Microwave imaging via space-time beamforming for early detection of breast cancer

A method of microwave imaging via space-time (MIST) beamforming is proposed for detecting early-stage breast cancer. An array of antennas is located near the surface of the breast and an ultrawideband (UWB) signal is transmitted sequentially from each antenna. The received backscattered signals are passed through a space-time beamformer that is designed to image backscattered signal energy as a function of location. The beamformer spatially focuses the backscattered signals to discriminate against clutter and noise while compensating for frequency-dependent propagation effects. As a consequence of the significant dielectric-properties contrast between normal and malignant tissue, localized regions of large backscatter energy levels in the image correspond to malignant tumors. A data-adaptive algorithm for removing artifacts in the received signals due to backscatter from the skin-breast interface is also presented. The effectiveness of these algorithms is demonstrated using a variety of numerical breast phantoms based on anatomically realistic MRI-derived FDTD models of the breast. Very small (2 mm) malignant tumors embedded within the complex fibroglandular structure of the breast are easily detected above the background clutter. The MIST approach is shown to offer significant improvement in performance over previous UWB microwave breast cancer detection techniques based on simpler focusing schemes.     

A subspace detection method of analog space-time codes for multiantenna ultra-wideband transmissions

In this letter, we propose a subspace based detection method for space-time block codes (STBC) wedded with ultra-wideband (UWB) transmissions. Without the need of channel information, the proposed algorithm yields the estimation of transmitted symbols by minimizing some quadratic form built on the orthogonality between signal and noise subspaces. Simulations in flat-faded application scenarios show that the subspace method can achieve the same diversity and a loss of about 2 dB at the 10/sup -3/ level with more than four successive space-time codes being decoded jointly, compared to the coherent decoding algorithm.     

Analog space-time coding for multiantenna ultra-wideband transmissions

Ultra-wideband (UWB) transmissions have well-documented advantages for low-power, peer-to-peer, and multiple-access communications. Space-time coding (STC), on the other hand, has gained popularity as an effective means of boosting rates and performance. Existing UWB transmitters rely on a single antenna, while ST coders have mostly focused on digital linearly modulated transmissions. In this paper, we develop ST codes for analog (and possibly nonlinearly) modulated multiantenna UWB systems. We show that the resulting analog system is able to collect not only the spatial diversity, but also the multipath diversity inherited by the dense multipath channel, with either coherent or noncoherent reception. Simulations confirm a considerable increase in both bit-error rate performance and immunity against timing jitter, when wedding STC with UWB transmissions.     

An ultra-wideband antenna for the reinforced concrete detection

In this paper, an Ultra-Wideband （UWB） planar antenna is proposed for the reinforced concrete detection, which consists of a pair of planar waterdrop arms, a microstrip to coplanar par- allel-strips transition and a shallow rectangular cavity. In order to overcome the disadvantages of the shallow cavity, some absorbing material is loaded to weaken the narrow-band effect of the cavity and the crosstalk interference. The simulated and measured results show that the proposed antenna has a large bandwidth from 0.48 GHz to 3.6 GHz with Voltage Standing Wave Ratio （VSWR） below 2 and a fractional bandwidth about 200% under the center frequency of 1.6 GHz, directional radiation char- acteristics and small late-time ringing in the time domain, which can be suitable for nondestructive detection of the reinforced concrete.     

Effect of lesion morphology on microwave signature in 2-D ultra-wideband breast imaging

This paper studies the possibility of distinguishing between benign and malignant masses by exploiting the morphology-dependent temporal and spectral characteristics of their microwave backscatter response in ultra-wideband breast cancer detection. The spiculated border profiles of 2-D breast masses are generated by modifying the baseline elliptical rings based upon the irregularity of their peripheries. Furthermore, the single- and multilayer lesion models are used to characterize a distinct mass region followed by a sharp transition to background, and a blurred mass border exhibiting a gradual transition to background, respectively. Subsequently, the complex natural resonances (CNRs) of the backscatter microwave signature can be derived from the late-time target response and reveal diagnostically useful information. The fractional sequence CLEAN algorithm is proposed to estimate the lesions' delay intervals and identify the late-time responses. Finally, it is shown through numerical examples that the locations of dominant CNRs are dependent on the lesion morphologies, where 2-D computational breast phantoms with single and multiple lesions are investigated. The analysis is of potential use for discrimination between benign and malignant lesions, where the former usually possesses a better-defined, more compact shape as opposed to the latter.     

