NMPPAS fiber optic microprobe for sub-surface brain tumor diagnosis

Abstract

Brain cancer affects approximately 16,500 people a year and individuals diagnosed with glioblastoma multiforme have an average life expectancy of less than 12-18 months after diagnosis. A portable fiber-optic probe capable of distinguishing between healthy and tumor tissues, with a high degree of spatial resolution, deep within a sample would be a valuable tool for tumor diagnosis and margining. A novel technique that combines 1-2 cm penetration depths with cellular level spatial resolution to chemically distinguish cancerous from non-cancerous tissues is non-resonant multiphoton photoacoustic spectroscopy (NMPPAS). This technique focuses pulsed near infrared light into a sample, creating a two-photon excitation event, and measures the resulting non-radiative decay as an ultrasonic signal. This paper discusses the optimization of a portable fiber-optic NMPPAS probe capable of delivering nanosecond laser pulses from 740nm-1100nm to a series of lens, which focus the light into the sample. The resulting ultrasonic signal is measured using a polyvinylidene fluoride based piezoelectric detector. The two-photon excitation efficiency of the portable NMPPAS probe system has been evaluated by measuring the two-photon excitation and emission spectra of common fluorescent dyes such as rhodamine B and fluorescein. In addition, this paper also demonstrates the diagnostic potential of this technique for tumor detection and margining without the need for acquisition of an entire spectrum.