Basics of photoacoustic imaging

Nowadays, there are many different biomedical imaging modalities. They each have their own different strengths and weaknesses. Generally, the comparative merits of photoacoustic tomography (PAT) over other mainstream modalities can be summarized as follows: (1) compared with optical microscopy, PAT breaks through the optical diffusion limit (~1 mm depth in the skin), with scalable spatial resolution and maximum imaging depth in both the optical and acoustic domains; (2) compared with medical ultrasonography, PAT images optical absorption contrast with 100% relative sensitivity, and provides images without speckle artifacts; (3) compared with fluorescence imaging, PAT can image more molecules, fluorescent or nonfluorescent, at their absorbing wavelengths; (4) compared with X-ray computed tomography (CT), PAT is devoid of ionizing radiation and capable of functional imaging using endogenous contrast agents; and (5) compared with magnetic resonance imaging (MRI) and positron emission tomography (PET), PAT is less expensive and has better resolution. With these merits, PAT is playing an increasingly important role in biomedical studies, complementing other modalities.