Advanced functions (PVG)
Author: MSc Marzena Zacirka, Ph.D. Marcin Just, Ph.D. Michał Tyc (DiagNova Technologies)Standard (one-dimensional) kymography allows for the analysis of the movement of the vocal folds in one selected cross-section. Advanced (two-dimensional) kymography allows for a full analysis of the movement of the vocal folds along their entire length in one image - phonovibrogram.
The phonovibrogram is a graph composed of all one-dimensional kymographic images. This allows the user to observe changes in the movement of the vocal folds in both the medial-lateral and antero-posterior directions.
The procedure of determining numerical parameters and the phonovibrogram graph requires marking the edges of the left and right vocal folds (blue in Fig. 1), the glottis area, back and front of the vocal folds (in Fig. 1 red points; the front of the fold) and the main axis of the glottis (in Fig. 1 marked with a yellow dotted line).
Fig. 1. The outline of the inner edge of the vocal folds with the defined glottis axis
The program determines the contours of the inner edge of the vocal folds for each possible cross-section of the vocal folds. An example of visualization of the course and changes in the appearance of the contour of the edge of the vocal folds is shown in the recordings (Fig. 2).
Fig. 2. The outline of the inner edge of the vocal folds along the entire length of the vocal folds
When creating a phonovibrogram, information about the movement of the contours of the oscillating vocal folds is collected from the video sequence and then transformed into a single-color image of the phonovibrogram.
Fig. 3. Phonovibrogram performance
The visualization of the entire characteristics of the movement of the vocal folds is shown in Figure 3. If the vocal folds are "cut" along the glottis axis, then the left fold will be rotated 180° relative to the T point, the resulting image of the vocal folds will look like Figure 3. The movement of the vocal folds changes in time (horizontal axis in green in the picture). In the graph, black indicates the state when the folds are closed, i.e. the edge of the fold is on the glottis axis. The intensity of the red color determines the distance from the glottis axis to the edge of the fold, i.e. the degree of opening of the folds (Fig. 4). Blue color refers to the situation when the edge of the fold exceeds the glottis axis.
Fig. 4. Phonovibrogram
The phonovibrogram allows you to compress the data from the "slow motion" sequence on one graph, preserving the key information about the work of the vocal folds. On the final graph, a map is obtained that carries information about the behavior of the fold edge during the entire analyzed "slow motion" sequence. One frame therefore contains all the information needed to diagnose a patient.
Having information about the edge of the vocal fold, it is possible to determine parameters such as the degree of regurgitation, the amplitude of work, asymmetry or phase difference. Below, there are exemplary graphs of parameters determined on the basis of the edge shape for the folds in Fig. 1.
Fig. 5.
Fig. 6. The contours of the edges of both vocal folds overlap
Fig. 7. The contour of the edge of the vocal folds in the kymographic image
The drawings show automatically the edges of the vocal folds, determined on the basis of the cropping and stabilizing performed earlier by the user. Figure 5 shows the edges determined from the cropped image of the vocal folds. Figure 6 shows the same edges but overlapping each other. In one plot there is an image of the edge of the left fold and a mirror image relative to the glottis axis of the image of the edge of the right fold. Figure 7 shows the edges of the folds based on a kymographic image.
Fig. 8. Graph of the amplitude of the movement of the vocal folds
Fig. 9. Time graph showing when the vocal folds are opening and closing
Fig. 10. Graph of the amplitude of the folds movement to the mean opening
Figure 8 shows a graph of the amplitude of the movement of the vocal folds. The vertical axis describes the position on the vocal fold and the horizontal axis describes the displacement from the glottis axis. Yellow points show the left vocal fold, blue points show the right fold, and green points show the width of the glottis gap. In the correct operation of the vocal folds, the yellow and blue graphs will overlap, while the green graph will be their sum. The smaller the shift in the green graph, the more one fold follows the other, rather than working the opposite.
Figure 9 shows the ratio of the vocal folds opening time to the closing time in each section (the result is given as a percentage). Figure 10 is the ratio of the amplitude of the folds movement to the mean opening.
Fig. 11. Assessment of the symmetry of the function of the vocal folds
Fig. 12. The phase difference between the movement of the right and left folds
Fig. 13. The result of fitting the edges of the vocal fold
The diagram in Figure 11 allows the assessment of the symmetry of the function of the vocal folds. It gives the value of the ratio of the amplitude of the movement of the center of the glottis region to the amplitude of the width of the glottis region. In the case of symmetrical operation of folds, the parameter should be equal to 0. The value of 0.5 means asymmetry, when one fold does not work at all. On the other hand, a value above 0.5 means that one of the folds works inversely, i.e. follows the other. In general, it can be said that the higher the value of this parameter, the lower the efficiency of the folds. Figure 12 shows the parameter that shows the phase difference between the movement of the right and left folds. For correct operation of the vocal folds, the phase difference should be 0 degrees. Figure 13 shows a graph showing the result of the fold edge fit (in the cropping and stabilization module). The chart uses a cropped single cycle of folds rotated by 90 °. A fit result was superimposed on the graph to determine the phase difference of movement between the folds.