# Intravital Visualization of Tattoo Particles After Picosecond Laser Treatment

## TL;DR

This study uses advanced imaging to track tattoo particles after laser treatment, showing they move upward over months and suggesting longer treatment intervals may be better.

## Contribution

The study provides in vivo visualization of tattoo particle clearance dynamics following picosecond laser treatment using non-invasive imaging.

## Key findings

- Tattoo particles were observed in both inter- and intracellular spaces in the epidermis and upper dermis six weeks post-treatment.
- Fluorescence lifetime measurements decreased over time but remained elevated at 12 weeks, indicating ongoing metabolic changes.
- The findings suggest transepidermal clearance of tattoo particles can take several months following laser treatment.

## Abstract

Picosecond (ps) laser treatments have been widely used for several years to remove unwanted tattoos. It is hypothesized that following the laser‐induced fragmentation of tattoo particles, transepidermal clearance occurs as one of the elimination processes alongside with the renewal of the skin. Nevertheless, the precise microscopic details of the tattoo clearance process following laser treatment remain unclear.

To analyze the transepidermal clearance of tattoo particles, along with the morphological and metabolic changes in the surrounding tissue, following ps laser treatment.

The study population comprised healthy male and female patients seeking laser‐assisted tattoo removal, who were recruited from the Laser Department at the University Medical Center Hamburg–Eppendorf. Each subject underwent a single ps laser treatment session, and follow‐up assessments were conducted at 6 and 12 weeks post‐treatment using multiphoton tomography with fluorescence lifetime imaging (MPT‐FLIM).

The study included a total of nine participants with eleven tattoos. In untreated skin, the tattoo particles were observed to be confined to the dermis, situated between collagen bundles. Six weeks following treatment, tattoo particles were observed in both inter‐ and intracellular spaces across all epidermal and the upper dermal layers. By the 12‐week follow‐up, particles were still present in the epidermis and dermis, although their quantity appeared to have decreased. In accordance with the aforementioned findings, the mean fluorescence lifetime measurements demonstrated a decrease across the follow‐up visits, although they remained elevated at 12 weeks.

Our in vivo, non‐invasive imaging data indicate that the transepidermal clearance of tattoo particles following ps laser treatment can extend over several months. This supports the hypothesis that longer intervals between ps laser treatments may be beneficial. Further prospective clinical studies are required to compare the efficacy and safety of short‐ and long‐term treatment intervals in laser‐assisted tattoo removal.

ClinicalTrials.gov identifier: NCT06431464