Search

Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. For this technique, usually large and costly Q-switched Nd:YAG lasers are used. These lasers provide a pulse energy of at least several milliJoules. In search of alternative light sources, we investigated the use of a small and compact pulsed laser diode to image blood vessels. We proved that a pulsed laser diode can be applied for imaging blood vessels in vivo.

A photoacoustic double-ring sensor, featuring a narrow angular aperture, is developed for laser-induced photoacoustic imaging of blood vessels. An integrated optical fiber enables reflection-mode detection of ultrasonic waves. By using the cross-correlation between the signals detected by the two rings, the angular aperture of the sensor is reduced by a factor of 1.9, from 1.5 to 0.8 deg. Consequently, photoacoustic images could be obtained in a manner analogous to the ultrasound B-scan mode. Next, the cross section of artificial blood vessels is visualized by reconstruction of the absorbed energy distribution. Finally, in vivo imaging and the subsequent reconstruction of the absorbed energy distribution is demonstrated for superficial blood vessels in the human wrist., (Copyright 2004 Society of Photo-Optical Instrumentation Engineers.)

A double-ring sensor was applied in photoacoustic tomographic imaging of artificial blood vessels as well as blood vessels in a rabbit ear. The peak-to-peak time (tau(pp)) of the laser (1064 nm) induced pressure transient was used to estimate the axial vessel diameter. Comparison with the actual vessel diameter showed that the diameter could be approximated by 2ctau(pp), with c the speed of sound in blood. Using this relation, the lateral diameter could also precisely be determined. In vivo imaging and monitoring of changes in vessel diameters was feasible. Finally, acoustic time traces were recorded while flushing a vessel in the rabbit ear with saline, which proved that the main contribution to the laser-induced pressure transient is caused by blood inside the vessel and that the vessel wall gives only a minor contribution.