Displaying publications 1 - 20 of 32 in total

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  1. Veerachamy S, Yarlagadda T, Manivasagam G, Yarlagadda PK
    Proc Inst Mech Eng H, 2014 Oct;228(10):1083-99.
    PMID: 25406229 DOI: 10.1177/0954411914556137
    Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants.
  2. Ganesan K, Acharya RU, Chua CK, Laude A
    Proc Inst Mech Eng H, 2014 Sep;228(9):962-70.
    PMID: 25234036 DOI: 10.1177/0954411914550847
    Identification of retinal landmarks is an important step in the extraction of anomalies in retinal fundus images. In the current study, we propose a technique to identify and localize the position of macula and hence the fovea avascular zone, in colour fundus images. The proposed method, based on varying blur scales in images, is independent of the location of other anatomical landmarks present in the fundus images. Experimental results have been provided using the open database MESSIDOR by validating our segmented regions using the dice coefficient, with ground truth segmentation provided by a human expert. Apart from testing the images on the entire MESSIDOR database, the proposed technique was also validated using 50 normal and 50 diabetic retinopathy chosen digital fundus images from the same database. A maximum overlap accuracy of 89.6%-93.8% and locational accuracy of 94.7%-98.9% was obtained for identification and localization of the fovea.
  3. Mehdikhani M, Khalaj N, Chung TY, Mazlan M
    Proc Inst Mech Eng H, 2014 Aug;228(8):819-23.
    PMID: 25205748 DOI: 10.1177/0954411914547714
    Feet displacement is recognized to be an important element in standing and is also linked to postural instability in elderly people with diabetes. This study investigates standing balance in diabetic patients in four asymmetric feet displacements. Quiet standing balance was investigated using the Biodex Balance System in 18 diabetic patients and compared with 18 control elderly subjects. The four standing conditions, namely, comfortable feet position, preferred feet position with a stance width of 17 cm and 15° angle between the medial borders, feet side by side, and heel side by side with a 30° angle between medial edges of feet were evaluated (i.e. eyes opened, eyes closed). The overall stability was calculated by measuring anterior-posterior and medial-lateral indices in standing conditions. Differences among feet positions were compared using an analysis of variance and the independent t-test. The diabetic patients were unstable in the medial-lateral direction when standing with feet side by side versus heel side by side with a 30° angle between medial edges of feet (p = 0.012 and 0.011, respectively), while in controls the anterior-posterior stability scores between standing in preferred foot position with stance width of 17 cm and 15° angle between the medial borders versus feet side by side, and heel side by side with a 30° angle between medial edges of feet versus preferred foot position with stance width of 17 cm and 15° angle between the medial borders had significant difference (p 
  4. Rosli R, Abdul Kadir MR, Kamarul T
    Proc Inst Mech Eng H, 2014 Apr;228(4):342-9.
    PMID: 24622982 DOI: 10.1177/0954411914527074
    Anterior corpectomy and reconstruction using a plate with locking screws are standard procedures for the treatment of cervical spondylotic myelopathy. Although adding more screws to the construct will normally result in improved fixation stability, several issues need to be considered. Past reports have suggested that increasing the number of screws can result in the increase in spinal rigidity, decreased spine mobility, loss of bone and, possibly, screw loosening. In order to overcome this, options to have constrained, semi-constrained or hybrid screw and plate systems were later introduced. The purpose of this study is to compare the stability achieved by four and two screws using different plate systems after one-level corpectomy with placement of cage. A three-dimensional finite-element model of an intact C1-C7 segment was developed from computer tomography data sets, including the cortical bone, soft tissue and simulated corpectomy fusion at C4-C5. A spinal cage and an anterior cervical plate with different numbers of screws and plate systems were constructed to a fit one-level corpectomy of C5. Moment load of 1.0 N m was applied to the superior surface of C1, with C7 was fixed in all degrees of freedom. The kinematic stability of a two-screw plate was found to be statistically equivalent to a four-screw plate for one-level corpectomy. Thus, it can be a better option of fusion and infers comparable stability after one-level anterior cervical corpectomy, instead of a four-screw plate.
