The central point artifact appears as either a bright or a dark dot precisely at the center of the image. I have reviewed MR scans in which this artifact was originally misinterpreted as a multiple sclerosis plaque or a lacunar infarction. Don't let this happen to you!
The central point artifact results from a constant direct current (DC)-offset in the receiver electronics. Ideally, the receiver voltage output should be zero when no signal is being recorded. Occasionally the receiver will drift and a small positive or negative output will be present even at rest. This small constant offset, when Fourier transformed, will produce a small spike in signal at the center of the image.
In the early days of MR, this artifact was a common nuisance. Today, however, it is rarely encountered because of the widespread use of RF-phase alternation and self-calibrating checks in the scanner circuitry. Occasionally, however, if a DC-offset error slips through, the central point artifact may appear in your images. So be prepared!
Improper calibration of the receiver amplifier gain can result in data clipping and an eerie, phantom-like image with a gray background. This artifact occurs whenever the gain setting is too high and the RF-signal exceeds the upper and lower cut-off levels of the RF amplifier (±Vmax). Careful recalibration and rescanning are the only means of overcoming this artifact.
Data Error Artifacts
From time-to-time a random "glitch" occurs in the data processing chain resulting in an image containing multiple lines that may be arrayed in a criss-cross or herringbone pattern. Several examples are shown. Often, simply reprocessing the raw data will remove this artifact and salvage an otherwise unreadable group of images.
Advanced Discussion (show/hide)»
The Fourier transform of a constant is the Dirac delta function δ(t), accounting for the central point artifact "spike".
Similarly, an erroneous data point at (kx, ky) accentuates a single spatial frequency, reflected by a set of parallel lines at that spatial frequency appearing in the final image.
Zhuo J, Gullapalli RP. AAPM/RSNA physics tutorial for residents. MR artifacts, safety, and quality control. Radiographics 2006;26:275-297.
Heiland S. From A as in aliasing to Z as in zipper: artifacts in MRI. Clin Neuroradiol 2008; 1:25-36.
We intermittently see zipper-like artifacts in our images. What causes them?
Why is receiver gain adjustment necessary? What happens if it is set incorrectly?