Multispectral Optoacoustic Tomography for Functional Imaging in Vascular Research

Summary

The present protocol describes the acquisition of multispectral optoacoustic images of in vivo human skin vasculature. These include the quantification of hemoglobin and melanin, regarded as chromophores of interest for functional analysis.

Abstract

Microcirculatory impairment has been recognized in various disease processes, underlying this growing theme within vascular research. In recent years, the development of live imaging systems has set the (analytical) pace in both basic and clinical research, with the objective of creating new instruments capable of providing real-time, quantifiable endpoints with clinical interest and application. Near-infrared spectroscopy (NIRS), positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI) are available, among other techniques, but cost, image resolution, and reduced contrast are recognized as common challenges. Optoacoustic tomography (OT) offers a new perspective on vascular functional imaging, combining state-of-the-art optical absorption and spatial resolution capacities (from micrometer optical to millimeter acoustic resolution) with tissue depth. In this study, we tested the applicability of multispectral optoacoustic tomography (MSOT) for functional imaging. The system uses a tunable optical parametric oscillator (OPO) pumped by an Nd: YAG laser, providing excitation pulses sensed by a 3D probe at wavelengths from 680 nm to 980 nm. Images obtained from the human forearm were reconstructed through a specific algorithm (supplied within the manufacturer's software) based on the response of specific chromophores. Maximal Oxygenated Hemoglobin (Max HbO₂) and Deoxygenated Hemoglobin (Max Hb), Total Hemoglobin (HbT), and mean Oxygen Saturation (mSO₂) to vascular density (µVu), inter-unit average distances (ζAd), and capillary blood volume (mm³) may be measured using this system. The applicability potential found with this OT system is relevant. Ongoing software developments will surely improve the utility of this imaging system.

Introduction

Cardiovascular diseases are recurrent top causes of death worldwide and represent a huge burden for any health system^1,2. Technology has been a major contributor to the expansion of our understanding of fundamental cardiac and vascular pathophysiology, providing more precise diagnostic tools and the possibility of early disease detection and more effective management. Imaging techniques offer the possibility to measure not only cardiac and major vessel performance but also, on a much smaller scale, to calculate the capillary density, local perfusion and volume, and endothelial dysfunction, among other characte....

Protocol

The experimental protocol was previously approved by the Ethics Committee of the University's School of Health Sciences (EC.ECTS/P10.21). Procedures fully respected the principles of good clinical practice defined for human research¹³. A convenient sample of six healthy participants of both sexes (n = 3 per sex) with a mean age of 32.8 ± 11.9 years old was chosen from the university community. Selected participants were required to be normotensive, non-smokers, and free of any medication or food supplementation. Blood pressure, cardiac frequency, and the Body Mass Index were also registered. All participants were previously informed of....

Results

Data provided by optoacoustic imaging can be analyzed in post-processed export images (Figure 2) and plotted data (Figure 3). The purpose here was to introduce the operation of optoacoustic functional imaging and to explore its application in more commonly known vascular research. For that, we compared images acquired during rest and after a 200 mmHg occlusion of a major supplying artery (Figure 2). These observations can be quantif.......

Discussion

This protocol emphasizes the working steps regarded as practical requirements to operate this new optoacoustic imaging instrument, from the adequate positioning (participant, probe) needed for 3D cup probe stabilization to image acquisition, ROI selection, and image reconstruction and analysis.

The proposed experimental approach, using "instantaneous" acquisitions together with images obtained under dynamic conditions, illustrates the interest and utility of this instrument in accessin.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cuff	PIC	107001
Drapes	Pajunk	021151-1501
Ethanol 70%	Sigma Aldrich	EX0281
Gogless	Univet	559G.00.00.201
Kimwipes	Amoos	5601856202331.00
MSOT	iThera	MSOTAcuity
Stabilizing arm	ITEM		Self designed and assemble
Ultrasound gel	Parker Laboratories	308
Waxing cream	Veet	kkdg08hagd