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Day 6: Who Do I Look Like?

The MRI Answer

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The correct answer is "b".

Here is an explanation from our imaging expert, Carl Gregory:

arc001 drop001

These images demonstrate intermittent corruption of the data, typically by electrical problems. They have been artificially generated by using viewit to modify the raw data from the reference image before transforming it. On the left, a few data points have been modified, as might happen if an electrical transient (such as a static discharge, sometimes called an "arc") occured during the digitization of one echo. Note the elevated background level. The venetian blind pattern becomes a crosshatch with two arcs, and with multiple arcs, may be indistinguishable from random noise. A transmitter arc looks different, since it affects the MR magnetization directly, and does not occur during digitization.

On the right, some part of each of three rows of the data has been set to zero, as might happen if a computer problem caused loss of data, or a loose cable momentarily (for a few milliseconds) prevented the received signal from being digitized (sometimes called "dropout"). Note the similarity (and differences) to the motion/instability case. The width of the band at the center is inversely proportional to the duration of the dropouts. Look closely to see the droputs.

For more information on artifacts, click here to visit the MRI Artifact Gallery.

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