超宽带微波滤波器研究现状

超宽带技术具有低功耗、高速率、保密性强等优势,在空间导航、空间通信、雷达等领域有广泛的应用与良好的发展前景。综合了国内外超宽带技术的最新进展,介绍了超宽带微波滤波器的作用、特点及关键问题。从z变换法、多模谐振器法、滤波器级联法等设计方法和微带结构、多层电路结构、腔体结构及新材料等实现结构对近期超宽带微波滤波器的设计进行归纳总结并举例说明。最后展望了超宽带滤波器小型化、高集成、高性能的发展趋势。     

Time-multiplexed beamforming for noninvasive microwave hyperthermia treatment

A noninvasive microwave beamforming strategy is proposed for selective localized heating of biological tissue. The proposed technique is based on time multiplexing of multiple beamformers. We investigate the effectiveness of the time-multiplexed beamforming in the context of brain hyperthermia treatment by using a high-fidelity numerical head phantom of an adult female from the Virtual Family (IT'IS Foundation) as our testbed. An operating frequency of 1 GHz is considered to balance the improved treatment resolution afforded by higher frequencies against the increased penetration through the brain afforded by lower frequencies. The exact head geometry and dielectric properties of biological tissues in the head are assumed to be available for the creation of patient-specific propagation models used in beamformer design. Electromagnetic and thermal simulations based on the finite-difference time-domain method are used to evaluate the hyperthermia performance of time-multiplexed beamforming and conventional beamforming strategies. The proposed time-multiplexing technique is shown to reduce the unintended heating of healthy tissue without affecting the treatment temperature or volume. The efficacy of the method is demonstrated for target locations in three different regions of the brain. This approach has the potential to improve microwave-induced localized heating for cancer treatment via hyperthermia or heat-activated chemotherapeutic drug release.     

Application of quasi-orthogonal space-time block codes in beamforming

It is well known that when channel information is available at the transmitter, transmit beamforming scheme can be employed to enhance the performance of a multiple-antenna system. Recently, Jongren et al. and Zhou-Giannakis proposed a new performance criterion based on partial channel side information at the transmitter. With this criterion, an optimal beamforming matrix was constructed for the orthogonal space-time block codes. However, the same method has not been applied to the recently proposed quasi-orthogonal space-time block codes (QSTBCs) due to the nonorthogonal nature of the quasi-orthogonal designs. In this paper, the issue of combining beamforming with QSTBCs is addressed. Based on our asymptotic analysis, we extend the beamforming scheme from Jongren et al. and construct the beamforming matrices for the quasi-orthogonal designs. The proposed beamforming scheme accomplishes high transmission rate as well as high-order spatial diversity. The new QSTBC beamformer can be presented as a novel four-directional or eight-directional eigen-beamformer that works for systems with four or more transmit antennas. Simulations for systems with multiple transmit antennas demonstrate significant performance improvement over several other widely used beamforming methods at various SNRs and for channels with different quality of feedback.     

A novel amplitude-phase weighting for analog microwave beamforming

A simple receiver and transmitter structure for smart antennas and phased array antennas is proposed. A new technique for amplitude and phase weighting in microwave domain is presented. Signals of different antenna elements are sampled using pulses with adjusted time delay and duty cycles. The first replica of the sampled signal is reconstructed to provide the proper phase shift and amplitude weighting. A new switch circuit is designed to improve the power efficiency of the proposed structure and to lower the effects of switching on the impedance matching. The effect of nonideal switching on the performance of the system is analyzed. Procedures are proposed to integrate the proposed structure with adaptive signal processing tasks. Signal to noise ratio of the structure is studied under different scenarios.     

A confocal microwave imaging algorithm for breast cancer detection

We present a computationally efficient and robust image reconstruction algorithm for breast cancer detection using an ultrawideband confocal microwave imaging system. To test the efficacy of this approach, we have developed a two-dimensional (2-D) anatomically realistic MRI-derived FDTD model of the cancerous breast. The image reconstruction algorithm is applied to FDTD-computed backscatter signals, resulting in a microwave image that clearly identifies the presence and location of the malignant lesion. These simulations demonstrate the feasibility of detecting and imaging small breast tumors using this novel approach     

一种改进的分层空时码检测算法

基于最小均方误差原则,本文给出一种改进的分层空时码权向量计算方法,该算法均衡考虑了信道特性矩阵和接收信号中的噪声对系统的影响,在一定程度上改进了系统性能。仿真结果显示,与ZF算法相比,若采用本文给出的MMSE算法,基于Turbo编码,采用两发两收的LST码系统可获得9~12dB的增益。     

Multi-aspect detection of surface and shallow-buried unexplodedordnance via ultra-wideband synthetic aperture radar

An ultra-wideband (UWB) synthetic aperture radar (SAR) system is investigated for the detection of former bombing ranges, littered by unexploded ordnance (UXO). The objective is detection of a high enough percentage of surface and shallow-buried UXO, with a low enough false-alarm rate, such that a former range can be detected. The physics of UWB SAR scattering is exploited in the context of a hidden Markov model (HMM), which explicitly accounts for the multiple aspects at which a SAR system views a given target. The HMM is trained on computed data, using SAR imagery synthesized via a validated physical-optics solution. The performance of the HMM is demonstrated by performing testing on measured UWB SAR data for many surface and shallow UXO buried in soil in the vicinity of naturally occurring clutter     