  5. Khalaj N, Abu Osman NA, Mokhtar AH, Mehdikhani M, Wan Abas WA
    Proc Inst Mech Eng H, 2014 Feb;228(2):190-9.
    PMID: 24458100 DOI: 10.1177/0954411914521155
    The knee adduction moment represents the medial knee joint load, and greater value is associated with higher load. In people with knee osteoarthritis, it is important to apply proper treatment with the least side effects to reduce knee adduction moment and, consequently, reduce medial knee joint load. This reduction may slow the progression of knee osteoarthritis. The research team performed a literature search of electronic databases. The search keywords were as follows: knee osteoarthritis, knee adduction moment, exercise program, exercise therapy, gait retraining, gait modification and knee joint loading. In total, 12 studies were selected, according to the selection criteria. Findings from previous studies illustrated that exercise and gait retraining programs could alter knee adduction moment in people with knee osteoarthritis. These treatments are noninvasive and nonpharmacological which so far have no or few side effects, as well as being low cost. The results of this review revealed that gait retraining programs were helpful in reducing the knee adduction moment. In contrast, not all the exercise programs were beneficial in reducing knee adduction moment. Future studies are needed to indicate best clinical exercise and gait retraining programs, which are most effective in reducing knee adduction moment in people with knee osteoarthritis.
    Study design: systematic review
  6. As'arry A, Md Zain MZ, Mailah M, Hussein M
    Proc Inst Mech Eng H, 2013 Nov;227(11):1171-80.
    PMID: 23901066 DOI: 10.1177/0954411913494325
    Patients with hand tremors may find routine activities such as writing and holding objects affected. In response to this problem, an active control technique has been examined in order to lessen the severity of tremors. In this article, an online method of a hybrid proportional-integral control with active force control strategy for tremor attenuation is presented. An intelligent mechanism using iterative learning control is incorporated into the active force control loop to approximate the estimation mass parameter. Experiments were conducted on a dummy hand model placed horizontally in a tremor test rig. When activated by a shaker in the vertical direction, this resembles a postural tremor condition. In the proportional-integral plus active force control, a linear voice coil actuator is used as the main active tremor suppressive element. A sensitivity analysis is presented to investigate the robustness of the proposed controller in a real-time control environment. The findings of this study demonstrate that the intelligent active force control and iterative learning controller show excellent performance in reducing tremor error compared to classic pure proportional, proportional-integral and hybrid proportional-integral plus active force control controllers.
  7. Ahamed NU, Sundaraj K, Poo TS
    Proc Inst Mech Eng H, 2013 Mar;227(3):262-74.
    PMID: 23662342
    This article describes the design of a robust, inexpensive, easy-to-use, small, and portable online electromyography acquisition system for monitoring electromyography signals during rehabilitation. This single-channel (one-muscle) system was connected via the universal serial bus port to a programmable Windows operating system handheld tablet personal computer for storage and analysis of the data by the end user. The raw electromyography signals were amplified in order to convert them to an observable scale. The inherent noise of 50 Hz (Malaysia) from power lines electromagnetic interference was then eliminated using a single-hybrid IC notch filter. These signals were sampled by a signal processing module and converted into 24-bit digital data. An algorithm was developed and programmed to transmit the digital data to the computer, where it was reassembled and displayed in the computer using software. Finally, the following device was furnished with the graphical user interface to display the online muscle strength streaming signal in a handheld tablet personal computer. This battery-operated system was tested on the biceps brachii muscles of 20 healthy subjects, and the results were compared to those obtained with a commercial single-channel (one-muscle) electromyography acquisition system. The results obtained using the developed device when compared to those obtained from a commercially available physiological signal monitoring system for activities involving muscle contractions were found to be comparable (the comparison of various statistical parameters) between male and female subjects. In addition, the key advantage of this developed system over the conventional desktop personal computer-based acquisition systems is its portability due to the use of a tablet personal computer in which the results are accessible graphically as well as stored in text (comma-separated value) form.
  8. Oshkour AA, Abu Osman NA, Yau YH, Tarlochan F, Abas WA
    Proc Inst Mech Eng H, 2013 Jan;227(1):3-17.
