Lambe Institute for Translational Research (Scholarly Articles)

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  • Publication
    Dielectric properties of bones for the monitoring of osteoporosis
    (Springer, 2018-08-29) Amin, Bilal; Elahi, Muhammad Adnan; Shahzad, Atif; Porter, Emily; McDermott, Barry; O’Halloran, Martin; European Research Council; Horizon 2020
    Osteoporosis is one of the most common diseases that leads to bone fractures. Dual-energy X-ray absorptiometry is currently employed to measure the bone mineral density and to diagnose osteoporosis. Alternatively, the dielectric properties of bones are found to be influenced by bone mineral density; hence, dielectric properties of bones may potentially be used to diagnose osteoporosis. Microwave tomographic imaging is currently in development to potentially measure in vivo dielectric properties of bone. Therefore, the foci of this work are to summarize all available dielectric data of bone in the microwave frequency range and to analyze the confounders that may have resulted in variations in reported data. This study also compares the relationship between the dielectric properties and bone quality reported across different studies. The review suggests that variations exist in the dielectric properties of bone and the relationship between bone volume fraction and dielectric properties is in agreement across all studies. Conversely, the evidence of a relationship between bone mineral density and dielectric properties is inconsistent across the studies. This summary of dielectric data of bone along with a comparison of the relationship between the dielectric properties and bone quality will accelerate the development of microwave tomographic imaging devices for the monitoring of osteoporosis.
  • Publication
    Multi-frequency symmetry difference electrical impedance tomography with machine learning for human stroke diagnosis
    (IOP Publishing, 2020-06-18) McDermott, Barry James; Elahi, Adnan; Santorelli, Adam; O'Halloran, Martin; Avery James; Porter, Emily
    Objective: Multi-Frequency Symmetry Difference Electrical Impedance Tomography (MFSD-EIT) can robustly detect and identify unilateral perturbations in symmetric scenes. Here, an investigation is performed to assess if the algorithm can be successfully applied to identify the aetiology of stroke with the aid of machine learning. Methods: Anatomically realistic four- layer Finite Element Method models of the head based on stroke patient images are developed and used to generate EIT data over a 5 Hz 100 Hz frequency range with and without bleed and clot lesions present. Reconstruction generates conductivity maps of each head at each frequency. Application of a quantitative metric assessing changes in symmetry across the sagittal plane of the reconstructed image and over the frequency range allows lesion detection and identification. The algorithm is applied to both simulated and human (n=34 subjects) data. A classification algorithm is applied to the metric value in order to differentiate between normal, haemorrhage and clot values. Results: An average accuracy of 85% is achieved when MFSD-EIT with Support Vector Machines (SVM) classification is used to identify and differentiate bleed from clot in human data, with 77% accuracy when differentiating normal from stroke in human data. Conclusion: Applying a classification algorithm to metrics derived from MFSD-EIT images is a novel and promising technique for detection and identification of perturbations in static scenes. Significance: The MFSD-EIT algorithm used with machine learning gives promising results of lesion detection and identification in challenging conditions like stroke. The results imply feasible translation to human patients.
  • Publication
    Association of blood pressure lowering with incident dementia or cognitive impairment: A systematic review and meta-analysis
    (American Medical Association (AMA), 2020-05-19) Hughes, Diarmaid; Judge, Conor; Murphy, Robert; Loughlin, Elaine; Costello, Maria; Whiteley, William; Bosch, Jackie; O'Donnell, Martin J.; Canavan, Michelle; Irish Clinical Academic Training; Wellcome Trust; Health Research Board; Health Service Executive; Health and Social Care, Research and Development Division, Northern Ireland; European Research Council
    The benefit of blood pressure lowering for the prevention of dementia or cognitive impairment is unclear. To determine the association of blood pressure lowering with dementia or cognitive impairment. Search of PubMed, EMBASE, and CENTRAL for randomized clinical trials published from database inception through December 31, 2019, that evaluated the association of blood pressure lowering on cognitive outcomes. The control groups consisted of either placebo, alternative antihypertensive agents, or higher blood pressure targets. Data were screened and extracted independently by 2 authors. Random-effects meta-analysis models were used to report pooled treatment effects and CIs. The primary outcome was dementia or cognitive impairment. The secondary outcomes were cognitive decline and changes in cognitive test scores. Fourteen randomized clinical trials were eligible for inclusion (96 158 participants), of which 12 reported the incidence of dementia (or composite of dementia and cognitive impairment [3 trials]) on follow-up and were included in the primary meta-analysis, 8 reported cognitive decline, and 8 reported changes in cognitive test scores. The mean (SD) age of trial participants was 69 (5.4) years and 40 617 (42.2%) were women. The mean systolic baseline blood pressure was 154 (14.9) mm Hg and the mean diastolic blood pressure was 83.3 (9.9) mm Hg. The mean duration of follow-up was 49.2 months. Blood pressure lowering with antihypertensive agents compared with control was significantly associated with a reduced risk of dementia or cognitive impairment (12 trials; 92¿135 participants) (7.0% vs 7.5% of patients over a mean trial follow-up of 4.1 years; odds ratio [OR], 0.93 [95% CI, 0.88-0.98]; absolute risk reduction, 0.39% [95% CI, 0.09%-0.68%]; I2¿=¿0.0%) and cognitive decline (8 trials) (20.2% vs 21.1% of participants over a mean trial follow-up of 4.1 years; OR, 0.93 [95% CI, 0.88-0.99]; absolute risk reduction, 0.71% [95% CI, 0.19%-1.2%]; I2¿=¿36.1%). Blood pressure lowering was not significantly associated with a change in cognitive test scores. In this meta-analysis of randomized clinical trials, blood pressure lowering with antihypertensive agents compared with control was significantly associated with a lower risk of incident dementia or cognitive impairment.
