Advances in thermal strain imaging: 3D motion and tumor validation studies

Targeted drug delivery therapies involving temperature sensitive vehicles and localized mild hyperthermia are emerging as an efficient way to non-invasively treat cancer [1]. To this end, control of hyperthermia is essential to efficiently release drugs while avoiding thermal damage to healthy tissue. Toward this end, thermal strain imaging (TSI) may be of great interest when combined with therapeutic ultrasound systems and has promise to non-invasively control hyperthermia in vivo. In this work, real time TSI with motion compensation was validated for 3D translational motion in a tissue mimicking phantom. The algorithm tracked temperature changes in the presence of 3-D motion spanning 8.7 mm, including oscillations resulting from out-of-plane displacement of the imaging array. A good agreement was found between the real-time temperature estimates at the motion extremes and the temperatures estimated when the array was placed at the two ends of the motion path. The RMSE in the temperature estimate was estimated as 0.11°C. The method was then tested in vivo on tumor bearing mice undergoing hyperthermia treatment. A custom therapeutic and imaging array designed for pre-clinical drug delivery studies facilitated temperature control while providing real-time mapping of the temperature change. Acquired temperature data were consistent with subcutaneous thermocouple measurements.