Photoacoustic Imaging of Tattoo Inks: Phantom and Clinical Evaluation

Abstract

Photoacoustic imaging (PAI) is a novel hybrid imaging modality that provides excellent optical contrast with the spatial resolution of ultrasound in vivo. The method is widely being investigated in the clinical setting for diagnostic applications in dermatology. In this report, we illustrate the utility of PAI as a non-invasive tool for imaging tattoos. Ten different samples of commercially available tattoo inks were examined for their optoacoustic properties in vitro. In vivo PAI of an intradermal tattoo on the wrist was performed in a healthy human volunteer. Black/gray, green, violet and blue colored pigments provided higher levels of PA signal compared to white, orange, red and yellow pigments in vitro. PAI provided excellent contrast and enabled accurate delineation of the extent of the tattoo in the dermis. Our results reveal the photoacoustic properties of tattoo inks and demonstrate the potential clinical utility of PAI for intradermal imaging of tattoos. PAI may be useful as a clinical adjunct for objective preoperative evaluation of tattoos and potentially to guide/monitor laser-based tattoo removal procedures.

Keywords: dermatology; photoacoustic imaging; tattoo; ultrasound.

Figure 1.

(a) Photograph showing the ten commercially available tattoo ink samples evaluated in vitro. (b) Set up for evaluation of photoacoustic properties of tattoo inks using hollow channels created in a tissue mimicking phantom.

Figure 2.

PAI of tattoo inks in vitro (a) Pseudo-colorized PA signal maps (680 nm) of the ten tattoo inks along with blood and PBS filled channels. (b-d) Plots showing PA signal from 680–900 nm from the ten tattoo ink samples along with blood and PBS.

Figure 3.

PAI of an intradermal tattoo. The panel of images on the top represents digital photograph (left), a B-mode surface rendering (middle), and a reconstructed maximum intensity projection (MIP; right) image (800 nm) of a black tattoo on the wrist of a healthy volunteer. Corresponding longitudinal (left) and transverse axial (right) images of a part of the tattoo (outlined in black) is shown. The images have been pseudo-colorized for enhanced visualization.