Displaying publications 1 - 20 of 1991 in total

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  1. Jong WL, Ung NM, Vannyat A, Jamalludin Z, Rosenfeld A, Wong JH
    Phys Med, 2017 Jan;33:127-135.
    PMID: 28089106 DOI: 10.1016/j.ejmp.2016.12.020
    Dosimetry in small radiation field is challenging and complicated because of dose volume averaging and beam perturbations in a detector. We evaluated the suitability of the "Edge-on" MOSkin (MOSFET) detector in small radiation field measurement. We also tested the feasibility for dosimetric verification in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). "Edge-on" MOSkin detector was calibrated and the reproducibility and linearity were determined. Lateral dose profiles and output factors were measured using the "Edge-on" MOSkin detector, ionization chamber, SRS diode and EBT2 film. Dosimetric verification was carried out on two SRS and five SRT plans. In dose profile measurements, the "Edge-on" MOSkin measurements concurred with EBT2 film measurements. It showed full width at half maximum of the dose profile with average difference of 0.11mm and penumbral width with difference of ±0.2mm for all SRS cones as compared to EBT2 film measurement. For output factor measurements, a 1.1% difference was observed between the "Edge-on" MOSkin detector and EBT2 film for 4mm SRS cone. The "Edge-on" MOSkin detector provided reproducible measurements for dose verification in real-time. The measured doses concurred with the calculated dose for SRS (within 1%) and SRT (within 3%). A set of output correction factors for the "Edge-on" MOSkin detector for small radiation fields were derived from EBT2 film measurement and presented. This study showed that the "Edge-on" MOSkin detector is a suitable tool for dose verification in small radiation field.
    Matched MeSH terms: Reproducibility of Results
  2. Sepucha KR, Matlock DD, Wills CE, Ropka M, Joseph-Williams N, Stacey D, et al.
    Med Decis Making, 2014 07;34(5):560-6.
    PMID: 24713692 DOI: 10.1177/0272989X14528381
    BACKGROUND: This review systematically appraises the quality of reporting of measures used in trials to evaluate the effectiveness of patient decision aids (PtDAs) and presents recommendations for minimum reporting standards.

    METHODS: We reviewed measures of decision quality and decision process in 86 randomized controlled trials (RCTs) from the 2011 Cochrane Collaboration systematic review of PtDAs. Data on development of the measures, reliability, validity, responsiveness, precision, interpretability, feasibility, and acceptability were independently abstracted by 2 reviewers.

    RESULTS: Information from 178 instances of use of measures was abstracted. Very few studies reported data on the performance of measures, with reliability (21%) and validity (16%) being the most common. Studies using new measures were less likely to include information about their psychometric performance. The review was limited to reporting of measures in studies included in the Cochrane review and did not consult prior publications.

    CONCLUSIONS: Very little is reported about the development or performance of measures used to evaluate the effectiveness of PtDAs in published trials. Minimum reporting standards are proposed to enable authors to prepare study reports, editors and reviewers to evaluate submitted papers, and readers to appraise published studies.

