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Calibration

  1. The calibration procedure for lateral canal calibrations has not changed and is clearly explained in the manual.

  2. You can begin testing without calibrating by just selecting a test and starting the impulses. In this case a default calibration will be taken. This is a good solution for difficult situation or challenging patients, but we still recommend that the user perform a calibration whenever possible.

  3. A new calibration is added now that allows the user to calibrate the head position of the patient before beginning impulses. You can click on the Head calibration heading in the recordings menu to begin.

  4. You can then hit prepare and instruct the patient.

  5. The head movements can be passive, the clinician moves the patients head, or active where the patient moves their own head.

  6. The patient is instructed to keep his eyes on the target on the wall and oscillating the head gently, first around the yaw axis (like shaking your head “no”) and, after a few oscillations, around the pitch axis (like nodding your head “yes”). The examiner can perform the head calibration by standing behind the patient and grabbing the head the same way as during head impulse testing of the lateral canals. About five sinusoidal oscillations in both yaw and pitch directions need to be performed at moderate peak head velocities not exceeding 100 deg/sec. The total duration of the head calibration is on the order of 15 sec.

  7. The procedure is finished by pressing the Stop button.

  8. You will see a graphical representation of the data. The areas of interest to you are (a) Head velocity in degrees per second, (b) eye position in degrees, (c) a circular plot of roll/pitch and (d) yaw/pitch

  9. The head calibration aligns the possibly oblique inertial sensor axes with the true earth-horizontal and earth-vertical directions. During head calibration the Real-Time Preview shows in the upper two diagrams the head velocity and eye position over time. Please try to keep peak head velocity around 50 deg/sec, although the exact value is not important. However, it is important to not exceed 100 deg/sec such that the patient can keep the eyes on the fixation target on the wall. At head velocities exceeding 100 deg/sec patients with a vestibular loss will not be able to keep their eyes on the target due to the limitations of the human smooth pursuit system.

  10. The lower two polar diagrams show the head movement directions in the coordinate system of the camera-attached inertial sensors. From this information the calibration analysis will automatically remap the alignment of the sensors.

  11. The Full Report for the head calibration presents the information in a similar way as the polar diagrams of the Real-Time Preview. However, the eye and head motions over time are not shown. Instead, a three-dimensional representation of head movements with respect to the earth horizontal and vertical directions is shown together with the head movements with respect to the possibly oblique axes of the inertial sensor. The three polar diagrams at the bottom of the report show the head movements from hree different perspectives.

  12. Saving Calibrations – after you have completed your first head calibration and are reviewing it, you will use the little red x up in the corner to exist this screen. When you do that you will be prompted: Do you want to use this calibration? (a) yes or (b) No, use default instead.

  13. If you have performed 2 or more head calibrations then you will be prompted, Do you want to use this calibration: (a) Yes (b) No, Use Previous or (c) No, Use Default Instead.

 
December 2016
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