Photoacoustic tomography (PAT) or optoacoustic tomography is a novel non-invasive imaging modality for visualizing inner structure as well as function of biological tissue. Based on photoacoustic effect, laser induced acoustic wave signal is detected by ultrasound transducer. Since cancerous tissue are 2-5 times more light absorbing than normal tissue due to increase in blood vessels, PAT potentially provides a more accurate method than previous available ones for cancer diagnosis.

Fig. 1 The high-resolution 3D photoacoustic image of blood vessels

As a hybrid imaging modality, PAT combines the advantages of optical imaging and ultrasound imaging by having the high contrast of the former and the deep penetration depth of the later. Considering functional imaging, optical imaging techniques are highly desirable because of their excellent spatial resolution and high contrast. However, since most biological tissues are highly light-scattering media, those back scattered photon detection based optical imaging modalities, such con-focal microscopy, tow-photon microscopy, optical coherence tomography, etc, has limited penetration depth compared with ultrasound imaging. To sum up, PAT has the penetration depth and resolution similar to ultrasound imaging technique, and high contrast similar to optical imaging technique. 

Table 1 Comparison of imaging modalities