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PC and ERT Control/Gating Module
The R-detect algorithm is based on 2 or 3 points and their positive and/or negative
slew rates or slopes (amplitude/time).
generation for factory defaults: positive peak with positive slope of 200µV/6.7ms and a
negative slope of 98µV/4.4ms. The gate is generated at the end of the negative slope.
In this example the R-wave is about 800µV in amplitude.
requirement is easily exceeded and the gate is generated as soon as the negative slope
requirement is satisfied. Note that the mid point that satisfies the gate requirement is
earlier in time than the R-wave peak. Thus the delay of the scanner gate is less than
the negative slope time (i.e. less than 4.4 msec)
Proper selection of parameters for R-wave detection are important in obtaining reliable
results. This is especially true when the ECG waveform contains large contributions
from blood flow, vibration or respiration.
Perform the following steps to determine optimum settings for ECG detection (note we
assume a positive R-wave for this discussion, but the software works in a similar
manner for a negative R-wave):
Select a wave feature to detect:
Selecting positive peak will give more reliable detection than selecting a rising
edge.
The only reason to select a rising edge would be to obtain a gate
occurring before the R-wave peak in time.
Pick the times for the slopes: There are a maximum of 31 sample points or
about 17 ms. Different animals have different rise times for the R-wave. Select
the largest time appropriate for the animal's rise time. For mice the rise time is
about 7.5 ms. Because the gate is generated at the end of the fall time, the fall
time is usually set to be less than the rise time.
Select the amplitude(s): Determine the peak amplitude of the R-wave: usually
500 µV to 1000 µV. In the case of mice with a rise and fall time selected of 6.7
and 4.4 ms respectively, we select rise & fall amplitudes of less than 6.7/7.5 =
90% and 4.4/7.5 = 60% of the peak amplitude. The system can be used to
determine the amplitudes: set the amplitudes smaller than you expect, but large
3-10
The waveform shown exhibits R-wave gate
Usually this is a positive going R-wave.
Revision C, August 2013
The positive slope
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