Cross-excitation artifact (MRI)

Discussion:

There are a few explanations for this finding:

  1. If a patient with sludge has been in the left decubitus position before the scan, the sludge may still be layering medially in the initial sequences, and slowly layers posteriorly during the rest of the exam. However, the lack of sludge in the subsequent T2 images in this patient excludes this possibility.  
  2. The other possibility, which is presumed to be the case here, is the cross-excitation artifact. This artifact happens when a tissue, which is currently being imaged, can not produce a signal because it is still under the influence of a prior excitation RF pulse from a different acquisition. In this case, the scouts were acquired in the following order: axial, sagittal and finally coronal. The sagittal FOV involved the medial gallbladder. Therefore, the immediate subsequent RF pulse of the coronal acquisition will result in a low signal in the medial gallbladder and can mimic sludge.  
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