Displaying publications 41 - 60 of 80 in total

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  1. Monte Carlo skin dose simulation in intraoperative radiotherapy of breast cancer using spherical applicators
    Moradi F, Ung NM, Khandaker MU, Mahdiraji GA, Saad M, Abdul Malik R, et al.
    Phys Med Biol, 2017 Jul 28;62(16):6550-6566.
    PMID: 28708603 DOI: 10.1088/1361-6560/aa7fe6
    The relatively new treatment modality electronic intraoperative radiotherapy (IORT) is gaining popularity, irradiation being obtained within a surgically produced cavity being delivered via a low-energy x-ray source and spherical applicators, primarily for early stage breast cancer. Due to the spatially dramatic dose-rate fall off with radial distance from the source and effects related to changes in the beam quality of the low keV photon spectra, dosimetric account of the Intrabeam system is rather complex. Skin dose monitoring in IORT is important due to the high dose prescription per treatment fraction. In this study, modeling of the x-ray source and related applicators were performed using the Monte Carlo N-Particle transport code. The dosimetric characteristics of the model were validated against measured data obtained using an ionization chamber and EBT3 film as dosimeters. By using a simulated breast phantom, absorbed doses to the skin for different combinations of applicator size (1.5-5 cm) and treatment depth (0.5-3 cm) were calculated. Simulation results showed overdosing of the skin (>30% of prescribed dose) at a treatment depth of 0.5 cm using applicator sizes larger than 1.5 cm. Skin doses were significantly increased with applicator size, insofar as delivering 12 Gy (60% of the prescribed dose) to skin for the largest sized applicator (5 cm diameter) and treatment depth of 0.5 cm. It is concluded that the recommended 0.5-1 cm distance between the skin and applicator surface does not guarantee skin safety and skin dose is generally more significant in cases with the larger applicators.

    HIGHLIGHTS: • Intrabeam x-ray source and spherical applicators were simulated and skin dose was calculated. • Skin dose for constant skin to applicator distance strongly depends on applicator size. • Use of larger applicators generally results in higher skin dose. • The recommended 0.5-1 cm skin to applicator distance does not guarantee skin safety.

    Matched MeSH terms: Monte Carlo Method*
  2. CHARACTERISATION AND EVALUATION OF AL2O3:C-BASED OPTICALLY STIMULATED LUMINESCENT DOSEMETER SYSTEM FOR DIAGNOSTIC X-RAYS: PERSONAL AND IN VIVO DOSIMETRY
    Wong JHD, Bakhsh M, Cheah YY, Jong WL, Khor JS, Ng KH
    Radiat Prot Dosimetry, 2019 Dec 31;187(4):451-460.
    PMID: 31650160 DOI: 10.1093/rpd/ncz186
    This study characterises and evaluates an Al2O3:C-based optically stimulated luminescent dosemeter (OSLD) system, commercially known as the nanoDot™ dosemeter and the InLight® microStar reader, for personal and in vivo dose measurements in diagnostic radiology. The system characteristics, such as dose linearity, reader accuracy, reproducibility, batch homogeneity, energy dependence and signal stability, were explored. The suitability of the nanoDot™ dosemeters was evaluated by measuring the depth dose curve, in vivo dose measurement and image perturbation. The nanoDot™ dosemeters were observed to produce a linear dose with ±2.8% coefficient variation. Significant batch inhomogeneity (8.3%) was observed. A slight energy dependence (±6.1%) was observed between 60 and 140 kVp. The InLight® microStar reader demonstrated good accuracy and a reproducibility of ±2%. The depth dose curve measured using nanoDot™ dosemeters showed slightly lower responses than Monte Carlo simulation results. The total uncertainty for a single dose measurement using this system was 11%, but it could be reduced to 9.2% when energy dependence correction was applied.
    Matched MeSH terms: Monte Carlo Method*
  3. X-ray spectra and quality parameters from Monte Carlo simulation and analytical filters
    Salehi Z, Ya Ali NK, Yusoff AL
    Appl Radiat Isot, 2012 Nov;70(11):2586-9.