    Matched MeSH terms: Reproducibility of Results
  3. Pavlov YG, Adamian N, Appelhoff S, Arvaneh M, Benwell CSY, Beste C, et al.
    Cortex, 2021 11;144:213-229.
    PMID: 33965167 DOI: 10.1016/j.cortex.2021.03.013
    There is growing awareness across the neuroscience community that the replicability of findings about the relationship between brain activity and cognitive phenomena can be improved by conducting studies with high statistical power that adhere to well-defined and standardised analysis pipelines. Inspired by recent efforts from the psychological sciences, and with the desire to examine some of the foundational findings using electroencephalography (EEG), we have launched #EEGManyLabs, a large-scale international collaborative replication effort. Since its discovery in the early 20th century, EEG has had a profound influence on our understanding of human cognition, but there is limited evidence on the replicability of some of the most highly cited discoveries. After a systematic search and selection process, we have identified 27 of the most influential and continually cited studies in the field. We plan to directly test the replicability of key findings from 20 of these studies in teams of at least three independent laboratories. The design and protocol of each replication effort will be submitted as a Registered Report and peer-reviewed prior to data collection. Prediction markets, open to all EEG researchers, will be used as a forecasting tool to examine which findings the community expects to replicate. This project will update our confidence in some of the most influential EEG findings and generate a large open access database that can be used to inform future research practices. Finally, through this international effort, we hope to create a cultural shift towards inclusive, high-powered multi-laboratory collaborations.
    Matched MeSH terms: Reproducibility of Results
  4. Abd Rahim MA, Johani FH, Shah SA, Hassan MR, Abdul Manaf MR
    Ann Glob Health, 2019 Jul 24;85(1).
    PMID: 31348624
    BACKGROUND: Helicobacter pylori (H. pylori) infection is known to be associated with peptic ulcer and gastric cancer. Detection of H. pylori infection is a significant part of peptic ulcer and gastric cancer prevention and management. 13C-urea breath test (UBT) provides a good option for the pathogen detection due to its accuracy and safety.

    OBJECTIVE: This review aims to evaluate the 13C-UBT diagnostic accuracy studies conducted among Asian population and validate its use for the Asian population.

    METHODS: Original articles were systematically searched in PubMed, Scopus, and Google Scholar using the PICOS strategy by applying relevant keywords. Only studies published in English and conducted in Asia were included. Our search returned 276 articles. After assessment, 11 articles which answered our research question and met the criteria set for systematic review and meta-analysis were accepted. A total of 15 study protocols were extracted from the 11 accepted articles.

    FINDINGS: Majority of the studies were conducted in Hong Kong (six), followed by Taiwan (five), Japan (two), and one each in Singapore and Israel. All studies had used histology as part of its gold standard of reference. All but one study was performed on adult populations. The summary estimate for sensitivity was 97% (95% CI: 96, 98%), and specificity was 96% (95% CI: 95, 97%), with significant heterogeneity between studies. Adjusting for the dose (50 mg) and breath sample collection time (20 minutes) had improved both accuracy estimates and significantly reduced heterogeneity.

    CONCLUSION: This review supports the test-and-treat strategy for H. pylori infection management. Prevalence and cost-effectiveness studies are mandatory for health authorities to adopt this strategy into national policy.

    Matched MeSH terms: Reproducibility of Results
  5. Fathinul Fikri AS, Dharmendran R, Vikneswaran P, Nordin AJ
    Abdom Imaging, 2015 Aug;40(6):1457-64.
    PMID: 25576048 DOI: 10.1007/s00261-014-0343-2
    A study was undertaken to investigate the value of pretreatment PET-CT in predicting survival in patients with oesophageal cancer (OC).
    Matched MeSH terms: Reproducibility of Results
  6. Leong SS, Wong JHD, Rozalli FI, Yahya F, Tee YC, Yamin LSM, et al.
    Skeletal Radiol, 2024 Mar;53(3):455-463.
    PMID: 37594519 DOI: 10.1007/s00256-023-04425-1
    OBJECTIVE: To establish the scanning protocol for 2-dimensional shear wave elastography (SWE) on normal entheses by investigating the possible confounding factors that may increase the variability of measured elasticity.

    MATERIAL AND METHODS: 30 normal quadriceps entheses were scanned using SWE to compare the stiffness and coefficient variation by changing the ultrasonic coupling gel thickness, knee position, region of interest size, and scanning plane.

    RESULTS: No significant difference in median shear wave velocity (SWV) was observed in different coupling gel thicknesses. The median SWV was higher in the knee flexion position than in the extended position (p  0.05). For interobserver reliability for the proposed protocol, the intraclass correlation coefficients was 0.763.

    CONCLUSION: In this study, we determined supine position with the knee extended; using 2.0 mm diameter region of interest and image acquisition at the longitudinal plane with thicker layer coupling gel seems most appropriate to reliably image healthy quadriceps entheses with SWE.

