Francesco Orsini

Development and preliminary characterization of a novel system for the force platforms dynamic calibration

In this work a transportable calibration system for dynamic performance testing of medical force platforms (FP) is proposed. Although in literature many devices have been proposed for the calibration of force platforms, most of them are static and among those proposed to simulate a dynamic phenomenon it is difficult to satisfy ergonomic needs (i.e. transportability) with performance characteristics as the capability to control the frequency and the amplitude of the calibration force with continuity in the useful range of the human gait analysis and posturography. In particular the system proposed is equipped with a calibrated load cell (LC) to provide force measurement feedback and can apply a calibration force in every point of the FP under testing, with amplitude range 0–1500N, frequency range 1–12 Hz and a preload range 300–1000N with an inclination to the FP of 0–15°. With the aim to do a first validation of the system some test and a first application to a novel Force Platform are described. Tests at different preloads (30–100 daN), frequencies (1–12Hz) and amplitudes (7.5–25 daN) are carried out to study the dynamic behavior of the device: some difference on the peak to peak measurements are shown, nevertheless the ratio of the mean force ratio platform/calibrator is very close to 1 in quite all cases, although a little distortion (<4%) is revealed at 2 Hz. Moreover the evaluation of the total harmonic distortion (THD) is carried out and results show some difference in the readings between the FP and the system LC. In future works it seems interesting to investigate how the frequency influences the dynamic behavior of FP and propose a calibration procedure where the calibration parameters are frequency dependent and the control software is optimized to improve the system performance and the force signal characteristics.

A preliminary study on the validation of anautomatic measurement method for functional reach assessment by stereophotogrammetry

In this work a preliminary study is proposed to assess the validity of an automatic and low cost measurement method for Functional ReachTest (FRT) implementation. To this aim FRT was performed on 10 trials of 4 healthy men and results from the system under validation are compared with the corresponding data from a calibrated stereo-photogrammetric system: the percentage variation between them is lower than 3% in all subjects — 3 outlier trials excluded — and it is significantly lower than the percentage variation obtained in daily clinical practice. Since none of the subjects is affected by pathologies, all of themhave normal visual acuity and have been trained to the experimental procedure, uncertainty of the outcomes may be mainly attributed to the calibration procedure and to the measurement system. Anyway results seem to confirm that the proposed system can be used to support the physician in acquiring the clinical information about the motor control deterioration or restoring in patients with various pathologies. Despite the encouraging results, further studies are needed to achieve a more accurate and quantitative evaluation of the sources of uncertainty, i.e. by extending the population sample and increasing the number of trials with the support of a Monte Carlo simulation.

Use of phantoms and test objects for local dynamic range evaluation in medical ultrasounds: A preliminary study

In the ultrasound image the relationship between echo amplitudes and gray levels is expressed by means of the Grayscale Mapping Function (GMF), that is the greyscale transfer function associated with the echo displayed. The GMF allows the determination of some image quality parameters and quantities, among which the Local Dynamic Range (LDR) is relevant, since it is defined as the 20·log10 of the ratio of the minimum echo amplitude that yields the maximum grey level in the digitized image to that of the echo that yields the lowest grey level at the same location in the image and the same settings. This study reports the implementation of a method for the automatic determination of the LDR on medical ultrasound scanners and its application by means of a commercial grayscale ultrasound phantom, nevertheless it can be used also with general purpose phantoms: the LDR is obtained from the estimation of the GMF, based on processing of a sequence of uncompressed bidimensional ultrasound images provided by the scanner. In the manuscript, some theoretical considerations have been done to determine the GMF and its fitting model, as well as the LDR values, after that an experimental setup is described and some results are shown for an ultrasound system equipped with two different probes

A preliminary characterization of a whole body vibration platform prototype for medical and rehabilitation application

Whole-body vibration (WBV) is receiving increasing interest as an exercise intervention in physiology and rehabilitation. Although there are many commercial and professional WBV platforms to provide controlled vibrations, very few have actually been tested in terms of amplitude (mm), frequency spectra (Hz) and shape of the vibratory motion wave. In this regard a prototype of a novel WBV platform where the vibration amplitude can be set to three values in the frequency range 20-60 Hz is here proposed. The device has been preliminarily characterized by processing the measurement signal from a piezoelectric monoaxial accelerometer mounted in the center of the WBV plate. In particular the accelerometer signal has been processed to evaluate frequency spectrum, waveform shape and displacement. Moreover to evaluate the performance of the prototype, same tests were carried out on an equivalent professional WBV platform, so that data coming from the two platforms have been compared and commented: test results have shown that the vibrations produced by the two WBV plates are very similar, nevertheless it has been found that the prototype works with a maximum error of about 5 % in frequency, that is less than in the other devices, furthermore the greater distortion of the signal is always at the twice of the operating frequency (second harmonic). Further investigations are needed to complete the characterization of the prototype and assess the vibration amplitude is not load dependent.

A preliminary uncertainty analysis of acceleration and displacement measurements on a novel WBV platform for biologic response studies

Over the last decade, many studies have been conducted on the effects of mechanical vibration on the physical hormonal and neuromuscular responses of muscles: in some works the growth hormone response showed a dependence on the acceleration provided by Whole Body Vibration (WBV) platforms with respect to subjects responsiveness. Therefore the accuracy of acceleration measurements related to the excitation system is important and should be assessed. To this aim a preliminary study on the identification and evaluation of the measurement uncertainty sources in the measurement chain of a novel WBV platform developed by the Authors is here proposed. After the main measurement error sources have been identified, a Monte Carlo simulation Method has been implemented to obtain the uncertainty in accelerations and displacements provided by the WBV platform. Since main causes of uncertainty has been identified in the accelerometer sensitivity, its mounting and the data acquisition processing, Results of the test showed a relative uncertainty of about ±4% for acceleration and displacement measurements for frequencies between 20Hz and 60Hz.