# Photoacoustic Imaging for Management of Breast Cancer: A Literature Review and Future Perspectives
## 4 Discussion
### Questions Raised by [PERSON]'s Research Group and Answers  
For the successful translation of a new imaging modality from the laboratory environment to the clinical environment, researchers have to provide answers, supported by experimental evidence, to certain questions related to the role and utility of the imaging technology for detection and diagnosis of particular diseases. [PERSON] et al. [127] identified some important questions to evaluate the utility of using PA technology in the clinical environment for imaging of breast cancer. In this subsection, we summarized the experimental evidence, obtained so far by the different groups to answer the questions raised by [PERSON] et al. [127]. _Question 1: What are the PA appearances of different varieties of breast cancer such as IDC, ILC, DCIS, and fibroadenoma?_  
An in vivo study reported that the centripetal blood vessel structure was observed in the PA images of IBC cases, whereas intratumoral spotty signals were observed in the PA images DCIS cases. In another in vivo study, appearance of IDC lesions in the PA images were divided into three categories, namely mass, non-mass, and ring structures. Details of these two studies were described below. In their in vivo study, [PERSON] et al. [39] selected five markers related to the vasculature in the detected lesion and on the basis of the presence of these five markers, compared the PA images of patients suffering from IBC with the PA images of DCIS patients. According to their findings, there was a significant difference of centripetal vasculature between the PA images of IBC patients and that of DCIS patients. An example of MR, PA, and their fused images of a 40-year-old woman with IBC, shown in Figure 5a-d, demonstrates the centripetal vasculature. Centripetal vasculature refers to vasculature which tends to converge towards the center of the tumor from the normal breast tissue. In this, the blood vessels tend to become rapidly narrowing at the periphery of the tumor and they seem to be almost vanishing at the center of the tumor. They also observed, although there was no statistical significance, that PA images of IBC cases contained more intratumoral vasculature-like linear signals, while PA images of DCIS cases contained more intratumoral spotty signals. In the in vivo PA imaging study conducted with primary patients suffering from IDC, [PERSON] et al. [25, 35] observed that appearances of the lesions in the corresponding PA images generally fall into three categories namely'mass or confined', 'non-mass or scattered', and 'ring'. [PERSON] et al. [39], observed that the PA images of five patients with DCIS contained intratumoral spotty signals as shown in Figure 5e-h for a 46-year-old woman with DCIS, while the PA images of 17 patients with IBC contained centripetal blood vessel structure as shown in Figure 5a-d for a 40-year-old woman with IBC and intratumoral vasculature-like linear signals. [PERSON] et al. [25, 35] reported that the PA images of breasts with IDC contained mass, non-mass, and ring-like structures. However, due to the small number of cases reported in these two studies, generalized comments on the specific PA markers corresponding to different types of breast cancer is not possible. _Question 2: What are the pathophysiological factors behind the PA signatures of the breast cancer and whether the PA signatures can be related to angiogenic or vasculature distribution? Can these PA signatures be used for breast cancer diagnosis?_  
Some studies have identified different patterns of vasculatures associated with different types of cancers and patients behind different PA signatures. However, the diagnostic capabilities of these PA signatures were not evaluated in these studies. [PERSON] et al. [25] compared the PA images of some of the breast cancer patients with the corresponding histopathology images. For the three cases with PA'mass' appearance, they observed that the vasculature was spread throughout the lesion from the corresponding CD31 histopathology.