Co-registered ultrasound Doppler with ultrasound and photoacoustic imaging to improve delineation of ovarian lesion for photoacoustic imaging

Ovarian cancer has the highest mortality rate among all other cancers related to reproductive system. We have developed co-registered ultrasound (US) and photoacoustic tomography (PAT) technique (US/PAT) for non-invasive diagnosis of ultrasound identified ovarian tissue. Ultrasound images provide structural information of human ovary and PAT provides information of blood vasculature and oxygen saturation inside the ovary. However, due to the lower contrast of transvaginal US images, it is not always easy to delineate the ovaries from the surrounding tissue, especially postmenopausal ovaries. Doppler US can identify large vessels around or inside the ovary if exist and also large celiac vessels which are often in the neighborhood of ovaries. If the region of interest (ROI) includes the surrounding celiac vessels, the tumor total hemoglobin and blood oxygen saturation cannot be quantified correctly. To optimize the selection of ROI for co-registered PAT imaging, we have developed co-registered display of Doppler US, ultrasound and photoacoustic for near real-time ovarian tissue diagnosis. Doppler images provide blood flow information of large vessels and assist co-registered gray-scale US to identify ROI. PAT maps out the total hemoglobin and oxygen saturation distributions. Data for Doppler imaging is collected using our customized commercial US machine which can simultaneously save US/PAT RF data. US RF data is used to reconstruct ultrasound and Doppler images. Conventional cross correlation technique assisted by advance image processing techniques is used to compute Doppler images. We report examples of how these co-displayed images help improve PAT mapping of tumor angiogenesis and oxygen saturation using phantom data.