    Matched MeSH terms: Reproducibility of Results
  7. Ahmad Fadzil MH, Prakasa E, Asirvadam VS, Nugroho H, Affandi AM, Hussein SH
    Comput Biol Med, 2013 Nov;43(11):1987-2000.
    PMID: 24054912 DOI: 10.1016/j.compbiomed.2013.08.009
    Psoriasis is an incurable skin disorder affecting 2-3% of the world population. The scaliness of psoriasis is a key assessment parameter of the Psoriasis Area and Severity Index (PASI). Dermatologists typically use visual and tactile senses in PASI scaliness assessment. However, the assessment can be subjective resulting in inter- and intra-rater variability in the scores. This paper proposes an assessment method that incorporates 3D surface roughness with standard clustering techniques to objectively determine the PASI scaliness score for psoriasis lesions. A surface roughness algorithm using structured light projection has been applied to 1999 3D psoriasis lesion surfaces. The algorithm has been validated with an accuracy of 94.12%. Clustering algorithms were used to classify the surface roughness measured using the proposed assessment method for PASI scaliness scoring. The reliability of the developed PASI scaliness algorithm was high with kappa coefficients>0.84 (almost perfect agreement).
    Matched MeSH terms: Reproducibility of Results
  8. Teo PC, Kassim AY, Thevarajan K
    J Orthop Surg (Hong Kong), 2013 Dec;21(3):340-6.
    PMID: 24366797
    To propose a novel method to measure the neck shaft angle and anteversion of the femur using anteroposterior and 45-degree oblique radiographs.
    Matched MeSH terms: Reproducibility of Results
  9. Sahathevan R, Mohd Ali K, Ellery F, Mohamad NF, Hamdan N, Mohd Ibrahim N, et al.
    Int Psychogeriatr, 2014 May;26(5):781-6.
    PMID: 24472343 DOI: 10.1017/S1041610213002615
    Many stroke research trials do not include assessment of cognitive function. A Very Early Rehabilitation Trial (AVERT) is an international multicenter study that includes the Montreal Cognitive Assessment (MoCA) as an outcome. At the Malaysian AVERT site, completion of the MoCA has been limited by low English proficiency in some participants. We aimed to develop a Bahasa Malaysia (BM) version of the MoCA and to validate it in a stroke population.
    Matched MeSH terms: Reproducibility of Results
  10. Chai JH, Lo CH, Mayor J
    J Speech Lang Hear Res, 2020 10 16;63(10):3488-3500.
    PMID: 32897770 DOI: 10.1044/2020_JSLHR-20-00361
    Purpose This study introduces a framework to produce very short versions of the MacArthur-Bates Communicative Development Inventories (CDIs) by combining the Bayesian-inspired approach introduced by Mayor and Mani (2019) with an item response theory-based computerized adaptive testing that adapts to the ability of each child, in line with Makransky et al. (2016). Method We evaluated the performance of our approach-dynamically selecting maximally informative words from the CDI and combining parental response with prior vocabulary data-by conducting real-data simulations using four CDI versions having varying sample sizes on Wordbank-the online repository of digitalized CDIs: American English (a very large data set), Danish (a large data set), Beijing Mandarin (a medium-sized data set), and Italian (a small data set). Results Real-data simulations revealed that correlations exceeding .95 with full CDI administrations were reached with as few as 15 test items, with high levels of reliability, even when languages (e.g., Italian) possessed few digitalized administrations on Wordbank. Conclusions The current approach establishes a generic framework that produces very short (less than 20 items) adaptive early vocabulary assessments-hence considerably reducing their administration time. This approach appears to be robust even when CDIs have smaller samples in online repositories, for example, with around 50 samples per month-age.
    Matched MeSH terms: Reproducibility of Results
  11. Ahmad NA, Yook Heng L, Salam F, Mat Zaid MH, Abu Hanifah S
    Sensors (Basel), 2019 Nov 05;19(21).
    PMID: 31694284 DOI: 10.3390/s19214813
