Monitoring And Gating; System Components - SA Instruments 1030 Operation Manual

Chapter 1
System Overview

Monitoring and gating

The Model 1030 monitoring and gating system was designed specifically to meet the
physiological monitoring and gating needs for anesthetized mice, rats and larger
animals in the high field MR environment. Both anesthesia and the local environment
can adversely alter animal physiology. For that reason, research experiments often
require measurement of physiologic parameters for heart rate, respiration rate,
temperature, blood pressure, etc. It can also be necessary to control the temperature of
the animal. For example, sedated mice can have heart and respiration rates depressed
by more than a factor of two when exposed to a room temperature environment.
Motion artifacts in MR images can be eliminated or greatly reduced by employing gating
techniques during the acquisition of the MR image data. By synchronizing MR data
collection with the electrocardiogram, images can be obtained at specific times during
the animal's cardiac cycle. These images, which are free of cardiac motion, can be
viewed individually or in a cine time sequence to visualize heart movement.
Motion artifacts due to breathing can also be eliminated or reduced by synchronizing
MR data collection with the respiratory cycle. Typically the largest movement of the
diaphragm and abdomen is during inspiration. Thus, selective acquisition of MR data
during expiration can be effective in reducing breathing artifacts.
In some cases it is advantageous to employ gating combinations to trigger MR data
acquisition. For example, both cardiac and respiratory gating can be employed to
selectively acquire cardiac data only during expiration. These acquisition techniques
can produce anatomic images free of breathing, heart and/or blood flow artifacts.

System Components

The Model 1030 monitoring and gating system consists of data acquisition modules
located near the animal and a Control/Gating Module connected to a PC located near
the operator console. The PC displays multiple waveforms, measured values, trends
and gating pulses, which can be used to trigger MR data collection. The data
acquisition modules are controlled by menu driven software from the PC. A SAII heater
system, either air or water, can be used with the monitoring system to regulate the
temperature of smaller animals in the magnet bore.
The in bore ERT Module measures ECG using three leads with needle or surface
electrodes, respiration from a small pneumatic pillow sensor and/or from the movement
of one ECG lead in the strong magnetic field and temperature with a small rectal
thermister probe. Power is supplied by an external, rechargeable battery. ECG,
respiration and temperature measurements are transmitted out the magnet bore on an
optical fiber to the ERT Control/Gating Module.
The ERT Control/Gating Module resides outside the RF shielded room near the MR
operation console. It receives data from the ERT Module and any of several optional
acquisition modules. The ERT Control/Gating Module sends data to the PC for display
and receives user instructions from the PC to control measurement and gating
functions. Gates from ECG, respiration and any of the available options are generated
by the ERT Control/Gating Module's microprocessor and sent to the MR system. The
delay from the R-wave peak to the MR system gate is user selectable as is the
Revision C, August 2013
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