Photoacoustic tomography is a recently developed imaging modality that can provide high spatial-resolution images of
hemoglobin distribution in tissues such as the breast. Because
breast cancer is an angiogenesis-dependent type of
malignancy, we evaluated the clinical acceptability of breast tissue images produced using our first prototype photoacoustic mammography (PAM) system in patients with known
cancer. Post-excisionally, histological sections of the
tumors were stained immunohistochemically (IHC) for CD31 (an endothelial marker) and
carbonic anhydrase IX (CAIX) (a marker of
hypoxia). Whole-slide scanning and image analyses were used to evaluate the
tumor microvessel distribution pattern and to calculate the total vascular perimeter (TVP)/area for each lesion. In this clinical study, 42 lesions were primarily scanned using PAM preoperatively, three of which were reported to be benign and were excluded from statistical analysis. Images were produced for 29 out of 39
cancers (visibility rate = 74.4%) at the median depth of 26.5 (3.25-51.2) mm. Age, menopausal status, body mass index, history of
neoadjuvant treatment, clinical stage and histological
tumor angiogenesis markers did not seem to affect the visibility. The oxygen saturation level in all of the measured lesions was lower than in the subcutaneous counterpart vessels (Wilcoxon test, p value<0.001), as well as in the counterpart contralateral normal breast region of interest (ROI) (Wilcoxon test, p value = 0.001). Although the oxygen saturation level was not statistically significant between CAIX-positive vs. -negative cases, lesional TVP/area showed a positive correlation with the oxygen saturation level only in the group that had received
therapy before PAM. In conclusion, the vascular and oxygenation data obtained by PAM have great potential for identifying functional features of
breast tumors.