| dc.description.abstract | Breast cancer is one of the most common cancers among women, and the incidence rate is increasing year by year. However, the statistical report shows that the survival rate of early breast cancer (stages 0 to 2) is higher than 90%, indicating the importance of early diagnosis and treatment of breast cancer. Existing clinical testing equipment, such as: X-ray mammography, Ultrasound and Magnetic Resonance Imaging, have radiation doubts, highly depending on operator’s skill, expensive price or restrictions on applicable objects. Therefore, frequency-domain near-infrared frequency domain diffuse optical tomography (NIR FDOT), which has the advantages of non-radiation, non-invasiveness, and can be adapted on broad age range, recent year it has become a popular research object.
The NIR FDOT is applying 25 - 1000 MHz AC power to drive 700 - 900 nm near-infrared light to measure the object (such as breasts), and uses a light receiver (such as a photomultiplier tube) to receive the light information comes out from the surface of the object, that is the amount of light attenuation (ΔA) and phase delay (Δθ) due to the difference between the absorption and scattering characteristics of tumor tissue and normal tissue. Using more frequencies to drive the light source can obtain more sets of light information, and it is expected to improve the quality of the reconstructed image, but it also increases the detection time due to sequential measurement. This thesis is based on the method of driving the light source with multiple frequencies, yet in the experiment, the function generator (AFG3102) is used to outputs a 29 MHz square wave to drive a 830 nm laser, measuring 80 mm in diameter, 90 mm in height cylindrical optical phantoms, its ＂μa＂ and ＂μs′ ＂ are 0.0074 mm-1 and 0.85 mm-1, embedding ellipsoid tumor phantoms of different sizes and contrasts of optical coefficients in columns with the same optical coefficients as the background phantom. There are four cases in which the off center distance of tumors of different sizes and contrasts is changed in a plug-in manner. Since the square wave is a characteristic of a composite sine wave, it can obtain several times light information compared to a single-frequency driving light source at the same measurement time. In the experiment, the optical information of the first two harmonic frequencies is collected, and using developed reconstructing software to reconstruct optical distribution images of ＂μa＂ and ＂μs′ ＂ inside the cylindrical phantom, and quantified by CSD value. The reconstructed images of the square wave and the single frequency drive light source were compared. Expected CSD value of large tumor will be higher than small one; and the CSD value of the tumor placed shallow will higher than the one in deep; the CSD value of high frequency measurement should be higher than low frequency measurement; the CSD value of square wave measurement should be higher than both high and low single frequency measurement. As a result, it can be found that the square wave output by the signal generator is not an ideal form, also some restrictions of equipment, so that the square wave measurement has no significant effect. It is expected that the composite periodic signal driving light source measurement can be applied and improved the result in the future. | en_US |