    PMID: 23516951
    This study aimed to develop a three-dimensional finite element model of a functionally graded femoral prosthesis. The model consisted of a femoral prosthesis created from functionally graded materials (FGMs), cement, and femur. The hip prosthesis was composed of FGMs made of titanium alloy, chrome-cobalt, and hydroxyapatite at volume fraction gradient exponents of 0, 1, and 5, respectively. The stress was measured on the femoral prosthesis, cement, and femur. Stress on the neck of the femoral prosthesis was not sensitive to the properties of the constituent material. However, stress on the stem and cement decreased proportionally as the volume fraction gradient exponent of the FGM increased. Meanwhile, stress became uniform on the cement mantle layer. In addition, stress on the femur in the proximal part increased and a high surface area of the femoral part was involved in absorbing the stress. As such, the stress-shielding area decreased. The results obtained in this study are significant in the design and longevity of new prosthetic devices because FGMs offer the potential to achieve stress distribution that more closely resembles that of the natural bone in the femur.
  9. Bajuri MN, Kadir MR, Amin IM, Ochsner A
    Proc Inst Mech Eng H, 2012 Jul;226(7):510-20.
    PMID: 22913098 DOI: 10.1177/0954411912445846
    The wrist is the most complex joint for virtual three-dimensional simulations, and the complexity is even more pronounced when dealing with skeletal disorders of the joint such, as rheumatoid arthritis (RA). In order to analyse the biomechanical difference between healthy and diseased joints, three-dimensional models of these two wrist conditions were developed from computed tomography images. These images consist of eight carpal bones, five metacarpal bones, the distal radius and ulna. The cartilages were developed based on the shape of the available articulations and ligaments were simulated via mechanical links. The RA model was developed accurately by simulating all ten common criteria of the disease related to the wrist. Results from the finite element (FE) analyses showed that the RA model produced three times higher contact pressure at the articulations compared to the healthy model. Normal physiological load transfer also changed from predominantly through the radial side to an increased load transfer approximately 5% towards the ulnar. Based on an extensive literature search, this is the first ever reported work that simulates the pathological conditions of the rheumatoid arthritis of the wrist joint.
  10. Al-Atabi M, Espino DM, Hukins DW, Buchan KG
    Proc Inst Mech Eng H, 2012 Apr;226(4):275-87.
    PMID: 22611868
    Repair of the mitral valve is defined (loosely) as a procedure that alters the valve structure, without replacement, enabling the natural valve itself to continue to perform under the physical conditions to which it is exposed. As the mitral valve is driven by flow and pressure, it should be feasible to analyse and assess its function, failure and repair as a mechanical system. This article reviews the current state of mechanical evaluation of surgical repairs of the failed mitral valve of the heart. This review describes the anatomy and physiology of the mitral valve, followed by the failure of the mitral valve from a mechanical point of view. The surgical methods used to repair failed valves are introduced, while the use of engineering analysis to aid understanding of mitral valve repair is also reviewed. Finally, a section on recommendations for development and future uses of engineering techniques to surgical repair are presented.
  11. Ibitoye AB, Hamouda AM, Wong SV, Umar RS
    Proc Inst Mech Eng H, 2009 Nov;223(8):1033-40.
    PMID: 20092099
    This study uses computer simulations to study the impact of a motorcycle with the conventional w-beam guardrail. A three-dimensional computer simulation of a scaled hybrid III 50th-percentile male dummy mounted on a motorcycle and colliding with a w-beam guardrail is carried out. A multi-body model of the motorcycle and finite element model of the guardrail are developed using commercially available software. The simulation model is validated with a physical crash test conducted with same initial impact configurations. Impacts at speeds of 32, 48, and 60 km/h at an impact angle at 45 degrees are considered. The predicted forces and accelerations are compared with the biomechanical limits for each body part and the risk of injury to the rider are evaluated. Speed was found to have a significant influence on the level of injury to the head, neck, chest, and femur. A significant reduction of the severity of injuries was found when the impact speed was reduced from 60 to 32km/h. The accelerations experienced by the head and chest are found to be higher than safe levels for impact speeds of 48 and 60 km/h. The biomechanical limit for the right femur is exceeded at all three considered impact speeds. Neck injuries are also a concern, with the predicted tension values and neck bending extent being higher than the biomechanical limit for the 60 km/h impact speed. In light of these results, it is suggested that the design of guardrails should be reviewed with a focus on the safety of motorcyclists.
