Plasmonic photothermal therapy is a new cancer thermotherapy method based on surface plasmon resonance of
nanoparticles. It is important to measure the temperature during thermotherapy for safety and efficacy. In this study, we
apply a photoacoustic (PA) method for real-time, non-invasive temperature measurements. In particular, this method can
be effectively combined with a photothermal therapy system that we developed in parallel. The method is based on the
fact that the PA pressure amplitude is linearly related to temperature. To explore its potential, a home-made, 20 MHz PA
transducer was used, in which an optical fiber was inserted in its center for emitting laser pulses while the PA signal was
simultaneously detected. Continuous wave (CW) laser was used to heat the subject, including both phantoms and mice.
The temperature of the region of interest was also measured by a fine-needle thermal couple. Results show that the
temperature was linearly proportional to the PA signal with good correlation with the CW laser irradiation. The in vivo
study also demonstrated potential of this technique.
Collagen shrinkage associated with denaturation from thermal treatment has a number of important clinical applications. However, individualized treatment is hindered by the lack of reliable noninvasive methods to monitor the process of collagen denaturation. We investigate the serial changes of collagen denaturation from thermal treatment of rat tail tendons at 58 °C by use of second harmonic generation (SHG) microscopy. We find that rat tail tendon shrinks progressively from 0 to 9 min of thermal treatment, and remains unchanged in length upon further thermal treatment. The SHG intensity also decreases from 0 to 9 min of thermal treatment and becomes barely detectable from further thermal treatment. Collagen shrinkage and the SHG intensity are well correlated in a linear model. In addition, SHG imaging reveals a tiger-tail-like pattern of collagen denaturation. The bands of denatured collagen progressively widen from increased thermal treatment and completely replace the adjacent bands of normal collagen after 9 min of thermal treatment. Our results show that collagen denaturation in rat tail tendon from thermal treatment is inhomogeneous, and that SHG intensity can be used to predict the degree of thermally induced collagen shrinkage. With additional development, this approach has the potential to be used in biomedical applications.