Volumetric Optoacoustic Temperature Mapping in Photothermal Therapy

Abstract

Photothermal therapy and ablation are commonplace medical procedures employed for treatment of tumors, vascular and brain abnormalities as well as other disorders that require selective destruction of tissues. Yet, accurate mapping of the dynamic temperature field distribution in the treated region represents an unmet clinical need, strongly affecting the clinical outcome of these interventions. We introduce a fast three-dimensional temperature mapping method based on real-time optoacoustic sensing of the treated region coupled with a thermal-diffusion-based model of heat distribution in tissues. Deviations of the optoacoustic temperature readings provided at 40 ms intervals remained below 10% in tissue-mimicking phantom experiments for temperature elevations above 3 °C, as validated by simultaneous thermocouple measurements. Performance of the new method to dynamically estimate the volumetric temperature distribution was further showcased in post-mortem mouse imaging experiments. The newly discovered capacity to non-invasively measure the temperature map in an entire treated volume with both high spatial and temporal resolutions holds potential for improving safety and efficacy of light-based therapeutic interventions.

Figure 1

Lay-out of the experimental setup. The drawings of the transducer array and the ablation system were developed by the authors.

Figure 2

Optoacoustic temperature estimations in a tissue mimicking phantom. (a–c) Transverse and coronal maximum intensity projection (MIP) optoacoustic images reconstructed for three different time points during laser heating of the phantom; (d) The temperature increase estimated from the optoacoustic signal variations (dashed curves) as compared to the temperature increase measured with thermocouples (solid curves). The regions of interest considered for the estimation are marked in panel a; (e) Relative deviation of the F factor from the theoretical value as a function of the temperature increase.

Figure 3

Volumetric optoacoustic monitoring of temperature during photothermal therapy performed in a mouse post mortem. (a) Transverse and lateral MIPs of the reconstructed optoacoustic volumes at different time points during the treatment. The tip of the ablation fiber is located approximately at the center of the displayed volumes. (b) Transverse and lateral MIPs of the estimated temperature maps at the same time points. (c) Actual temporal traces of temperature from the points labeled in (a).