CT Scanning Gerald R Aben MD FACR Department
CT Scanning Gerald R. Aben, MD, FACR Department of Radiology College of Osteopathic Medicine 11/21/2020 DEPARTMENT OF RADIOLOGY 1
Computed Tomography (CT) • Donut Shaped machine • Uses x-ray energy and computer generation of images • Advantages • Sensitive to slight density difference • Cross sectional anatomy • Attenuation: reductions in intensity of x-ray beam as it traverses matter either by absorption or deflection • Special terms used on CT reports • High attenuation, Low attenuation 11/21/2020 DEPARTMENT OF RADIOLOGY 2
CT Terms • High attenuation • Absorption of x-ray photon • Presented as white on image • Low attenuation • Free passage of photon • Presented as black on image 11/21/2020 DEPARTMENT OF RADIOLOGY 3
CT Scanner Tilting Gantry Examination Bed or Couch 11/21/2020 DEPARTMENT OF RADIOLOGY 4
64+ Slice CT • • • Faster scan times Reduced patient motion Increased resolution 0. 35 mm isotropic resolution 3 -D reconstructions Improved diagnostic accuracy Reduced need for ‘high risk’ somewhat more invasive examinations 11/21/2020 DEPARTMENT OF RADIOLOGY 5
CT Scanner Patient couch or bed 11/21/2020 DEPARTMENT OF RADIOLOGY Gantry with Rotating Tube and Detector 6
Basic Principles of CT • CT imaging system moves around the body part at a fixed location • Attenuation information obtained in multiple planes • Reconstruct of this attenuation information into a simple grid 7 11/21/2020 DEPARTMENT OF RADIOLOGY
Basic Principles of CT • Each body section divided into 3 dimensional boxes – voxel • 2 dimension grid of pixels • Calculate attenuation in each direction • Add up all attenuations in each pixel • Normalize to a common scale 11/21/2020 DEPARTMENT OF RADIOLOGY 8
Basic Principles of CT • Density of each pixel varies resulting in a pictorial representation of the density of structures within that section • Repeat for each subsequent slice • The smaller the pixel, the higher the resolution 11/21/2020 DEPARTMENT OF RADIOLOGY 9
Spiral (Helical) CT: • Table moves at constant speed • X-ray tube and detectors continuously rotating • Multiple views are acquired which are not in-plane (helical data set-volumetric data) • Computer reconstructs views to form a slice (similar principle to that presented earlier) 11/21/2020 DEPARTMENT OF RADIOLOGY 10
Spiral (Helical) CT: • Faster image acquisition than conventional CT (less motion artifact) • Allows high resolution 2 -D and 3 -D reformations • Isotropic Voxels • Can also obtain conventional axial image at a single location (i. e. head CT, high resolution lung CT) 11/21/2020 DEPARTMENT OF RADIOLOGY 11
Spiral (Helical) CT Scanning Continuous Tube Rotation 11/21/2020 2000# Spinning Instrument Package <1 rps DEPARTMENT OF RADIOLOGY Continuous Table Motion 12
Hounsfield Units Hounsfield units (HU) = CT Numbers = Arbitrary scale based on attenuation with water assigned a CT number of 0 One CT number (HU) = 1/1000 of water attenuation value = 0. 1% change in attenuation relative to water -1, 000 Air 11/21/2020 0 Water DEPARTMENT OF RADIOLOGY +1, 000 Dense bone 13
Typical CT Numbers (HU) +1000 ------Dense Bone 100 Fresh Blood(+45 to +90 HU) Liver, spleen, muscle, Aorta, gray matter, white matter, (+25 to +75 HU) 0 CSF, cystic lesions, water 50 0 -100 -700 Fat Lung -1000 11/21/2020 DEPARTMENT OF RADIOLOGY 14
Scanogram or Scout View 11/21/2020 DEPARTMENT OF RADIOLOGY 15
Brain CT Scalp Hematoma 11/21/2020 DEPARTMENT OF RADIOLOGY 16
CT Brain Contrast 11/21/2020 DEPARTMENT OF RADIOLOGY 17
CT Brain Axial MIP 11/21/2020 DEPARTMENT OF RADIOLOGY 18
CT Brain Coronal MIP 11/21/2020 DEPARTMENT OF RADIOLOGY 19
CT Brain Sagital MIP 11/21/2020 DEPARTMENT OF RADIOLOGY 20
CT Abdomen 11/21/2020 DEPARTMENT OF RADIOLOGY 21
3 -D CT Cervical Spine 11/21/2020 DEPARTMENT OF RADIOLOGY 22
CT Colonography 11/21/2020 DEPARTMENT OF RADIOLOGY 23
11/21/2020 Courtesy Dr. Jim Potchen DEPARTMENT OF RADIOLOGY 25
Courtesy Dr. Jim Potchen 11/21/2020 DEPARTMENT OF RADIOLOGY 26
CTA Coronary 11/21/2020 DEPARTMENT OF RADIOLOGY 27
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