A Reusable Thermochromic Phantom for Testing High Intensity Focused Ultrasound Technologies.

High Intensity Focused Ultrasound (HIFU) surgery is a promising technology for the treatment of several pathologies, including cancer. Testing is a fundamental step for verifying treatment efficacy and safety. Ex-vivo tissues represent the most common solution for replicating the properties of human tissues in the HIFU operative scenario. However, they constitute an avoidable waste of resources. Thus, tissue mimicking phantoms have been investigated as a more sustainable and reliable alternative. In this scenario, we proposed a reusable silicone-based thermochromic phantom. It is cost-effective and can be rapidly fabricated. The acoustic, mechanical, and thermal characterization of the phantom are reported. The phantom usability was evaluated with a HIFU robotic platform. 18 different working conditions were tested by varying both sonication power and duration. Temperature and simulated lesions' size were quantified for all testing conditions. An accordance between temperature and lesion dimension trend over time was found. The proposed phantom results a valid alternative to ex-vivo tissues, especially in the early stages of developing novel HIFU treatment paradigms.

Highly controlled and usable system for Low-Intensity Pulsed Ultrasound Stimulation of Cells.

This work aims to describe the design and development of an in vitro highly controlled ultrasonic stimulation system able to guarantee, at the same time, high usability and full sterility of the tested samples. After creating the first prototype of an ultrasound-transparent three-chambers culture well, sealing tests were conducted to prove its impermeability to external contaminants and in vitro tests were carried out to verify the usability of this system for ultrasonic stimulation of cells in vitro. No statistically significant differences were found between control and tested samples during sealing tests, thus demonstrating optimal sealing ability towards external contaminants. Furthermore, the thin polystyrene membrane used to guarantee US-transparency guaranteed a good adhesion and viability of both human fibroblasts and induced pluripotent stem cells.

A Pilot Study for a Quantitative Evaluation of Acoustic Coupling in US-guided Focused Ultrasound Surgery.

In Ultrasound-guided High Intensity Focused Ultrasound (USgHIFU) surgery, the verification of the acoustic coupling correctness between the HIFU transducer and the patient's body is a fundamental step for an efficient and safe therapy. Nowadays, clinicians perform this check by qualitative inspecting Ultrasound images. The aim of this study is the introduction of an objective index to quantitively evaluate the coupling on the base of the radiofrequency echo signals acquired during a low-energy HIFU shot. The experimental session involved a tissue mimicking phantom and a robotic system composed by a HIFU therapeutic transducer and a 2D confocal Ultrasound probe. 15 different coupling conditions between the phantom and the transducer were tested: in each of them, the maximum absolute value of the Fourier Transform of the echo signals was computed and employed to determine an Acoustic Coupling (AC) coefficient.This metrics showed a sigmoidal trend between AC coefficient and coupling increase. This curve can be employed as a calibration tool to quantitatively assess the correctness of the therapeutic set-up before starting the HIFU treatment.