## 5 Discussions and Conclusions  
In this project, the breast model was rapidly collected from a series of angles to obtain data from different perspectives. The vertical slices and horizontal slices could be reconstructed retrospectively and the 3D image could be further processed and displayed. The detection of the size, position and shape of different masses was realized with the minimum size of 1 cm. Even the image of the injection pinhole could be seen. Furthermore, each perspective image had its own characteristics. For the vertical slice, the image had a uniform resolution and was relatively easy to obtain. However, it required a  
Figure 10: Ultrasonic vertical tomography images using this setup. (**a**) Angle = 24\({}^{\circ}\). (**b**) Angle = 64\({}^{\circ}\). (**c**) Angle = 96\({}^{\circ}\). (**d**) Angle = 164\({}^{\circ}\). (**e**) Angle = 196\({}^{\circ}\). (**f**) Angle = 258\({}^{\circ}\).  
Figure 9: Ultrasonic horizonal tomography images using this setup. (**a**) Slice N = 2. (**b**) Slice N = 15. (**c**) Slice N = 25. (**d**) Slice N = 40. (**e**) Slice N = 50. (**f**) Slice N = 72.  
larger detection depth. To some extent, the transmitter frequency of the transducer was limited. As for the horizontal slice, the algorithm was relatively complex, with the internal resolution higher than the edge, which is more suitable for the detection of breast deep mass. Meanwhile, it can reduce the demand for transducer detection depth. Thus, it is beneficial to the application of high frequency probes. The 2D slice sequence diagnosis requires more experience for the operator, whereas the information of the breast model and the masses can be shown intuitively through 3D imaging. Therefore, masses can be comprehensively detected from different perspectives and this approach will help to improve the specificity and sensitivity of ultrasonic diagnosis. However, it is still difficult to differentiate between benign over growths in breast tissue (or even calcifications) from malignant tumors. The mechanical and elastic changes in cancerous tissues result in higher density and sound velocity in breast cancer. Mean values of the sound velocity are as follows: fat, 1478 m/s; glandular breast, 1510 m/s; benign breast tumors, 1513 m/s; and malignant breast tumors, 1548 m/s [30]. These data manifest that breast density can be assessed by sound velocity and attenuation. Thus, the multi-perspective imaging technology convergence sound velocity and attenuation imaging algorithm will help with the more specific detection of breast lesions. Meanwhile, the improvement in the sensitivity depends on the study of high density integrated ultrasonic transducer arrays. These methods will overcome the roadblocks in using this approach in the clinic along with biopsies for the breast cancer diagnosis, which will be helpful to reduce the retest rate and improve its accuracy.  
This work was supported by the National Key Research and Development Project under Grants 2016 YFC0101900 and 2016 YFC0105004 and was sponsored by the Fund for Shanxi '1331 Project' Key Subject Construction.  
Methodology, C.L.; Software, Y.C.; Formal Analysis, C.L.; Investigation, G.Z.; Data Curation, C.L.; Writing-Original Draft Preparation, C.L.; Writing-Review & Editing, W.Z.; Supervision, C.X. and B.Z.; Funding Acquisition, B.Z., C.Z. and G.Z.  
The authors declare no conflict of interest.