  • Publication
    Bi-frequency symmetry difference EIT - feasibility and limitations of application to stroke diagnosis
    (Institute of Electrical and Electronics Engineers (IEEE), 2019-12-19) McDermott, Barry; O'Halloran, Martin; Avery, James; Porter, Emily; European Research Council; Horizon 2020; Science Foundation Ireland; Hardiman Research Scholarship, National University of Ireland Galway; RESPECT
    Objective: Bi-Frequency Symmetry Difference (BFSD)-EIT can detect, localize and identify unilateral perturbations in symmetric scenes. Here, we test the viability and robustness of BFSD-EIT in stroke diagnosis. Methods: A realistic 4-layer Finite Element Method (FEM) head model with and without bleed and clot lesions is developed. Performance is assessed with test parameters including: measurement noise, electrode placement errors, contact impedance errors, deviations in assumed tissue conductivity, deviations in assumed anatomy, and a frequency-dependent background. A final test is performed using ischemic patient data. Results are assessed using images and quantitative metrics. Results: BFSD-EIT may be feasible for stroke diagnosis if a signal-to-noise ratio (SNR) of ≥60dB is achievable. Sensitivity to errors in electrode positioning is seen with a tolerance of only ±5mm, but a tolerance of up to ±30mm is possible if symmetry is maintained between symmetrically opposite partner electrodes. The technique is robust to errors in contact impedance and assumed tissue conductivity up to at least ±50%. Asymmetric internal anatomy affects performance but may be tolerable for tissues with frequency-dependent conductivity. Errors in assumed external geometry marginally affect performance. A frequency-dependent background does not affect performance with carefully chosen frequency points or use of multiple frequency points across a band. The Global Left-Hand Side (LHS) & Right-Hand Side (RHS) Mean Intensity metric is particularly robust to errors. Conclusion: BFSD-EIT is a promising technique for stroke diagnosis, provided parameters are within the tolerated ranges. Significance: BFSD-EIT may prove an important step forward in imaging of static scenes such as stroke.
  • Publication
    Gamma band light stimulation in human case studies: Groundwork for potential Alzheimer's disease treatment
    (IOS Press, 2019-05-27) Jones, Marggie; McDermott, Barry; Oliveira, Bárbara Luz; O'Brien, Aoife; Coogan, Declan; Lang, Mark; Moriarty, Niamh; Dowd, Eilis; Quinlan, Leo; Mc Ginley, Brian; Dunne, Eoghan; Newell, David; Porter, Emily; Elahi, Muhammad Adnan; O' Halloran, Martin; Shahzad, Atif
    It is known that proteins associated with Alzheimer's disease (AD) pathogenesis are significantly reduced by 40¿Hz entrainment in mice. If this were to translate to humans, verifying that such a light stimulus can induce a 40¿Hz entrainment response in humans and harnessing insights from these case studies could be one step in the development of a multisensory device to prevent and treat AD. Verify the inducement of a 40¿Hz response in the human brain by a 40¿Hz light stimulus and obtain insights that could potentially aid in the development of a multisensory device for the prevention and treatment of AD. Electroencephalographic brain activity was recorded simultaneously with application of stimulus at different frequencies and intensities. Power spectral densities were analyzed. Entrainment to visual stimuli occurred with the largest response at 40¿Hz. The high intensity 40¿Hz stimulus caused widespread entrainment. The number of electrodes demonstrating entrainment increased with increasing light intensity. Largest amplitudes for the high intensity 40¿Hz stimulus were consistently found at the primary visual cortex. There was a harmonic effect at double the frequency for the 40¿Hz stimulus. An eyes-open protocol caused more entrainment than an eyes-closed protocol. It was possible to induce widespread entrainment using a 40¿Hz light stimulus in this sample cohort. Insights gleaned from these case studies could potentially aid in the development of a multisensory medical device to prevent and treat AD.
