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MR Image quality and artifacts

Image quality

by Denis Hoa

 

The quality of an MR image depends on several factors:

  • Spatial resolution and image contrast
  • Signal to noise ratio (and contrast to noise ratio)
  • Artifacts

An MR exploration is a compromise between scan time and image quality. An MR exploration protocol and its sequence parameters will have to be optimized in function of the organs and pathology.

 

La résolution spatiale correspond à la "finesse" de l’image, c’est-à-dire à la taille du plus petit détail que l’on pourra détecter. Ainsi, plus les voxels de signal enregistrés seront petits, plus la résolution spatiale sera élevée. Le volume du voxel est défini par la dimension de la matrice (256 x 256 ou 512 x 512 etc..), le champ de vue (10 cm, 20 cm, etc.…), et l’épaisseur de coupe.

 

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Spatial resolution corresponds to the size of the smallest detectable detail. The smaller the voxels are, the higher the potential spatial resolution will be. Voxel volume is determined by the matrix size (256 x 256 or 512 x 512 etc..), the field of view (10 cm, 20 cm, etc....), and slice thickness.

 

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Image contrast varies with the type of pulse sequence and its parameters. Tissue-contrast is also modified by pre-saturation pulses or contrast agents.
Image contrast and signal weighting have to be adapted to the imaging objectives: anatomy, edema, tissue-characterization (fat, hemorrhage, water), vascularization...

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