Electrical Impedance Tomography/Spectroscopy (EITS): a Code Division Multiplexed (CDM) approach

Electrical Impedance Tomography and Spectroscopy (EITS) is a noninvasive imaging technique that creates images of cross-sections "tomos" of objects by discriminating them based on their electrical impedance. This thesis investigated and successfully confirmed the use of Code Division Multiplexing (CDM) using Gold codes in Electrical Impedance Tomography and Spectroscopy. The results obtained showed 3.5% and 6.2% errors in determining the position and size of imaged anomalies respectively, with attainable imaging speed of 462 frames/second. These results are better, compared to those reported when using Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM).This new approach provides a more robust mode of EITS for fast changing dynamic systems by eliminating temporal data inconsistencies. Furthermore, it enables robust use of frequency difference imaging and spectroscopy in EITS by eliminating frequency data inconsistencies. In this method of imaging, electric current patterns are safely injected into the imaged object by a set of electrodes arranged in a single plane on the objects surface, for 2-Dimensional (2D) imaging. For 3-Dimensional (3D) imaging, more electrode planes are used on the objects surface. The injected currents result in measurable voltages on the objects surface. Such voltages are measured, and together with the input currents, and a Finite Element Model (FEM) of the object, used to reconstruct an impedance image of the cross-sectional contents of the imaged object. The reconstruction process involves the numerical solutions of the forward problem; using Finite Element solvers and the resulting ill-posed inverse problem using iterative Optimization or Computational Intelligence methods. This method has applications mainly in the Biomedical imaging and Process monitoring fields. The primary interests of the author are, in imaging and diagnosis of cancer, neonatal pneumonia and neurological disorders which are leading causes of death in Africa and world-wide

ACE-inhibition and skeletal muscle dysfunction in chronic obstructive pulmonary disease

This thesis addresses the impact of quadriceps wasting and physical inactivity across disease severity (GOLD stages I-IV) in Chronic Obstructive Pulmonary Disease (COPD) and assesses the influence of angiotensin-converting enzyme (ACE)-inhibition on quadriceps dysfunction in these patients. In a cross-sectional study of 161 COPD patients, ultrasound measurement of rectus femoris cross-sectional area was reduced in mild as well as advanced disease when compared to controls. Daily physical activity, measured using an armband accelerometer, was reduced in COPD subjects across all GOLD stages compared to controls. Physical activity was independently associated with quadriceps wasting in GOLD stage I, but not stage II-IV disease where residual volume to total lung capacity ratio was the only independent predictor of activity level. This data suggests that quadriceps wasting is not an end-stage phenomenon in COPD and highlights the need for early identification of these patients to guide lifestyle and therapeutic interventions. The effect of the ACE-inhibitor, fosinopril on quadriceps dysfunction in COPD was then investigated in a double-blind randomised controlled trial of 80 COPD patients with quadriceps weakness. Despite a significant reduction in systolic blood pressure and serum ACE activity in the treatment group compared to placebo, no significant differences were observed at 3 months in the primary outcome of non-volitional quadriceps endurance. Quadriceps strength improved in both groups, but there was a greater increase in the placebo arm. No significant changes were observed in mid-thigh cross-sectional area or incremental shuttle walk distance. The trial also assessed the effect of ACE-inhibition on vastus lateralis atrogene expression in COPD, with no significant differences observed between groups. In conclusion, although evidence from observational cohorts suggest a role for the renin-angiotensin system in the control of muscle phenotype, data from this thesis found that ACE-inhibition did not improve quadriceps function in a COPD population with quadriceps weakness.Open Acces

DICOM for EIT

With EIT starting to be used in routine clinical practice [1], it important that the clinically relevant information is portable between hospital data management systems. DICOM formats are widely used clinically and cover many imaging modalities, though not specifically EIT. We describe how existing DICOM specifications, can be repurposed as an interim solution, and basis from which a consensus EIT DICOM ‘Supplement’ (an extension to the standard) can be writte

Development of real-time cellular impedance analysis system

The cell impedance analysis technique is a label-free, non-invasive method, which simplifies sample preparation and allows applications requiring unmodified cell retrieval. However, traditional impedance measurement methods suffer from various problems (speed, bandwidth, accuracy) for extracting the cellular impedance information. This thesis proposes an improved system for extracting precise cellular impedance in real-time, with a wide bandwidth and satisfactory accuracy. The system hardware consists of five main parts: a microelectrode array (MEA), a stimulation circuit, a sensing circuit, a multi-function card and a computer. The development of system hardware is explored. Accordingly, a novel bioimpedance measurement method coined digital auto balancing bridge method, which is improved from the traditional analogue auto balancing bridge circuitry, is realized for real-time cellular impedance measurement. Two different digital bridge balancing algorithms are proposed and realized, which are based on least mean squares (LMS) algorithm and fast block LMS (FBLMS) algorithm for single- and multi-frequency measurements respectively. Details on their implementation in FPGA are discussed. The test results prove that the LMS-based algorithm is suitable for accelerating the measurement speed in single-frequency situation, whilst the FBLMS-based algorithm has advantages in stable convergence in multi-frequency applications. A novel algorithm, called the All Phase Fast Fourier Transform (APFFT), is applied for post-processing of bioimpedance measurement results. Compared with the classical FFT algorithm, the APFFT significantly reduces spectral leakage caused by truncation error. Compared to the traditional FFT and Digital Quadrature Demodulation (DQD) methods, the APFFT shows excellent performance for extracting accurate phase and amplitude in the frequency spectrum. Additionally, testing and evaluation of the realized system has been performed. The results show that our system achieved a satisfactory accuracy within a wide bandwidth, a fast measurement speed and a good repeatability. Furthermore, our system is compared with a commercial impedance analyzer (Agilent 4294A) in biological experiments. The results reveal that our system achieved a comparable accuracy to the commercial instrument in the biological experiments. Finally, conclusions are given and the future work is proposed