    PMID: 22940409 DOI: 10.1016/j.apradiso.2011.12.007
    BEAMnrc was used to derive the X-ray spectra, from which HVL and homogeneity coefficient were determined, for different kVp and filtration settings. Except for the peak at 61 keV, the spectra are in good agreement with the IPEM report 78 data for the case of filtered beams, whereas the unfiltered beams exhibit softer spectra. Although the current attenuation data deviates from the IPEM 78 data by ~±0.5%, this has negligible effects on the calculated HVL values.
    Matched MeSH terms: Monte Carlo Method
  4. Fulltext Monte Carlo Simulations for the Detection of Buried Objects Using Single Sided Backscattered Radiation
    Yip M, Saripan MI, Wells K, Bradley DA
    PLoS One, 2015;10(9):e0135769.
    PMID: 26348619 DOI: 10.1371/journal.pone.0135769
    Detection of buried improvised explosive devices (IEDs) is a delicate task, leading to a need to develop sensitive stand-off detection technology. The shape, composition and size of the IEDs can be expected to be revised over time in an effort to overcome increasingly sophisticated detection methods. As an example, for the most part, landmines are found through metal detection which has led to increasing use of non-ferrous materials such as wood or plastic containers for chemical based explosives being developed.
    Matched MeSH terms: Monte Carlo Method
  5. Design considerations in the estimation of intraclass correlation
    Donner A, Koval JJ
    Ann. Hum. Genet., 1982 07;46(3):271-7.
    PMID: 7125598 DOI: 10.1111/j.1469-1809.1982.tb00718.x
    The design of family studies to estimate the value of an intraclass correlation coefficient p is considered when ni individuals are to be selected from each of k families, i = 1, 2, ..., k. In particular, the accuracy of a balance design (ni = n, i = 1, 2, ..., k) for estimating p is compared with the accuracy of an unbalanced "natural" design, in which the ni are sampled at random from family size distributions that tend to occur in practice. It is found for two different estimators of p that the balanced design is usually preferable, but only to a small degree if the number of families sampled is greater than 50.
    Matched MeSH terms: Monte Carlo Method
  6. Radiation risk for patients undergoing cardiac computed tomography examinations
    Alkhorayef M, Sulieman A, Alzahrani K, Abuzaid M, Alomair OI, Almuwannis M, et al.
    Appl Radiat Isot, 2021 Feb;168:109520.
    PMID: 33307438 DOI: 10.1016/j.apradiso.2020.109520
    The various technological advancements in computed tomography (CT) have resulted in remarkable growth in the use of CT imaging in clinical practice, not the least of which has been its establishment as the most valuable imaging examination for the assessment of cardiovascular system disorders. The objective of this study was to assess the effective radiation dose and radiation risk for patients during cardiac CT procedures, based on studies from four different hospitals equipped with 128 slice CT equipment. A total of eighty-three patients were investigated in this study with different clinical indications. Effective doses were also calculated using software based on Monte Carlo simulation. The mean patient age (years), weight (kg), and body mass index (BMI (kg/m2)) were 49 ± 11, 82 ± 12, and 31 ± 6, respectively. The results of the study revealed that the tube voltage (kVp) and tube current-exposure time product (mAs) ranged between 100 to 140 and 50 to 840 respectively. The overall average patient dose values for the volume CT dose index [(CTDIvol), in mGy)] and dose length product (DLP) (in mGy·cm) were 34.8 ± 15 (3.7-117.0) and 383.8 ± 354 (46.0-3277.0) respectively. The average effective dose (mSv) was 15.2 ± 8 (1.2-61.8). The radiation dose values showed wide variation between different hospitals and even within the same hospital. The results indicate the need to optimize radiation dose and to establish diagnostic reference levels (DRLs) for patients undergoing coronary computed tomography angiography (CCTA), also to harmonize the imaging protocols to ensure reduced radiation risk.
    Matched MeSH terms: Monte Carlo Method
  7. Fulltext Validity and reliability of the Patient Activation Measure® (PAM®)-13 Malay version among patients with Metabolic Syndrome in primary care
    Bahrom NH, Ramli AS, Isa MR, Baharudin N, Badlishah-Sham SF, Mohamed-Yassin MS, et al.
    Malays Fam Physician, 2020;15(3):22-34.
