Tremor and moving disorders are one of the main and relatively difficult symptoms for a patient neurodegenerative illness. While the clinical analysis of the patient is performed it is vital to identify the type of tremor to set the right diagnosis.
For exact measurement of tremor – its frequencies and amplitudes, the method of spiralography using the digital tablets is most useful. The use of digital tablets for tremor identification enables more accurate tremor data in comparison with old methods of drawing evaluation. Those methods usually determine only subjective classification of tremor to normal, gentle, intermediate and strong, while the use of digital tablets accurately quantifies the tremor.
○ Easy data acquisition
○ Patient friendly and not demanding exam
○ Accurate measurement of tremor,
○ We can distinguish between different types of tremor.
Easy and fast diagnostic.
11 criteria on which we determine the types of tremor.
Data acquisition with digital tablets is user friendly, because it does not utilize any signal preamplification and A/D converters. All the user needs to do is to hook up the tablet with a computer and start the data acquisition software.
Under the writing surface of the digital tablet is a network of wires. The pen creates electromagnetic field which excites parts of network enabling the calculation of pen position. The more wires in the surface area, the greater the resolution and sensitivity of the digital tablet. This is important for identification of specific types of tremors. The bigger the resolution, the easier it is to determine the type of tremor in a response to person's physiological properties. It is noted that the tablet, which can identify physiological tremor, can also sense other types of tremor, which are in the lower frequency ranges.
When measuring we must obey Nyquist theorem, which dictates that we need sample frequency at least twice as high as the highest frequency for correct reproduction of the signal . If we predict that the highest frequency of the signal is 13 Hz, we must use a frequency of at least 26 Hz for data sampling. To avoid possible aliasing, the most common frequency is 50 Hz, and in our case we sample the signal with a frequency of 100 Hz.
Common expanded task of tremor measurement is represented with the drawing of Archimedes spiral, which is defined with equation:
R = a × ∅
R – radius in coordinate system, a – constant, which controls the distance between different revolutions of the spiral, ∅ - angle in the coordinate system
During measurement the patient sits on the chair and is drawing a spiral on programmed graphical tablet with tablet's pen – free hand and on generated template. With computer analysis and given criteria we get data nedeed to determine tremor type on the basis of joint characteristic, typical for certain clinical group.
During the draw process the patient is required to keep the pen on tablet surface for the whole time of drawing. It frequently occurs that for patients with severe tremor this condition is not met, but newer digital tablets track the pen position even if it is raised from the surface for a few centimeters. This makes the measurements of people with strong tremor easier and without the need for custom adjustments.
Because each tremor has unique oscillation, it is easy to use spectral analysis, which is the most common method of tremor quantification.
The data we acquired with the help of digital tablets are organized according to 11 criteria.
That makes possible to watch the data about the tremor from more different perspectives. The results are: the drawing of the actual spiral, time versus trace of spiral, radius/angle transform, absolute, radial and tangential speed in response to time, tremor spectra, direction of the tremor, pen pressure versus time, pressure cone and pressure spectra.
The results are assessed, and on the basis of the properties of individual clinical group we can identify the present tremor.
Indications for use: