Emma Pickwell-MacPherson

The Chinese University of Hong Kong, Hong Kong, Hong Kong

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Publications (65)74.88 Total impact

  • Shuting Fan, Yuezhi He, Benjamin S Ung, Emma Pickwell-MacPherson
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    ABSTRACT: Interest in biomedical terahertz research is growing rapidly and there are now several terahertz groups in Asia, Europe and the US investigating potential applications such as pharmaceutical quality control, protein characterization and cancer detection. This review article outlines the technological bottlenecks that have been overcome which have made biomedical terahertz research possible. Key research findings will be presented, and the limitations that remain and the research initiatives that strive to address them will also be discussed.
    Journal of Physics D Applied Physics 08/2014; 47(37):374009. · 2.53 Impact Factor
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    Xiaolin Zhou, Hongxia Ding, Benjamin Ung, Emma Pickwell-Macpherson, Yuanting Zhang
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    ABSTRACT: Atrial fibrillation (AF) is the most common and debilitating abnormalities of the arrhythmias worldwide, with a major impact on morbidity and mortality. The detection of AF becomes crucial in preventing both acute and chronic cardiac rhythm disorders. Our objective is to devise a method for real-time, automated detection of AF episodes in electrocardiograms (ECGs). This method utilizes RR intervals, and it involves several basic operations of nonlinear/linear integer filters, symbolic dynamics and the calculation of Shannon entropy. Using novel recursive algorithms, online analytical processing of this method can be achieved. Four publicly-accessible sets of clinical data (Long-Term AF, MIT-BIH AF, MIT-BIH Arrhythmia, and MIT-BIH Normal Sinus Rhythm Databases) were selected for investigation. The first database is used as a training set; in accordance with the receiver operating characteristic (ROC) curve, the best performance using this method was achieved at the discrimination threshold of 0.353: the sensitivity (Se), specificity (Sp), positive predictive value (PPV) and overall accuracy (ACC) were 96.72%, 95.07%, 96.61% and 96.05%, respectively. The other three databases are used as testing sets. Using the obtained threshold value (i.e., 0.353), for the second set, the obtained parameters were 96.89%, 98.25%, 97.62% and 97.67%, respectively; for the third database, these parameters were 97.33%, 90.78%, 55.29% and 91.46%, respectively; finally, for the fourth set, the Sp was 98.28%. The existing methods were also employed for comparison. Overall, in contrast to the other available techniques, the test results indicate that the newly developed approach outperforms traditional methods using these databases under assessed various experimental situations, and suggest our technique could be of practical use for clinicians in the future.
    BioMedical Engineering OnLine 02/2014; 13(1):18. · 1.61 Impact Factor
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    ABSTRACT: A thin-film terahertz polarizer is proposed and realized via a tunable bilayer metal wire-grid structure to achieve high extinction ratios and good transmission. The polarizer is fabricated on top of a thin silica layer by standard micro-fabrication techniques to eliminate the multireflection effects. The tunable alignment of the bilayer aluminum-wire grid structure enables tailoring of the extinction ratio and transmission characteristics. Using terahertz time-domain spectroscopy (THz-TDS), a fabricated polarizer is characterized, with extinction ratios greater than 50 dB and transmission losses below 1 dB reported in the 0.2-1.1 THz frequency range. These characteristics can be improved by further tuning the polarizer parameters such as the pitch, metal film thickness, and lateral displacement. This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-4-793. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
    Optics Letters 02/2014; 39(4):793-6. · 3.39 Impact Factor
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    Materials Horizons. 01/2014; 1(2):251.
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    Anthony J Fitzgerald, Emma Pickwell-MacPherson, Vincent P Wallace
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    ABSTRACT: The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues.
    PLoS ONE 01/2014; 9(7):e99291. · 3.53 Impact Factor
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    ABSTRACT: A robust thin-film wire-grid terahertz (THz) polarizer was fabricated via a low-cost, mass-producible manufacturing approach. This polarizer is built on a very thin silica layer structurally supported by a silicon substrate. In addition, the metal grating is protected by a polymer thin film, which eliminates the multireflection effect and enhances the robustness of the polarizer for easy packaging. The polarizer can be easily mounted onto a Newport rotation holder for immediate use. A THz time-domain spectrometer is used to characterize its performance, and an excellent agreement is found between the FDTD-simulated results and the experimental results. The polarizer offered 20-40 dB and 0.8 dB of extinction ratio and transmission loss over a frequency range of 0.2-2.0 THz, respectively.
