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.