Biomedical Engineering Reference
In-Depth Information
5
Correcting for Scanner Errors in CT, MRI,
Spect, and 3
D Ultrasound
Louis Lemieux, Dale L. Bailey, and David Bell
CONTENTS
5.1
Introduction .................................................................................................. 88
5.1.1
Image Artifacts, Geometric Distortions, and Their Origins....... 89
5.2
Geometric Distortion in Computed Tomography................................... 90
5.3
Spatial Inaccuracies in Magnetic Resonance Imaging ............................ 91
5.3.1
Magnitude of Geometric Distortions in MRI ............................... 92
5.3.2
Geometric Distortion Due to Gradient Field Nonlinearity........ 93
5.3.2.1
Correction........................................................................... 93
5.3.3
Geometric Distortion Due to Field Inhomogeneity .................... 93
5.3.3.1
Correction........................................................................... 95
5.3.4
Error in Field of View (Voxel Dimensions) Due to Variations
in Gradient Strength ........................................................................ 96
5.3.4.1
Correction........................................................................... 96
5.3.5
Signal Nonuniformity Due to RF Inhomogeneity....................... 96
5.3.5.1
Correction........................................................................... 97
5.4
Spatial Inaccuracies in Emission Tomography ........................................ 97
5.4.1
Sources of Spatial Inaccuracies and Measures to Prevent
or Minimize Them ........................................................................... 98
5.4.1.1
Geometric and Alignment Effects................................... 99
5.4.1.1.1
Center of Rotation Errors............................... 99
5.4.1.1.2
Nonuniform Sampling Effects ...................... 99
5.4.1.1.3
Voxel Dimensions ........................................... 99
5.4.1.2
Physical Effects Causing Intensity Artifacts
and Spatial Distortions ................................................... 100
5.4.1.2.1
Attenuation Effects ....................................... 100
5.4.1.2.2
Reconstruction Artifacts............................... 102
5.5
Spatial Inaccuracies in 3D Ultrasound Imaging .................................... 102
5.5.1
Sources of Geometric Inaccuracies and Measures to Prevent
or Minimize Them ......................................................................... 103