    PMID: 33329860
    Introduction: The Patient Activation Measure (PAM) is one of the most extensively used, widely translated, and tested instruments worldwide in measuring patient activation levels in self-management. This study aimed to determine the validity and reliability of the PAM-13 Malay version among patients with Metabolic Syndrome (MetS) attending a primary care clinic.
    Methods: This work is a cross-sectional validation study among patients with MetS attending a university primary care clinic in Selangor. The PAM-13 Malay version underwent a validation process and field testing. Psychometric properties were examined using principal component analysis (PCA) with varimax rotation, scree plot, Monte Carlo simulation, internal consistency, and test-retest reliability analyses.
    Results: The content of the PAM-13 Malay version and the original version were conceptually equivalent. The questionnaire was refined after face validation by 10 patients with MetS. The refined version was then field-tested among 130 participants (response rate 89.7%). The Kaiser-Meyer-Olkin test was 0.767, and Bartlett's test of sphericity was ≤0.001, indicating sampling adequacy. Two factors were identified and labeled as (1) Passive and Building Knowledge, and (2) Taking Action and Maintaining Behavior. These labels were chosen as they were conceptually consistent with the items representing the levels of activation in PAM-13. The validated PAM-13 Malay version consisted of 13 items, framed into two domains. The overall Cronbach's α was 0.79, and the intraclass correlation coefficient was 0.45.
    Conclusions: The PAM-13 Malay version is valid, reliable, and fairly stable over time. This questionnaire can be used to evaluate the levels of activation among patients with MetS in primary care in Malaysia.
    Study site: Universiti Teknologi MARA (UiTM) primary care clinic, Sungai Buloh, Selangor, Malaysia
    Matched MeSH terms: Monte Carlo Method
  8. Fulltext Tailoring bismuth borate glasses by incorporating PbO/GeO2 for protection against nuclear radiation
    Kumar A, Jain A, Sayyed MI, Laariedh F, Mahmoud KA, Nebhen J, et al.
    Sci Rep, 2021 Apr 08;11(1):7784.
    PMID: 33833308 DOI: 10.1038/s41598-021-87256-1
    Nuclear radiation shielding capabilities for a glass series 20Bi2O3 - xPbO - (80 - 2x)B2O3 - xGeO2 (where x = 5, 10, 20, and 30 mol%) have been investigated using the Phy-X/PSD software and Monte Carlo N-Particle transport code. The mass attenuation coefficients (μm) of selected samples have been estimated through XCOM dependent Phy-X/PSD program and MCNP-5 code in the photon-energy range 0.015-15 MeV. So obtained μm values are used to calculate other γ-ray shielding parameters such as half-value layer (HVL), mean-free-path (MFP), etc. The calculated μm values were found to be 71.20 cm2/g, 76.03 cm2/g, 84.24 cm2/g, and 90.94 cm2/g for four glasses S1 to S4, respectively. The effective atomic number (Zeff)values vary between 69.87 and 17.11 for S1 or 75.66 and 29.11 for S4 over 0.05-15 MeV of photon-energy. Sample S4, which has a larger PbO/GeO2 of 30 mol% in the bismuth-borate glass, possesses the lowest MFP and HVL, providing higher radiation protection efficiency compared to all other combinations. It shows outperformance while compared the calculated parameters (HVL and MFP) with the commercial shielding glasses, different alloys, polymers, standard shielding concretes, and ceramics. Geometric Progression (G-P) was applied for evaluating the energy absorption and exposure buildup factors at energies 0.015-15 MeV with penetration depths up to 40 mfp. The buildup factors showed dependence on the MFP and photon-energy as well. The studied samples' neutron shielding behavior was also evaluated by calculating the fast neutron removal cross-section (ΣR), i.e. found to be 0.139 cm-1 for S1, 0.133 cm-1 for S2, 0.128 cm-1 for S3, and 0.12 cm-1 for S4. The results reveal a great potential for using a glass composite sample S4 in radiation protection applications.
    Matched MeSH terms: Monte Carlo Method
  9. Fulltext Initial testing of a pixelated silicon detector prototype in proton therapy
    Wroe AJ, McAuley G, Teran AV, Wong J, Petasecca M, Lerch M, et al.
    J Appl Clin Med Phys, 2017 Sep;18(5):315-324.
