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jim.voyvodic
BIAC Faculty
138 Posts |
 Posted - Sep 15 2006 : 1:30:03 PM
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We have just discovered that occasionally a small imaging artifact appears in some of the high-resolution anatomical images we acquire on our 3T scanner. The artifact appears as small regularly-shaped hyperintensities near the midbrain region. They do not appear in every image.
This artifact only appears in some anatomical images -- it does not occur in functional images (spiral or EPI). It therefore is not a factor in any of the fMRI results we have obtained.
Susan Music has investigated the source of these artifacts and discovered that they are a distorted "ghost" of the new auditory headphones caused by the ASSET image reconstruction software. The artifact only appears when the new headphones are used and multi-channel images are reconstructed using the ASSET option. (This is not a SCIC image enhancement problem.) It appears using both 2-D and 3-D pulse sequences, but only when ASSET is used.
The headphones themselves do not cause imaging problems, but they are not completely MR invisible. My guess is that GE's multi-channel image reconstruction software is confused by the presence of a signal from the auditory headphones outside of the head. A normal head does not have tissue floating out in the air like that.
Because of its regular shape and sporadic appearance, the artifact is easy to distinguish from true tissue signals, once you know to ignore it. On first glance, however, it could be misinterpreted as a tissue abnormality, which might cause undue concern.
We will have to look into ways to avoid this artifact in the future. For any scans that do not need audio inside the scanner we can use a different set of headphones that is completely MR invisible and therefor causes no artifact. We will plan to modify the new headphones to replace the MR visible component (it seems to be only the decorative plastic cover that shows up) but first we will check with the manufacturer about this issue. In the meantime, if you need sound inside the 3T you can either choose to not use the ASSET option with anatomical scans (they will take a few minutes longer) or you can accept the small image artifacts and ignore them.
Because of the location and infrequency of these structural imaging artifacts it is unlikely that they will cause any problems in any 3T scans already acquired. If anybody finds that they are a problem (e.g. for automatic tissue segmentation software) please let me know and we can probably create a program to detect and remove those artifacts from existing data sets.
This problem probably dates from sometime in June, when we began using these new headphones in some scans. I apologize that we did not detect this problem earlier. I would like to thank Susan for her expert troubleshooting to pinpoint its source.
Jim
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structural image artifact at 3T with headphones
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