Photoacoustic tomography (PAT) has been receiving growing attention in the last decade, since it combines good acoustic resolution in deep tissue with the optical absorption contrast. It has been widely applied to small animal imaging, vasculature visualization, osteoarthritis assessment, and so on.
PAT is usually limited to the biological tissues with relatively homogeneous acoustical properties. Many efforts, including ultrasound tomography, time reversal method, and coherence factor optimization have been done to improve the PAT in inhomogeneous tissue. However, these studies usually need to have some prior knowledge of tissue inhomogeneity or only consider some relatively simple scenario of tissue inhomogeneous, such as speed inhomogeneity or single scattering.
Scientists from the Nanjing University and the Institute of Acoustics, Chinese Academy of Sciences propose an ultrasound-photoacoustics (US-PA) imaging scheme to break the limitation PAT in acoustically inhomogeneous tissue. The US technique is carried out to determine the Green's function between each transducer element and the region of interest. By utilizing US to make up the PAT limitation in acoustically heterogeneous tissue, PA images could be extracted from speckle noise with the determined Green’s function. Figure 1 represents the scenario considered in this research.
Fig. 1. The sketch of the scenario considered. Scatters (circles) are randomly distributed in
tissue. A 16-element transducer array is utilized to send and record ultrasound, and record
generated photoacoustic signals (Image by WU).
Research results show that the method can effectively decrease the distortion and false intensity contrast in limited-view PA images. The information extracted from the speckle noise significantly improves the image quality. The US-PA method does not depend on the prior knowledge of tissue and the complexity of the medium perturbation. Moreover, the estimation of Green’s function and the detection of PA signal are performed by the same ultrasound transducer. Therefore, the proposed scheme could be easily integrated into a classical PAT system and improve PAT in acoustically inhomogeneous tissue.
This research was supported by the National Basic Research Program of China under Grant No. 2012CB921504, the Natural Science Foundation of China under Grant Nos. 11274167 and 11274171, and SRFDP Grant No. 20120091110001.
The "Photoacoustic Tomography Extracted from Speckle Noise in Acoustically Inhomogeneous Tissue" has been published in Optics Express (Vol. 21, No.15, pp. 18061-18067, 29 July 2013) with the URL of http://dx.doi.org/10.1364/OE.21.018061 online.