    PMID: 28719019 DOI: 10.1002/acm2.12120
    As technology continues to develop, external beam radiation therapy is being employed, with increased conformity, to treat smaller targets. As this occurs, the dosimetry methods and tools employed to quantify these fields for treatment also have to evolve to provide increased spatial resolution. The team at the University of Wollongong has developed a pixelated silicon detector prototype known as the dose magnifying glass (DMG) for real-time small-field metrology. This device has been tested in photon fields and IMRT. The purpose of this work was to conduct the initial performance tests with proton radiation, using beam energies and modulations typically associated with proton radiosurgery. Depth dose and lateral beam profiles were measured and compared with those collected using a PTW parallel-plate ionization chamber, a PTW proton-specific dosimetry diode, EBT3 Gafchromic film, and Monte Carlo simulations. Measurements of the depth dose profile yielded good agreement when compared with Monte Carlo, diode and ionization chamber. Bragg peak location was measured accurately by the DMG by scanning along the depth dose profile, and the relative response of the DMG at the center of modulation was within 2.5% of that for the PTW dosimetry diode for all energy and modulation combinations tested. Real-time beam profile measurements of a 5 mm 127 MeV proton beam also yielded FWHM and FW90 within ±1 channel (0.1 mm) of the Monte Carlo and EBT3 film data across all depths tested. The DMG tested here proved to be a useful device at measuring depth dose profiles in proton therapy with a stable response across the entire proton spread-out Bragg peak. In addition, the linear array of small sensitive volumes allowed for accurate point and high spatial resolution one-dimensional profile measurements of small radiation fields in real time to be completed with minimal impact from partial volume averaging.
    Matched MeSH terms: Monte Carlo Method
  10. Fulltext Norm-dist Monte-Carlo integrative method for the improvement of fuzzy analytic hierarchy process
    Wicaksono FD, Arshad YB, Sihombing H
    Heliyon, 2020 Apr;6(4):e03607.
    PMID: 32346625 DOI: 10.1016/j.heliyon.2020.e03607
    This paper presents the novel approach of the Norm-dist Monte-Carlo fuzzy analytic hierarchy process (NMCFAHP) to incorporate probabilistic and epistemic uncertainty due to human's judgment vagueness in multi-criteria decision analysis. Normal distribution is applied as the most appropriate distribution model to approximate the probability distribution function of the criteria and alternatives within Monte-Carlo simulation. To test the applicability of the proposed NMCFAHP, the case study of non-destructive test (NDT) technology selection is performed in the Petroleum Company in Borneo, Indonesia. When compared with the conventional triangular fuzzy-AHP, the proposed NMCFAHP method reduces the standard error of mean values by 90.4-99.8% at the final evaluation scores. This means that the proposed NMCFAHP significantly involves fewer errors when dealing with fuzzy uncertainty and stochastic randomness. The proposed NMCFAHP delivers reliable performance to overcome probabilistic uncertainty and epistemic vagueness in the group decision making process.
    Matched MeSH terms: Monte Carlo Method
  11. Tabulation of organ dose conversion factors for terrestrial radioactivity monitoring program
    Sanusi MSM, Hassan WMSW, Hashim S, Ramli AT
    Appl Radiat Isot, 2021 Aug;174:109791.
    PMID: 34062400 DOI: 10.1016/j.apradiso.2021.109791
    Terrestrial radioactivity monitoring of 238U and 232Th series, and 40K in soil is an essential practice for radioactivity and radiation measurement of a place. In conventional practice, only basic data can be in-situ measured using a survey instrument, for example radioactivity concentration in soil and ambient dose equivalent rate. For other physical quantities, for example organ absorbed dose and organ equivalent dose, the measurement is impossible to be performed and can only be computed using Monte Carlo radiation transport simulations. In the past, most of the works only focused on calculating air-kerma-to-effective dose conversion factors. However, the information on organ dose conversion factors is scarcely documented and reported. This study was conducted to calculate organ absorbed and tissue-weighted equivalent dose conversion factors as a result of exposure from terrestrial gamma radiation. Series of organ dose conversion factors is produced based on computations from Monte Carlo MCNP5 simulations using modelled gamma irradiation geometry and established adult MIRD phantom. The study found out that most of the radiation exposed organs absorb energy at comparable rates, except for dense and superficial tissues i.e., skeleton and skin, which indicated slightly higher values. The good agreement between this work and previous studies demonstrated that our gamma irradiation geometry and modelling of gamma radiation sources are adequate. Therefore, the proposed organ dose conversion factors from this study are reasonably acceptable for dose estimation in environmental radioactivity monitoring practices.
