A multimodal instrument for breast imaging was developed, combining ultrasound (morphology), shear wave elastography (stiffness), and time domain multiwavelength diffuse optical tomography (blood, water, lipid, collagen) to improve the non-invasive diagnosis of breast cancer.
To improve non-invasively the specificity in the diagnosis of breast cancer after a positive screening mammography or doubt/suspicious ultrasound examination, the SOLUS project developed a multimodal imaging system that combines: Bmode ultrasound (US) scans (to assess morphology), Color Doppler (to visualize vascularization), shear-wave elastography (to measure stiffness), and time domain multi-wavelength diffuse optical tomography (to estimate tissue composition in terms of oxy- and deoxy-hemoglobin, lipid, water, and collagen concentrations). The multimodal probe arranges 8 innovative photonic modules (optodes) around the US transducer, providing capability for optical tomographic reconstruction. For more accurate estimate of lesion composition, US-assessed morphological priors can be used to guide the optical reconstructions. Each optode comprises: i) 8 picosecond pulsed laser diodes with different wavelengths, covering a wide spectral range (635-1064 nm) for good probing of the different tissue constituents; ii) a large-area (variable, up to 8.6 mm2 ) fast-gated digital Silicon Photomultiplier; iii) the acquisition electronics to record the distribution of time-of-flight of the re-emitted photons. The optode is the basic element of the optical part of the system, but is also a stand-alone, ultra-compact (about 4 cm3 ) device for time domain multi-wavelength diffuse optics, with potential application in various fields.
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.
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