Instrumentation and Measurement Physics(DIMP)
Physique des instruments et mesures (DPIM)

---

Andreas MANDELIS
University of Toronto

Laser Laser Photo-thermo-acoustic Frequency Swept Heterodyned Lock-in Depth Profilometry \for Three-Dimensional Sub-surface Tissue Imaging^*

---

In conventional biomedical photoacoustic imaging systems, a pulsed laser is used to generate time-of-flight acoustic information of the subsurface features. This paper reports the theoretical and experimental development of a new frequency-domain (FD) photo-thermo-acoustic (PTA) principle featuring frequency sweep (chirp) and heterodyne modulation and lock-in detection of a continuous-wave laser source at 1064 nm wavelength. PTA imaging is a promising new technique, which is being developed to detect tumor masses in turbid biological tissue. Owing to the linear relationship between the depth of acoustic signal generation and the delay time of signal arrival to the transducer, information specific to a particular depth can be associated with a particular frequency in the chirp signal. Scanning laser modulation with a linear frequency sweep method preserves the depth-to-delay time linearity and recovers FD-PTA signals from a range of depths. Preliminary results performed on rubber samples and solid tissue phantoms indicate that the FD-PTA technique has the potential to be a reliable tool for biomedical depth-profilometric imaging.

^*In coordination with Ying Fan, Gloria Spirou and Alex Vitkin