Towards Photoacoustic Mammography

Materials for solid photoacoustic breast phantoms based on poly(vinyl alcohol) hydrogels are presented. Phantoms intended for use in photoacoustics must possess both optical and acoustic properties of tissue. To realize the optical properties of tissue, one approach was to optimize the number of freezing and thawing cycles of aqueous poly(vinyl alcohol) solutions, a procedure which increased the turbidity of the gel while rigidifying it. The second approach concentrated on forming a clear matrix of the rigid poly(vinyl alcohol) gel without any scattering, so that appropriate amounts of optical scatterers could be added extraneously at the time of formation to achieve tunability of optical properties as per requirement. The optical and acoustic properties relevant to photoacoustic studies of such samples were measured to be close to the average properties of human breast tissue. Tumor simulating gel samples of suitable absorption coefficient were created by adding appropriate quantities of dye at the time of formation; the samples were then cut into spheres. A breast phantom embedded with such ‘tumors’ was developed for studying the applicability of photoacoustics in mammography. The results of this chapter have been published in: Kharine, A., Manohar, S., Seeton, R., Kolkman, R. G. M., Bolt, R. A., Steenbergen, W., & de Mul, F. F. M. 2003. Poly(vinyl alcohol) gels for use as tissue phantoms in photoacoustic mammography. Phys. Med. Biol., 48, 357–70.