Spatial monitoring of temperature estimation during ultrasound heating therapy

Ultrasound instrumentation is being increasingly used for therapeutic purposes but its usage for heating treatments still requires more investigation in terms of spatial-temporal characterization of induced tissue´s temperature. Non-invasive ultrasound temperature estimation is accepted to be well performed when based on ultrasound imaging´s temporal eco-shifts calculations. Present paper reports experiments developed to analyze temperature propagation on a plane parallel to the heating transducer´s face, enlarging as so the spatial range previously tested. Relationship between the reference and the echo delayed signals between pairs of spatial locations symmetrically located in regard to the heating transducer´s face have been analyzed in detail. Results demonstrate that ultrasound heating transducer should not be assumed to produce symmetrical pressure field patterns, and, more relevant, that the frequently used temporal eco-shift algorithm do not produce precise estimations of temperature in spatial locations above the axial line of the heating transducer´s face towards the imaging transducer.