ObjectiveTo assess the impact of photoacoustic imaging (PAI) on improving ultrasound (US) O‐RADS assessment in women undergoing oophorectomy who have an adnexal lesion(s) suggestive of malignancy.MethodThis prospective study enrolled women referred for oophorectomy. Participants underwent clinical US followed by co‐registered US and photoacoustic imaging (PAI) before oophorectomy. Each ovarian/adnexal lesion was graded by two radiologists using the US O‐RADS scale. PAI was used to compute relative total hemoglobin concentration (rHbT) and blood oxygenation saturation (%sO2) maps in the region of interest. Lesions were categorized by histopathology into malignant ovarian/ adnexal lesion, malignant fallopian tube, and several benign categories to assess the impact of PAI in assisting O‐RADS for risk assessment. rHbT and %sO2 were compared between malignant and benign histologic groups using a one‐way ANOVA test followed by a post‐hoc Dunnett test of significance. Logistic‐regression models were developed based on tumor marker CA125 alone, US‐based O‐RADS alone, PAI rHbT and %sO2. AUC under ROC was used to compare the diagnostic performance of the models.ResultsThere were 93 lesions among 68 women (mean age 52 years, range 21–79). Surgical pathology revealed 14 patients with malignant ovarian/ adnexal lesions, 2 patients with malignant fallopian tubes, and 52 patients with benign findings. rHbT was significantly different between malignant lesions and benign cases; %sO2 was lower in malignant lesions, but not statistically significant in all benign categories. Feature analysis revealed that rHbT, O‐RADS, CA125, and %sO2 were the most important predictors of malignancy. Logistic‐regression models revealed AUC=0.79 (95% CI: 0.626‐0.953) for CA125 alone, AUC=0.86 (95% CI: 0.732‐0.981) for O‐RADS only, AUC=0.88 (95% CI: 0.7596‐1) for CA125 and O‐RADS, AUC=0.90 (95% CI: 0.815‐0.985) for rHbT and %sO2. A model utilizing all four features (CA125, O‐RADS, rHbT, and %sO2) achieved a superior performance of AUC=0.97 (95% CI: 0.932‐1) with sensitivity of 100% and specificity of 82%.ConclusionsThe additional PAI rHbT and %sO2 information significantly improved the US O‐RADS in the accurate diagnosis of adnexal lesions.This article is protected by copyright. All rights reserved.