    Matched MeSH terms: Monte Carlo Method
  12. Fulltext Naturally Occurring Radioactive Materials in Bracelets and Necklaces: Radiological Risk Evaluation
    Hassan HJ, Hashim S, Abu Hanifah NZH, Ghoshal SK, Sanusi MSM, Binti Suhailin FH, et al.
    Int J Environ Res Public Health, 2021 10 24;18(21).
    PMID: 34769689 DOI: 10.3390/ijerph182111170
    A particular category of jewelry is one involving bracelets and necklaces that are deliberately made to contain naturally occurring radioactive material (NORM)-purveyors making unsubstantiated claims for health benefits from the release of negative ions. Conversely, within the bounds of the linear no-threshold model, long-term use presents a radiological risk to wearers. Evaluation is conducted herein of the radiological risk arising from wearing these products and gamma-ray spectrometry is used to determine the radioactivity levels and annual effective dose of 15 commercially available bracelets (samples B1 to B15) and five necklaces (samples N16 to N20). Various use scenarios are considered; a Geant4 Monte Carlo (Geant4 MC) simulation is also performed to validate the experimental results. The dose conversion coefficient for external radiation and skin equivalent doses were also evaluated. Among the necklaces, sample N16 showed the greatest levels of radioactivity, at 246 ± 35, 1682 ± 118, and 221 ± 40 Bq, for 238U, 232Th, and 40K, respectively. For the bracelets, for 238U and 232Th, sample B15 displayed the greatest level of radioactivity, at 146 ± 21 and 980 ± 71 Bq, respectively. N16 offered the greatest percentage concentrations of U and Th, with means of 0.073 ± 0.0002% and 1.51 ± 0.0015%, respectively, giving rise to an estimated annual effective dose exposure of 1.22 mSv, substantially in excess of the ICRP recommended limit of 1 mSv/year.
    Matched MeSH terms: Monte Carlo Method
  13. Generalized Likelihood Uncertainty Estimation (GLUE) methodology for optimization of extraction in natural products
    Maulidiani, Rudiyanto, Abas F, Ismail IS, Lajis NH
    Food Chem, 2018 Jun 01;250:37-45.
    PMID: 29412925 DOI: 10.1016/j.foodchem.2018.01.023
    Optimization process is an important aspect in the natural product extractions. Herein, an alternative approach is proposed for the optimization in extraction, namely, the Generalized Likelihood Uncertainty Estimation (GLUE). The approach combines the Latin hypercube sampling, the feasible range of independent variables, the Monte Carlo simulation, and the threshold criteria of response variables. The GLUE method is tested in three different techniques including the ultrasound, the microwave, and the supercritical CO2 assisted extractions utilizing the data from previously published reports. The study found that this method can: provide more information on the combined effects of the independent variables on the response variables in the dotty plots; deal with unlimited number of independent and response variables; consider combined multiple threshold criteria, which is subjective depending on the target of the investigation for response variables; and provide a range of values with their distribution for the optimization.
    Matched MeSH terms: Monte Carlo Method
  14. Small field output factor measurement and verification for CyberKnife robotic radiotherapy and radiosurgery system using 3D polymer gel, ionization chamber, diode, diamond and scintillator detectors, Gafchromic film and Monte Carlo simulation
    Al Kafi MA, Arib M, Al Moussa A, Alzorkany F, Shehadeh M, Mohd Yusof MF, et al.
    Appl Radiat Isot, 2023 Feb;192:110576.
