Combined real time Ultrasound-thermometry and Elastography imaging during HIFU therapy: ex-vivo results

Bastien Arnal (1, 2) , Mathieu Pernot (1, 2) , Mickael Tanter (1, 2)

1 IL - Institut Langevin - Ondes et Images (UMR7587)
2 Physique des ondes pour la médecine

The use of High intensity Focused Ultrasound (HIFU) for non invasive therapy requires improving real-time monitoring of the lesion formation during treatment, to avoid damage of the surrounding healthy tissues. The goal of this study is to show the feasibility of a full ultrasound approach that relies on the assessment of the changes in both tissue elasticity and temperature implemented on conventional ultrasonic imaging probes. HIFU treatment and monitoring were performed using a confocal set made up of a 8MHz ultrasound diagnostic probe (Vermon) and a 2.5MHz single element transducer focused at 30mm (Imasonic) on ex-vivo porcine samples. 2D temperature estimation was combined with Supersonic Shear Imaging (SSI) on the same device (Aixplorer, SuperSonic Imagine). To lower the thermo-acoustic lens effect, the ultrasound thermometry was performed using plane wave emissions steered at 13 angles (+/-12 degrees). The SSI sequence consisted in 2 successive shear waves induced at different lateral positions. Each wave was created thanks to pushing beams of 100?s at 3 depths. The shear wave propagation was acquired at 17000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions allowing a duty cycle of more than 90%. Elasticity and temperature mapping was achieved every 5 seconds during treatment. Tissue stiffness was found to decrease at the focal zone with temperature up to 50°C. Ultrasound-based temperature estimation was highly-correlated to stiffness variation maps. The lesion formation comes with a strong increase (up to four-fold) of the elastic modulus. These combined methods provide complementary measurements of tissue properties and overcome the limitations of US-thermometry alone as SSI acquisitions are motion-insensitive. A full ultrasoundbased monitoring technique was developed to achieve elasticity and temperature mapping of soft tissues under HIFU treatment. It demonstrated the feasibility of monitoring and detecting the HIFU thermal lesion.

Mots clés: HIFU; Monitoring; Elastographie; Thermométrie

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

Bastien Arnal, Mathieu Pernot, Mickael Tanter. Combined real time Ultrasound-thermometry and Elastography imaging during HIFU therapy: ex-vivo results. 10ème Congrès Français d'Acoustique, Apr 2010, Lyon, France. ⟨hal-00538352⟩