Quantification of the drawing of an Archimedes spiral through the analysis of its digitized picture.

We have developed a new quantitative analysis of spiral drawing that is able to evaluate any spiral execution and it has not temporal or spatial limitations in the obtaining of specimens. Thirty-one patients with action tremor and 24 control subjects were asked to draw an Archimedes spiral over a print template. Specimens were scanned and then treated through a semiautomatic computer program that reconstructs the temporal sequence of the spiral drawing by the subject. The spirals were first analysed by means of the cross-correlation coefficient with the spiral template. Secondly, the mean and the standard deviation of the distance between each point of the spiral drawing and the corresponding point of the spiral model were determined. Finally, the reconstructed spiral was analysed using the Fourier Transform. Its results were interpreted with the aid of a computer model of a tremulous spiral. The experimental variables were greater in the patients group respect to age-matched controls. There was also a high linear correlation between them and the clinical score given by three neurologists. Finally, Receiver Operating Characteristic (ROC) curves analysis shown that the method classified the spirals better than human ratters.