Implementation of a fast simulation tool for the analysis of contrast mechanisms in HMMDI and enhancement of the SNR in the experimental set-up

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2021-9-06
İrgin, Ümit
Clinical method for breast tumor detection is Mammography (X-rays), which have limitations and may yield inaccurate results. Alternative novel techniques are required to characterize the breast tissues and extract accurate information for identification of malignancies in the tissue. Harmonic Motion Microwave Doppler Imaging (HMMDI), which enhances hybridizing microwave signals and ultrasound techniques, has been recently proposed for detection of tumors in the tissue. In HMMDI method, the data is a combination of dielectric, elastic and acoustic properties of the focused volume. The contrast levels in the dielectric and elastic properties of the malignant and normal breast tissues enable the detection of the tumorous tissues. However, the level of the received Doppler signal is not a linear function of the contrast levels, especially for the mechanical properties. In this study, the effect of contrast in the dielectric and elastic properties between a 3 mm sized inclusion and the surrounding breast as functions of position of the inclusion and vibration frequency (in 10 Hz to 95 Hz range) is analyzed. To solve the forward problem of HMMDI, a Discrete Dipole Approximation (DDA) based simulation method is developed. DDA solver decreased the simulation time by a factor of 146 compared to the Finite Difference Time Domain method. Increasing the dielectric constant by a factor of 3.2 increased the received signal by 5.1 dB in the whole vibration frequency range. On the other hand, increasing the Young’s modulus by a factor of 3.3 resulted in 1 dB and 2.5 dB decrease in Doppler signal level for vibration frequencies of 40 Hz and 95 Hz, respectively. When the focus was moved away from the inclusion, dielectric and\or elastic contrast variation did not change the relative received signal level significantly. The simulation results showed that the received signal level behavior as a function of vibration frequency can provide useful information on the elastic properties of the inclusion. In the HMMDI experimental set-up there are two main limitations on the sensitivity of the method: i) the phase noise of the transmitter source and ii) the coupling between transmitting and receiving antennas. In this study, a signal cancellation circuit is designed to suppress the coupled signal and to increase the signal to noise ratio (SNR) of the Doppler component. The transmit signal coupled to the receiving antenna was decreased more than 30 dB, enhancing the SNR about 17 dB. Hard inclusions inside a fat phantom were resolved using the HMMDI system with the proposed signal cancellation circuit.

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Citation Formats
Ü. İrgin, “Implementation of a fast simulation tool for the analysis of contrast mechanisms in HMMDI and enhancement of the SNR in the experimental set-up,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.