    IEEE Photonics Technology Letters 01/2013; 25(1):81-84. · 2.04 Impact Factor
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    ABSTRACT: Structural evolution with temperature of tetraphenylethene (TPE) is followed using THz-TDS. The observed changes in the terahertz spectra are rationalized by performing DFT calculations on experimentally determined low and high temperature crystal structures, thus allowing the changes to be rationalized in terms of the subtle changes in the supramolecular structure.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013 38th International Conference on; 01/2013
  • Shuting Fan, E.P.J. Parrott, Yi-Xiang Wang, E. Pickwell-MacPherson
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    ABSTRACT: Terahertz time domain spectroscopy has been used to characterize various tissues in biomedical research to date. In this paper the terahertz properties of three groups of rat skin tissues treated with different injections (normal saline control, high dose of Dotarem, and high dose of Omniscan) are measured. The difference in terahertz properties of the tissues can be clearly observed from the results.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013 38th International Conference on; 01/2013
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    ABSTRACT: We report the terahertz spectrum of a high birefringence liquid crystalline mixture 2002 from 0.2 to 1.6 THz, using terahertz time domain spectroscopy (THz-TDS). Furthermore, the phase transition from nematic to isotropic phases was observed using temperature-dependent THz-TDS.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013 38th International Conference on; 01/2013
  • E. Pickwell-MacPherson, E. P. J. Parrott, H. Park, F. Fan, V. G. Chigrinov
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    ABSTRACT: Liquid crystals have been employed for several decades in devices such as phase shifters, Fabry-Perot filters, polarizers, phase gratings, and Bragg switches at optical frequencies. However it is only recently that such devices have been demonstrated at terahertz frequencies. This is because of several fundamental frequency dependent relationships between device properties and frequency of operation. When designing liquid crystal devices, we need to find liquid crystals with high birefringence, low viscosity and low absorption at terahertz frequencies. In this paper we will present some measurements and simulations of potentially suitable liquid crystal mixtures.
    Proc SPIE 10/2012;
  • Emma Pickwell-MacPherson, Yiwen Sun, Edward P. J. Parrott
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    ABSTRACT: Terahertz spectroscopy is able to probe several aspects of biological systems. Most well known is its sensitivity to water due to the strong water absorptions at terahertz frequencies. However an increasing number of studies have shown that it is not just water content that terahertz is sensitive to and that other factors such as tissue structure, molecular arrangement or even temperature can also affect the signal. Examples ranging from breast cancer spectroscopy to antibody protein spectroscopy will be presented and discussed.
    Proc SPIE 10/2012;
  • H. Park, E. P. J. Parrott, Z. Huang, H. P. Chan, E. Pickwell-MacPherson
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    ABSTRACT: The horizontal and vertical polarizations of the terahertz radiation emitted from a small-gap dipole photo-conductive antenna are characterised using a single detector and a homemade thin-film wire grid polarizer. The two polarizations are seen to be temporally distinct. In addition, the dependence of the position of the excitation spot on the dipole with the polarity of the horizontal polarization is studied where a reversal in the horizontal polarization is observed between the two edges of the antenna anode.
    Applied Physics Letters 09/2012; 101(12). · 3.79 Impact Factor
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    ABSTRACT: Despite the wide application of liquid crystals (LCs) in the visible frequency range, their properties in the terahertz range have not yet been extensively investigated. In this paper we have investigated the terahertz properties of LCs E7, BL037, RDP-94990 and RDP-97304 using terahertz time-domain-spectroscopy. We find that RDP-94990 has the largest birefringence and smallest absorption in the terahertz range compared to E7 and BL037. We highlight the importance of investigating all parameters, not just the birefringence, when designing fast, efficient and transmissive terahertz LC devices. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-20-11-11899. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
    Optics Express 05/2012; 20(11):11899-905. · 3.55 Impact Factor
