Photoacoustic characterisation of vascular tissue at NIR wavelengths.

Photoacoustic spectroscopy has been shown to be able to discriminate between normal and atheromatous areas of arterial tissue in the visible range (410nm-680nm). However, at these wavelengths haemoglobin absorption is also very high. This makes it challenging to apply photoacoustic techniques using an intravascular probe, as a significant amount of the excitation light will be absorbed by the blood present in the artery. In this study we investigate the use of a wider range of excitation wavelengths (740-1800nm) for discriminating between normal arterial tissue and lipid rich plaques and minimise the effect of blood absorption. Special attention will be given to the near infra-red (NIR) wavelength range (900-1300nm) as in this region blood absorption is relatively weak and there are expected to be significant differences in the absorption spectrum of each tissue type. To investigate this, tissue samples were obtained and imaged at a range of wavelengths, the samples were illuminated first through water, then blood. This study demonstrated that the photoacoustic technique can discriminate between normal arterial tissue and lipid rich plaques, even when blood is present.