How to remove glitches from an analysis using TAR10s
11 Sep 2012

Glitches are due to transitory electromagnetic phenomena collected by the acquisition hardware. They appear as short spikes added on the recorded biological signals.
To eliminate the glitches, NOTOCORD® proposes to use the triggered artifact remover TAR10s. The module needs a trigger to mark the glitch position and then reconstructs the signal by a polynomial or linear interpolation in a defined zone around the trigger.

Periodic glitch

In isolated heart experiments the stimulation pulse may induce in the recording channel a stimulation artifact that appears as a glitch. In the configuration below, the trigger necessary to TAR10s action is generated by acquiring a digital signal synchronized with the stimulation pulse.

Example configuration of TAR10s in isolated heart experiment

As seen in the figure below, TAR10s then replaces the stimulation artifact (red) marked by the trigger (orange) by a linear interpolated segment.

Stimulation artifact removal on an isolated heart ECG signal


Random glitch

Here is another example of glitch, induced in arterial pressure measurement in a telemetry study. To evaluate the performance of TAR10s on such a signal, let's first try to reduce the glitch with other filters and make a comparison. 

On the figure below, the left screenshot shows the signal (blue) treated with the low pass filter IRF10a  (green). The right screenshot shows the same signal (blue) processed with the glitch noise filter DEG10a (red). In these examples, the glitch is so important that only the most aberrant signal samples are excluded, hence the artifact removal is not complete.

Glitch removal with IRF10a (left) and DEG10a (right)

 

Now, let's try to remove that glitch with the Trigger artifact remover TAR10s. The trigger needed by the module to reconstruct the signal is generated by the glitch itself using the threshold detector THR10a as shown in the configuration below. The trigger is produced each time the signal crosses a user-defined value.

TAR10s is triggered by the threshold detector THR10a

 

The arterial pressure signal is thus processed with TAR10s and results are visible on the figure below.

  • In red: the original signal showing the glitch.
  • In green: the trigger generated by THR10a
  • In blue: the signal processed by TAR10s. The whole section initially containing the glitch has been removed and the signal has been successfully "rebuilt".

Random glitch removal with TAR10s

 

For small amplitude glitches, compared to the signal amplitude, check the option "Remove baseline" in THR10a properties window and adjust threshold and "Baseline computed on" parameters.