Fast 3-d tomographic microwave imaging for breast cancer detection

Microwave breast imaging (using electromagnetic waves of frequencies around 1 GHz) has mostly remained at the research level for the past decade, gaining little clinical acceptance. The major hurdles limiting patient use are both at the hardware level (challenges in collecting accurate and noncorrupted data) and software level (often plagued by unrealistic reconstruction times in the tens of hours). In this paper we report improvements that address both issues. First, the hardware is able to measure signals down to levels compatible with sub-centimeter image resolution while keeping an exam time under 2 min. Second, the software overcomes the enormous time burden and produces similarly accurate images in less than 20 min. The combination of the new hardware and software allows us to produce and report here the first clinical 3-D microwave tomographic images of the breast. Two clinical examples are selected out of 400+ exams conducted at the Dartmouth Hitchcock Medical Center (Lebanon, NH). The first example demonstrates the potential usefulness of our system for breast cancer screening while the second example focuses on therapy monitoring.     

Wideband synthetic aperture beamforming for through-the-wall imaging

Through-the-wall radar imaging (TWRI) and sensing is emerging as an important area of research and development. A TWRI system provides enhanced situational awareness in operational environments for a variety of civilian and military applications. In particular, a TWRI system facilitates realtime information gathering and intelligent decision-making about the contents of the indoor scene. Compared to other radar applications, TWRI faces unique challenges due to signal propagation through walls. The composition and thickness of the wall, its dielectric constant, and the angle of incidence affect the strength and characteristics of the propagating signal. The change in propagation speed and wave refraction must be taken into account for effective and accurate imaging. In this article, we present a synthetic aperture beamforming approach that uses ray perturbation theory to account for the effects of transmission through a single uniform wall.     

An iterative singular vectors estimation scheme for beamforming transmission and detection in MIMO systems

A novel iterative singular vector estimation scheme has been proposed for a beamforming transmission and detection in wireless multiple input multiple output (MIMO) systems. Two singular channel matrix vectors, which correspond to the largest singular value, are iteratively obtained at the transmitter and the receiver without estimating the channel coefficients. The proposed singular vectors estimation strategy has advantages over the conventional MIMO channel estimation schemes in terms of both frame-error-rate performance, bandwidth efficiency and computation complexity.     

Confocal microwave imaging for breast cancer detection: delay-multiply-and-sum image reconstruction algorithm

A new image reconstruction algorithm, termed as delay-multiply-and-sum (DMAS), for breast cancer detection using an ultra-wideband confocal microwave imaging technique is proposed. In DMAS algorithm, the backscattered signals received from numerical breast phantoms simulated using the finite-difference time-domain method are time shifted, multiplied in pair, and the products are summed to form a synthetic focal point. The effectiveness of the DMAS algorithm is shown by applying it to backscattered signals received from a variety of numerical breast phantoms. The reconstructed images illustrate improvement in identification of embedded malignant tumors over the delay-and-sum algorithm. Successful detection and localization of tumors as small as 2 mm in diameter are also demonstrated.     

Frontal methods for the space-time processing of ultra-wideband signals in exploration seismology and ground penetrating radar

Methods for the space-time processing of ultra-wideband signals used in short-range and ground penetrating radar as well as exploration seismology for execution of migration transformation procedures are analyzed. Procedures for obtaining the geometricalal parameters (position, shape, and orientation) of reflecting boundaries and diffracting objects from signals recorded during scanning in some spatial zone are proposed. Different methods for the implementation of linear and nonlinear migration transformations are analyzed. Frontal migration transformation methods are analyzed in more detail and advantages of these methods are demonstrated. Interactive and computer-aided versions of such methods are presented. Analytical relationships for the implementation of these versions of the space-time signal processing are presented.     

Exact bit-error rate analysis for the combined system of beamforming and Alamouti's space-time block code

The simplest Alamouti's space-time block code can be coupled with more than two transmit antennas via the beamforming technique to enhance the performance gain without code rate reduction. Beamforming is performed at the transmitter, dependent on the channel state information (CSI) which is obtained by using feedback through a feedback link or estimated using reciprocity in duplexing schemes. In this letter, we derived the exact bit-error rate for the combined system with two transmit and one receive antennas in slow Rayleigh flat fading channels. It is assumed that the receiver has the perfect CSI. The expression can be easily extended to more than two transmit antennas.     

Graph-based detection algorithms for layered space-time architectures

We consider a unified framework to develop various graph-based detection algorithms for layered space-time architectures. We start with a factor graph representation for the communication channel, apply a belief propagation (BP) based algorithm for channel detection, and show that the detector achieves a near optimal performance even when number of receive antennas is smaller than number of transmit antennas. Based on this baseline algorithm, we further develop three different extensions of the BP detector that provide a good complexity/performance trade-off, which are especially useful for systems with a large number of antennas or when we encounter a frequency-selective fading channel with a long ISI span. Moreover, all the proposed detectors are soft-input soft-output in nature and they can be directly applied for use in turbo processing without any additional modifications. We study the performance of the new detectors via both simulations and convergence analysis using the measure of average mutual information.