While PAT has been shown so far to be particularly powerful in imaging vasculatures and tissue-absorption related parameters such as hemoglobin and oxygenation, PAT has limitations. For example, PAT can provide high-quality images only for certain sizes of targets due to the limited detection band of an ultrasound transducer. It is difficult to accurately detect a relatively large size target (e.g., ≥ 6 mm) using a typical ≥1 MHz transducer. In addition, the limited directivity of a transducer may lead to imbalanced image quality for the entire imaging area/volume. Yet, it still remains a major challenge for PAT to recover tissue-scattering coefficients, an important parameter for breast cancer detection (Jiang 2010).