Purpose

This page lists the most common error windows seen on the Skyra host computer, and briefly explains what usually causes them and how to fix/clear them. This table of contents lists the error text you can expect to see on the window or warning.

Chilled Water Temperature is Too Low

The Skyra's gradient amplifiers and coils are cooled by chilled water from the building infrastructure. Unfortunately, the building chilled water is maintained a 0.5°C below the Siemens specification. Since the water temperature is determined by demand for the entire campus, we have no control over it, and just have to deal. We knew about this issue did in the design stage of the center, and accounted for it by insulating the chilled water loop to prevent condensation, which is the primary reason for the choice of Siemens's spec. So, there is no danger in getting a low temp warning. If you ever get a *high* temp warning ... That's a real problem!

Door of the Examination Room is Open

The door to the magnet room is part of the RF shielding that filters out unwanted noise that creates artifacts in MR images. Running with the door open virtually guarantees that you will see "RF streaking" or "Tiger striping" in your images as seen in these examples:

This error warns you that the door is not fully closed in an attempt to help you avoid these artifacts. It is not a safety issue. Check that the door is fully closed.

Preparation of the Measurement System Failed

This is usually the result of improper landmarking. The first prescan that the scanner runs is designed to set the resonant frequency. This is necessary because the scanner's magnetic field is not constant. It slowly drifts, and since even small errors in the resonant frequency can cause big problems for EPI and other scans, it must be calibrated for every subject. To do this, the scanner selects an axial/transverse slice at the magnet isocenter, and measures the frequency of the signal from that slice. This fails if the subject is not at the magnet isocenter. Make sure you set the laser corsshair landmark correctly.

1. Press the "Home" button on the face of the magnet to move the table to the home position.
2. Once the table has moved to the home position, ask your subject to close their eyes. Once they do, press the laser landmark button.
3. Use the jog wheel to move the subject forward (into the bore) until the laser aligns with the landmark on the coil you're using.
4. Press and hold the jog wheel until the table starts to move, then immediately release it.
5. Try running your scan again.

It is also possible that the RF coil you're using is not plugged in. If landmarking your subject does not work, check to make sure your coil is plugged in.

Stimulation Monitor - Warning!

This warning appears when the scan you have prescribed will exceed the FDA's first level slew rate (aka dB/dt) limits. Normally, this is not an issue as long as your subject is healthy and not an child/adolescent. If you see this warning, you should remind your subject to squeeze the alert ball if they experience Peripheral Nerve Stimulation (as small as tingling to twitching and even sharp pains). If your subject is a child, an adolescent, or unhealthy, you should not run the scan until this warning is cleared. Some things you can do to reduce the slew rate are:

1. Reduce the pixel bandwidth on the Sequence > Part 2 parameter card.
2. Reduce the Gradient Mode from Fast or Fast* to Normal on the Sequence > Part 1 parameter card.
3. Increase the field of view on the Routine parameter card.
4. For DWI scans, reduce the b-value on the Diff parameter card.

Transmitter Adjustment Did Not Converge

See the entery for Preparation of the Measurement System Failed above.

Warning: Examination Interrupted!

This warning appears whenever the table is manually moved out of the scanner during a scan. This is meant to help ensure that the person being scanned is the right one, and you didn't move on to the next subject. This almost never happens in a research setting, but is more common than you might think in a clinical setting. If you are scanning the same subject, you can clear this by making sure that the tickbox is checked next to the text "Patient is unchanged in this scan position" as in the figure above.

Patient Table Error

This error appears whenever one of the Table Stop Buttons are pressed. These are the emergency red buttons on each side of the table near the magnet bore that shut down and prevent electronic/automatic table motion. To clear this error:

1. Turn the engaged red table stop button clockwise until it pops back into the normal, "ready" position.
2. Ensure that the table is properly docked.
3. Simultaneously press and hold the buttons above and below the job wheel on the front of the magnet. It doesn't matter which jog wheel you use - both will work.

Clipped RF Pulse Detected

This error appears when the scanner tries to put more power than it should into the RF coil. It is an error almost exclusively limted to the CMRR multiband sequence. It arises when, in order to afect the prescribed flip angle for a particular RF pulse, too much power is needed in too short a period of time. It can happen with one RF pulse, or with both RF pulses (in a spin-echo experiment). The problem can be alleviated by either reducing teh flip angle (which is usually not amenable to experimental requirements) or by increasing the length of the RF pulse. When using the CMRR multiband sequence, you can find the pulse width on the Sequence > Special parameter card. The RF pulse should be selected by clicking through the list using the right/left arrow buttons until the pulse that matches the one needing modification (obtained from the error window itself, MBExc, MBRef, or both of those). Then, it is possible to set the length of the pulse in the parameter entry window; the units are microseconds. Ideally, the RF pulse should be as short as possible, but practically, you really want to set it longer than the minimum.  You'll want to set it with some buffer over the minimum value so that you won't have an issue with other subjects later, which will have different RF demands than the one you currently have in the magnet. I recommend increasing the RF pulse length until you no longer get the error, and the adding another 10-15% to the value. This should be sufficient to avoid the issue for all future scans with that protocol.

Image Send Error

Occasionally, network, or server downtime might prevent images from being sent to either DCM4CHEE (the IRC's image archive system) or OsiriX (the IRC's image distrobution system). Neither of these faults is reason for concern. We can still get your images to the right places. But, if you see these warnings/errors, you should send an e-mail to irc-help@utlists.utexas.edu to ensure that we know about it and can properly address the issue.

Protocol Was Fixed

This warning appears whenever incompatible parts of a protocol are loaded. They might be incompatible because the wrong RF coil(s) are plugged in, sequence parameters aren't possible, or features don't exist. Whenever necessary, the scanner will attempt to rectify the issues. Unfortunately, dpending on the nature of the fix, the corrective course of action can be . . . um . . . "suboptimal." You should pay close attention to whatever changes are made to ensure that they are reasonable for your experiment. Things to watch out for are changes to the selected RF coil(s) and to the prescan normalize setting. Check the RF coil(s) on the System > Coil parameter card, and check the prescan normalize setting on the Resolution > Filter parameter card.

AutoAlign Coverage Warning

This means that AutoAlign might have prescribed slices that do not cover all the anatomy in all your scans. In other words, some of your scans might not cover the whole head in all slices. The tip of the nose might have been cut off in an MR-RAGE, the most posterior part of the most inferior slice might have cut off the base of the skull, or something like those examples. This is a warning you that might not get everything in the images it prescribed, so you should double check its work to make sure it's acceptable. 

Why does this happen? There are two situations that most commonly result in this warning. First, the scout FOV might not be big enough to cover the subject's head, or the position of the scout (AAScout) volume might be off. You should try to adjust eh scout to cover all the anatomy you might scan. The other situation - and much more common occurrence, is when AutoAlign fails to properly coregister its scout with the reference head (e.g. MNI space) it has in its library. Failure modes include when the anatomy is highly diseased or distorted from the reference, when the position of the subject is just too far off from the reference, or when the optimization code just barfed. If the anatomy isn't close enough to the reference, there's not a lot you can do except manually prescribe the slices. If the subject's position is way off, you should reposition them. And in the event of barfing . . . well . . . try and rerun the AutoAlign scout. If that doesn't fix it, you'll probably have to manually prescribe and curse the sky. 

No Magnetic Field Detected

Yeah, um . . . don't call us.  We'll call you.