| Breast cancer is one of the most dangerous malignant tumors of middle-aged and older women in the world. In the latest twenty years, the incidence and mortality of breast cancer in China increase rapidly. Techologies for early breast cancer detection have been eagerly desired for years.A multichannel photon counting system is designed for breast dynamic diffuse optical tomography (DOT) which adopts continuous-wave (CW), based on photon counting mode. Our prototype is eight channels and adopts extendable interface with PC.The research work in the paper mainly includes the following three parts:1. The principium of diffuse optical tomography is introduced in detail, including the optical properties of tissue, the theories of mammography, three measurement modes of DOT system, and the technologies for faint light detecting.2. Based on the deliberate analysis of the detection equipment, we establish the measurement system which contains steady optic source, 1:8 optical switch, tapered breast, optoelectronic detector, amplifier, discriminator with threshold, shaper, eight channels counters system and extendable PC interface.3. The design of eight channels counters system and the universal serial bus (USB) 2.0 is completed, including their hardware and software. The width of the measurement gate (τ) can be changed from 50 microseconds to about 10 seconds, and correspondingly the total temporal span of the measurement ranges from several milliseconds to minute. The amount of gates (M) is 1~8192.Pre-evaluation of the system:The limit of gate widthτmin is 37μs, whileτmax is about 4.5min. The highest electronic counting frequency is about 50MHz. The lowest resolution of electronic pulse is about 20ns.Conclusion:USB2.0 communication is tested in order to verify the reliability of data transfer. The speed of bulk transmission is 85.1 Kbyte/s. |
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