  12. Noordin MY, Jiawkok N, Ndaruhadi PY, Kurniawan D
    Proc Inst Mech Eng H, 2015 Nov;229(11):761-8.
    PMID: 26399875 DOI: 10.1177/0954411915606169
    There are millions of orthopedic surgeries and dental implantation procedures performed every year globally. Most of them involve machining of bones and cartilage. However, theoretical and analytical study on bone machining is lagging behind its practice and implementation. This study views bone machining as a machining process with bovine bone as the workpiece material. Turning process which makes the basis of the actually used drilling process was experimented. The focus is on evaluating the effects of three machining parameters, that is, cutting speed, feed, and depth of cut, to machining responses, that is, cutting forces and surface roughness resulted by the turning process. Response surface methodology was used to quantify the relation between the machining parameters and the machining responses. The turning process was done at various cutting speeds (29-156 m/min), depths of cut (0.03 -0.37 mm), and feeds (0.023-0.11 mm/rev). Empirical models of the resulted cutting force and surface roughness as the functions of cutting speed, depth of cut, and feed were developed. Observation using the developed empirical models found that within the range of machining parameters evaluated, the most influential machining parameter to the cutting force is depth of cut, followed by feed and cutting speed. The lowest cutting force was obtained at the lowest cutting speed, lowest depth of cut, and highest feed setting. For surface roughness, feed is the most significant machining condition, followed by cutting speed, and with depth of cut showed no effect. The finest surface finish was obtained at the lowest cutting speed and feed setting.
  13. Ngadiman NH, Mohd Yusof N, Idris A, Kurniawan D
    Proc Inst Mech Eng H, 2016 Aug;230(8):739-49.
    PMID: 27194535 DOI: 10.1177/0954411916649632
    Electrospinning is a simple and efficient process in producing nanofibers. To fabricate nanofibers made of a blend of two constituent materials, co-axial electrospinning method is an option. In this method, the constituent materials contained in separate barrels are simultaneously injected using two syringe nozzles arranged co-axially and the materials mix during the spraying process forming core and shell of the nanofibers. In this study, co-axial electrospinning method is used to fabricate nanofibers made of polyvinyl alcohol and maghemite (γ-Fe2O3). The concentration of polyvinyl alcohol and amount of maghemite nanoparticle loading were varied, at 5 and 10 w/v% and at 1-10 v/v%, respectively. The mechanical properties (strength and Young's modulus), porosity, and biocompatibility properties (contact angle and cell viability) of the electrospun mats were evaluated, with the same mats fabricated by regular single-nozzle electrospinning method as the control. The co-axial electrospinning method is able to fabricate the expected polyvinyl alcohol/maghemite nanofiber mats. It was noticed that the polyvinyl alcohol/maghemite electrospun mats have lower mechanical properties (i.e. strength and stiffness) and porosity, more hydrophilicity (i.e. lower contact angle), and similar cell viability compared to the mats fabricated by single-nozzle electrospinning method.
  14. Arifin N, Abu Osman NA, Ali S, Gholizadeh H, Wan Abas WA
    Proc Inst Mech Eng H, 2015 Jul;229(7):491-8.
    PMID: 26019139 DOI: 10.1177/0954411915587595
    In recent years, computerized posturography has become an essential tool in quantitative assessment of postural steadiness in the clinical settings. The purpose of this study was to explore the ability of the Biodex(®) Stability System (BSS) to quantify postural steadiness in below-knee amputees. A convenience sample of 10 below-knee amputees participated in the study. The overall (OSI), anterior-posterior (APSI) and medial-lateral (MLSI) stability indexes as well as the percentage of time spent in left and right quadrants and four concentric zones were measured under altered sensory conditions while standing with solid ankle cushion heel (SACH), single-axis (SA) and energy storage and release (ESAR) feet. Significant difference was found between sensory conditions in SACH and ESAR feet for OSI (SACH, p = 0.002; ESAR, p = 0.005), APSI (SACH, p = 0.036; ESAR, p = 0.003) and MLSI (SACH, p = 0.008; ESAR, p = 0.05) stability indexes. The percentage of time spent in Zone A (0°-5°) was significantly greater than the other three concentric zones (p < 0.01). The loading time percentage on their intact limb (80%-94%) was significantly longer than the amputated limb (20%-6%) in all conditions for all three prosthetic feet. Below-knee amputees showed compromised postural steadiness when visual, proprioceptive or vestibular sensory input was altered. The findings highlight that the characteristics of postural stability in amputees can be clinically assessed by utilizing the outcomes produced by the BSS.
