms for ultrasound and photoacoustic imaging. Glycerol dispersion has been proposed to further tune the acoustic properties and to incorporate hydrophilic additives into SEBS gel. However, this type of material has not been investigated to produce wall-less vascular flow phantom for these imaging modalities. In this paper, the development of a wall-less vascular phantom for ultrasound and photoacoustic imaging is reported. Mixtures of glycerol/TiO2-in-SEBS gel samples were manufactured at different proportions of glycerol (10%, 15%, and 20%) and TiO2(0% to 0.5%) to characterize their optical and acoustic properties. Optical absorption in the 500-950 nm range was independent of the amount of glycerol and TiO2, while optical scattering increased linearly with the concentration of TiO2. Acoustic attenuation and speed of sound were not influenced by the presence of TiO2. The sample manufactured using weight percentages of 10% SEBS, 15% glycerol, and 0.2% TiO2was selected to make the vascular phantom. The phantom proved to be stable during the pulsatile blood-mimicking fluid (BMF) flow, without any observed damage to its structure or leaks. Ultrasound color Doppler images showed a typical laminar flow, while the B-mode images showed a homogeneous speckled pattern due to the presence of the glycerol droplets in the gel. The photoacoustic images of the phantom showed a well-defined signal coming from the surface of the phantom and from the vessels where BMF was flowing. The Spearman's correlations between the photoacoustic and tabulated spectra calculated from the regions containing BMF, in this case a mixture of salt solutions (NiCl2and CuSO4), were higher than 0.95. Our results demonstrated that glycerol-in-SEBS gel was an adequate material to make a stable vascular flow phantom for ultrasound photoacoustic imaging.