Relative transmissivity of ultrasound coupling agents commonly used by therapists in the UK.

Coupling agents are required when using therapeutic ultrasound (US) to maximize acoustic contact between the transducer and the insonated tissue. US beam power is attenuated to varying extents by different couplants and this may influence treatment efficacy, since therapeutic effects are dose-dependent. It is therefore important to know how well different couplants transmit US. In this study, the transmission characteristics of a range of gel couplants were measured using a radiation force balance. Data were collected for gels commonly used by UK therapists and at the powers and frequencies advocated for low-intensity therapeutic practice. Transmissivities of standard couplants relative to degassed water varied between 95% and 108% (nominal 95% confidence intervals between 0% and 11%). The spread and ranking of transmissivities changed when the US frequency was varied. For clinical purposes, however, there was no significant difference between transmissivities of the gels under test.