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Chapter 4
ERT Module
Overview
The animal's electrocardiograph (ECG) is obtained from two or three leads connected to
sub-dermal needle electrodes, gold disk surface electrodes or pads.
A respiration
signal may be superimposed on the measured ECG waveform by closely coupling one
of the active ECG lead wires to the animal's abdomen. This coupling is accomplished
by attaching the ECG lead wire to a cradle configured to conform to the animal's
abdomen. As the animal breaths, the lead wire moves in the strong static magnetic field
creating a signal (E-resp) that is superimposed on the ECG waveform.
Another
measurement of the animal's respiration can be made using a small pneumatic
respiration pillow sensor. Temperature is measured using a temperature probe in the
animal's rectum.
ERT Module signals are passed sequentially through an RF filter, amplifier and pulsed
gradient filter before being combined and digitized. The digitized signal is transmitted
out the magnet bore to the ERT Control/Gating Module using a long fiber optic cable.
ERT Modules have both a fiber optic transmitter and receiver. Under normal operation,
only the gray transmitter is used and no connection is made to the blue receiver.
Valuable information on generating reliable ECG gates is presented in Appendix C
Troubleshooting.
Positioning the ERT Module
The ERT Module powered by an external battery pack is positioned in the magnet bore
close to the animal. It may be positioned near the head or near the tail. A rectal probe
temperature extension cable is provided for use when the module is near the head.
Because the module can move during gradient activity, it is sometimes necessary to
provide restraint by taping it to a stationary object. If the module vibrates during data
collection, artifacts will be present on the ECG waveform. Do not tape the ERT Battery
Pack to the ERT Module.
Caution: The ERT Module should be taped to eliminate
unwanted movement from gradient vibration.
Alternatively, if space is limited inside the bore the ERT Module can be located away
from the imaging volume using ECG, respiration and temperature extension cables.
Two or more sets of extension cables can be connected to each other to locate the ERT
Module outside the bore if required.
Revision C, August 2013
4-1
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