Nt86 381

A schematic of the PAI system is shown in Fig. 1a. A tunable Ti:Sapphire laser (LT-2211A, LOTIS TII) with 8–30 ns pulse duration and 10 Hz repetition rate was used. The laser beam was split and coupled into two optical fiber bundles. Induced photoacoustic waves were collected by a focused 3.5 MHz ultrasound transducer with 15 mm aperture and 35 mm focal length. The imaging probe consisting of transducer and optical fiber bundles was mounted on a two-dimensional (2D) moving stage that scanned two-dimensionally to form a three-dimensional (3D) image. The imaging area was 20 mm × 20 mm, with a 200 μm interval step. All in vivo experiments were performed with a light intensity of 8 mJ/cm² to intentionally remain well below the American National Standards Institute safety limit (20 mJ/cm²).
Figure 1b shows the schematic of the planar fluorescence imaging system. Two laser beams generated from two 785 nm CW lasers (M5-785-0080; Thorlabs, Newton, NJ) were coupled into optical fiber bundle I and optical fiber bundle II. An EMCCD equipped with a high-performance fluorescent band-pass filter (NT86-381; Edmund Optics, Barrington, NJ) was used to collect the fluorescence signals. All experiments were conducted using the same illumination pattern and camera exposure times.

A conventional near-infrared planar fluorescence imaging system was built to obtain 2D fluorescence images after each endoscopic imaging experiment for further cross validation. As schematically shown in Figure 3, a CW 785 nm laser (M5-785-0080, Thorlabs, Newton, NJ, USA) was used as the light source. The light beam was split into two parts that were respectively coupled into two fiber bundles, and then traveled through light diffusers (DG10-1500, Thorlabs, Newton, NJ, USA) in order to generate homogeneous illumination on the sample mounted on the sample holder. The induced fluorescence signal was collected by a fast charge-coupled device camera (CoolSNAP EZ, Photometrics, Tucson, AZ, USA) with a high performance fluorescent band-pass filter (NT86-381, Edmund Optics, Barrington, NJ, USA) mounted in the front for filtering out non-fluorescence signals. The laser power used for illumination was the same in all experiments.