A novel needle probe for deeper photoacoustic viscoelasticity measurement

We present for the first time,to the best of our knowledge,a needle probe for photoacoustic viscoelasticity[PAVE]measurements at a depth of 1 cm below the sample surface.The probe uses a gradient index rod lens,encased within a side-facing needle[0.7 mm outer diameter],to direct excitation light[532 nm]and detection light[1325 nm]focused on the sample,collecting and directing the returned detection light in a spectral domain low coherence interfer-ometry system,which allows for obtaining optical phase differences due to photoacoustic oscillations.The feasibility of needle probe for PAVE depth characterization was investigated on gelatin phantoms and in vitro biological tissues.The experimental results in an in vivo animal model predict the great potential of this technique for in vivo tumor boundary detection.