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Kavitha Arunachalam

Bio: Kavitha Arunachalam is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Antenna (radio) & Deformable mirror. The author has an hindex of 15, co-authored 105 publications receiving 676 citations. Previous affiliations of Kavitha Arunachalam include Duke University & Indian Institutes of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the feasibility of a far-field microwave NDE technique for concrete imaging is investigated via numerical simulations and experiments on cement-based samples using farfield microwave reflection coefficients.
Abstract: Periodic assessment of ageing civil structures is important for structural integrity and public safety. Numerous destructive and non-destructive techniques employing different energy sources have been proposed for structural health monitoring. Amongst the non-destructive evaluation techniques proposed for monitoring material strength and contents of concrete structures, techniques employing microwaves offer distinct advantages in that they are non-radioactive and provide good penetration, excellent contrast between steel reinforcement bar and concrete, and insensitivity to ambient temperature. In this paper, the feasibility of a far-field microwave NDE technique for concrete imaging is investigated via numerical simulations and experiments on cement based samples using far-field microwave reflection coefficients.

56 citations

Journal ArticleDOI
TL;DR: The accuracy and stability data obtained in water test loads of several configurations support the expectation that single band radiometry should be sufficient for sub-surface temperature monitoring and power control of large multielement array superficial hyperthermia applicators.
Abstract: Microwave radiometry has been proposed as a viable noninvasive thermometry approach for monitoring subsurface tissue temperatures and potentially controlling power levels of multielement heat applicators during clinical hyperthermia treatments. With the evolution of technology, several analog microwave radiometry devices have been developed for biomedical applications. In this paper, we describe a digital microwave radiometer with built-in electronics for signal processing and automatic self-calibration. Performance of the radiometer with an Archimedean spiral receive antenna is evaluated over a bandwidth of 3.7–4.2GHz in homogeneous and layered water test loads. Controlled laboratory experiments over the range of 30–50°C characterize measurement accuracy, stability, repeatability and penetration depth sensitivity. The ability to sense load temperature through an intervening water coupling bolus of 6mm thickness is also investigated. To assess clinical utility and sensitivity to electromagnetic interference (EMI), experiments are conducted inside standard clinical hyperthermia treatment rooms with no EM shielding. The digital radiometer provided repeatable measurements with 0.075°C resolution and standard deviation of 0.217°C for homogeneous and layered tissue loads at temperatures between 32–45°C. Within the 3.7–4.2GHz band, EM noise rejection was good other than some interference from overhead fluorescent lights in the same room as the radiometer. The system response obtained for ideal water loads suggests that this digital radiometer should be useful for estimating subcutaneous tissue temperatures under a 6mm waterbolus used during clinical hyperthermia treatments. The accuracy and stability data obtained in water test loads of several configurations support our expectation that single band radiometry should be sufficient for sub-surface temperature monitoring and power control of large multielement array superficial hyperthermia applicators.

52 citations

Journal ArticleDOI
TL;DR: The CMA applicator is an effective thermal therapy device for heating large-area superficial disease such as diffuse chest wall recurrence, able to cover over three times the treatment area of conventional hyperthermia devices while conforming to typical body contours.
Abstract: Purpose: This article summarises the evolution of microwave array applicators for heating large area chest wall disease as an adjuvant to external beam radiation, systemic chemotherapy, and potentially simultaneous brachytherapy.Methods: Current devices used for thermotherapy of chest wall recurrence are reviewed. The largest conformal array applicator to date is evaluated in four studies: (1) ability to conform to the torso is demonstrated with a CT scan of a torso phantom and MR scan of the conformal water bolus component on a mastectomy patient; (2) specific absorption rate (SAR) and temperature distributions are calculated with electromagnetic and thermal simulation software for a mastectomy patient; (3) SAR patterns are measured with a scanning SAR probe in liquid muscle phantom for a buried coplanar waveguide CMA; and (4) heating patterns and patient tolerance of CMA applicators are characterised in a clinical pilot study with 13 patients.Results: CT and MR scans demonstrate excellent conformity of ...

50 citations

Journal ArticleDOI
TL;DR: Lab testing of the radiometry system in temperature-controlled phantoms supports the feasibility of passive kidney thermometry for VUR detection and demonstrates no deterioration in power reception and effective EM shielding in the presence of a metal cup.
Abstract: Microwave (MW) radiometry is proposed for passive monitoring of kidney temperature to detect vesicoureteral reflux (VUR) of urine that is externally heated by a MW hyperthermia device and thereafter reflows from the bladder to kidneys during reflux. Here, we characterize in tissue-mimicking phantoms the performance of a 1.375 GHz radiometry system connected to an electromagnetically (EM) shielded microstrip log spiral antenna optimized for VUR detection. Phantom EM properties are characterized using a coaxial dielectric probe and network analyzer (NA). Power reflection and receive patterns of the antenna are measured in layered tissue phantom. Receiver spectral measurements are used to assess EM shielding provided by a metal cup surrounding the antenna. Radiometer and fiberoptic temperature data are recorded for varying volumes (10-30 mL) and temperatures (40-46°C) of the urine phantom at 35 mm depth surrounded by 36.5°C muscle phantom. Directional receive pattern with about 5% power spectral density at 35 mm target depth and better than -10 dB return loss from tissue load are measured for the antenna. Antenna measurements demonstrate no deterioration in power reception and effective EM shielding in the presence of the metal cup. Radiometry power measurements are in excellent agreement with the temperature of the kidney phantom. Laboratory testing of the radiometry system in temperature-controlled phantoms supports the feasibility of passive kidney thermometry for VUR detection.

