A STUDY OF THE HEATING CAPABILITIES OF DIAGNOSTIC ULTRASOUND BEAMS

A simple device for the experimental study of the heating capabilities of diagnostic ultrasound beams is described. Some results are reporte d that demonstrate the manner in which the device may be used to explo re the heating potential of any particular commercial transducer, oper ating over the full range of output conditions. The heat generated in the base of a polyethylene container, filled with water, was measured using a fine-wire thermocouple, attached externally. The majority of m easurements were carried out in beams generated by a curved array oper ating with a modern commercial scanner (Doppler, 2.5 MHz: imaging 3 MH z.). A temperature rise in excess of 30-degrees-C was generated by a p ulsed Doppler beam, when the water path and scanner controls were set appropriately. Comparable temperatures were measured at comparable int ensities generated by Doppler beams of other scanners. Of the imaging beams studied, the greatest temperature rise observed was less than 2- degrees-C, when the highest frame rate and line density were selected. The greatest temperature rise in colour Doppler mode was 7.8-degrees- C. It was observed that the position of the fixed (nonelectronic) focu s was significant in controlling the heating profile with depth, for s canned beams. As expected, there was a strong dependence of temperatur e rise on axial time-average intensity. A weak dependence on -6 dB bea m area was observed over a range of beam area of about 7 to 70 mm2. A strong dependence on finite amplitude effects was observed, resulting from energy loss associated with acoustic shock