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Pulse Oximetry
Note the following:
• There is a delay between the ECG and plet gates, because blood flows to a
peripheral site after the heart beats.
• There is continuous presence of baseline interference in the ECG waveform,
because the MR scanner is running continuously. i.e. not being triggered.
• The plethysmogram waveform has no interference from the MR scanner.
• There is a small modulation of the plethysmogram waveform from respiration.
Plethysmogram gate threshold
A threshold parameter is used to detect the plethysmogram gates for oximetry. In the
current version of the software, the threshold's default value can be changed in real
time by the user.
The figure on the next page shows how to open the window that controls the pulse ox
threshold. Factory default for the threshold is 11 counts. However, the best selection
depends on the signal strength which is reported on the left side of the pleth waveform
display. The higher the signal strength, the larger the optimum setting for the threshold.
11-6
Revision C, August 2013
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