Photoacoustic Imaging of Atherosclerotic Plaques

Overview

Stroke is a major cause of death and disability worldwide. Stenotic carotid arteries can lead to stroke if the cause of the stenosis is a vulnerable atherosclerotic plaque. Recent studies reveal that if a patient has a plaque in the carotid artery it is highly probable that he/she will develop plaques in other superficial arteries like the femoral artery. Currently, duplex ultrasound is used to determine the grade of stenosis and is the main criterion for intervention (endarterectomy) planning. However, the stability, or instability of the plaque cannot be determined non-invasively. Photoacoustics is a novel, non-invasive imaging modality that uses pulsed laser light to generate laser induced ultrasound in the absorbing region of the tissue. Photoacoustic imaging provides optical contrast of biological tissue chromophores with an acoustic resolution and imaging depth, which is promising for visualization of plaque composition. The advantage of photoacoustics is the use of multiple wavelengths, since different tissues respond differently to different wavelengths. Hence, non-invasive, in vivo, morphology assessment is a future application of this new modality that would improve diagnosis and clinical decision making. The drawback is the limited penetration depth of the laser light and the signals generated by surrounding tissue. A new, integrated photoacoustic device has been developed that meets all safety requirements and has an improved penetration depth, suitable for imaging of carotid arteries with the aim to distinguish between plaques with different morphology.

Objective: The aim of this study is to investigate the feasibility of atherosclerotic plaque imaging using multispectral photoacoustic imaging. Study design: This is a pilot study where 60 patients with a plaque in one of the carotids, scheduled for an endarterectomy procedure, will be included. Each subject will get a multi-wavelength photoacoustic examination of the carotid plaque. In one group (N = 30), photoacoustic imaging will be performed noninvasively at the TU/e laser lab, which is compliant with laser safety standards, to verify non-invasive, multi-angle, multi-wavelength photoacoustic imaging (Study A). In the second group (N = 30), photoacoustic imaging will be performed pre- and per-operatively (Study B) prior to plaque removal. Here, to ensure a 100% (laser) safe environment, all acquisitions will be performed in the operating theatre. The latter group will be subjected to additional Magnetic Resonance Imaging for validation. After carotid endarterectomie the plaque sample of each patient (Study A and B) will be transported to TU/e for in vitro PA scanning and histology analysis. Study population: A total of 60 patients with carotid artery disease scheduled for endarterectomy (stenosis grade of \> 70% and \< 99%). Intervention (if applicable): endarterectomy (following normal procedure), with an additional photoacoustic image acquisition after incision, before removal of the plaque. Main study parameters/endpoints: The acoustic (i.e., echographic) and photoacoustic images will be analyzed to determine the ability of distinguishing between different plaque components (intraplaque hemorrhage, lipid pool, vessel wall), examine penetration depth, resolution, and contrast.