# Noninvasive Mapping of Extracellular Potassium in Breast Tumors via Multi-Wavelength Photoacoustic Imaging

## TL;DR

Researchers used a new imaging technique to noninvasively map potassium levels in breast tumors, finding higher levels in larger tumors.

## Contribution

A solvatochromic dye-based nanoprobe enabled noninvasive potassium mapping in tumors using multi-wavelength photoacoustic imaging.

## Key findings

- Potassium levels in breast tumors increased significantly with tumor size.
- Photoacoustic chemical imaging results matched ICP-MS measurements, validating the method.
- The technique provides a foundation for studying tumor microenvironment chemistry and immunotherapy response.

## Abstract

Elevated extracellular potassium (K+) in the tumor microenvironment (TME) of breast and other cancers is increasingly recognized as a critical factor influencing tumor progression and immune suppression. Current methods for noninvasive mapping of the potassium distribution in tumors are limited. Here, we employed photoacoustic chemical imaging (PACI) with a solvatochromic dye-based, potassium-sensitive nanoprobe (SDKNP) to quantitatively visualize extracellular potassium levels in an orthotopic metaplastic breast cancer mouse model, Ccn6-KO. Tumors of three distinct sizes (5 mm, 10 mm, and 20 mm) were imaged using multi-wavelength photoacoustic imaging at five laser wavelengths (560, 576, 584, 605, and 625 nm). Potassium concentration maps derived from spectral unmixing of the photoacoustic images at the five laser wavelengths revealed significantly increased potassium levels in larger tumors, confirmed independently by inductively coupled plasma mass spectrometry (ICP-MS). The PACI results matched ICP-MS measurements, validating PACI as a robust, noninvasive imaging modality for potassium mapping in tumors in vivo. This work establishes PACI as a promising tool for studying the chemical properties of the TME and provides a foundation for future studies evaluating the immunotherapy response through ionic biomarker imaging.