# Photoacoustic Imaging for Management of Breast Cancer: A Literature Review and Future Perspectives
## 3 Results
### Endogenous Contrast Agents
#### 3.1.4 In Vivo Studies
[PERSON] et al. [73] developed a 3D PA imaging system at 756 nm using a spherical detector aperture with 512 detectors with rectilinear scanning. They claimed that the system parameters of this 3D breast imaging system were sufficient enough to accommodate up to 90% of the breast volumes in the United States. [PERSON] et al. [107] developed a dual-modality PAT-US Imaging system at 650 nm and 1064 nm and tested its performance on sixteen patients. They found that clinically negative nodes in the axilla were observed in twelve patients, and clinically positive lymph nodes were observed in four patients. Their dual mode PA-US imaging system acted as a real-time imaging technology for SLN biopsy  
Figure 2: Comparison of PA imaging with X-ray mammograms. (**Left**): cranio-caudal (CC) X-ray mammogram; middle: PA images were overlaid on CC X-ray mammograms to show lesions in both modalities; (**Right**): detailed 3D representation of the lesion of interest. (**a–c**): Case 1, a 79-year-old patient with IDC, (**d–f**): Case 2, a 79-year-old patient with IDC, (**g–i**): Case 3, an 83-year-old patent with MC, and (**j–l**): Case 4, a 65-year-old patient with ILC. PXX indicates patient identifier used in this study. Reproduced from [PERSON] et al. [35], which is distributed under the terms of the Creative Commons Attribution-Non Commercial4.0 International License ([[http://creativecommons.org/licenses/by-nc/4.0/](http://creativecommons.org/licenses/by-nc/4.0/)]([http://creativecommons.org/licenses/by-nc/4.0/](http://creativecommons.org/licenses/by-nc/4.0/))). (SLNB) in locating the SLN first and then guiding the needle for lymph node sampling. As shown in Figure 3a,b, the respective US and PA images revealed the SLN and the needle used to insert the titanium marking clip. Figure 3c shows the co-registered PA-US image, which revealed the capability of this dual mode technology to locate the lymph nodes through anatomical features provided by US image as well as to verify the lymph node as sentinel through the PA image. The experimental results of this study showed that this system could detect SLNs and lymphatic vessels using methylene blue dye and also it could eliminate the need for invasive axillary staging procedures. [PERSON] et al. (2016) developed a 3D PA imaging system using a full ring 512-element ultrasonic transducer array, and conducted a pilot study on eight patients with this system. In one patient, they could detect a tumor, which was located at a depth of \(\sim\)32 mm. The spatial resolution of this system was 255 \(\upmu\)m while the scanning time, which was approximately 15 s, was within a single breath. This system acquired images of seven breast cancer patients with breast sizes ranging from B cup to DD cup, which could accommodate 99% of the U.S. population. [PERSON] et al. (2018) evaluated the performance of their prototype machine (PAM-01) at 1064 nm, 825 nm, 797 nm, and 756 nm on 27 breast cancer lesions. From the measurements, they found that this system could give images of tumor vasculature and oxygenation, which could not be obtained either with X-ray mammography or US imaging. They also found that the PAM tumor images were comparable to that of MRI at relevant depths. Using the same prototype machine (PAM-01), [PERSON] et al. (2019) successfully visualized 29 out of 39 lesions. They claimed that the vascular and oxygenation data obtained by this system represent a new, non-invasive imaging method that could potentially provide functional features of breast tumors. [PERSON] et al. (2017) developed a second generation prototype PAM (PAM-02) at 756 nm and 797 nm to simultaneously acquire PA and US images. They found that, unlike PAM-01, PAM-02 exhibited better PA image quality and improved spatial resolution from 2 mm to 1 mm. [PERSON] et al. (2018) developed a PA imaging system (PAM-03) at 755 nm and 795 nm with a hemispherical detector array and tested its performance on 22 malignant cases. High-resolution 3D images obtained with this system showed finer vasculature.