Figure 1
Cartoon of a Motion Sensor (Green) Mounted on the Dorsum of the Hand. In general, tremor in a body part will consist of rotation and translation in three-dimensional space. Many modern motion sensors contain a triaxial accelerometer and gyroscope for capturing this motion.
Table 1
Examples of Motion Transducers and their Technical Specifications
| Sensor | Axes | Range | Mass | Resolution | Accuracy | Sampling Rate (samples/s) | Recording Duration |
|---|---|---|---|---|---|---|---|
| Kinesia One | |||||||
| Accelerometer | 3 | ±5 g | 8.5 grams | 12 bit | ±2% | 64 | 8 hr |
| Gyroscope | 3 | ±2000 deg/s | ±4% | 64 | 8 hr | ||
| ADPM Opal | |||||||
| Accelerometer | 3 | ±6 g or ±2 g | 22 grams | 14 bit | 2% | 20-128 | 12-24 hr** |
| Gyroscope | 3 | ±2000 deg/s* | 2% | ||||
| ActiGraph GT9X | |||||||
| Accelerometer | 3 | ±16 g | 14 grams | 16 bit | 3% | 100 | >24 hr |
| Gyroscope | 3 | ±2000 deg/s | 4% | 100 | |||
| Wacom Intuos tablets | 2 | ≥10 cm*** | ≥700 grams*** | 0.005 mm | ±0.25 mm | ≥100 | As long as the pen is on the tablet |
Figure 2
Amplitude Spectra (Degrees/Second) of Hand Tremor Recorded with a Gyroscope Transducer. Tremor was recorded from the dorsum of the hand while the upper limb was at rest, extended horizontally and anteriorly, and while performing finger-to-nose movements (graphs left to right). The patient has a Holmes tremor due to a previous midbrain hemorrhage. The tremor spectral peaks are very sharp during rest and posture. During movement, the tremor peak is superimposed on spectral activity produced by the voluntary movement. The mean tremor amplitude in degrees is the peak amplitude divided by 2πf, where f is the tremor frequency (3.8 Hz).
Figure 3
Tremor in an Archimedes Spiral Recorded with a Digitizing Tablet. In the left column, the X component of an Archimedes spiral (displacement) is shown with its first and second derivatives (velocity and acceleration), computed with a frequency impulse response differentiator in MATLAB. The power spectrum of displacement, velocity, and acceleration are shown on the right. Note how differentiation accentuates the 4.3 Hz tremor relative to the lower-frequency voluntary movement.
Figure 4
The Time-frequency Power Spectrum of Tremor Recorded with a Triaxial Gyroscope on the Wrist of a Patient with Parkinson Disease. This recording was made during normal uncontrolled activities. The resultant power spectrum is the sum of the power spectra of the X, Y, and Z channels. The image color intensity shows how the signal power (radians2/second2; 2π radians = 360 degrees) is distributed over time and frequency. Note how the presence and amplitude of tremor fluctuate with time. The 5 Hz tremor nearly stops at 21 minutes, when there is an abrupt increase in normal voluntary movement.
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