120 Questions
What is the primary advantage of Electron Beam CT (EBCT) compared to mechanical CT?
Faster temporal resolution
What is the main benefit of multi-slice CT acquisition?
Increased longitudinal coverage
What is the primary purpose of the tungsten ring in EBCT?
To generate and direct electrons
What is the maximum number of slices that can be acquired simultaneously with current state-of-the-art CT technology?
320 slices
Which of the following is NOT a benefit of multi-slice CT acquisition?
Improved spatial resolution
What is the primary purpose of increasing the number of detector rows in EBCT?
To acquire multiple channels of data simultaneously
What is the main advantage of using a dual-source CT scanner?
Increased scan speed
What type of artifact occurs when the X-ray beam is attenuated by a dense object, such as a metal implant?
Beam hardening artifact
What is the primary component of an EBCT scanner that generates and directs electrons?
Stationary tungsten ring
What determines the image quality in a CT scanner?
Detector size and number of angular projections
What enables spiral CT scanners to rotate continuously during acquisition?
Electrically conductive brushes and rotating rings
What is a limitation of mechanical CT scanners, including multi-slice spiral CT?
Forces created during rotation restrict rotation speed
What is a characteristic of the path of acquisition in spiral CT scanners?
It resembles a helix or spiral
What is required to accommodate the extended period of X-ray tube energy generation in spiral CT scanners?
More heat storage capacity
What was the electron beam CT (EBCT) developed to image?
The heart
What is the primary determinant of image quality in a CT scanner?
Detector size
What is the purpose of collimators in CT scanners?
To reduce image noise and artifacts
What is the effect of a larger focal spot on image quality?
It blurs the image
What is the trade-off when choosing a higher slice thickness in CT scanning?
Reduced axial resolution and improved SNR
What is the typical resolution of clinical CT scanners?
0.2–1 mm
What is the primary advantage of spiral CT scanners over traditional stop-and-shoot CT scanners?
Faster acquisition of data
What type of artefact is illustrated in Figure 1?
Beam hardening artefact
Which component of a CT scanner is responsible for detecting X-rays?
CT detector
What technology enables continuous rotation of the X-ray tube and detector in spiral CT scanners?
Slip ring technology
Which of the following can be corrected instantly to improve the signal-to-noise ratio (SNR) in a CT image?
Increase slice thickness
What is the primary advantage of double z-sampling in CT acquisitions?
Improved longitudinal resolution
How does the increase in the number of detectors affect the detector width in Multi-Slice CT?
It decreases the detector width
What is the primary advantage of Dual-Source CT scanners?
Improved temporal resolution
What is the purpose of dual-energy CT in Dual-Source CT scanners?
To improve tissue differentiation
What is the primary benefit of overlapping reconstruction of slices in Multi-Slice CT?
Improved longitudinal resolution
What is the primary benefit of increasing the number of active detector rows in Multi-Slice CT scanners?
Increased coverage
What is the primary advantage of Spiral acquisition method in CT?
Reduced total scan time
What is the primary component of Dual-Source CT scanners that improves temporal resolution?
Two X-Ray tubes
What is the primary benefit of Slip ring technology in CT?
Continuous rotation of the X-Ray tube
What is the primary purpose of Image reconstruction algorithms in CT?
To reconstruct images from raw data
What is the primary advantage of spiral CT scanning over sequential scanning?
Reduced scan time
What technology enables continuous rotation of the gantry during CT scanning?
Slip ring technology
What type of artifact is caused by the preferential absorption of lower-energy X-rays by the patient's body?
Beam hardening artifact
What is the primary function of image reconstruction algorithms in CT scanning?
To reconstruct the cross-sectional image from raw data
Which component of a CT scanner is responsible for detecting the X-ray photons?
Detector array
What is the primary factor that determines the image quality in a CT scanner?
Detector size and number of angular projections
What is the effect of increasing the slice thickness in a CT scan?
