1,065 research outputs found

    An optimized ultrasound detector for photoacoustic breast tomography

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    Photoacoustic imaging has proven to be able to detect vascularization-driven optical absorption contrast associated with tumors. In order to detect breast tumors located a few centimeter deep in tissue, a sensitive ultrasound detector is of crucial importance for photoacoustic mammography. Further, because the expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is inversely proportional to the dimensions of light absorbing structures (0.5 to 10+ mm), proper choices of materials and their geometries, and proper considerations in design have to be made for optimal photoacoustic detectors. In this study, we design and evaluate a specialized ultrasound detector for photoacoustic mammography. Based on the required detector sensitivity and its frequency response, a selection of active material and matching layers and their geometries is made leading to a functional detector models. By iteration between simulation of detector performances, fabrication and experimental characterization of functional models an optimized implementation is made and evaluated. The experimental results of the designed first and second functional detectors matched with the simulations. In subsequent bare piezoelectric samples the effect of lateral resonances was addressed and their influence minimized by sub-dicing the samples. Consequently, using simulations, the final optimized detector could be designed, with a center frequency of 1 MHz and a -6 dB bandwidth of ~80%. The minimum detectable pressure was measured to be 0.5 Pa, which will facilitate deeper imaging compared to the currrent systems. The detector should be capable of detecting vascularized tumors with resolution of 1-2 mm. Further improvements by proper electrical grounding and shielding and implementation of this design into an arrayed detector will pave the way for clinical applications of photoacoustic mammography.Comment: Accepted for publication in Medical Physics (American Association of Physicists in Medicine

    Fundamental issues in antenna design for microwave medical imaging applications

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    This paper surveys the development of microwave medical imaging and the fundamental challenges associated with microwave antennas design for medical imaging applications. Different microwave antennas used in medical imaging applications such as monopoles, bow-tie, vivaldi and pyramidal horn antennas are discussed. The challenges faced when the latter used in medical imaging environment are detailed. The paper provides the possible solutions for the challenges at hand and also provides insight into the modelling work which will help the microwave engineering community to understand the behaviour of the microwave antennas in coupling media

    A Sinusoidal Current Driver With an Extended Frequency Range and Multifrequency Operation for Bioimpedance Applications

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    This paper describes an alternative sinusoidal current driver suitable for bioimpedance applications where high frequency operation is required. The circuit is based on a transconductor and provides current outputs with low phase error for frequencies around its pole frequency. This extends the upper frequency operational limit of the current driver. Multifrequency currents can be generated where each individual frequency is phase corrected. Analysis of the circuit is presented together with simulation and experimental results which demonstrate the proof of concept for both single and dual frequency current drivers. Measurements on a discrete test version of the circuit demonstrate a phase reduction from 25 ^{\circ} to 4 ^{\circ} at 3 MHz for 2 mAp-p output current. The output impedance of the current driver is essentially constant at about 1.1 M \Omega over a frequency range of 100 kHz to 5 MHz due to the introduction of the phase compensation. The compensation provides a bandwidth increase of a factor of about six for a residual phase delay of 4 ^{\circ

    Electrical impedance mammography : the key to low-cost, portable and non-invasive breast cancer screening?

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    Breast cancer is a major public health problem with 1.7 million cases diagnosed per year and is the leading cause of cancer deaths in women worldwide (Siegel, Miller & Jemal, 2016). The two main determinants of survival are early detection and optimal treatment. Despite the advances in medicine, breast cancer is detected at advanced stages in developing countries (DCs) because early detection, diagnosis and treatment cannot be efficiently promoted. Thus, disease burden is particularly high in DCs, where more than half of breast cancer cases and 62% of the deaths now occur. The “Breast Health Global Initiative” (BHGI) evaluated the complexity of healthcare systems in relation to breast cancer. Specifically, at the basic level, breast self- examination is encouraged, whereas diagnostic ultrasound and X-ray mammography are available at a limited level. At the increased level, patients have access to diagnostic mammography with opportunistic breast screening, and at a maximum level, the population undergoes organized screening for breast cancer (Anderson et al., 2006).peer-reviewe

    Low Frequency Bio-Electrical Impedance Mammography and Dielectric Measurement

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    Assessment of electrical impedance of biological tissues at low frequencies offers a great potential for a safe, simple, and low-cost medical breast imaging techniques such as mammography. As such, in this dissertation a mammography method which uses tissue electrical impedance to detect breast malignancies was developed. The dissertation also introduces a new technique for measuring the dielectric properties of biological tissues at low frequencies. The impedance mammography technique introduced in this study is founded on the assumption that dielectric values of breast malignancies are significantly higher than the dielectric values of normal breast tissues. While previous studies have shown that this assumption is valid at high frequencies (50MHz-20GHz), less research efforts have been dedicated to ascertain the validity of such assumption at low frequencies (in silico and tissue mimicking phantom studies. Results of this investigation suggest that imaging the electrical impedance properties of biological tissues through the proposed electrical impedance mammography can be potentially employed for breast cancer detection in a reliable and safe manner

    Diagnostic System in Electrical Impedance Mammography: Background

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    Electrical impedance mammography (EIM) belongs to nonlocal techniques of image creation. It is based on a number of data collection methods, including the cross-sectional approach, the back-projection method with the weight function applied horizontally and vertically, and the static image method. The analysis of data acquired by applying the above methods enabled to work out the EIM diagnostic system. It involves the following diagnostic categories: structural percentile limits and the mammary gland structure, age-related percentile limits and age-related electric conductivity, outlying values statistics and early diagnostics of breast cancer, D-statistics and distortion of the mammographic scheme in the presence of breast cancer, diagnostic table, and the assessment of the electrical impedance image
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