  • Calvin Yu, Shuting Fan, Yiwen Sun, Emma Pickwell-Macpherson
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    ABSTRACT: The terahertz region lies between the microwave and infrared regions of the electromagnetic spectrum such that it is strongly attenuated by water and very sensitive to water content. Terahertz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. Because of these characteristic properties, there has been an increasing interest in terahertz imaging and spectroscopy for biological applications within the last few years and more and more terahertz spectra are being reported, including spectroscopic studies of cancer. The presence of cancer often causes increased blood supply to affected tissues and a local increase in tissue water content may be observed: this acts as a natural contrast mechanism for terahertz imaging of cancer. Furthermore the structural changes that occur in affected tissues have also been shown to contribute to terahertz image contrast. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques. In particular investigations relating to the potential of terahertz imaging and spectroscopy for cancer diagnosis will be highlighted.
    Quantitative imaging in medicine and surgery. 03/2012; 2(1):33-45.
  • Emma Pickwell-MacPherson, Anthony J. Fitzgerald, Vincent P. Wallace
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    ABSTRACT: This paper investigates the feasibility of using terahertz pulsed imaging to detect breast cancer in a reflection imaging geometry. Spectroscopic terahertz data is used to simulate the reflected time domain response functions of healthy fibrous breast tissue and breast cancer tissue. Previously we have looked at the refractive index and absorption coefficient separately to characterize tissues. In this work we investigate their combined effects and identify parameters of the simulated reflected impulse response function and corresponding spectroscopic properties with a view to improving our ability to distinguish between the fibrous and cancer tissues in the breast.
    Proc SPIE 02/2012;
  • V.P. Wallace, A.J. Fitzgerald, E. Pickwell-MacPherson
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    ABSTRACT: Here we describe our efforts to improve our understanding of differences detected between normal and cancerous tissue in the THz regime. By using a model and plugging in data extracted from spectroscopy measurements we are able to calculate expected reflections from diseased and healthy tissues which help to identify sources of image contrast.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
  • Hongkyu Park, Huang Zhe, E.P.J. Parrott, A. Chan, E. Pickwell-MacPherson
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    ABSTRACT: We have developed a novel wire grid polarizer on a thin film substrate to overcome multiple reflection issues found in conventional polarizers. In this paper, we show how our polarizer can be used to characterize the vertical and horizontal polarization components of a THz photoconducting antenna.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
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    ABSTRACT: The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (T(D)). In particular, we show that below T(D) the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above T(D), the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization.
    PLoS ONE 01/2012; 7(11):e50306. · 3.53 Impact Factor
  • E.P.J. Parrott, H. Park, E. Pickwell-MacPherson
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    ABSTRACT: This paper highlights the issue of variable power fibre-coupling in THz-TDS systems and suggests an effective subtraction approach to remove this dependence and return a useful signal.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
  • Zhe Huang, Hau Ping Chan, Hongkyu Park, E.P. Parrott, E. Pickwell-MacPherson
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    ABSTRACT: The low-cost fabrication of a metal wire-grid polarizer for the terahertz (THz) region was demonstrated. An aluminium grid was patterned onto a thin silica (SiO2) layer. The performance of the THz polarizer was evaluated through experimental measurements. The experimental results were compared with the simulation results.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012

Publication Stats

175 Citations
74.88 Total Impact Points

Institutions

  • 2007–2014
    • The Chinese University of Hong Kong
      • Department of Electronic Engineering
      Hong Kong, Hong Kong
  • 2012
    • Shenzhen University
      Bao'an, Guangdong, China
  • 2010–2012
    • The Hong Kong University of Science and Technology
      • Department of Electronic and Computer Engineering
      Kowloon, Hong Kong
  • 2010–2011
    • University College London
      • Department of Medical Physics and Bioengineering
      London, ENG, United Kingdom
  • 2009
    • Chinese Academy of Sciences
      Peping, Beijing, China
    • University of Cambridge
      • Department of Physics: Cavendish Laboratory
      Cambridge, ENG, United Kingdom