We use a custom made cradle with 2 leads for ECG, respiration and temperature monitoring during cardiac MRI in our mice. We use the PC-SAM computer interface. We have been having several different problems with erratic ECG:
1. The ECG looks fine on PC-SAM but gating is erratic, missing beats etc. so that shimming takes a long time. The problem seems to be only during certain scan sequences.
2. We have a good ECG signal then slowly infuse manganese chloride through a tail vein cannula (remotely from outside the scanner room) while the mouse is still in the scanner. This causes the ECG to become so noisy that gating is not possible and the heart rate registers as being over 1000bpm. The problem often resolves itself a while after manganese infusion is ceased. We do not believe that any moisture is reaching the ECG monitoring module.
Anyone have any ideas? These problems are driving us crazy.
There's a lot of potential problems - maybe if you describe your setup, and how you secure the egg pads etc, i might have some suggestions.
Certainly, by increasing the blanking period (the time where the software won't count any ECG signal) you can avoid the software reading an increase in heart rate - I suggest that once you have a stable heart rate, set the blanking period manually in ms (to 80-90% of RR interval). You could then infuse your manganese and hopefully the early signal won't be counted.
You don't say if your scans are also respiratory gated - shimming will take much longer and be much worse if the scans aren't respiratory gated.
Hi,
I did myself a lot of mice cardiac MRI scans (also with manganese) on a 3T scanner and using the PC-SAM system for gating. Following my experience, the ECG at the beginning of the experiment shouldn't be only good, but excellent : you should have very large peaks while the animal is outside the scanner, in order to keep small noisy peaks at least when scanning.
I never had problem at the particular time of Manganese injection but was using a serrynge pump outside the scanner room...
Also and probably most important, we never achieved to get a sufficiently good ECG signal with electrodes pads, we were using the 2 thin leads electrode that you place subcutaneously at the sides of the thorax. The animal was prone and the leasds were secured at maximum with tape to avoid any vibration/motion during the scans...
Hope this can help
Hi there. Thanks for your answers. We use a 7T scanner but our setup sounds very much like yours Benedicte but we use a purpose made cradle with integrated ECG contacts which we place gel pads onto for the ECG (we shave the mouse and use hair removal cream to get the skin really smooth at the points that the ECG pads contact).. We also use an infusion pump outside the scanner room. The cradle measures respiration and temp but we do not respiratory gate the scans, only cardiac gate them. We usually get an excellent ECG to begin with and then it randomly becomes erratic. It's so inconsistent that we are beginning to wonder if it is a hardware issue- we never used to have such issues with ECG.
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