Imaging of acoustic attenuation and speed of sound maps using photoacoustic measurements

Photoacoustic imaging is an upcoming medical imaging modality with the potential of imaging both optical and acoustic properties of objects. We present a measurement system and outline reconstruction methods to image both speed of sound and acoustic attenuation distributions of an object using only pulsed light excitation. These acoustic properties can be used in a subsequent step to improve the image quality of the optical absorption distribution. A passive element, which is a high absorbing material with a small cross-section such as a carbon fiber, is introduced between the light beam and the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated acoustic signal to propagate through the object. From these measurements we can extract measures of line integrals over the acoustic property distribution for both the speed of sound and the acoustic attenuation. Reconstruction of the acoustic property distributions then comes down to the inversion of a linear system relating the obtained projection measurements to the acoustic property distributions. We show the results of applying our approach on phantom objects. Satisfactory results are obtained for both the reconstruction of speed of sound and the acoustic attenuation.