Photoacoustic radiofrequency spectroscopy for monitoring cancer treatment response

Frequency analysis of the photoacoustic (PA) signals was combined with functional PA estimations of tumor oxygenation to monitor the in-vivo response of a temperature sensitive liposome treatment. Mouse breast cancer tumors were imaged using the Vevo LAZR system (Fujifilm VisualSonics, Toronto, Canada) before treatment and 30 min/2h/5h/24h/7d post-treatment. Treatment consisted of an injection of either the liposome (HaT-DOX) or saline followed by heating of the tumor in a water bath for 1 hour at 43°C. The tumor oxygenation and the slope of the normalize power spectrum decreased by 22% and 45% at 750 nm, respectively as early as 30 minutes post-treatment. The combined analysis was able to differentiate responding mice from their non-responding counterparts and the control group. These results suggest that probing both structural (spectral slope) and functional (oxygen saturation) changes that occur during cancer treatment can aid in identifying treatment response.