Enhancement of photoacoustic signal from contrast agent with pre-illumination

Abstract

We report our experimental study on enhancement of photoacoustic (PA) signal from contrast dye by pre-illumination of the dye with continuous wave (CW) light beam other than optical pulse (pulse width ~ nsec) that is employed to irradiate tissue sample for inducing thermoelastic expansion and subsequently, generation of photoacoustic waves. This unique technique is in contrast to the conventional approaches of shift of optical absorption peak - in the characteristic absorption spectrum of (PA signal) contrast dyes, say, nano-particles by control of the physical parameters including structure, shape and size. Experiments were conducted employing home-built photoacoustic (acoustic resolution) microscopy imaging system for measurement of PA signal strength induced - under various conditions: (1) without any pre-illumination of the dye with CW laser beam, i.e., only pulse laser beam is employed to irradiate the dye and (2) with pre-illumination of the organic dye at various time durations of pre-illumination. In this second case, the dye is exposed, firstly, to CW laser beam (of wavelength, 642nm) for a pre-specified time interval that is followed by irradiation of the dye with pulse laser ( 6nsec) for inducing PA waves. The experimental results demonstrate that pre-illumination of the organic dye improves significantly the strength of pulse-laser induced photo-acoustic signal strength. It is a promising technique for end application in biomedical and clinical applications (more specifically, for enhancement of PA signal strength).