    A developed colorimetric pH sensor film based on edible materials for real-time monitoring of food freshness is described. The mixed natural dyes from edible plants Clitoria sp and Brassica sp were extracted and incorporated into ι-carrageenan film as a colorimetric pH sensor film for monitoring food spoilage and its freshness. The color changes of the developed colorimetric sensor film were measured with chromametry and UV-vis spectroscopy, respectively. Experimental results show that colorimetric pH sensor film demonstrated statistically significant differences (p < 0.05) between CIE-L*a*b* coordinates color system indicated that the developed colorimetric sensor film was able to give a gradual change in color over a wide pH range. The color of the colorimetric sensor film also changes discretely and linearly with factors that contribute to food spoilage using shrimp and durian samples. Moreover, the developed colorimetric pH sensor film has the potential to be used as a safe, non-destructive testing and also a flexibly visual method for direct assessment of food freshness indicator during storage.
    Matched MeSH terms: Reproducibility of Results
  12. Shamsudin S, Selamat J, Sanny M, A R SB, Jambari NN, Khatib A
    Molecules, 2019 Oct 29;24(21).
    PMID: 31671885 DOI: 10.3390/molecules24213898
    Stingless bee honey produced by Heterotrigona itama from different botanical origins was characterised and discriminated. Three types of stingless bee honey collected from acacia, gelam, and starfruit nectars were analyzed and compared with Apis mellifera honey. The results showed that stingless bee honey samples from the three different botanical origins were significantly different in terms of their moisture content, pH, free acidity, total soluble solids, colour characteristics, sugar content, amino acid content and antioxidant properties. Stingless bee honey was significantly different from Apis mellifera honey in terms of physicochemical and antioxidant properties. The amino acid content was further used in the chemometrics analysis to evaluate the role of amino acid in discriminating honey according to botanical origin. Partial least squares-discriminant analysis (PLS-DA) revealed that the stingless bee honey was completely distinguishable from Apis mellifera honey. Notably, a clear distinction between the stingless bee honey types was also observed. The specific amino acids involved in the distinction of honey were cysteine for acacia and gelam, phenylalanine and 3-hydroxyproline for starfruit, and proline for Apis mellifera honey. The results showed that all honey samples were successfully classified based on amino acid content.
    Matched MeSH terms: Reproducibility of Results
  13. Mumtaz W, Malik AS
    Brain Topogr, 2018 09;31(5):875-885.
    PMID: 29860588 DOI: 10.1007/s10548-018-0651-x
    The choice of an electroencephalogram (EEG) reference has fundamental importance and could be critical during clinical decision-making because an impure EEG reference could falsify the clinical measurements and subsequent inferences. In this research, the suitability of three EEG references was compared while classifying depressed and healthy brains using a machine-learning (ML)-based validation method. In this research, the EEG data of 30 unipolar depressed subjects and 30 age-matched healthy controls were recorded. The EEG data were analyzed in three different EEG references, the link-ear reference (LE), average reference (AR), and reference electrode standardization technique (REST). The EEG-based functional connectivity (FC) was computed. Also, the graph-based measures, such as the distances between nodes, minimum spanning tree, and maximum flow between the nodes for each channel pair, were calculated. An ML scheme provided a mechanism to compare the performances of the extracted features that involved a general framework such as the feature extraction (graph-based theoretic measures), feature selection, classification, and validation. For comparison purposes, the performance metrics such as the classification accuracies, sensitivities, specificities, and F scores were computed. When comparing the three references, the diagnostic accuracy showed better performances during the REST, while the LE and AR showed less discrimination between the two groups. Based on the results, it can be concluded that the choice of appropriate reference is critical during the clinical scenario. The REST reference is recommended for future applications of EEG-based diagnosis of mental illnesses.
    Matched MeSH terms: Reproducibility of Results
  14. Endarti D, Riewpaiboon A, Thavorncharoensap M, Praditsitthikorn N, Hutubessy R, Kristina SA
    Value Health Reg Issues, 2018 May;15:50-55.
    PMID: 29474178 DOI: 10.1016/j.vhri.2017.07.008
    OBJECTIVES: To gain insight into the most suitable foreign value set among Malaysian, Singaporean, Thai, and UK value sets for calculating the EuroQol five-dimensional questionnaire index score (utility) among patients with cervical cancer in Indonesia.

