Frequency-domain correlation and spectral analysis photothermoacoustic (FD-PTA) imaging is a promising new technique, which is being developed to detect tumor masses in turbid biological tissue. Unlike conventional biomedical photoacoustics which uses time-of-flight acoustic information induced by a pulsed laser to indicate the tumor size and location, in this research, a new FD-PTA instrument featuring frequency sweep (chirp) and heterodyne modulation and lock-in detection of a continuous-wave laser source at 1064 nm wavelength is constructed and tested for its depth profilometric capabilities in turbid media imaging. 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-fluence modulation frequencies with a linear frequency sweep method preserves the depth-to-delay time linearity and recovers FD-PTA signals from a range of depths. A report on two-dimensional spatial scans, performed on tissue mimicking control phantoms with various optical, acoustical and geometrical properties will be presented. Combining with the depth information carried by the back-propagated chirp signal at each scanning position, one could rapidly generate sub-surface three-dimensional images of the scanning area, a combination of tasks that is difficult or impossible by use of pulsed photoacoustic detection. It is concluded that frequency domain photothermoacoustics using a linear frequency sweep method and heterodyne lock-in detection has the potential to be a reliable tool for biomedical depth-profilometric imaging.

Date Published: 12 July 2004
PDF: 15 pages
Proc. SPIE 5320, Photons Plus Ultrasound: Imaging and Sensing, (12 July 2004); doi: 10.1117/12.537856

Published in SPIE Proceedings Vol. 5320:
Photons Plus Ultrasound: Imaging and Sensing
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)