  15. Dambatta MS, Murni NS, Izman S, Kurniawan D, Froemming GR, Hermawan H
    Proc Inst Mech Eng H, 2015 May;229(5):335-42.
    PMID: 25991712 DOI: 10.1177/0954411915584962
    This article reports the in vitro degradation and cytotoxicity assessment of Zn-3Mg alloy developed for biodegradable bone implants. The alloy was prepared using casting, and its microstructure was composed of Mg2Zn11 intermetallic phase distributed within a Zn-rich matrix. The degradation assessment was done using potentiodynamic polarization and electrochemical impedance spectrometry. The cell viability and the function of normal human osteoblast cells were assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and alkaline phosphatase extracellular enzyme activity assays. The results showed that the degradation rate of the alloy was slower than those of pure Zn and pure Mg due to the formation of a high polarization resistance oxide film. The alloy was cytocompatible with the normal human osteoblast cells at low concentrations (<0.5 mg/mL), and its alkaline phosphatase activity was superior to pure Mg. This assessment suggests that Zn-3Mg alloy has the potential to be developed as a material for biodegradable bone implants, but the toxicity limit must be carefully observed.
  16. Khalid YM, Gouwanda D, Parasuraman S
    Proc Inst Mech Eng H, 2015 Jun;229(6):452-63.
    PMID: 25979442 DOI: 10.1177/0954411915585597
    Ankle rehabilitation robots are developed to enhance ankle strength, flexibility and proprioception after injury and to promote motor learning and ankle plasticity in patients with drop foot. This article reviews the design elements that have been incorporated into the existing robots, for example, backdrivability, safety measures and type of actuation. It also discusses numerous challenges faced by engineers in designing this robot, including robot stability and its dynamic characteristics, universal evaluation criteria to assess end-user comfort, safety and training performance and the scientific basis on the optimal rehabilitation strategies to improve ankle condition. This article can serve as a reference to design robot with better stability and dynamic characteristics and good safety measures against internal and external events. It can also serve as a guideline for the engineers to report their designs and findings.
  17. Thompson MS, Bajuri MN, Khayyeri H, Isaksson H
    Proc Inst Mech Eng H, 2017 May;231(5):369-377.
    PMID: 28427319 DOI: 10.1177/0954411917692010
    Tendons are adapted to carry large, repeated loads and are clinically important for the maintenance of musculoskeletal health in an increasing, actively ageing population, as well as in elite athletes. Tendons are known to adapt to mechanical loading. Also, their healing and disease processes are highly sensitive to mechanical load. Computational modelling approaches developed to capture this mechanobiological adaptation in tendons and other tissues have successfully addressed many important scientific and clinical issues. The aim of this review is to identify techniques and approaches that could be further developed to address tendon-related problems. Biomechanical models are identified that capture the multi-level aspects of tendon mechanics. Continuum whole tendon models, both phenomenological and microstructurally motivated, are important to estimate forces during locomotion activities. Fibril-level microstructural models are documented that can use these estimated forces to detail local mechanical parameters relevant to cell mechanotransduction. Cell-level models able to predict the response to such parameters are also described. A selection of updatable mechanobiological models is presented. These use mechanical signals, often continuum tissue level, along with rules for tissue change and have been applied successfully in many tissues to predict in vivo and in vitro outcomes. Signals may include scalars derived from the stress or strain tensors, or in poroelasticity also fluid velocity, while adaptation may be represented by changes to elastic modulus, permeability, fibril density or orientation. So far, only simple analytical approaches have been applied to tendon mechanobiology. With the development of sophisticated computational mechanobiological models in parallel with reporting more quantitative data from in vivo or clinical mechanobiological studies, for example, appropriate imaging, biochemical and histological data, this field offers huge potential for future development towards clinical applications.
