MOIRÉ - introduction

PURPOSE OF EXAMINATION

Faulty postures are becoming nowadays one of the most serious civilization diseases. In this day and age children spend more and more time sitting in front of television or computer, they also spend a lot of time at school. Lack of movement, psychical factors (stage fright, fear, depression) as well as vision and hearing defects cause that children do not always grow and develop correctly.

The onset of a faulty posture is often difficult to notice. It the majority of cases it is a long process coming to light along with child development. At first there are not any alarming symptoms. As soon as some complains appear (e.g. pains, decreased physical fitness, worse function of respiratory and circulatory systems) the changes have already been strongly fixed and they require a prolonged and systematic treatment.

Doctors alarm that 80-90% of children have faulty postures, which unattended and neglected cause serious consequences in short term. They lead to worsening of efficiency of organism, body statics is disturbed, range of joint mobility becomes limited. The research works show that every third child has low physical fitness, and almost 50% of them have poor motorial efficiency.

The apparatus for computer-based examination of body posture is a tool that allows a non-invasive, precise and objective diagnostics of body posture. High measurement accuracy gives us a chance to early notice the deformities at their onset stage.

Patient’s data are collected in electronic form, thanks to which it is easy to observe and compare the progress of the therapeutic treatment.

The device takes advantage of the photogrammetric method and applies the Moire effect, which is recommended by specialists in physiotherapy, rehabilitation and orthopaedics because in a lot of case it allows to eliminate x-rays. In short, it consists in making by means of a video camera a computer photograph. Thanks to special optical system the computer draws a three-dimensional picture of the patient’s back and precisely analyses over 50 parameters in the frontal and sagittal plane. The apparatus is especially useful for children screening examinations in schools, and its small dimensions makes its transport very easy.

EXAMINATION METHOD

A Physical bases

Examinations are carried out basing on assumptions of photogrammetry and consist in performing anthropometric measurements on the basis of a picture of examined surface. It is possible to obtain a three-dimensional picture („third dimension”) because the apparatus “projects” lines with specific parameters on patient’s back. The lines falling on the back at a specified angle, get deformed depending on whether a given point is located nearer to or further from the device. Distortion of line picture is registered by computer that thanks to numeric algorithms transforms them into a contour-map of the examined surface. The physical basis of this phenomenon is called in optics Moire effect (hence Moire projection method).

B Technical implementation.

A practical implementation of the method consists in this that a picture observed by a CCD-camera is transformed into a digital signal and sent to computer memory by means of a special board. Analysis, projection and printing are carried out by computer software. To lighten the patient a low-power halogenous bulb (50-150W) is used. All patient’s data, the picture of his/her back as well as three-dimensional picture are stored in computer memory and can be easily transferred onto other data carriers (floppy discs, CD-ROMs), analysed, statistically edited etc.

C Measurement repeatability and accuracy

Thanks to the fact that the photo is taken under specific conditions (i.e. constant examination distance, identical parameters of optical system, exact levelling of camera position, body profile positioned on „0” of pelvic torsion, specific light conditions), the measurement is repeatable.

Analysing measurement accuracy we have to pay attention to specifity of the examined object which is human body. Practically, it is not possible to show physiological points on patient’s skin with accuracy greater than 5mm. Considering this, the parameter ‘height difference in shoulder-blade angles’ is struck with accidental error of 1cm. That is why we have to assume that the value of 1 cm is accuracy limit of the method in view of physiological features.

However, the accuracy of the apparatus itself, as far as picture resolution and the value of calculated parameters is concerned, amounts to 1 mm, which means that it is ten times better than it is necessary in view of physiology. It has a practical implication because it allows to notice already some first symptoms of distortion still not visible with the naked eye.

3D animation

Printout patterns