Time-Domain Wideband Adaptive Beamforming for Radar Breast Imaging

Abstract

A novel wideband microwave radar imaging method is presented to detect regions of significant dielectric contrast within the breast. Clutter reduction is paramount to any radar imaging algorithm, especially with clinical patient data where the tissue composition of the breast is inhomogeneous. Time-domain Data-Adaptive imaging methods have been previously applied in a narrowband manner for microwave radar breast imaging when the received signal spectral content was wideband. In this study, a wideband time-domain adaptive imaging approach is presented to perform Data-Adaptive focusing across the spectrum to reduce clutter. An equalisation filter is adapted to compensate for the propagation distortion through tissue using a calculated estimate of the average dielectric properties of the breast. The effectiveness of the proposed wideband adaptive imaging approach is evaluated in conjunction with the Delay-And-Sum (DAS) method using numerical, experimental and clinical data. Target scatterers are clearly detected while clutter levels are reduced significantly, between 4 and 6 dB, when compared to the DAS technique. Index Terms-Microwave Imaging, Biomedical Radar Imaging, Ultra-Wideband, Beamforming0018-926X (c)

Compound Radar Approach for Breast Imaging

“…The authors have previously used angles between ten and fifteen degrees as the skin contour will rarely be perfectly hemispherical and experience has shown that larger rotation angles can result in inadequate skin reflection suppression. A Peak/Mean ratio is presented to aid in comparing methodologies where the peak energy voxel is compared to the average energy within the imaged 3D space [22]. T W in is set to 0.7ns for both the compound imaging approach and the differential DAS method in each phantom experiment.…”

“…Prior to the insertion of the breast or phantom, more of the matching liquid is applied to ensure there are no air gaps present. This setup has been discussed in detail in previous studies [22], [26]. The relative permittivity and conductivity of the liquid is 9.3 and 0.22 S/m, respectively at 6 GHz and the ceramic cup has a relative permittivity of 10 and a loss tangent of 0.0005.…”

“…Once the targets are positioned in the phantom, the volume is filled with the matching liquid to represent fatty tissue. The dispersive characteristic plot of the dielectrics discussed above are given in [22].…”

“…However, the scattering response from within the breast also becomes distorted in the process as twin targets are often reconstructed from single scatterers and significant targets located near the axis of rotation are often eliminated. Radar images can be created using data-dependent [21], [22] or dataindependent [23]- [26] receive beamforming methods.…”

A Directional Antenna in a Matching Liquid for Microwave Radar Imaging

“…BMR approaches are currently being tested in midscale clinical trials and the goal is to detect breast lesions of at least 4 mm. Although progress in image resolution and 3D imaging and faster data acquisition have been made [8][9][10], hardware design and imaging algorithm still require improvements if this technology is to be used for routine clinical use. In particular, the antenna design is important, because the antenna directs the signal to the breast to be imaged, while antennas or other sensors receive the scattered signal.…”