A Wideband Microwave Tomography System With a Novel Frequency Selection Procedure

Abstract

In this paper, we describe a 2-D wideband microwave imaging system intended for biomedical imaging. The system is capable of collecting data from 3 to 6 GHz, with 24 coresident antenna elements connected to a vector network analyzer via a 2 x 24 port matrix switch. As one of the major sources of error in the data collection process is a result of the strongly coupling 24 coresident antennas, we provide a novel method to avoid the frequencies where the coupling is large enough to prevent successful imaging. Through the use of two different nonlinear reconstruction schemes, which are an enhanced version of the distorted born iterative method and the multiplicative regularized contrast source inversion method, we show imaging results from dielectric phantoms in free space. The early inversion results show that with the frequency selection procedure applied, the system is capable of quantitatively reconstructing dielectric objects, and show that the use of the wideband data improves the inversion results over single-frequency data.

Permittivity Profile Estimation Based on Non-Radiating Equivalent Source (2d Case)

“…In comparison with MRI, CT scanner is an obvious choice for dental radiology [14], but high required dose of ionizing radiation to one's head is an important concern [32]. Threedimensional terahertz pulse imaging is another approach, which has its own challenges and difficulties [15], particularly for the large size tooth samples [11]. Three-dimensional terahertz continuous wave imaging [15] and pulse imaging [28] have been used for very low contrast objects.…”

“…Threedimensional terahertz pulse imaging is another approach, which has its own challenges and difficulties [15], particularly for the large size tooth samples [11]. Three-dimensional terahertz continuous wave imaging [15] and pulse imaging [28] have been used for very low contrast objects. However, since these image reconstruction approaches are based on filter back projection (the scattered field or beam diffraction is ignored), the approaches can not be applied to the high-contrast objects or low-contrast objects, particularly with the large size one.…”

“…The Born approximation initial guess has frequently been used to linearize the electromagnetic inverse scattering problem [8,15,16,20,[33][34][35]. This is a good initial estimate for the field inside a low-contrast scatterer as long as the scatterer size is a fraction of a wavelength [15].…”

“…This initial guess eases the formulation of the inverse scattering problem. However, the Born approximation initial guess was found in [15] to be a problematic assumption for a large size object (large in terms of wavelength).…”

“…The resulting linear equation can be solved for the radiating part of VECS by means of the pseudo-inverse, mean square error [22,27,31], singular value decomposition (SVD) [25], regularization, statistical [1,5], or Fourier (holography) [37] based approaches. Initializing the internal total electric field with the incident field in the first iteration transforms the forward scattering problem into a linear equation [8,15,16,[33][34][35].…”