Download CT Imaging

CT Scanner
Presented by:
Dr M A Oghabian
Medical Physics Department,
Tehran University of Medical
Sciences
Computed Tomography
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CT uses a rotating x-ray tube, with the beam
in the form of a thin slice (about 1 - 10 mm)
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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)
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180 translational movement
180 Rotary movement
160 parallel rays across a 24 cm FOV
Each 2 slices=4.5 min.
Processing time=1.5min.
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Second generation CT scanners
Rotate/Translate Narrow fan beam~10 degree
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Narrow fan beam~10 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)
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Wide fan beam
More than 800 detectors
No translational motion
Scan time ~ 0.5 Sec.
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4th Generation CT Scanners
Rotate/Stationary
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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, microwaveaccelerated 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(CONT’D)
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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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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
X-Ray
Tube
Detector
Array
Note:
how most
of the
electronics
is
placed on
the rotating
gantry
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 Features:
Multislice 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
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
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
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
Multi slice CT collimation
5mm
2,5mm
1mm
0,5mm
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Speed: Single vs. 4 Slice
Single Slice
Chest
Coverage
Thickness
Time (s)
mA
Abdomen/Pelvis
Coverage
Thickness
Time (s)
mA
Scan Time (s)
Tube Load (mAs)
4 slice
235 mm
5 mm
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240
235 mm
5 mm
8
240
255 mm
5 mm
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300
255 mm
5 mm
9
300
65
17,720
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4,725
MULTISLICE SPIRAL CT
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Introduced at the 1998.
They are based multiple
detector. rows ranging between 8,
16, 24, 32 and 64 depending on the
manufacturer.
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The overall goal is to improve
the volume coverage speed
performance.
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Complete x-ray tube/detector
array rotation in less than 1s.
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Partial scan images can be
obtained in approximately
100ms.
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MULTISLICE IMAGING(CONT’D)
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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
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Real Time Guidance
Great Image Quality
Low Risk
Faster Procedures
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REAL-TIME CT FLUOLOROSCOPY
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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)
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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
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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:
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data acquisition
image processing
3D rendering
image display and analysis.
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