3D parallel-detection microwave tomography for clinical breast imaging

Abstract

A biomedical microwave tomography system with 3D-imaging capabilities has been constructed and translated to the clinic. Updates to the hardware and reconfiguration of the electronic-network layouts in a more compartmentalized construct have streamlined system packaging. Upgrades to the data acquisition and microwave components have increased data-acquisition speeds and improved system performance. By incorporating analog-to-digital boards that accommodate the linear amplification and dynamic-range coverage our system requires, a complete set of data (for a fixed array position at a single frequency) is now acquired in 5.8 s. Replacement of key components (e.g., switches and power dividers) by devices with improved operational bandwidths has enhanced system response over a wider frequency range. High-integrity, low-power signals are routinely measured down to -130 dBm for frequencies ranging from 500 to 2300 MHz. Adequate inter-channel isolation has been maintained, and a dynamic range >110 dB has been achieved for the full operating frequency range (500-2900 MHz). For our primary band of interest, the associated measurement deviations are less than 0.33% and 0.5° for signal amplitude and phase values, respectively. A modified monopole antenna array (composed of two interwoven eight-element sub-arrays), in conjunction with an updated motion-control system capable of independently moving the sub-arrays to various in-plane and cross-plane positions within the illumination chamber, has been configured in the new design for full volumetric data acquisition. Signal-to-noise ratios (SNRs) are more than adequate for all transmit/receive antenna pairs over the full frequency range and for the variety of in-plane and cross-plane configurations. For proximal receivers, in-plane SNRs greater than 80 dB are observed up to 2900 MHz, while cross-plane SNRs greater than 80 dB are seen for 6 cm sub-array spacing (for frequencies up to 1500 MHz). We demonstrate accurate recovery of 3D dielectric property distributions for breast-like phantoms with tumor inclusions utilizing both the in-plane and new cross-plane data.

Electrical Characterization of Glycerin: Water Mixtures: Implications for Use as a Coupling Medium in Microwave Tomography

“…The antenna array is moved vertically to acquire data at multiple planes of the object. Each antenna operates as both as transmitter and receiver, and data are typically collected at seven frequencies from 700 to 1900 MHz in 200 MHz increments [15]. In terms of patient imaging, glycerin is ideal as a potential coupling fluid because it is non-toxic and bacteria static, and presents no health risks.…”

“…To accommodate extra signal loss, we developed a custom measurement system which has a noise floor of -140 dBm for a 0 dBm transmit signal and channel-to-channel isolation also on the order of 140 dB [15]. At our highest frequency of operation (~1900 MHz), measured signals range from -50 to -120 dBm during a typical breast exam, which implies the signal to noise ratio (SNR) ranges from 90 dB for antennas closest to the transmitter to 20 dB for those furthest away (and on the opposite side of the breast from the transmitter).…”

“…The approach is advantageous for transmission systems. For example, antenna bandwidth is broadened considerably because of the resistive loading [13]; however, large dynamic range is needed in the measurement system [14],[15]. …”

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.…”

A Novel Time Reversal Based Microwave Imaging System

“…This is an alternative to conventional microwave imaging systems with significant advantages. A traditional tomographic setup needs an array of costly transceivers to be placed all around the object [6][7][8][9][10][11]. This requires complicated circuitry and results in a high production cost of the system.…”