Given that breast cancer is the second leading cause of cancer-related deaths among women in the United States, it is necessary to continue improving the sensitivity and specificity of the breast imaging systems that diagnose breast lesions. Photoacoustic (PA) imaging has been shown to provide functional information during in-vivo studies and can augment the structural information provided by ultrasound (US) imaging. Our research demonstrated a novel PA tomography (PAT) imaging system based on a full-ring, breast encircling, illumination source and a full-ring US receiver. In addition, we compared the full-ring illumination with single point illumination system. Our findings show that full-ring illumination increases the uniformity of the PA signals with respect to the depth of the object image and has great potential for future beast imaging.