title: Limited interchangeability of methods of applying 1MHz ultrasound.
abstract: OBJECTIVE
  To investigate the interchangeability of two different methods used to apply 1 MHz ultrasound for deep tissue heating, namely, the direct contact and the subaqueous methods.
  
  
  METHODS
  An intervention study with a crossover design.
  
  
  METHODS
  The setting was a laboratory.
  
  
  METHODS
  Four specimens, cross-sections of nonliving pig tissue, were used.
  
  
  METHODS
  Specimens were each exposed to 1 MHz ultrasound under five different conditions: in contact with gel, and subaqueous at 0, 1, 2, and 4 cm from the applicator to the skin.
  
  
  METHODS
  Tissue temperatures were measured at six thermocouple sites at different depths from the skin surface.
  
  
  RESULTS
  Subaqueous ultrasound applied at a distance of 0 cm from the skin produced significantly less tissue heating than direct contact (with gel) ultrasound at the same intensity. Increasing the distance from the applicator to the skin from 0 to 1, 2 and 4 cm resulted in significantly lower mean maximum temperature increases of 69%, 56%, and 44%, respectively, of the 0 cm values.
  
  
  CONCLUSIONS
  The methods used clinically to apply ultrasound have only limited interchangeability. Large corrections to the power output are required to compensate when using subaqueous rather than direct (in air) ultrasound, and for applicator to skin distances of beyond 0 cm in subaqueous ultrasound.
authors.affiliation: School of Physiotherapy, La Trobe University, Victoria, Australia.
authors.forename: V J
authors.initials: VJ
authors.lastname: Robertson
authors.forename: A R
authors.initials: AR
authors.lastname: Ward
mesh_terms: D000818:Animals; D018592:Cross-Over Studies; D006358:Hot Temperature; D066298:In Vitro Techniques; D008722:Methods; D013552:Swine; D014465:Ultrasonics