Volume of confidence ellipsoid: a technique for quantifying trunk sway during stance

Kutílek, Patrik; Čakrt, Ondřej; Socha, Vladimír; Hána, Karel

doi:10.1515/bmt-2014-0012

Cited by 6 publications

(6 citation statements)

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“…The second analysis is focused to describe the peculiar behaviour of each group in the three tasks. To explicitly analyse postural control differences between participants, we considered the three-dimensional data of COP and COM positions and compared the volumes of prediction ellipsoid [25][26][27][28][29] of each group by means of the Generalized Variance (GV), a scalar measure of dispersion defined as the determinant of the sample covariance matrix and proportional to specific equal- probability contour (i.e., standard ellipsoid) of the measured data. Between groups inferential tests were conducted on GVs with a Chi-square log-Likelihood Ratio Test [30,31].…”

Section: Discussionmentioning

confidence: 99%

Postural control deficit during sit-to-walk in patients with Parkinson’s disease and freezing of gait

et al. 2018

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Section: Discussionmentioning

confidence: 99%

Postural control deficit during sit-to-walk in patients with Parkinson’s disease and freezing of gait

et al. 2018

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“…The data, that is, the three Euler angles (roll ( Φ ), yaw (Ψ), and pitch (Θ)) [ 13 , 14 ] and three orthogonal accelerations (a Sx , a Sy , and a Sz ), in the accelerometer coordinate system [ 15 ] were measured by the MTx unit placed on the patient's trunk (Pts) and healthy subjects (control group (CG)) while they were standing still on a fixed stationary platform of the Synapsys posturography system. Conventions for the Euler angles are described in [ 13 , 16 , 17 ].…”

Section: Methodsmentioning

confidence: 99%

Postural Stability Evaluation of Patients Undergoing Vestibular Schwannoma Microsurgery Employing the Inertial Measurement Unit

Kutílek

Svoboda

Čakrt

et al. 2018

Journal of Healthcare Engineering

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The article focuses on a noninvasive method and system of quantifying postural stability of patients undergoing vestibular schwannoma microsurgery. Recent alternatives quantifying human postural stability are rather limited. The major drawback is that the posturography system can evaluate only two physical quantities of body movement and can be measured only on a transverse plane. A complex movement pattern can be, however, described more precisely while using three physical quantities of 3-D movement. This is the reason why an inertial measurement unit (Xsens MTx unit), through which we obtained 3-D data (three Euler angles or three orthogonal accelerations), was placed on the patient's trunk. Having employed this novel method based on the volume of irregular polyhedron of 3-D body movement during quiet standing, it was possible to evaluate postural stability. To identify and evaluate pathological balance control of patients undergoing vestibular schwannoma microsurgery, it was necessary to calculate the volume polyhedron using the 3-D Leibniz method and to plot three variables against each other. For the needs of this study, measurements and statistical analysis were made on nine patients. The results obtained by the inertial measurement unit showed no evidence of improvement in postural stability shortly after surgery (4 days). The results were consistent with the results obtained by the posturography system. The evaluated translation variables (acceleration) and rotary variables (angles) measured by the inertial measurement unit correlate strongly with the results of the posturography system. The proposed method and application of the inertial measurement unit for the purpose of measuring patients with vestibular schwannoma appear to be suitable for medical practice. Moreover, the inertial measurement unit is portable and, when compared to other traditional posturography systems, economically affordable. Inertial measurement units can alternatively be implemented in mobile phones or watches.

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“…The EV is based on the mathematical tools for static posturography employed to analyze body sway [24]. In the case presented, the distribution of the measured 3-D data was modelled by 3-D ellipsoid and its volume [7]. The volume of an ellipsoid was given by an ellipsoid matrix and the ellipsoid matrix was composed of entries from the covariance matrix [25].…”

Section: Fig 2: 3-d Plot Of Linear Accelerations During 60 S With Sampling Frequency 100 Hzmentioning

confidence: 99%

“…set of points is obtained by plotting three accelerations against each other. The calculation of the EV is described in detail in [7]. In the case described, the distribution of the measured 3-D data was modelled by a 3-D ellipsoid.…”

Section: Fig 2: 3-d Plot Of Linear Accelerations During 60 S With Sampling Frequency 100 Hzmentioning

confidence: 99%

“…To monitor and train a posture, a non-commercial IMU system, a diagnostic tool for trunk movement, has been developed; in this way, non-expensive accelerometers and gyroscopes used in modern cell phones and electronic watches have further potential for monitoring posture. Traditional and more complex methods for processing measured data and assessing postural instability use at least two measured variables; these methods are based on the convex hull [6], confidence ellipse [7], or length of trajectory obtained by plotting two variables against each other [8]. These methods are used to evaluate data obtained from the force platform [9], or an IMU system placed on a segment of the axial skeleton.…”

Section: Introductionmentioning

confidence: 99%

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Methods Evaluating Upper Arm and Forearm Movement During a Quiet Stance

et al. 2019

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The article focuses on designing methods for quantitative assessment of the postural stability in a quiet stance by measuring segments of the appendicular skeleton, namely upper and forearms by inertial measurement units (IMU). Although an array of quantitative analysis methods assessing data of postural stability in the quiet stance exist by measuring the head and trunk movement, these methods have not been used to date to assess the behaviour of appendicular skeleton segments, namely the upper limbs. The applicability of methods assessing arm movement during the quiet stance has been verified by comparing the values of healthy subjects performing various stance tasks. The tests determined the quantitative evaluation of acceleration measured on individual anatomical axes. The quantities included: the volume of a convex polyhedron (PV), the volume of confidence ellipsoid (EV) and average velocity (AV) obtained by plotting three accelerations against each other. The most important findings in this study concern significant differences of PV and AV between dominant and non-dominant upper extremities and significant differences of EV, PV and AV between the data measured with a subject's eyes closed and open. Higher values of indicators were in the non-dominant extremities when subjects were measured with closed eyes. Interestingly, statistically significant differences between dominant and non-dominant arm movements were documented in PV and AV cases. This is due to the PV calculation being more sensitive to random deviations, i.e. the range of measured data, since the polyhedron bounds all the measured data, as opposed to the method, where the ellipse bounds only 95% of the measured data. In the case of the AV method, it is due to higher sensitivity to movements corresponding with arm tremors; the AV calculation relates not only to the range of measured data but, above all, to the intensity of data changes in the segment measured in a particular space and time interval. These conclusions demonstrate that it is possible to apply the proposed methods in the assessment of arm movement during a quiet stance since the differences between individual stance tasks and the dominant and non-dominant arms in specific cases of quiet stance have been identified. These conclusions also indicate a potentially more extensive medical application of the proposed quantitative data evaluation obtained from IMU, for example, within the rehabilitation process of injured appendicular skeleton segments. The use of cheaper IMU methods in mobile phones or watches can be of significant benefit in measuring the segmental movement of the appendicular skeleton in quiet stance. The methods outlined in this paper have remarkable potential in the field of telemedicine.

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Volume of confidence ellipsoid: a technique for quantifying trunk sway during stance

Cited by 6 publications

References 25 publications

Postural control deficit during sit-to-walk in patients with Parkinson’s disease and freezing of gait

Postural control deficit during sit-to-walk in patients with Parkinson’s disease and freezing of gait

Postural Stability Evaluation of Patients Undergoing Vestibular Schwannoma Microsurgery Employing the Inertial Measurement Unit

Methods Evaluating Upper Arm and Forearm Movement During a Quiet Stance

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