Background: High frequency ultrasound is increasingly used in both clinical and small-animal (preclinical) imaging. Test phantoms are an important part of the quality control of ultrasound equipment. The main design criterion is that they should be made from a tissue-mimicking material (TMM) that has acoustic properties equivalent to soft tissue e.g. speed of sound and acoustic attenuation. The IEC agar-based TMM (IEC 61685:2001) is recommended and has been extensively used for clinical phantoms. However, recent
trials in developing wall-less flow phantoms for preclinical studies have revealed the need for a stronger TMM, due to the rupturing and shedding of material of the agar-based TMM. A konjac-carrageenan-based TMM was developed for a similar problem by Meagher et al (Ultrasound in Med. & Biol., 33(2) 303–310, 2007), and here we investigate the acoustic properties at preclinical ultrasound frequencies.
Methods: Acoustic characterisation was performed using two methods; a commercially available preclinical ultrasound scanner (Vevo 770, FUJIFILM VisualSonics, Toronto, Canada) and a dedicated high-frequency ultrasound facility developed at the National Physical
Laboratory. The speed of sound and attenuation were measured using a broad-band substitution technique. The frequency range covers 5-60 MHz, typical of preclinical scanners.
Results: The speed of sound was found to be 1552±12 m.s-1 and 1552.1±3.3 m.s-1 respectively. The attenuation exhibited a nonlinear dependence on frequency in the form of a polynomial function.
Conclusion: The characterisation of this TMM indicates that it could potentially be a suitable material for use in high-frequency ultrasound assessment and applications, such as small-animal flow phantom design, which require a TMM more physically robust than those currently used for clinical systems.
David Kenwright is representing the British Medical Ultrasound Society after winning the Young Investigators Award at the BMUS 45th Annual Scientific Meeting in December 2013.
