L5 Computed Tomography 1 Flashcards
What is a Tomogram?
A tomogram is an image of a plane or slice within the body.
Briefly explain CT
Computed Tomography
One way to think about the basic mechanism of Computed Tomography (CT) is to image taking a series of conventional chest x-rays, where the patient is rotated slightly around the axis running from head to foot between each exposure. The projection data is used to reconstruct crosssectional images
What is the main advantage of CT over Radiographic Imaging.
Compared to Radiographic Imaging, CT eliminates the artifacts from overlaying tissues.
When was the first clinical CT scanner developed?
The first clinical CT scanner developed by Houndsfield in 1971
Explain a 1st Generation CT.
1st Generation CT:
- Single Source
- Single detector
- Moving along the line (linear scan)
- Both source and detector rotate
- Adv: Scattered energy undetected
Explain a 2nd Generation CT.
2nd Generation
- Single Source
- Multiple Detectors
- Fan-beam
- Additional detectors obtain additional projections from different angles
- Larger rotation
- Less Time (Poor Noise)
Explain a 3rd Generation CT.
Explain a 3rd Generation CT.
- Fan Beam
- Multiple Detectors (500-700)
- Rotates Only
- Dramatic decrease in scan time
- Higher Noise level compared to 1G and 2G
- Expensive
Explain a 4th Generation CT.
4th Generation CT
- One Rotating Source
- Detectors are not beam restricted
- Received Scattered radiation
- Image Quality comparable to 3G systems
Explaing 5th Generation CT.
5th Generation CT.
- Electron Beam Computed Tomography (EBCT)
- Flying electron beam
- Hitting one of the four tungsten anode strips
- No moving parts
- Scan time down to 50ms
Explain 6th Generation CT.
6th Generation CT.
- Helical/Spiral Scanning
- Source and Detector Rotates (1-2sec per rev) (same as 3G and 4G)
- Patient Table slides
- Fast 3D Images
- Slightly more expensive
Explain 7th Generation CT.
7th Generation CT.
- Multi-slice CT
- Similar to Helical CT except it has multiple detector rings
- Provided that the X-ray tube is far enough from the detector, simultaneous data are collected from the parallel rows of detectors correspond to parallel planes
- Speed is increased
What is Collimation?
Collimation = beam restriction
Explain a Solid-state Detector for CT.
Solid-state Detector for CT.
- X-ray interacts with crystal by photoelectric effect (similar to phosphor in an intensifying screen)
- Electrons are excited and emitted visible light when they spontaneously de-excite.
- Such scintillation process results in a burst of light
- The light is converted to electric current using photo-diode
Explain Xenon Gas detector for CT.
Xenon Gas detector for CT.
- Small and highly directional detectors required for 3G system
- Use Xenon gas in long, thin tubes.
- When Xenon gas ionized, it generates current between an anode and cathode
- Less efficient, but highly directional
- For same performance, solid state detectors must be accomplished by external collimations
Another name for Parallel Beam Projection.
Parallel Beam Projection = Radon Transform
Briefly explain Parallel beam projection..
Parallel beam projection.
Explain briefly Parallel Beam Projection
Parallel Beam Projection
What is g(l,theta) called for Parallell Beam Projection?
Projection
Explain Sinogram.
Parallel Beam Projection - Sinogram
- An image of g(l,theta) with l and theta as rectilinear coordinates is called a sinogram.
- g(l,theta) is also known as the radon transform of f(x,y).
What may be seen in a reconstructed image using Back projection?
Image Formation and Reconstruction - Back projection