  • Publication
    Detection of vesicoureteral reflux using electrical impedance tomography
    (IEEE, 2018-12-14) Dunne, Eoghan; O'Halloran, Martin; Craven, Darren; Puri, Prem; Frehill, Paul; Loughney, Sarah; Porter, Emily; Horizon 2020; Seventh Framework Programme; H2020 Marie Skłodowska-Curie Actions
    Objective: The purpose of this study is to detect vesicoureteral reflux (VUR) non-invasively using electrical impedance tomography (EIT). VUR is characterized by the backflow of urine from the bladder to the kidneys. Methods: Using porcine models, small quantities of a solution mimicking the electrical properties of urine were infused into each ureter. EIT measurements were taken before, during and after the infusion using electrodes positioned around the abdomen. The collected data from 116 experiments were then processed and time-difference images reconstructed. Objective VUR detection was determined through statistical analysis of the mean change in the voltage signals and EIT image pixel intensities. Results: Unilateral VUR was successfully detected in 94.83% of all mean voltage signals and in over 98.28% of the reconstructed images. The images showed strong visual contrast between the region of interest and the background. Conclusion: In animal models, EIT has the capability to detect reflux in the kidneys with high accuracy. The results show promise for EIT to be used for screening of VUR in children. Significance: VUR is the most common congenital urinary tract abnormality in children. The condition predisposes children to urinary tract infections (UTIs) and kidney damage. The current gold standard diagnostic test, a voiding cystourethrogram (VCUG), is invasive and uses ionizing radiation; therefore, there is a need for new tools for identifying VUR in children. This study presents a non-invasive method to detect VUR in animal models, illustrating the potential for EIT as a screening tool in clinical scenarios.
  • Publication
    Bi-frequency symmetry difference electrical impedance tomography a novel technique for perturbation detection in static scenes
    (IOP Publishing, 2019-02-20) McDermott, Barry; Avery, James; O'Halloran, Martin; Aristovich, Kirill Y.; Porter, Emily; Horizon 2020; European Research Council; Science Foundation Ireland; Hardiman Research Scholarship, NUI Galway; Seventh Framework Programme
    Objective: A novel method for the imaging of static scenes using Electrical Impedance Tomography (EIT) is reported with implementation and validation using numerical and phantom models. The technique is applicable to regions featuring symmetry in the normal case, asymmetry in the presence of a perturbation, and where there is a known, frequency-dependent change in the electrical conductivity of the materials in the region. Methods: The stroke diagnostic problem is used as a motivating sample application. The head is largely symmetrical across the sagittal plane. A haemorrhagic or ischaemic lesion located away from the sagittal plane will alter this natural symmetry, resulting in a symmetrical imbalance that can be detected using EIT. Specifically, application of EIT stimulation and measurement protocols at two distinct frequencies detects deviations in symmetry if an asymmetrically positioned lesion is present, with subsequent identification and localisation of the perturbation based on known frequency-dependent conductivity changes. Anatomically accurate computational models are used to demonstrate the feasibility of the proposed technique using different types, sizes, and locations of lesions with frequency-dependent (or independent) conductivity. Further, a realistic experimental head phantom is used to validate the technique using frequency-dependent perturbations emulating the key numerical simulations. Results: Lesion presence, type, and location are detectable using this novel technique. Results are presented in the form of images and corresponding robust quantitative metrics. Better detection is achieved for larger lesions, those further from the sagittal plane, and when measurements have a higher signal-to-noise ratio. Conclusion: Bi-Frequency Symmetry Difference EIT is an exciting new modality of EIT with the ability to detect deviations in the symmetry of a region that occur due to the presence of a lesion. Notably, this modality does not require a time change in the region and thus may be used in static scenarios such as stroke detection.
  • Publication
    Feasibility of water content-based dielectric characterisation of biological tissues using mixture models
    (IEEE, 2019-01-23) Balduino, Roberta; McDermott, Barry; Porter, Emily; Elahi, Muhammad Adnan; Shahzad, Atif; O'Halloran, Martin; Cavagnaro, Marta; Horizon 2020; Science Foundation Ireland; Hardiman Research Scholarship, NUI Galway; RESPECT; Seventh Framework Programme
    This study quantitatively examines the validity of mixture formulae as models to describe the microwave-range dielectric properties of biological tissue of varying water content. Mixture formulae, specifically the Maxwell Garnett and Bruggeman models, are used to predict the dielectric properties of ex-vivo bovine muscle and liver tissue samples varying in water content. The tissues are modelled as comprising of cell and macromolecule inclusions in a water matrix. The model predictions are compared to dielectric measurements performed with a network analyser and dielectric probe in the 0.5 8.5 GHz band. There was a poor match between the properties predicted by the models and the measured results at most frequency points, for both tissue types. However, the overall predicted and measured trends over the measured band correlated well. The Maxwell Garnett and Bruggeman models may prove a valuable tool aiding in the characterisation of the dielectric properties of materials with different water contents, however, currently, direct application of the model with the assumption of solid inclusions in a water matrix is not feasible without substantial improvement to the models. The dielectric properties of biological tissue are of fundamental importance for many medical technologies ranging from diagnostic to therapeutic. There is a need for continuous improvements to be made to the techniques used to measure and characterise the dielectric properties of tissues. Mixture models are investigated in this study as potentially a valuable candidate modelling technique for the dielectric profiling of tissues based on water content.