Real-Time Trimodal Ultrasound, Photoacoustic, and Thermoacoustic Imaging for Biomedical Applications

As a real-time high resolution imaging modality, pulse echo ultrasound (US) is a common screening tool for breast, thyroid, and other types of cancer. However, US has low specificity for detecting cancer due to poor contrast in soft tissue. Hybrid US techniques like photoacoustic (PA) and thermoacoustic (TA) imaging provide additional sources of contrast for cancer detection but are still mostly independent research tools not readily available in the clinic. The goal of this study was to develop and demonstrate advantages of a real-time trimodal imaging system that combines US, PA, and TA integrated into a commercial US system. Our trimodal system provided real-time feedback on near-infrared absorbing contrast agents, water content, and acoustic backscatter for structure, all important contrast features for accurate diagnostics and feedback during thermal therapy. Real-time video of the pumped Methylene Blue (MB, 0.025% in diH2O) was captured at a velocity resolution of 280 mm/s. Spectrally probed MB resulted in unique PA spectral responses, as well as qualitative images in false colors. Thermometry revealed a correlation between the PA and TA signal responses and MB temperature each with
$\mathrm{R}^{2}=0.99$
. By combining all three modalities, the system is capable of detecting different sources of contrast, including acoustic backscatter (US), optical (PA) and microwave (TA) absorption, and changes in temperature (PA and TA).