| Breast cancer is a common malignant tumor,which seriously threatens women's health and even life safety.The early detection and treatment can reduce significantly the morbidity and improve the survival rate after operations,so they have become the main methods to cope with the breast cancers.As a new type of optical functional imaging technology,diffused optical tomography(DOT)has much potential in benign and malignant analysis and the diagnosis of the early breast tumors.In this paper,a multi-wavelength steady-state DOT system is established for early detection of breast tumors.The light source module,phase-lock photon-counting module and measurement controlling module are designed and implemented.The details are shown below.Firstly,the near-infrared lasers working at wavelengths of685 nm,785 nm and 830 nm are used as light sources.The constant power driving circuits are designed to drive the laser diode(LD)to output stable light.Secondly,a single photon counting technology is combined with a lock-in technique to effectively detect the weak light.Four square wave signals of different frequency are chosen to realize 4 channels in one group parallel measuring and time-sharing switch of 8groups of channels.Based on this,the system balances both the cost and the measuring efficiency and implements high sensitivity,high signal-to-noise ratio counting function.(3)The control to the automatic measurement process of the system and the demodulate counting of the mixed frequency signal are designed and realized based on FPGA.The switching of the detector optical switch and the measurement and preservation of the number of photons in each channel are completed by the cooperation between LabVIEW and slave computer.To investigate the performances of the system,some phantom experiment are conducted using the LD working at the wavelength of 785 nm.The results demonstrate that the system can reconstruct the correct positions and sizes of the targets. |
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