We have conducted a pilot study to image and characterize ovarian masses using a co-registered ultrasound (US) and photoacoustic imaging (PAI) system. A total of seven patients who have ovarian masses and scheduled for surgical removal of both ovaries and Fallopian tubes, has enrolled to the study. A standard transvaginal US probe is used first to locate ovarian masses, measure ovary sizes in long and short axises . Then a second probe with four light-delivery fibers surrounded the US probe is inserted transvaginally to perform co-registered US and photoacoustic imaging in real-time with four optical wavelengths (730, 780, 800 and 830 nm). For the total of 7 patients, one patient had high-grade serous carcinoma involving both ovaries, one patient had a 2.2 cm endometrioid adenocarcinoma in right ovary, one patient had metastatic appendiceal adenocarcinoma involving both ovaries, one patient has serous borderline carcinoma involving both ovaries and the rest three patients had either abnormal or benign ovaries. For the malignant ovaries, photoacoustic images have showed significantly higher signal levels as quantitatively evaluated from maximum signal strengths from region-of-interest identified by co-registered US. Additionally, the quantitative features extracted from co-registered US and photoacoustic images, such as spectral slope, mid-band fit and zero MHz intercept, spatial heterogeneity of PAI distribution, the blood oxygen saturation, have showed significant differences between malignant and benign ovaries. Our initial results have demonstrated that photoacoustic imaging has a great potential to aid transvaginal US to quantitatively and effectively image and diagnose ovarian cancer.
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