    METHODS: Data from 87 patients with cervical cancer recruited from a referral hospital in Yogyakarta province, Indonesia, from an earlier study of health-related quality of life were used in this study. The differences among the utility scores derived from the four value sets were determined using the Friedman test. Performance of the psychometric properties of the four value sets versus visual analogue scale (VAS) was assessed. Intraclass correlation coefficients and Bland-Altman plots were used to test the agreement among the utility scores. Spearman ρ correlation coefficients were used to assess convergent validity between utility scores and patients' sociodemographic and clinical characteristics. With respect to known-group validity, the Kruskal-Wallis test was used to examine the differences in utility according to the stages of cancer.

    RESULTS: There was significant difference among utility scores derived from the four value sets, among which the Malaysian value set yielded higher utility than the other three value sets. Utility obtained from the Malaysian value set had more agreements with VAS than the other value sets versus VAS (intraclass correlation coefficients and Bland-Altman plot tests results). As for the validity, the four value sets showed equivalent psychometric properties as those that resulted from convergent and known-group validity tests.

    CONCLUSIONS: In the absence of an Indonesian value set, the Malaysian value set was more preferable to be used compared with the other value sets. Further studies on the development of an Indonesian value set need to be conducted.

    Matched MeSH terms: Reproducibility of Results
  15. Solayar GN, Chinappa J, Harris IA, Chen DB, Macdessi SJ
    Malays Orthop J, 2017 Jul;11(2):45-52.
    PMID: 29021879 MyJurnal DOI: 10.5704/MOJ.1707.006
    Introduction: Optimal coronal and sagittal component positioning is important in achieving a successful outcome following total knee arthroplasty (TKA). Modalities to determine post-operative alignment include plain radiography and computer tomography (CT) imaging. This study aims to determine the accuracy and reliability of plain radiographs in measuring coronal and sagittal alignment following TKA. Materials and Methods: A prospective, consecutive study of 58 patients undergoing TKA was performed comparing alignment data from plain radiographs and CT imaging. Hip-knee-angle (HKA), sagittal femoral angle (SFA) and sagittal tibial angle (STA) measurements were taken by two observers from plain radiographs and compared with CT alignment. Intra- and inter-observer correlation was calculated for each measurement. Results: Intra-observer correlation was excellent for HKA (r>0.89) with a mean difference of <1.9°. The least intra-observer correlation was for SFA (mean r=0.58) with a mean difference of 8°. Inter-observer correlation was better for HKA (r>0.95) and STA (r>0.8) compared to SFA (r=0.5). When comparing modalities (radiographs vs CT), HKA estimations for both observers showed the least maximum and mean differences while SFA observations were the least accurate. Conclusion: Radiographic estimation of HKA showed excellent intra- and inter-observer correlation and corresponds well with CT imaging. However, radiographic estimation of sagittal plane alignment was less reliably measured and correlated less with CT imaging. Plain radiography was found to be inferior to CT for estimation of biplanar prosthetic alignment following TKA.
    Matched MeSH terms: Reproducibility of Results
  16. Gupta H, Batta NS, Kataria H, Batra V, Upadhyay AD, Jain V, et al.
    Malays Orthop J, 2020 Mar;14(1):34-41.
    PMID: 32296480 DOI: 10.5704/MOJ.2003.006
    Introduction: An increased tibial tuberosity-trochlear groove (TTTG) distance is used for deciding a treatment plan in patello-femoral instability (PFI). The centre of the patellar tendon and the chondral trochlear groove can be directly visualised on MRI, and measured, giving the patellar tendon-trochlear groove (PTTG) distance. A study was designed to compare the inter-rater and the test-retest reliabilities of PTTG and TTTG measurements in MRI of patients without PFI and in a group with PFI.