Estimation of thorax shape for forward modelling in lungs EIT

The thorax models for pre-term babies are developed based on the CT scans from new-borns and their effect on image reconstruction is evaluated in comparison with other available models

Rapid generation of subject-specific thorax forward models

For real-time monitoring of lung function using accurate patient geometry, shape information needs to be acquired and a forward model generated rapidly. This paper shows that warping a cylindrical model to an acquired shape results in meshes of acceptable mesh quality, in terms of stretch and aspect ratio

Torso shape detection to improve lung monitoring

Two methodologies are proposed to detect the patient-specific boundary of the chest, aiming to produce a more accurate forward model for EIT analysis. Thus, a passive resistive and an inertial prototypes were prepared to characterize and reconstruct the shape of multiple phantoms. Preliminary results show how the passive device generates a minimum scatter between the reconstructed image and the actual shap

Nanoparticle electrical impedance tomography

We have developed a new approach to imaging with electrical impedance tomography (EIT) using gold nanoparticles (AuNPs) to enhance impedance changes at targeted tissue sites. This is achieved using radio frequency (RF) to heat nanoparticles while applying EIT imaging. The initial results using 5-nm citrate coated AuNPs show that heating can enhance the impedance in a solution containing AuNPs due to the application of an RF field at 2.60 GHz

1D TiO2 nanostructures probed by 2D transmission electron microscopy

Hybrid solar cells based on nanoparticulate TiO2, dye and poly(3-hexylthiophene) are a common benchmark in the field of solid-state dye-sensitized solar cells. One-dimensionally nanostructured titanium dioxide is expected to enhance power-conversion efficiency (PCE) due to a high surface area combined with a direct path for electrons from the active interface to the back electrode. However, current devices do not meet those expectations and cannot surpass their mesoporous counterparts. This work approaches the problem by detailed investigation of diverse nanostructures on a nanoscale by advanced transmission electron microscopy (TEM). Anodized TiO2 nanotubes are analyzed concerning their crystallinity. An unexpectedly large grain size is found, and its implication is shown by corresponding solar cell characteristics which feature an above-average fill factor. Quasi-single crystalline rutile nanowires are grown hydrothermally, and a peculiar defect structure consisting of free internal surfaces is revealed. A growth model based on Coulombic repulsion and steric hindrance is developed to explain the resulting V-shaped defect cascade. The influence of the defects on solar cell performance is investigated and interpreted by a combination of TEM, electronic device characterization and photoluminescence spectroscopy, including lifetime measurements. A specific annealing treatment is proposed to counter the defects, suppressing several loss mechanisms and resulting in an improvement of PCEs by 35 %. Simultaneously, a process is developed to streamline electron-tomographic reconstruction of complex nanoparticles. Its suitability is demonstrated by the reconstruction of a gold nanostar and a number of iron-based particles distributed on few-layered graphene

The Boston University Photonics Center annual report 2007-2008

This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2007-2008 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.The following report summarizes activities of the Boston University Photonics Center (BUPC) during the period July 2007 through June 2008. These activities span the Center’s complementary missions in education, research, technology development, and commercialization. Faculty research activity reached an all time high when evaluated by the accepted metrics of external funding, scholarly publications, honors and awards. The Center’s educational programs were bolstered by two summer programs hosting more than 40 undergraduate interns, and by the renewal of a competitive graduate fellowship program sponsoring ten BUPC graduate fellowships. In technology development, the prototype RedOwl sniper detection system pioneered by Center faculty, staff, and industry partners was field-tested by the US Department of Defense. RedOwl has been officially transitioned to industry partners for further commercial development along with the soldier wearable Enhanced Acoustic Gear for Locating Enemies (EAGLE) system. Three defense/security prototypes were developed by BUPC to address critical national defense needs in the past year. Four faculty development projects were supported in collaboration with the Army Research Laboratory’s Sensors and Electron Devices Directorate (ARL-SEDD) to fill the technology pipeline for our future defense-related prototyping efforts. The Center’s business incubator is at capacity with various technology companies ranging from photonics to life sciences. The incubator provides a stimulating intellectual environment, outstanding facilities, and professional business expertise to participating companies