A treatment apparatus and method are disclosed for applying mechanical ultrasonic vibrations to an area of tissue. The apparatus comprises an applicator movable by an operator over the area of tissue to be treated. Mounted within the applicator are an ultrasonic transducer for generating mechanical vibrations and a sonotrode for transmitting the vibrations generated by the transducer to the tissue to be treated. The apparatus further comprises a sensor for measuring an operating parameter indicative of the efficiency of the acoustic coupling between the sonotrode and the tissue to be treated, and electronic circuitry for generating a signal (e.g. an alarm signal) when the efficiency of the acoustic coupling drops below a threshold.
