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What is computed tomography (CT)?
What is computed tomography (CT)?
An imaging procedure that uses x-ray equipment and computer-processed measurements taken from different angles to produce cross-sectional images.
What does the term 'tomography' mean?
What does the term 'tomography' mean?
A slice
Who invented computed tomography?
Who invented computed tomography?
Sir Godfrey Hounsfield
When was the first clinical CT scan done?
When was the first clinical CT scan done?
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What are some limitations of projection radiography? (Select all that apply)
What are some limitations of projection radiography? (Select all that apply)
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What is the function of a CT detector?
What is the function of a CT detector?
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Solid State Detectors (SSD) have a higher efficiency compared to Xenon detectors.
Solid State Detectors (SSD) have a higher efficiency compared to Xenon detectors.
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What are the advantages of metal ceramic tubes in CT x-ray tubes?
What are the advantages of metal ceramic tubes in CT x-ray tubes?
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What is a slip ring in CT technology?
What is a slip ring in CT technology?
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Which generation of CT scanners was developed specifically for cardiac scanning?
Which generation of CT scanners was developed specifically for cardiac scanning?
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What does attenuation measure in CT imaging?
What does attenuation measure in CT imaging?
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What does the attenuation coefficient (µ) describe?
What does the attenuation coefficient (µ) describe?
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Study Notes
Computed Tomography (CT)
- An imaging procedure using x-ray equipment and computer processing to create cross-sectional images.
- Derives its name from the Greek word "tomos" meaning "a slice".
- Formerly known as Computed Axial Tomography or CAT scan.
- Invented by British electrical engineer Sir Godfrey Hounsfield.
- The first person to process x-ray images using a computer.
History of CT
- First clinical CT scan performed on October 1st, 1971 at Atkinson Morley Hospital, Wimbledon.
- Each scan required 160 readings and took over five minutes.
- Image processing from these scans took 2.5 hours on a large computer.
Why CT?
- Overcomes limitations of projection radiography, such as:
- Superimposition of structures.
- Differentiation of structures with low contrast resolution.
CT Scanners Today
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Overall CT Process:
- Motorized x-ray tube rotating within a gantry.
- Fan-shaped beam "slices" the anatomical area being scanned.
- An array of digital detectors opposite the x-ray source capture the attenuated beam.
- Processed images visualized in multiple planes.
CT Detectors
- Function: Conversion of x-rays into an electrical signal.
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Types:
- Xenon Detectors: 60-70% efficiency.
- Solid State Detectors (SSD): 98% efficiency.
Characteristics of Solid State Detectors
- Small size for improved spatial resolution.
- Allow for multiple detectors to form a detector array.
- High detection efficiency and sensitivity for processing a wide range of x-ray intensities.
- Fast response time with negligible afterglow.
- High stability for operation at high speeds of the rotating gantry.
CT X-Ray Tube
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Features:
- Longer continuous exposure times at higher KV & mA.
- Larger and thicker anode for heat absorption and dissipation.
- Modified cathode assembly for a smaller focal spot (0.6mm).
- Metal envelope and ceramic insulators replace the glass envelope for improved heat dissipation (metal ceramic tube).
- "Flying" focal spot for controlling the focus position on the anode.
Advantages of Metal Ceramic Tubes
- Higher tube loading.
- Longer tube life.
- Spiral groove bearing uses liquid metal alloy (gallium) as a lubricant.
Straton X-Ray Tube
- Rotates the entire tube body instead of just the anode.
- Magnetic deflection coil shapes and controls the electron beam.
- Bearings are located outside the evacuated tube.
- More efficient anode cooling.
- Low heat storage capacity, cooling down within 20 seconds.
Slip Ring Technology
- Function: Transmits power and electrical signals from a stationary to rotating structure.
How Slip Ring Technology Works
- Similar to bumping cars receiving power from a conductive ceiling, slip rings have grooves where electrical contactor brushes slide.
- Power and data transmission are made possible by stationary brushes pressing against rotating circular conductors.
- Eliminates the need for wired connections.
CT Scanner Generations
- 5th Generation (EBCT): Developed for cardiac scanning, known as electron beam scanners.
- 6th Generation (Helical CT): Spiral/helical CT scanners utilizing slip ring technology.
- 7th Generation (MDCT): Multi-detector array CT.
Image Acquisition
- What CT Measures: Attenuation - the degree to which a material can be penetrated by an x-ray beam.
- How Attenuation is Measured: The density of the tissue is determined through calculation of the attenuation coefficient.
Attenuation Coefficient
- Represents the fraction of an x-ray beam absorbed or scattered per unit thickness of the absorber.
- Varies with the physical characteristics of the material, such as:
- Density
- Atomic number
- X-ray energy
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Description
Explore the fascinating world of Computed Tomography (CT), an imaging procedure that revolutionized medical diagnostics. Learn about its history, technical advancements, and the reasons why CT is preferred over traditional radiography. This quiz delves into the origins, development, and current applications of CT scanners.
