Focal signal drop
Global signal drop, blurring
Motion corrupted images
Sometimes, you will see images that are corrupted, typically caused by subtle motion such as swallowing. A couple of examples (shown next to good images from the same study):
The tensorcalc program attempts to identify corrupted images by
comparing overall signal intensity in the image to a reference signal that
is based on the other diffusion weighted images in the series.
In addition, noise corrupted images can be manually excluded from
further calculations by using the input option "-excl".