Photoacoustic imaging of atherosclerotic plaques

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.

The aim of this study is to investigate the feasibility of atherosclerotic
plaque imaging using multispectral photoacoustic imaging.

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.

For this study, the subject undergoes a regular 2D echography and additional
non-invasive photoacoustic imaging. In study A, the patients will be requested
to visit the PULS/e lab at the Eindhoven University of Technology for
multi-wavelength photoacoustic imaging. The total exam will take 30 minutes of
time. In study B, patients will be imaged during the endarterectomy procedure
at CZE. First, photoacoustic images are acquired in the neck, prior to
incision. The PA acquisition will be repeated after incision and exposure of
the carotid bifurcation, before the surgeon will remove the plaque. Prior to
the intervention, a sub-group of patients will be asked to visit the hospital
for additional MR imaging.
The test subjects will not benefit from this examination. However, this pilot
study will clarify whether the use of photoacoustic imaging of carotid arteries
is feasible. It is expected that there are no risks or adverse outcomes for the
subjects. A cost-effective device to identify plaque stability in patients to
prevent stroke and reduce overtreatment will benefit the future population by
reducing health care costs and risks involved.