Photoacoustic imaging detects valves in superficial veins
Intravenous access is one of the most frequently applied procedures
in medicine; yet, when accessing the veins with a needle, there is always a risk
of puncturing these venous valves. Researchers from the University of Twente in
Enschede, the Netherlands, have investigated whether photoacoustic imaging, which
images the lumen of blood vessels, can be used to detect these valves.
As reported in the September issue of Lasers
in Surgery and Medicine, the researchers performed photoacoustic imaging on
the superficial dorsal veins in the hands of 21 healthy volunteers. The imaging
involved a combination of high optical contrast with high ultrasound resolution.
They first located a valve on a volunteer’s
hand by palpation and visual inspection. Next, they positioned their homebuilt photoacoustic
sensor above the center of the vessel. The sensor consisted of two concentric ring-shaped
electrodes with equal areas.
Using an Nd:YAG laser with 1.25 mJ
of energy from IB Laser AG of Berlin, light pulses with a duration of 8 ns were
guided to the tissue every 10 ms at 1064 nm with a 600-μm glass fiber that
was integrated into the sensor. Acoustic waves were generated by the pulsed light
being absorbed by the hemoglobin in the blood. The induced temperature rise created
an increase in pressure, which the researchers could detect using a 25-μm-thick
polyvinylidine difluoride film from Piezotech SA of Saint-Louis, France, which was
glued to the electrodes. The amplitude of the pressure, which was dependent on the
amount of absorbed light, along with the time of arrival of the photoacoustic signals,
allowed the researchers to image the contour of the lumen of the vessel. The valves
then appeared in the scans as local discontinuities in the vessels.
The researchers clearly identified
venous valves in 16 of the 21 volunteers; in most cases, valves showed up in the
images as a clear discontinuity in the contour of the lumen (see figure). The scientists
want to carry out further research with people who suffer from intravenous access
problems, such as elderly and obese patients.
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