46 citations

Journal ArticleDOI
TL;DR: The modeling efforts on antenna design, frequency selection and receiver sensitivity estimation to detect vesicoureteral reflux (VUR) using microwave (MW) radiometry as warm urine from the bladder maintained at fever range temperature using a MW hyperthermia device reflows into the kidneys are presented.
Abstract: We present the modeling efforts on antenna design, frequency selection and receiver sensitivity estimation to detect vesicoureteral reflux (VUR) using microwave (MW) radiometry as the warm urine from the bladder maintained at fever range temperature using a MW hyperthermia device reflows into the kidneys. Radiometer center frequency (fc), frequency band (Δf), and aperture radius (ra) of the physical antenna for kidney temperature monitoring are determined using a simplified universal antenna model with circular aperture. Anatomical information extracted from computed tomography (CT) images of children age 4–6 years is used to construct a layered 3D tissue model. Radiometric antenna efficiency is evaluated in terms of the ratio between the power collected from the target at depth and the total power received by the antenna (η). Power ratio of the theoretical antenna is used to design a microstrip log spiral antenna with directional radiation pattern over fc ± Δf/2. Power received by the log spiral from the deep target is enhanced using a thin low-loss dielectric matching layer. A cylindrical metal cup is proposed to shield the antenna from electromagnetic interference (EMI). Transient thermal simulations are carried out to determine the minimum detectable change in antenna brightness temperature (δTB) for 15–25 mL urine refluxes at 40–42°C located 35 mm from the skin surface. Theoretical antenna simulations indicate maximum η over 1.1–1.6 GHz for ra = 30–40 mm. Simulations of the 35 mm radius tapered log spiral yielded higher power ratio over fc ± Δf/2 for the 35–40 mm deep targets in the presence of an optimal matching layer. Radiometric temperature calculations indicate δTB ≥ 0.1 K for the 15 mL urine at 40°C and 35 mm depth. Higher η and δTB were observed for the antenna and matching layer inside the metal cup. Reflection measurements of the log spiral in saline phantom are in agreement with the simulation data. Numerical study suggests a radiometer with fc =1.35 GHz, Δf = 500 MHz and detector sensitivity better than 0.1 K would be the appropriate tool to noninvasively detect VUR using the log spiral antenna.

42 citations


Cited by
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Journal ArticleDOI
TL;DR: Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis.
Abstract: Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

13,246 citations

Journal Article

510 citations

Journal ArticleDOI
TL;DR: Benefits of combining gold nanoparticle-mediated PTT with other treatment strategies can enhance the therapeutic success of both PTT and the secondary treatment while lowering the required doses of the individual agents, leading to fewer off-target effects.
Abstract: Photothermal therapy (PTT), in which nanoparticles embedded within tumors generate heat in response to exogenously applied laser light, has been well documented as an independent strategy for highly selective cancer treatment. Gold-based nanoparticles are the main mediators of PTT because they offer: (1) biocompatibility, (2) small diameters that enable tumor penetration upon systemic delivery, (3) simple gold-thiol bioconjugation chemistry for the attachment of desired molecules, (4) efficient light-to-heat conversion, and (5) the ability to be tuned to absorb near-infrared light, which penetrates tissue more deeply than other wavelengths of light. In addition to acting as a standalone therapy, gold nanoparticle-mediated PTT has recently been evaluated in combination with other therapies, such as chemotherapy, gene regulation, and immunotherapy, for enhanced anti-tumor effects. When delivered independently, the therapeutic success of molecular agents is hindered by premature degradation, insufficient tumor delivery, and off-target toxicity. PTT can overcome these limitations by enhancing tumor- or cell-specific delivery of these agents or by sensitizing cancer cells to these additional therapies. All together, these benefits can enhance the therapeutic success of both PTT and the secondary treatment while lowering the required doses of the individual agents, leading to fewer off-target effects. Given the benefits of combining gold nanoparticle-mediated PTT with other treatment strategies, many exciting opportunities for multimodal cancer treatment are emerging that will ultimately lead to improved patient outcomes. WIREs Nanomed Nanobiotechnol 2017, 9:e1449. doi: 10.1002/wnan.1449 For further resources related to this article, please visit the WIREs website.

494 citations

Journal ArticleDOI
TL;DR: The review summarizes the outcomes from various clinical studies where hyperthermia is used as a thermal sensitizer of radiotherapy and-/or chemotherapy in various solid tumors and presents an overview of the progresses in loco-regionalhyperthermia.

407 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide a comprehensive review of microwave composites research, from processing to structural and property evaluations with a focus on the multi-functionalities presented in these microwire composites.

286 citations