An Analysis on Various Techniques of Effective Microwave Imaging For Possibility of Earlier Breast Cancer Diagnosis |
Active microwave imaging is explored as an imagingmodality for early detection of breast cancer. When exposed to microwaves,breast tumor exhibits electrical properties that are significantly differentfrom that of healthy breast tissues. The two approaches of active microwaveimaging — confocal microwave technique with measured reflected signals andmicrowave tomographic imaging with measured scattered signals are addressedhere. Normal and malignant breast tissue samples of same person are subjectedto study within 30 minutes of mastectomy. Corn syrup is used as couplingmedium, as its dielectric parameters show good match with that of the normalbreast tissue samples. As bandwidth of the transmitter is an important aspectin the time domain confocal microwave imaging approach, wideband bowtie antennahaving 2:1 VSWR bandwidth of 46% is designed for the transmission and receptionof microwave signals. Same antenna is used for microwave tomographic imagingtoo at the frequency of 3000 MHz. Experimentally obtained time domain resultsare substantiated by finite difference time domain (FDTD) analysis. 2-Dtomographic images are reconstructed with the collected scattered data usingdistorted Born iterative method. Variations of dielectric permittivity inbreast samples are distinguishable from the obtained permittivity profiles. In this dissertation, an adaptive microwave concept isdemonstrated for breast cancer applications. The general approach is to detectand identify the tumor-specific resonance, determine the electrical location ofthe tumor, and apply the focused microwave hyperthermia using the identifiedresonance and the electrical location. The natural resonances vary depending onthe tumor size, shape, and breast tissue configuration. Therefore, an adaptivetuning of the microwave source to tumor-specific resonance frequencies couldimprove the overall efficiency of hyperthermia treatment by allowing for afaster and more effective heating to achieve a desired therapeutic temperaturelevel. Abstract: Early breast cancer detection can save thewomen infected by malignant tumors. Microwave imaging has recently beenproposed for detecting small malignant breast tumors at early stages. This typeof cancer is the top-most cause of death among women due to malignant tumors.The detection of early-stage tumors in the breast by microwave imaging ischallenged by both the moderate endogenous dielectric contrast between healthyand malignant glandular tissues and the spatial resolution available fromillumination at microwave frequencies. The high endogenous dielectric contrastbetween adipose and fibro glandular tissue structures increases the difficultyof tumor detection due to the high dynamic range of the contrast function to beimaged and the low level of signal scattered from a tumor relative to theclutter scattered by normal tissue structures. Microwave inverse scatteringtechniques, used to estimate the complete spatial profile of the dielectricproperties within the breast, have the potential to reconstruct both normal andcancerous tissue structures. However, the ill-posedness of the associatedinverse problem often limits the frequency of microwave illumination to theultra-high frequency (UHF) band within which early-stage cancers havesub-wavelength dimensions. This review presents the research status ofmicrowave imaging for malignant tumor detection.