Registration of surface structures using airborne focused ultrasound.

A low-cost measuring system, based on a personal computer combined with standard equipment for complex measurements and signal processing, has been assembled. Such a system increases the possibilities for small hospitals and clinics to finance advanced measuring equipment. A description of equipment developed for airborne ultrasound together with a personal computer-based system for fast data acquisition and processing is given. Two air-adapted ultrasound transducers with high lateral resolution have been developed. Furthermore, a few results for fast and accurate estimation of signal arrival time are presented. The theoretical estimation models developed are applied to skin surface profile registrations.

The dysrhythmia and the exponential constants of the postrotatory nystagmus qualities.

In 5 healthy individuals the postrotatory, exponential constants were estimated for each of the four nystagmus qualities, viz. the velocities and durations of fast and slow components. The residual spread (Sr) of each quality in a semilogarithmic plot was also determined. The value of the constant for postrotatory decay indicated a decrease of the velocity and an increase for the duration of the slow component, both with a significant difference between individuals, while for the corresponding values of the fast components no systematic change in the postrotatory reactions was indicated, nor any difference between individuals. The constant that corresponds to the value at maximum stimulus showed differences between individuals for each of the four nystagmus qualities, while Sr presented differences between individuals only for the two slow phase qualities. This technique to describe postrotatory nystagmus reactions by the two exponential constants for each of the four nystagmus qualities together with the residual spread for each of the qualities is intended for future 'on-line' nystagmus analysis.

Compact digital storage of ECG's.

The technique of predictive coding is applied to the problem of reversible compression of digitized electrocardiograms. Integer-based predictors and MMSE predictors are studied as regards performance at varying sampling rates and digital resolutions for both long-term ECGs and ECGs recorded at rest. It is concluded that MMSE predictors are to be preferred only in the case when the ECG is oversampled (i.e., the sampling rate is much higher than twice the cut-off frequency of the presampling filter). In other cases the integer predictor which yields the so-called 2nd differences is superior. The problem of encoding the resulting residuals with a variable-length code is studied for long-term ECGs digitized at 100 Hz and using 8 bits digital resolution. The code has a simple struture leading to speed of execution while the efficiency loss is small.

Quantification of vestibular dysrhythmia.

Quantification of dysrhythmia in a nystagmus response has hitherto not been seriously attempted, possibly because the nystagmus response does not easily lend itself to description in mathematical or physical terms. Ideally the nystagmus response consists of a sequence of triangles. Each such triangle is determined by four qualities, i.e. the velocities and the durations of the fast and slow components. Thus, without serious loss of information it is possible to represent a nystagmus reaction by four sequences of values, one for each of the four above mentioned qualities. From each such sequence we have extracted relevant information and presented it in graphical form. It may be assumed that each of the four nystagmus qualitiees reflects the activity within separate 'neuronal systems'. Each of these four systems is then informed upon by three parameters for each nystagmus quality, i.e. by its mean, by its variation coefficient and by its sequential variation coefficient. It is claimed that these three diagrams contain nystagmus information not earlier considered.