User guide
ELI
O
S
ECH001XN111-A4 – 07/2022
113
Measurement on ECHOSOFT
6.2 ASSR
6.2.3
Measurement progress
1.
Indicates, for each frequency being recorded, the signal
level (in green) compared to the noise level (in red). It
corresponds to the signal at the modulation frequency
and the surrounding noise.
The more the signal comes out of the noise, the more
the measurement will tend to validate a response.
It is normal that at the first moments of the measure-
ment, the signal and the noise leave the scale of the
graph, it takes several acquisitions to arrive in the order
of magnitude expected.
A noise threshold is displayed, it determines a limit be-
low which, if the frequency has still not validated a re-
sponse, the measurement will stop without waiting for
the time limit. Indeed, below a certain level, the noise
will stop decreasing and, if the signal has not yet
emerged, there is no point in continuing the measure-
ment.
This threshold is adjustable, our system is able to go
down to a noise level between 5 and 10 nanovolts.
2.
Response validation curve for each frequency being
tested. With the elapsed time in minutes on the abscissa
and the validation percentage on the ordinate.
For a response to be validated, the curve must reach
100% (the top of the graph) and remain there for a few
seconds. Validation between frequencies is independ-
ent.
The validation is based on a statistical calculation
(MSC / "Magnitude-Squared Coherence" a = 0.05) tak-
ing into account the signal and the phase at the modu-
lation frequency as well as the surrounding noise level.
3.
Visualization of the signal in real time and rejection ad-
justment.
This allows to asses the quality of the measurement con-
ditions. Normally, if the conditions are good, the signal
should be contained in the default rejection area (10
µV). If this is not the case, several factors can intervene:
-The impedances are not good.
-The patient is not relaxed or is not well installed which
produces too much muscle activity.
-A source of electromagnetic radiation disturbs the sig-
nal. Make sure you are not near any device that could
produce this type of radiation. Possibly unplug any de-
vices in the room that are not in use.
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