    PMID: 36473319 DOI: 10.1016/j.apradiso.2022.110576
    The dosimetry of small fields has become tremendously important with the advent of intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery, where small field segments or very small fields are used to treat tumors. With high dose gradients in the stereotactic radiosurgery or radiotherapy treatment, small field dosimetry becomes challenging due to the lack of lateral electronic equilibrium in the field, x-ray source occlusion, and detector volume averaging. Small volume and tissue-equivalent detectors are recommended to overcome the challenges. With the lack of a perfect radiation detector, studies on available detectors are ongoing with reasonable disagreement and uncertainties. The joint IAEA and AAPM international code of practice (CoP) for small field dosimetry, TRS 483 (Alfonso et al., 2017) provides guidelines and recommendations for the dosimetry of small static fields in external beam radiotherapy. The CoP provides a methodology for field output factor (FOF) measurements and use of field output correction factors for a series of small field detectors and strongly recommends additional measurements, data collection and verification for CyberKnife (CK) robotic stereotactic radiotherapy/radiosurgery system using the listed detectors and more new detectors so that the FOFs can be implemented clinically. The present investigation is focused on using 3D gel along with some other commercially available detectors for the measurement and verification of field output factors (FOFs) for the small fields available in the CK system. The FOF verification was performed through a comparison with published data and Monte Carlo simulation. The results of this study have proved the suitability of an in-house developed 3D polymer gel dosimeter, several commercially available detectors, and Gafchromic films as a part of small field dosimetric measurements for the CK system.
    Matched MeSH terms: Monte Carlo Method
  15. Assessment of bioethanol yield by S. cerevisiae grown on oil palm residues: Monte Carlo simulation and sensitivity analysis
    Samsudin MD, Mat Don M
    Bioresour Technol, 2015 Jan;175:417-23.
    PMID: 25459850 DOI: 10.1016/j.biortech.2014.10.116
    Oil palm trunk (OPT) sap was utilized for growth and bioethanol production by Saccharomycescerevisiae with addition of palm oil mill effluent (POME) as nutrients supplier. Maximum yield (YP/S) was attained at 0.464g bioethanol/g glucose presence in the OPT sap-POME-based media. However, OPT sap and POME are heterogeneous in properties and fermentation performance might change if it is repeated. Contribution of parametric uncertainty analysis on bioethanol fermentation performance was then assessed using Monte Carlo simulation (stochastic variable) to determine probability distributions due to fluctuation and variation of kinetic model parameters. Results showed that based on 100,000 samples tested, the yield (YP/S) ranged 0.423-0.501g/g. Sensitivity analysis was also done to evaluate the impact of each kinetic parameter on the fermentation performance. It is found that bioethanol fermentation highly depend on growth of the tested yeast.
    Matched MeSH terms: Monte Carlo Method
  16. Fulltext Cross-border sexual transmission of the newly emerging HIV-1 clade CRF51_01B
    Cheong HT, Ng KT, Ong LY, Chook JB, Chan KG, Takebe Y, et al.
    PLoS One, 2014;9(10):e111236.
    PMID: 25340817 DOI: 10.1371/journal.pone.0111236
    A novel HIV-1 recombinant clade (CRF51_01B) was recently identified among men who have sex with men (MSM) in Singapore. As cases of sexually transmitted HIV-1 infection increase concurrently in two socioeconomically intimate countries such as Malaysia and Singapore, cross transmission of HIV-1 between said countries is highly probable. In order to investigate the timeline for the emergence of HIV-1 CRF51_01B in Singapore and its possible introduction into Malaysia, 595 HIV-positive subjects recruited in Kuala Lumpur from 2008 to 2012 were screened. Phylogenetic relationship of 485 amplified polymerase gene sequences was determined through neighbour-joining method. Next, near-full length sequences were amplified for genomic sequences inferred to be CRF51_01B and subjected to further analysis implemented through Bayesian Markov chain Monte Carlo (MCMC) sampling and maximum likelihood methods. Based on the near full length genomes, two isolates formed a phylogenetic cluster with CRF51_01B sequences of Singapore origin, sharing identical recombination structure. Spatial and temporal information from Bayesian MCMC coalescent and maximum likelihood analysis of the protease, gp120 and gp41 genes suggest that Singapore is probably the country of origin of CRF51_01B (as early as in the mid-1990s) and featured a Malaysian who acquired the infection through heterosexual contact as host for its ancestral lineages. CRF51_01B then spread rapidly among the MSM in Singapore and Malaysia. Although the importation of CRF51_01B from Singapore to Malaysia is supported by coalescence analysis, the narrow timeframe of the transmission event indicates a closely linked epidemic. Discrepancies in the estimated divergence times suggest that CRF51_01B may have arisen through multiple recombination events from more than one parental lineage. We report the cross transmission of a novel CRF51_01B lineage between countries that involved different sexual risk groups. Understanding the cross-border transmission of HIV-1 involving sexual networks is crucial for effective intervention strategies in the region.
