Ultrasound transducers are known to suffer from heating issues, but the body’s tissues that are resonated can also be damaged from the mechanically built-up heat. Moreover, the pattern of the ultrasound waves coming off the transducers is not uniform, creating areas of varying pressures and temperature. This can lead to attenuated imaging in certain areas with “overexposure” in other parts.
Now researchers at UK’s National Physical Laboratory (NPL) have developed a method to provide information about the distribution of ultrasound energy coming off the transducer head. The system relies on embedding special color changing crystals that respond to heat into tiles. Applying ultrasound to the tiles provides a nearly immediate visual representation of the energy being delivered, offering clinicians a better ability of gauging the effect on tissues, as well as helping engineers developing ultrasounds better understand the performance of their prototypes.
More details from NPL:
The tool consists of two-layers. The bottom layer is made up of the thermochromic crystals embedded in a polyurethane rubber matrix which absorbs sound. The top layer is colourless and is used to trap the heat within the tile. The tile heat produced by the acoustic energy is quickly and evenly trapped, and the crystals turn white as they reach the trigger temperature. This then produces a pattern on the tile which represents the temperature distribution generated by the treatment head, which in turn relates to the spatial distribution of the acoustic intensity. The pattern can be clearly visible after only 10 seconds of exposure to the ultrasound.
Bajram Zeqiri, an NPL Science Fellow who led the project, describes how you would test an ultrasound treatment head with the tiles: “In clinical practice the new ‘imager’ tiles would be used in much the same way you would treat a patient: by applying coupling gel to the treatment head, coupling it to the tile, switching on for typically 10 seconds, and then removing and observing the resulting image.”
This means that the tiles can be used to quickly check for treatment head damage, asymmetric beam-patterns or ‘hot-spots’, and more simply to confirm whether the devices are actually working at all.
More from NPL: Testing Tiles for Ultrasound Treatment…