<p>Optoacoustic (OA) imaging was employed to distinguish normal from neoplastic tissues in a transgenic murine model of prostate cancer. OA images of five tumor-bearing mice and five age-matched controls across a <strong>14 mm</strong>×<strong>14 mm</strong> region of interest (ROI) on the lower abdomen were acquired using a reverse-mode OA imaging system (Seno Medical Instruments Inc., San Antonio, Texas). Neoplastic prostate tissue was identified based on the OA signal amplitude in

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... with spectral analysis of the OA radio frequency (RF) data. Integration of the signal amplitude images was performed to construct two-dimensional images of the ROI. The prostate tumors generated higher amplitude signals than those of the surrounding tissues, with contrast ratios ranging from 31 to 36 dB. The RF spectrum analysis showed significant differences between the tumor and the control mice. The midband fit was higher by 5 dB (62%), the intercept higher by 4 dB (57%) and the spectral slope higher by <strong>0.4 dB</strong>/<strong>MHz</strong> (50%) for neoplastic prostate tissue compared to normal tissues in the control mice. The results demonstrate that OA offers high contrast imaging of prostate cancer in vivo. </p>