Solid heterogeneous phantoms for multimodal ultrasound and diffuse optical imaging: an outcome of the SOLUS project for standardization

In the last decade, multimodal imaging raised increasing interest to overcome the limits of single techniques and improve the diagnostic potential during the same examination. This gives rise to the need for phantoms and procedures for standardizing performance assessment of the multimodal instrument. The SOLUS1 project adopts this methodology with the aim to build a multimodal instrument (based on diffuse optics -DO-, shear wave elastography -SWE-, and ultrasound imaging -US-) to increase the specificity of breast cancer diagnosis. Here we propose a long-lasting phantom based on silicone material (easier to manipulate with respect to other material for bimodal phantom such as polyvinyl alcohol, PVA) and suitable for both diffuse optical imaging/tomography and ultrasound acquisitions, designed within the SOLUS project. To achieve this goal, we explored a new silicone material for diffuse optics and ultrasound (Ecoflex 00-30), creating a new fabrication recipe and demonstrating its suitability for multimodal imaging if coupled to another silicone elastomer (Sylgard 184), featuring similar optical and acoustical performances except for the echogenicity. The main advantage of the proposed phantom is the capability of tuning independently optical and acoustical performances, thus allowing one to mimic a wide range of clinical scenarios.