    Materials and Methods: This cross-sectional reliability study was done on archival MRI films of 50 patients without patellar instability and 20 patients with patellar instability. TTTG and PTTG distances were independently measured by two orthopaedic surgeons and two radiologists. A hybrid PTTG measurement with bony landmarks on the femoral side and the patellar tendon landmark on the tibial side, was used to estimate the influence of the differences in the femoral and tibial landmarks on the difference in reliabilities. The intra-class correlation coefficient (ICC) was calculated for all four raters, as well as separately for each rater.

    Results: The PTTG distance had a higher inter-rater reliability (ICC=0.86, 95% CI=0.79-0.92) compared to the TTTG distance (ICC=0.70, 95% CI=0.59-0.80) in patients without PFI. Similar trends were seen in patients with PFI (0.83 vs 0.66). The inter-rater reliability for the hybrid PTTG distance was found to lie in between the TTTG and PTTG.

    Conclusions: The MRI-based PTTG distance had better inter-rater reliability compared with the MRI-based TTTG distance.

    Matched MeSH terms: Reproducibility of Results
  17. Sharif Nia H, Lehto RH, Pahlevan Sharif S, Mashrouteh M, Goudarzian AH, Rahmatpour P, et al.
    Omega (Westport), 2021 Sep;83(4):760-776.
    PMID: 31366310 DOI: 10.1177/0030222819865407
    Ensuring use of valid and reliable scales for evaluating death anxiety that are relevant to the cultural context where they are applied is essential. The purpose of the study was to conduct a systematic review of the psychometric properties of Templer's Death Anxiety Scale (DAS) across cultures. PubMed, Scopus, Web of Knowledge, SID, and Magiran databases were systematically searched for studies published between 1970 and 2017 using Mesh terms. Two independent researchers used Quality Assessment of Diagnostic Accuracy Studies and Checklist of Standards for Reporting of Diagnostic Accuracy to evaluate study quality. Included studies were conducted in Iran, United States, Italy, China, Egypt, Spain, and Australia. Overall study quality was acceptable in 15 evaluated articles. However, findings demonstrated that two (one study), three (seven studies), four (four studies), and five factors (three studies) were extracted across the respective studies. Confirmatory concurrent validity was assessed in two studies. While Templer's DAS has stood the test of time as a commonly used index of capturing the conscious experience of death anxiety, there are psychometric inconsistencies in identified factor solutions across cultures. Findings emphasize the need for continued evaluation of how the DAS is translated in specific countries with assessment in relation to other death construct tools.
    Matched MeSH terms: Reproducibility of Results
  18. Nguyen HN, Nguyen TY, Tran KV, Tran TT, Nguyen TT, Phan VD, et al.
    Materials (Basel), 2019 Feb 16;12(4).
    PMID: 30781542 DOI: 10.3390/ma12040598
    Triple-layered composite plates are created by joining three composite layers using shear connectors. These layers, which are assumed to be always in contact and able to move relatively to each other during deformation, could be the same or different in geometric dimensions and material. They are applied in various engineering fields such as ship-building, aircraft wing manufacturing, etc. However, there are only a few publications regarding the calculation of this kind of plate. This paper proposes novel equations, which utilize Mindlin's theory and finite element modelling to simulate the forced vibration of triple-layered composite plates with layers connected by shear connectors subjected to a moving load. Moreover, a Matlab computation program is introduced to verify the reliability of the proposed equations, as well as the influence of some parameters, such as boundary conditions, the rigidity of the shear connector, thickness-to-length ratio, and the moving load velocity on the dynamic response of the composite plate.
    Matched MeSH terms: Reproducibility of Results
  19. Ahmed S, Rahman T, Ripon MSH, Rashid HU, Kashem T, Md Ali MS, et al.
    Nutrients, 2021 Dec 17;13(12).
    PMID: 34960076 DOI: 10.3390/nu13124521
