Fig. 1. Breast photoacoustic images captured with representative breast cancer photoacoustic screening devices based on linear or planar ultrasound arrays. (a) Imaging results of DSM-2 developed by Professor Xia’s team^[28] (from left to right, image captured by the top probe of the device, image captured by the bottom probe, and the merged image are shown in turn); (b) fusion image of breast tumor ultrasound and blood oxygen saturation from a linear ultrasound array handheld breast photoacoustic imaging device jointly developed by Professor Li Changhui’s team and Mindray Corporation^[30]; (c) breast imaging results captured by PAM-02 jointly developed by Kyoto University and Canon Corporation^[33] (from left to right, ultrasound image, photoacoustic structural image, and photoacoustic functional image captured by the device are shown in turn)

Fig. 2. Representative photoacoustic screening devices for breast cancer based on curved or circular ultrasound arrays and breast photoacoustic images. (a) MSOT device schematic and imaging results^[39] (from left to right, the device photo and schematic, schematic of breast tissue structure, MSOT image of a healthy breast, and MSOT image of a breast tumor are shown in turn, with a scale of 5 mm); (b) SBH-PACT device schematic and breast images^[19] [from left to right, the cross-sectional view of the device, X-ray mammography image of a stage 2 infiltrating ductal carcinoma patient (RCC, right cranio-caudal; RML, right medio-lateral), depth-encoded photoacoustic image of the same breast (tumor outlined by white dashed line), photoacoustic image of breast sagittal plane, photoacoustic image overlaid with vascular density map, and photoacoustic elasticity imaging are shown in turn, with a scale of 1 cm]

Fig. 3. Schematics of representative photoacoustic screening devices for breast cancer based on a hemispherical ultrasound detection matrix and breast photoacoustic images. (a) LOUISA-3D device schematic and breast images^[41] (from left to right, the schematic of the device and coronal plane projection, sagittal plane projection, and horizontal plane projection of breast photoacoustic imaging are shown in turn); (b) schematic of multifunctional three-dimensional imaging system (left) developed by Professor Wang’s team and breast images (right)^[42] [from left to right, the system cross-sectional view after removing the imaging platform, vascular projection image of the breast (top) and vascular projection image of the breast lateral view (bottom), and cross-sectional images at different coronal planes from the nipple to the chest wall are shown in turn. Each cross-sectional image represents a projection of a 1 cm thick slice of the breast]

Fig. 4. Representative results of photoacoustic diagnosis of breast tumors. (a) Imagio^TM breast photoacoustic imaging device developed by Seno Medical, USA (left), ultrasound image (middle) and photoacoustic-ultrasound fusion image (right) of a patient with triple-negative invasive ductal carcinoma^[46]. Ultrasound imaging shows that the mass was grade 3 BI-RADS, but the ultrasound-photoacoustic fusion image shows a high content of deoxygenated hemoglobin inside the tumor. The tumor boundary zone (arrow), radioactive peripheral artery (green), and vein (red, arrow) also show abundant hyperplastic vessels, so the BI-RADS 3 assessment was correctly upgraded to 4a or 4b. (b) PAM-2 imaging device developed by Prof. Srirang Manohar’s team (left), the photoacoustic lateral projection (middle) and sagittal projection (right) of a mucinous carcinoma patient^[56], with the blue dotted line indicating the location of the tumor, with a scale of 20 mm. (c) Imaging results of the PAM-03 device jointly developed by Kyoto University and Canon Corporation on on a patient with inflammatory breast cancer with a tumor diameter of 47 mm^[57]. The left image shows the enhanced MRI image with the lesion circled in red, the middle image is the original photoacoustic image, and the right image is a fusion image of photoacoustic (cyan) and MRI (red) images. Angiogenesis of the tumor microenvironment mostly converges from normal breast tissue to the center of the tumor, becomes very narrow at the edge of the tumor, and gradually decreases near the center. (d) Photoacoustic-ultrasound imaging system guided sentinel lymph node puncture biopsy^[63]. The left picture is the ultrasound image, in which the sentinel lymph node contrast is low, the middle picture is the photoacoustic real-time image, in which the biopsy needle and the sentinel lymph node are clearly visible, and the right picture is the superposition of ultrasound and photoacoustic images in the same image coordinate system. Both ultrasound and photoacoustic imaging jointly guide the sentinel lymph node biopsy

Fig. 5. Photoacoustic imaging to evaluate the therapeutic efficacy of breast tumors. (a) Human breast images acquired before and after neoadjuvant chemotherapy using photoacoustic (left) and contrast-enhanced MRI (right)^[40] (compared with contrast-enhanced MRI, photoacoustic imaging provides a higher level of vascular structural detail in 15 s without contrast injection, in which associated structures are marked with white arrows); (b) ultraviolet photoacoustic images of a fixed and unsectioned breast tumor sample (top) and histopathological images of H&E staining obtained after sectioning and staining^[73], in which the blue dotted line represents the boundary between normal tissue and tumor area ( IDC: invasive ductal carcinoma; DCIS: ductal carcinoma in situ)