  18. Ngadiman NHA, Noordin MY, Idris A, Kurniawan D
    Proc Inst Mech Eng H, 2017 Jul;231(7):597-616.
    PMID: 28347262 DOI: 10.1177/0954411917699021
    The potential of electrospinning process to fabricate ultrafine fibers as building blocks for tissue engineering scaffolds is well recognized. The scaffold construct produced by electrospinning process depends on the quality of the fibers. In electrospinning, material selection and parameter setting are among many factors that contribute to the quality of the ultrafine fibers, which eventually determine the performance of the tissue engineering scaffolds. The major challenge of conventional electrospun scaffolds is the nature of electrospinning process which can only produce two-dimensional electrospun mats, hence limiting their applications. Researchers have started to focus on overcoming this limitation by combining electrospinning with other techniques to fabricate three-dimensional scaffold constructs. This article reviews various polymeric materials and their composites/blends that have been successfully electrospun for tissue engineering scaffolds, their mechanical properties, and the various parameters settings that influence the fiber morphology. This review also highlights the secondary processes to electrospinning that have been used to develop three-dimensional tissue engineering scaffolds as well as the steps undertaken to overcome electrospinning limitations.
  19. Sia SF, Zhao X, Li R, Zhang Y, Chong W, He L, et al.
    Proc Inst Mech Eng H, 2016 Nov;230(11):1051-1058.
    PMID: 28095764 DOI: 10.1177/0954411916671752
    BACKGROUND: Internal carotid artery stenosis requires an accurate risk assessment for the prevention of stroke. Although the internal carotid artery area stenosis ratio at the common carotid artery bifurcation can be used as one of the diagnostic methods of internal carotid artery stenosis, the accuracy of results would still depend on the measurement techniques. The purpose of this study is to propose a novel method to estimate the effect of internal carotid artery stenosis on the blood flow based on the concept of minimization of energy loss.

    METHODS: Eight internal carotid arteries from different medical centers were diagnosed as stenosed internal carotid arteries, as plaques were found at different locations on the vessel. A computational fluid dynamics solver was developed based on an open-source code (OpenFOAM) to test the flow ratio and energy loss of those stenosed internal carotid arteries. For comparison, a healthy internal carotid artery and an idealized internal carotid artery model have also been tested and compared with stenosed internal carotid artery in terms of flow ratio and energy loss.

    RESULTS: We found that at a given common carotid artery bifurcation, there must be a certain flow distribution in the internal carotid artery and external carotid artery, for which the total energy loss at the bifurcation is at a minimum; for a given common carotid artery flow rate, an irregular shaped plaque at the bifurcation constantly resulted in a large value of minimization of energy loss. Thus, minimization of energy loss can be used as an indicator for the estimation of internal carotid artery stenosis.

  20. Genisa M, Shuib S, Rajion ZA, Arief EM, Hermana M
    Proc Inst Mech Eng H, 2018 Oct 11.
    PMID: 30309283 DOI: 10.1177/0954411918806333
    The aim of this study is to investigate the estimation of density from the Hounsfield unit of cone beam computed tomography data in dental imaging, especially for dental implant application. A jaw phantom with various known densities of anatomical parts (e.g. soft tissue, cortical bone, trabecular bone, tooth enamel, tooth dentin, sinus cavity, spinal cord and spinal disc) has been used to test the accuracy of the Hounsfield unit of cone beam computed tomography in estimating the mechanical density (true density). The Hounsfield unit of cone beam computed tomography data was evaluated via the MIMICS software using both two-dimensional and three-dimensional methods, and the results showed correlation with the true density of the object. In addition, the results revealed that the Hounsfield unit of cone beam computed tomography and bone density had a logarithmic relation, rather than a linear one. To this end, the correlation coefficient of logarithmic correlation (R2 = 0.95) is higher than the linear one (R2 = 0.77).
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