Computed Tomography Outline X-RAY Computed Tomography Artifacts - PowerPoint PPT Presentation

Computed Tomography

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

X-RAY: radiation type X-rays are ionizing, invisible and highly penetrating electromagnetic radiation

X-RAY: how to generate? Heated filament Electrons are emits electrons by accelerated by thermionic emission a high voltage X-RAY produced when high speed electrons hit metal target

X-RAY: attenuation  Attenuation depends on:  Thickness  Density  Effective atomic number  Energy of the X-RAY beam

X-RAY  Projection:  Projections over 180 o  Reconstruct to 3D  Fast  Non-destructive  Direct 3D calculations

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

CT – Back Projection  In standard back-projection, images are taken for a number of angles positions and then smeared back to form the section

CT – Back Projection Original Back projection Shadow

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

Artifacts and Sources of Error  Radiation dose 7 Total exposure in mGy in mice: 6 5 4 3 2 1 0 0.0 10.0 20.0 30.0 40.0 50.0 Scan resolution (microns)

Artifacts and Sources of Error  Beam hardening:  Theoretical model: beam with only high energy photons 20% 35% 50% 60% 20% 35% High energy photons Low energy photons

Artifacts and Sources of Error  Beam hardening:  Beam hardening:  Theoretical model: beam with only high energy photons 35% 20% 60% 50% 35% 20%  True model: 35%  75% error mixed beam 60%  20% error 35% High energy photons Low energy photons

Artifacts and Sources of Error  Rat femur with titanium implant:

Artifacts and Sources of Error  Beam hardening, correction via:  Physical filter (aluminum)  Correction afterwards using software Unfiltered Filtered

Artifacts and Sources of Error  Ring artifacts: due to drift and nonlinearities in the response of individual elements in the detector

Artifacts and Sources of Error  Alignment error:

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

Micro-CT analysis  3D-models: Lateral Medial Trabecular bone Epiphysis Cross-section

Bone Control Osteoarthritis induced

Bone  Architectural bone changes validated with histology New bone Resorbed bone

Bone  Femur defect  Filled with porous titanium structure

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

uCTa: microCT-arthrography Synovial fluid Healthy microCT Cartilage Bone

uCTa: microCT-arthrography Synovial fluid Healthy microCT Cartilage Bone

uCTa: microCT-arthrography Synovial fluid OA microCT Cartilage Bone

Contrast-enhanced microCT Healthy OA-induced / mono-iodoacetate control Low attenuation High attenuation (high GAG) (low GAG)

Micro-CT analysis

Outline  X-RAY  Computed Tomography  Artifacts and Sources of Error  Imaging studies  Bone  Cartilage  Other

Contrast-enhanced microCT  Mouse lung sample  With contrast agent  5.7 μ m pixel size Source: http://www.skyscan.be/applications/biomedical/biomed002.htm

Contrast-enhanced microCT  Mouse kidney sample  With contrast agent  80 μ m pixel size Source: http://www.scanco.ch/applications/biomedical.html

Contrast-enhanced microCT  Rat vascular system  With contrast agent  75 μ m pixel size  vivaCT Source: http://www.scanco.ch/applications/biomedical.html

Cardiac function Cranial Caudal Diastole Systole

Contrast-enhanced microCT  Mouse (in-vivo)  NO contrast agent  160 μ m pixel size Source: http://www.skyscan.be/applications/biomedical/biomed006.htm

Contrast-enhanced microCT  Mouse (in-vivo)  WITH contrast agent  160 μ m pixel size  Real-time radiography of heart activity and contrast propagation Source: http://www.skyscan.be/applications/biomedical/biomed006.htm