    Matched MeSH terms: Monte Carlo Method
  17. Scattering noise estimation of range-gated imaging system in turbid condition
    Tan C, Seet G, Sluzek A, Wang X, Yuen CT, Fam CY, et al.
    Opt Express, 2010 Sep 27;18(20):21147-54.
    PMID: 20941011 DOI: 10.1364/OE.18.021147
    The range-gated imaging systems are reliable underwater imaging system with the capability to minimize backscattering effect from turbid media. The tail-gating technique has been developed to fine tune the signal to backscattering ratio and hence improve the gated image quality. However, the tail-gating technique has limited image quality enhancement in high turbidity levels. In this paper, we developed a numerical model of range-gated underwater imaging system for near target in turbid medium. The simulation results matched the experimental work favorably. Further investigation using this numerical model shows that the multiple scattering components of the backscattering noise dominate for propagation length larger than 4.2 Attenuation Length (AL). This has limited the enhancement of tail-gating technique in high turbidity conditions.
    Matched MeSH terms: Monte Carlo Method
  18. Transabdominal fetal heart rate detection using NIR photopleythysmography: instrumentation and clinical results
    Gan KB, Zahedi E, Mohd Ali MA
    IEEE Trans Biomed Eng, 2009 Aug;56(8):2075-82.
    PMID: 19403354 DOI: 10.1109/TBME.2009.2021578
    In obstetrics, fetal heart rate (FHR) detection remains the standard for intrapartum assessment of fetal well-being. In this paper, a low-power (< 55 mW) optical technique is proposed for transabdominal FHR detection using near-infrared photoplesthysmography (PPG). A beam of IR-LED (890 nm) propagates through to the maternal abdomen and fetal tissues, resulting in a mixed signal detected by a low-noise detector situated at a distance of 4 cm. Low-noise amplification and 24-bit analog-to-digital converter resolution ensure minimum effect of quantization noise. After synchronous detection, the mixed signal is processed by an adaptive filter to extract the fetal signal, whereas the PPG from the mother's index finger is the reference input. A total of 24 datasets were acquired from six subjects at 37 +/- 2 gestational weeks. Results show a correlation coefficient of 0.96 (p-value < 0.001) between the proposed optical and ultrasound FHR, with a maximum error of 4%. Assessment of the effect of probe position on detection accuracy indicates that the probe should be close to fetal tissues, but not necessarily restricted to head or buttocks.
    Matched MeSH terms: Monte Carlo Method
  19. Predicting graded young modulus values of Ti alloys modified by ion implantation
    Hassan MH
    Med J Malaysia, 2004 May;59 Suppl B:164-5.
    PMID: 15468869
    There has been, and is still, concern about the high elastic modulus of Ti alloys compared to bone. Any reduction in the Young's modulus value of the implant is expected to enhance stress redistribution to the adjacent bone tissues, minimize stress shielding and eventually prolong device lifetime. Dynamic Monte Carlo simulation is used to predict the gradual reduction in Young's modulus values between the bulk of Ti alloys and the modified surface layers due to Ca ion implantation. The simulation can be used as a screening step when applying new alloys and/or coatings.
    Matched MeSH terms: Monte Carlo Method
  20. The specific absorbed dose constant: comparison of values published for 60Co photons
    Samat SB, Evans CJ
    Radiat Prot Dosimetry, 2003;103(4):341-7.
    PMID: 12797557
    For the specific absorbed dose constant for 60Co photons, three values quoted directly in the literature and two derived indirectly from published information are reported. The three publications giving the direct values mentioned no medium of absorption, whereas the other two specify tissue. A database of the specific absorbed dose constant is generated for each of 14 media namely air, water, bone and 11 types of soft tissue. These values are consistent with the three directly quoted values plus one of the indirectly obtained values. Air is found to be unlikely as the medium for the first three; and appropriate media for these are suggested. For the other two values, the generated database suggests that one is too small to be accurate; while the other is correct for tissue (as stated in the publication). An apparent error of 10(3) is identified in one of the values directly quoted.
    Matched MeSH terms: Monte Carlo Method
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