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Technical Briefs

# Photoacoustic Detection of Melanoma Micrometastasis in Sentinel Lymph Nodes

[+] Author and Article Information
Devin McCormack, Benjamin S. Goldschmidt, Kiran Bhattacharyya

Department of Biological Engineering, University of Missouri, Columbia, MO 65211

Mays Al-Shaer, Paul S. Dale, Chris Papageorgio

School of Medicine, University of Missouri, Columbia, MO 65212

Carolyn Henry

College of Veterinary Medicine, University of Missouri, Columbia, MO 65211

John A. Viator

Department of Biological Engineering, University of Missouri, Columbia, MO 65211; School of Medicine, University of Missouri, Columbia, MO 65212; Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211viatorj@missouri.edu

J Biomech Eng 131(7), 074519 (Jul 16, 2009) (5 pages) doi:10.1115/1.3169247 History: Received October 15, 2008; Revised June 11, 2009; Published July 16, 2009

## Abstract

Melanoma is the deadliest form of skin cancer and has the fastest growth rate of all cancer types. Proper staging of melanoma is required for clinical management. One method of staging melanoma is performed by taking a sentinel node biopsy, in which the first node in the lymphatic drainage path of the primary lesion is removed and tested for the presence of melanoma cells. Current standard of care typically involves taking fewer than ten histologic sections of the node out of the hundreds of possible sections available in the tissue. We have developed a photoacoustic method that probes the entire intact node. We acquired a lymph node from a healthy canine subject. We cultured a malignant human melanoma cell line HS 936. Approximately $1×106$ cells were separated and injected into the lymph node. We also had a healthy lymph node in which no melanoma cells were implanted. We used a tunable laser system set at 532 nm to irradiate the lymph nodes. Three piezoelectric acoustic detectors were positioned near the lymph node to detect photoacoustic pulses generated within the lymph nodes. We also acquired lymph nodes from pigs and repeated the experiments with increased amplification and improved sensors. We detected photoacoustic responses from a lymph node with as few as 500 melanoma cells injected into the tissue, while normal lymph nodes showed no response. Photoacoustic generation can be used to detect melanoma micrometastasis in sentinel lymph nodes. This detection can be used to guide further histologic study of the node, increasing the accuracy of the sentinel lymph node biopsy.

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## Figures

Figure 1

A histological section of a human lymph node stained with hematoxylin and eosin. (left) The intersecting double arrows span the area, which is infiltrated with melanoma cells. This area is located at the periphery of this lymph node. (right) The indicated area is infiltrated heavily by melanoma cells, which are large cells with abundant cytoplasm. The arrow indicates a single melanoma cell.

Figure 2

The photoacoustic setup for detecting micrometastasis in intact lymph nodes. The position of only one of three acoustic transducers is shown here.

Figure 3

(left) Photoacoustic response from lymph nodes without melanoma for all three detectors show no signal with a noise floor of approximately 100 μV. (right) For the lymph nodes with melanoma, each sensor shows a distinct photoacoustic wave, with detector 1 showing one at 9.5 μs, detector 2 showing one at 5 μs, and detector 3 showing one at 4 μs.

Figure 4

The average signals from irradiating pig lymph nodes are shown here. The error bars denote standard deviation of the measurements. The amplitudes are shown in millivolts and correspond approximately by 100 mV per bar of pressure.

## Errata

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