CT Scanner

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CT Scanner

• Presented by
• Dr M A Oghabian
• Medical Physics Department,
• Tehran University of Medical Sciences

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Computed Tomography

• CT uses a rotating x-ray tube, with the beam in
  the form of a thin slice (about 1 - 10 mm)
• The image is a simple array of x-ray intensity
  (Projections), and many hundreds of these are
  used to make the CT image, which is a slice
  through the patient

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First generation CT Scanner(Rotate/Translate
Pencil beam)

• 180 translational movement
• 180 Rotary movement
• 160 parallel rays across a 24 cm FOV
• Each 2 slices4.5 min.
• Processing time1.5min.

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Second generation CT scannersRotate/Translate
Narrow fan beam10 degree

• Narrow fan beam10 degree
• Linear array of 30 detectors
• 6 linear movement
• 6 rotary movement
• Scan time 18 Sec.

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Third generation CT Scanners(Rotate/Rotate ,
Wide fan beam)

• Wide fan beam
• More than 800 detectors
• No translational motion
• Scan time 0.5 Sec.

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4th Generation CT ScannersRotate/Stationary

• Fan beam geometry
• More than 4800 detectors

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Electron Beam Computed Tomography (EBCT)

• - x-ray source is not x-ray tube but a focused,
  steered, microwave-accelerated EB incident on a
  tungsten target.
• - It has no moving parts .
• - Target covers one-half of the imaging circle
  detector array covers the other half.
• - Images in less than 50ms.

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EBCT(CONTD)

• There are 4 targets and 4 detector arrays
  resulting in 4 contiguous images simultaneously.
• The detector array may consists of two separate
  rings
• Each solid -state detector consists of a
  luminescent crystal and cadmium tungstate coupled
  with silicon photodiodes.
• Heat dissipation is no problem in EBCT.
• Developed for fast imaging.
• Used for cardiac imaging

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A look inside a rotate/rotate CT
Detector Array and Collimator
X-Ray Tube
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Helical Scanning

• Continuous Gantry Rotation
• Continuous Table Movement
• Continuous Data Acquisition
• One set of detectors
• Beam collimation slice thickness

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Comparison of data acquisition for axial and
helical technologies.
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Reciprocating rotation (A) versus fast continuous
rotation using slip-ring technology (B)
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A Look Inside a Slip Ring CT
Note how most of the electronics is placed
on the rotating gantry
X-Ray Tube Detector Array Slip Ring
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(A) Pitch 1 (B) Pitch 2
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Comparison of the accuracy of 3D reconstruction
for conventional (A) and spiral/helical (B) CT
scanning.
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More New CT FeaturesMultislice Scanning
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• Multislice CT, where up to 64 variable thickness
  slices can be collected simultaneously
• CT fluoroscopy, where the patient is stationary,
  but the tube continues to rotate
• 3-dimensional CT and CT endoscopy

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Clinical Benefits Of Multi-Slice

• Multi-phase Organ Studies
• Liver Pancreas Arterial, Renal Nephrogram
• Arterial Phase Scanning
• Hypervascular Tumors
• CT Angiography
• Multi-Plane Reconstructions, Contrast Enhancement
• New CT Applications
• CT fluoroscopy
• CT Colonography
• Cardiac morphology, function
• Advanced Lung Analysis

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Detector Configurations
X-ray Tube Focal Spot
X-ray Beam Collimator
a
4 x 1.25 mm Detector Configuration
16-row Mosaic Detector
Flex Connector A
Flex Connector B
Diode
FET Switching Array
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Detector Configurations
X-ray Tube Focal Spot
X-ray Beam Collimator
4 x 2.5 mm Detector Configuration
16-row Mosaic Detector
Flex Connector A
Flex Connector B
Diode
FET Switching Array
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Detector Configurations
X-ray Tube Focal Spot
X-ray Beam Collimator
4 x 3.75 mm Detector Configuration
16-row Mosaic Detector
Flex Connector A
Flex Connector B
Diode
FET Switching Array
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Detector Configurations
X-ray Tube Focal Spot
X-ray Beam Collimator
4 x 5.0 mm Detector Configuration
16-row Mosaic Detector
Flex Connector A
Flex Connector B
Diode
FET Switching Array
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Multi slice CT collimation

5mm
2,5mm
1mm
0,5mm
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Speed Single vs. 4 Slice
Single Slice 235 mm 5 mm 31 240 255 mm 5
mm 34 300 65 17,720
4 slice
235 mm 5 mm 8 240 255 mm 5 mm 9 300 17 4,725
Chest Coverage Thickness Time
(s) mA Abdomen/Pelvis Coverage Thickness Time
(s) mA Scan Time (s) Tube Load (mAs)
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MULTISLICE SPIRAL CT

• Introduced at the 1998.
• They are based multiple detector. rows ranging
  between 8, 16, 24, 32 and 64 depending on the
  manufacturer.
• The overall goal is to improve the volume
  coverage speed performance.
• Complete x-ray tube/detector array rotation in
  less than 1s.
• Partial scan images can be obtained in
  approximately 100ms.

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MULTISLICE IMAGING(CONTD)

• ADVANTAGES
• Improved spatial resolution this advantage
  improved MPR,3D images.
• Reduction of radiation exposure.
• Motion artifacts are greatly reduced.
• Patient breathhold is much less demanding.
• Imaging larger z-axis volume in less time is
  possible with MI.
• Less contrast medium required.
• Because of imaging speed, coronary artery is
  comparable with EBCT.
• Improved accuracy in needle placement CT
  fluoroscopy.

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CT Fluoroscopy

• Real Time Guidance
• Great Image Quality
• Low Risk
• Faster Procedures

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REAL-TIME CT FLUOLOROSCOPY

• CT fluoroscopy acquire dynamic images in real
  time.
• Fast continuous imaging, fast image
  reconstruction continuous image display.
• Patient movement is low during Tube rotation.
• Fast image Reconstruction algorithm is required.

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CT ANGIOGRAPHY (CTA)

• CTA allows maximum visualization of the pulmonary
  artery and its segmental braches.
• CTA requires low kVp and MA, for example
  90Kvp/100mA.
• CTA employs MIP and MPR to maximum advantage.

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3D Stereo Imaging

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Enhanced 3D
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CT Endoscopy
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CT VIRTUAL REALITY IAMAGING

• The use of virtual reality is the creation the
  inner views of tubular structures.
• Offers both endoluminal and extra luminal
  information.
• It reduces complication (eg. infection and
  perforation).
• Four requirements
• data acquisition
• image processing
• 3D rendering
• image display and analysis.