Reduces axial resolution and improves signal-to-noise ratio
What is the purpose of collimators in front of the X-ray tube in a CT scanner?
To reduce the beam size and limit beam thickness
What is the effect of a larger focal spot on image quality in a CT scanner?
Reduces image quality and improves axial resolution
What is the trade-off between axial resolution and signal-to-noise ratio in CT scanning?
Higher signal-to-noise ratio is achieved at the cost of reduced axial resolution
What is the effect of partial volume effects on image quality?
Blurs the intensity distinction between adjacent tissues
Why is it important to calibrate detectors in CT scanners?
To prevent ring artefacts in the reconstruction
What is the effect of metal materials on CT images?
They cause streaking artefacts
What is the effect of patient motion on CT images?
It causes motion blur
What can reduce the risk of motion blur in CT scans?
Shorter acquisition times and helical scanning principle
What is the main advantage of increasing the number of detector rows in Multi-Slice CT scanners?
Increased longitudinal coverage
What is the trade-off when choosing a higher slice thickness in CT scanning?
Reduced image quality
How does the increase in the number of detectors affect the detector width in Multi-Slice CT?
Decreases the detector width
What is a factor that affects the signal-to-noise ratio in a CT image?
All of the above
What is the primary determinant of image quality in a CT scanner?
Signal-to-noise ratio
Which of the following CT scanner generations is characterized by a fixed outer ring of detectors and a rotation-only tube movement?
Fourth generation
What is the primary disadvantage of sequential scanning in CT?
Longer scan time
What is the effect of increasing the slice thickness in a CT scan?
Increases signal-to-noise ratio
Which of the following is a characteristic of spiral CT scanners?
Continuous rotation of the x-ray tube
What is the effect of increasing the number of detectors in a CT scanner?
Improves axial resolution
What is the effect of decreasing the detector width on image quality in Multi-Slice CT?
Improved longitudinal resolution
What is the primary trade-off for improving longitudinal resolution in CT scanning?
Increased scan time
What is the effect of overlapping reconstruction of slices in Multi-Slice CT?
Improved longitudinal resolution
What is the primary factor affecting the detector width in Multi-Slice CT?
Number of detectors
What is the primary benefit of increasing the number of active detector rows in Multi-Slice CT?
Improved longitudinal resolution
What is the primary factor that affects the signal-to-noise ratio in a CT image?
Detector size
Which of the following can be instantly corrected to improve the axial resolution in a CT image?
Decrease slice thickness
What is the effect of increasing the slice thickness on the signal-to-noise ratio in a CT image?
It increases the signal-to-noise ratio
What is the primary benefit of using a smaller detector size in CT imaging?
Better axial resolution
What is the effect of decreasing the focal spot size on the image quality in a CT scanner?
It improves the image quality
What is the primary advantage of using a smaller slice thickness in CT imaging?
Better axial resolution
What is the effect of detector size on the image quality in a CT scanner?
It improves the image quality
What is the primary benefit of using a larger detector size in CT imaging?
Improved signal-to-noise ratio
What is the effect of axial resolution on the image quality in a CT scanner?
It improves the image quality
What is the primary trade-off between axial resolution and signal-to-noise ratio in CT imaging?
Improved axial resolution results in decreased signal-to-noise ratio
What is the primary cause of streaking artifacts in CT images?
Photon starvation
Which of the following factors affects the axial resolution of a CT image?
Slice thickness
What is the effect of increasing the number of detector rows on the signal-to-noise ratio (SNR) in a CT image?
Increases the SNR
What is the relationship between detector size and slice thickness in a CT scanner?
Detector size is inversely proportional to slice thickness
Which of the following is a limitation of increasing the slice thickness in a CT scanner?
Reduced image quality
What is the primary factor that affects the signal-to-noise ratio in a CT image?
X-ray beam intensity
What is the effect of increasing the slice thickness in a CT scan?
