Photoacoustic drug delivery is a method for local drug delivery that uses a laser to create a laser-induced vapor bubble to force ambient drug into the surrounding tissue. We used flash photography to visualize this process. The tissue was modeled by transparent gelatin (60-175 bloom) targets submerged in light absorbing solutions (50-300cm-1) of the hydrophobic dye (D&C Red #17) and mineral oil. One microsecond laser pulses of 20-100 mJ energy were delivered via solid core fibers up to 3mm above the gelatin surface. The laser-induced vapor bubbles were photographed using a one microsecond flash strobe 10-1500 microseconds after the laser pulse. Bubble dimensions were measured as a function of time for different absorption coefficients and fiber configurations. The individual events were very reproducible. Observations: 1) The penetration of dye in gelatin targets depends on the laser pulse energy and absorption coefficient of the solution. 2) Increasing the absorption coefficient of the liquid increases the lifetime of vapor bubbles and the bubble size. 3) The bubble size strongly depends on the radiant exposure. 4) The hardness of the target affects the bubble size. 5) Deep penetration of dye into gelatin targets follows the collapse of the vapor bubble.
H. Shangguan, A. Shearin, and S. A. Prahl. Visualization of photoacoustic drug delivery dynamics. Lasers Surg. Med., 57:4-5, 1995 (abstract).