Photoacoustic (PA) tomography (PAT) is a promising technology for noninvasive temperature sensing. However, traditional PA thermometry can measure only the temperature changes relative to a baseline. Here we report a new thermal-energy-memory-based PA thermometry (TEMPT) to quantify the Grüneisen parameter and recover the absolute temperature distribution in deep tissues. We have validated the feasibility of TEMPT on tissue-mimicking phantoms and achieved a measurement accuracy of ~0.5 °C at 1.5 cm depth. As proof-of-concept, we applied TEMPT for temperature mapping during focused ultrasound treatment in mice in vivo. TEMPT is expected to find applications in thermotherapy on small animal models.
We report a photoacoustic computed tomography (PACT) system using a customized optical fiber with a cylindrical diffuser to internally illuminate deep targets. The traditional external light illumination in PACT usually limits the penetration depth to a few centimeters from the tissue surface, mainly due to strong optical attenuation along the light propagation path from the outside in. By contrast, internal light illumination, with external ultrasound detection, can potentially detect much deeper targets. Different from previous internal illumination PACT implementations using forward-looking optical fibers, our internal-illumination PACT system uses a customized optical fiber with a 3-cm-long conoid needle diffuser attached to the fiber tip, which can homogeneously illuminate the surrounding space and substantially enlarge the field of view. We characterized the internal illumination distribution and PACT system performance. We performed tissue phantom and in vivo animal studies to further demonstrate the superior imaging depth using internal illumination over external illumination. We imaged a 7.5-cm-deep leaf target embedded in optically scattering medium and the beating heart of a mouse overlaid with 3.7-cm-thick chicken tissue. Our results have collectively demonstrated that the internal light illumination combined with external ultrasound detection might be a useful strategy to improve the penetration depth of PACT in imaging deep organs of large animals and humans.