Examination of suitable material for phantoms used in photoacoustics

Abstract: A fundamental part of modern medicine is the ability to study and analyze images, especially for diagnostic purposes. A relatively new imaging system is photoacoustics, where laser- and ultrasound technology are combined to create images in a non-invasive way. It is absorption of the laser that is responsible for the creation of the ultrasound signal. Thus, it is the optic properties of tissue that enable differentiating. Normally it is the amplitude of the returning signal which is utilized for image contrasting in photoacoustics. Instead, this study has examined the center frequency to wavelength dependence of the returning signal. Two parameters assumed to have an effect on the center frequency spectrum are the size and colour of particles. The aim of this study was to investigate whether microsphere phantoms can be used to confirm this assumption. Phantoms consisting of microspheres in different sizes in the colours blue, green and transparent were created. The photoacoustic system at Lund University Hospital (VisualSonics Vevo LAZR-X, Toronto, Canada) was used to make nine measurements, during three different days, for each one of these. After analysis of the data from the amplitude of the returning signal, it was concluded that the spheres in blue and green are appropriate for future research in this field. The results from analyzing the mean and standard deviation of the center frequency was that there is a nonlinear correlation between sphere size and center frequency. There was also a distinct difference between the center frequency spectrum for the blue and green spheres.