'Seeing’ HIFU lesions with ultrasound

Tissue undergoes changes in optical properties after ablation but “seeing” those changes at depth in tissue is challenging as light becomes diffuse after propagating a few millimetres resulting in insufficient resolution to see thermal lesions. In acousto-optic (AO) sensing a focused ultrasound beam is used to modulate photons that pass through a small region and by detecting the modulated photons the optical properties from a localised area can be determined. During high-intensity focused ultrasound (HIFU) the ultrasound can be used to modulate the diffuse light during treatment and so the interaction volume coincides with the treatment volume and light modulation can be measured in real-time. A full numerical model captures these effects and can be used to determine the optimal sensing geometry and most appropriate tissues