Photoacoustic (PA) endoscopy has the potential to diagnose early diseases in the gastrointestinal tract. For the first time, to our knowledge, we developed an autofocusing PA endoscope (AF-PAE) for the usually irregular gastrointestinal tract imaging to solve the deterioration of transverse resolution caused by the defocus scanning of the probe. The 9-mm-diameter AF-PAE probe integrated a 6-mm aspheric lens and 6-mm liquid lens to automatically adjust the optical focal length, and an unfocused ultrasonic transducer with a center frequency of 15 MHz is coaxially set for detecting PA signals. With this probe, the AF-PAE achieved a focus-shifting range from approximately 2 to 10 mm with high transverse resolution and image contrast in a 360° field of view. Phantom experiment and vasculature distribution of a resected rabbit rectum have been performed to demonstrate the imaging ability of the AF-PAE for potential clinical applications in colorectal vessel imaging and subsequent diagnosis.

Melanoma is the most dangerous type of skin cancer with high lethal rate. Tumor thickness and tumor-associated vasculature are two key parameters for staging melanoma. Previous techniques for diagnosing melanoma have insurmountable restrictions, such as invasive, low specificity, or inaccurate depth measurement. Here we develop an integrated photoacoustic (PA) and ultrasound (US) imaging system dedicated to overcome these limitations. An integrated detector with sound-light coaxial/confocal design and flexible coupling mode is employed for the combined PA/US imaging strategy. PA imaging results enable a clear characterization of tumor angiogenesis with high resolution and high contrast. Furthermore, accurate thickness measurements of melanoma in different stages can be resolved with the simultaneously obtained PA/US image. Phantom experiments and in vivo animal experimental results demonstrate the integrated PA/US system could provide potential for noninvasive biopsy of melanoma.

We propose a dual-parameter detection method to realize the simultaneous optical absorption and viscoelasticity imaging based on photoacoustic lock-in measurement. Both optical absorption and viscoelasticity properties can be obtained simultaneously by analyzing the amplitude and phase of photoacoustic signals. This method is experimentally verified by imaging of gelatin phantoms with different absorption coefficients and viscoelastic coefficients. Furthermore, pilot experiments were performed on an in vivo murine EMT6 tumor from the back of a BALB/c mouse. Results demonstrate that the method can be used to measure the optical absorption and viscoelasticity of different biological tissues.