A NEW METHOD FOR MEASURING THE EFFECTIVE RADIATING AREA OF PHYSIOTHERAPY TREATMENT HEADS

This paper describes the investigation and validation of a new method for measuring the effective radiating area (A(ER)) of physiotherapy ul trasound treatment heads. The method is based on the use of a conventi onal radiation force balance, but employs special attenuating aperture s that are used to selectively mask off different areas of the treatme nt head. The resultant reduction in the radiating surface is accompani ed by a decrease in output power that is measured using the force bala nce. The A(ER) of the treatment head is derived from an analysis of th e measurements, which essentially involves initially evaluating the mi nimum area through which 75% of the acoustic power is transmitted. A(E R) values derived using the new method are presented for 17 treatment heads representative of the range of physiotherapy systems commonly us ed in clinical practice. These are compared to reference values derive d using hydrophone scanning, according to the recently published Inter national Standard, IEC 1689, Typical levels of agreement between value s of A(ER) derived using the two techniques are +/- 11%, The potential of the method as a rapid, relatively low-cost, means of measuring tre atment head A,,, applicable in both manufacturing and hospital environ ments, is assessed. (C) Crown Copyright 1998, Reproduced by permission of the Controller of HMSO. Published by Elsevier Science.