Developing In Vivo And Label Free Photoacoustic Flow Cytometry (PAFC) Technique For Melanoma Cancer Detection

Biological tissues have photoacoustic effect. When circulating targets(e.g., cells) in blood flow are illuminated by high-pulsed repetition ratelaser, they will generate acoustic waves of different frequencies afterabsorbing electromagnetic energy, followed by local temperature rise andvolume expansion. In this master project, student Rongrong Liu appliedthe photoacoustic effect theory to in vivo flow cytometry and developed anovel in vivo photoacoustic flow cytometry (PAFC) for early cancerdetection. By in vivo assessment of circulating targets, PAFC can be usedto detect cells, contrast agents, pathogens and so on, which is proposed todetect circulating tumor cells (CTCs) in microvasculature with highsensitivity, and serve the purpose of reducing cancer mortality. The mainframework of PAFC contains the PA signal excitation part, the opticalmicroscopic imaging part, and the PA signal detection part. An infraredhigh-pulsed laser with a wavelength of1064nm served to excite targetingbiological tissues to generate photoacoustic waves. The opticalmicroscopic imaging part served the purpose to navigate blood vessels andfocus the laser spot on the right place. A function generator is used tosynchronously trigger the pulsed laser and DAQ card to selectively acquirePA signals within limited PC memory, with MATLAB GUI to combineseveral small programs of GaGe DAQ card to record targeting PA signalsin real time without loss. For signal processing of PA signals detected by PAFC, the Wavelet de-noising was used to reduce noises generated bybackground tissues, and the signal digital averaging was used to increasethe signal to noise ratio (SNR) by N. For biomedical applications of invivo PAFC, PAFC successfully in vitro detected the PA signals of humanblack hair and murine high metastatic melanoma tumor cell B16F10.Furthermore, this PAFC has been used to in vivo count the number ofcirculating tumor cells of melanoma cancer bearing mice from the mouseear microvasculature. The CTC number within a certain period of time canserve as a very important index both for early melanoma cancer diagnosisand melanoma metastasis monitoring. For future developments of in vivoPAFC, we plan to improve this system through several aspects, includingcombining optical setup with in vivo fluorescent flow cytometry, exploringsignal processing algorithms, and extending biomedical applications suchas anticancer therapy efficacy evaluation and so on.