    Diet is a recognized risk factor and cornerstone for chronic kidney disease (CKD) management; however, a tool to assess dietary intake among Bangladeshi dialysis patients is scarce. This study aims to validate a prototype Bangladeshi Hemodialysis Food Frequency Questionnaire (BDHD-FFQ) against 3-day dietary recall (3DDR) and corresponding serum biomarkers. Nutrients of interest were energy, macronutrients, potassium, phosphate, iron, sodium and calcium. The BDHD-FFQ, comprising 132 food items, was developed from 606 24-h recalls and had undergone face and content validation. Comprehensive facets of relative validity were ascertained using six statistical tests (correlation coefficient, percent difference, paired t-test, cross-quartiles classification, weighted kappa, and Bland-Altman analysis). Overall, the BDHD-FFQ showed acceptable to good correlations (p < 0.05) with 3DDR for the concerned nutrients in unadjusted and energy-adjusted models, but this correlation was diminished when adjusted for other covariates (age, gender, and BMI). Phosphate and potassium intake, estimated by the BDHD-FFQ, also correlated well with the corresponding serum biomarkers (p < 0.01) when compared to 3DDR (p > 0.05). Cross-quartile classification indicated that <10% of patients were incorrectly classified. Weighted kappa statistics showed agreement with all but iron. Bland-Altman analysis showed positive mean differences were observed for all nutrients when compared to 3DDR, whilst energy, carbohydrates, fat, iron, sodium, and potassium had percentage data points within the limit of agreement (mean ± 1.96 SD), above 95%. In summary, the BDHD-FFQ demonstrated an acceptable relative validity for most of the nutrients as four out of the six statistical tests fulfilled the cut-off standard in assessing dietary intake of CKD patients in Bangladesh.
    Matched MeSH terms: Reproducibility of Results
  20. Masroor K, Jeoti V, Drieberg M, Cheab S, Rajbhandari S
    Sensors (Basel), 2021 Apr 22;21(9).
    PMID: 33922288 DOI: 10.3390/s21092943
    The bi-directional information transfer in optical body area networks (OBANs) is crucial at all the three tiers of communication, i.e., intra-, inter-, and beyond-BAN communication, which correspond to tier-I, tier-II, and tier-III, respectively. However, the provision of uninterrupted uplink (UL) and downlink (DL) connections at tier II (inter-BAN) are extremely critical, since these links serve as a bridge between tier-I (intra-BAN) and tier-III (beyond-BAN) communication. Any negligence at this level could be life-threatening; therefore, enabling quality-of-service (QoS) remains a fundamental design issue at tier-II. Consequently, to provide QoS, a key parameter is to ensure link reliability and communication quality by maintaining a nearly uniform signal-to-noise ratio (SNR) within the coverage area. Several studies have reported the effects of transceiver related parameters on OBAN link performance, nevertheless the implications of changing transmitter locations on the SNR uniformity and communication quality have not been addressed. In this work, we undertake a DL scenario and analyze how the placement of light-emitting diode (LED) lamps can improve the SNR uniformity, regardless of the receiver position. Subsequently, we show that using the principle of reciprocity (POR) and with transmitter-receiver positions switched, the analysis is also applicable to UL, provided that the optical channel remains linear. Moreover, we propose a generalized optimal placement scheme along with a heuristic design formula to achieve uniform SNR and illuminance for DL using a fixed number of transmitters and compare it with an existing technique. The study reveals that the proposed placement technique reduces the fluctuations in SNR by 54% and improves the illuminance uniformity up to 102% as compared to the traditional approach. Finally, we show that, for very low luminous intensity, the SNR values remain sufficient to maintain a minimum bit error rate (BER) of 10-9 with on-off keying non-return-to-zero (OOK-NRZ) modulation format.
    Matched MeSH terms: Reproducibility of Results
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