SHORT- AND LONGTIME STABILITY OF THERAPEUTIC ULTRASOUND REFERENCE SOURCES FOR DOSIMETRY AND EXPOSIMETRY PURPOSES

The objective of this work was to create highly stable therapeutic ultrasound fields with well-known exposimetry and dosimetry parameters that are reproducible and hence predictable with well-known uncertainties. Such well-known and reproducible fields would allow validation and secondary calibrations of different measuring capabilities, which is already a widely accepted strategy for diagnostic fields. For this purpose, a reference setup was established that comprises two therapeutic ultrasound sources (one High Intensity Therapeutic Ultrasound (HITU) source and one physiotherapy-like source), standard rf electronics for signal creation, and computer-controlled feedback to stabilize the input voltage. The short- and longtime stability of the acoustic output were evaluated - for the former, measurements over typical laboratory measurement time periods (i.e. some seconds or minutes) of the input voltage stability with and without feedback control were performed. For the latter, measurements of typical acoustical exposimetry parameters were performed bimonthly over one year. The measurement results show that the short- and the longtime stability of the reference setup are very good and that it is especially significantly improved in comparison to a setup without any feedback control.