Increased partial volume effects
What is the primary advantage of using a smaller detector size in CT imaging?
Improved axial resolution
What is the primary determinant of image quality in a CT scanner?
Axial resolution
What is the effect of decreasing the focal spot size on the image quality in a CT scanner?
Improved image quality
What is the primary factor that affects the axial resolution in a CT image?
Number of angular projections
What is the trade-off when choosing a higher slice thickness in CT scanning?
Improved signal-to-noise ratio and decreased axial resolution
What is the effect of a larger detector size on the image quality in a CT scanner?
It decreases the image quality
What is the primary advantage of using a smaller slice thickness in CT imaging?
Improved axial resolution
What is the effect of a larger focal spot size on the image quality in a CT scanner?
It decreases the image quality
What is the effect of decreasing the detector width in Multi-Slice CT on the spatial resolution in the longitudinal direction?
It improves the spatial resolution
What is the primary trade-off for improving the longitudinal resolution in CT scanning using double z-sampling?
A longer total scan time
What is the effect of increasing the slice thickness on the signal-to-noise ratio in a CT image?
It increases the signal-to-noise ratio
What is the relationship between the detector size and the slice thickness in a CT scanner?
As the detector size decreases, the slice thickness decreases
What is the effect of overlapping reconstruction of slices in Multi-Slice CT on the axial resolution?
It improves the axial resolution
What is the advantage of increasing the number of detector rows in Multi-Slice CT scanners?
Increases the longitudinal coverage that can be achieved per rotation
What is the effect of decreasing the slice thickness in a CT scanner?
Improves the axial resolution of a CT image
What is the primary factor that affects the detector width in Multi-Slice CT?
Number of detector rows
How does the increase in the number of detector rows affect the signal-to-noise ratio (SNR) in a CT image?
Increases the SNR
What is the effect of increasing the slice thickness in a CT scanner on image quality?
Reduces the image quality
What is the primary factor affecting the axial resolution in a CT scanner?
Detector size
What happens to the signal-to-noise ratio (SNR) when the slice thickness is increased in a CT image?
It increases
What is the effect of decreasing the detector size on the image quality in a CT scanner?
It improves the axial resolution
What is the primary advantage of increasing the slice thickness in a CT scanner?
Improved signal-to-noise ratio
What is the relationship between detector size and axial resolution in a CT scanner?
Smaller detectors result in better axial resolution
What is the effect of increasing the focal spot size on the image quality in a CT scanner?
It decreases the signal-to-noise ratio
What is the main effect of partial volume effects on CT images?
It blurs the intensity distinction between adjacent tissues
Why do uncalibrated detectors create RING ARTIFACTS in the reconstruction?
Because they have different output signal intensities for the same incident X-ray intensity
What is the primary factor affecting the signal-to-noise ratio in a CT scanner?
Slice thickness
What is the primary effect of patient motion on CT images?
It creates motion blur
What happens to the axial resolution when the detector size is increased in a CT scanner?
It decreases
What is the trade-off between axial resolution and signal-to-noise ratio in CT scanning?
Increasing signal-to-noise ratio decreases axial resolution
What is the effect of metal materials on CT images?
They create streaking artefacts
What is the effect of patient motion on the image quality in a CT scanner?
It creates artefacts
What is the purpose of repositioning the patient in CT scanning?
To reduce partial volume effects
What is the primary factor that affects the axial resolution of a CT image?
Detector size
What is the effect of increasing the slice thickness on the signal-to-noise ratio in a CT image?
It increases the signal-to-noise ratio
What is the primary determinant of image quality in a CT scanner?
Detector size and slice thickness
What is the effect of decreasing the detector size on the image quality in a CT scanner?
It improves the image quality
What is the trade-off when choosing a higher slice thickness in CT scanning?
Decreased signal-to-noise ratio
Study Notes
Electron Beam CT (EBCT)
- Generates and directs electrons along a stationary tungsten ring, eliminating rotating parts.
- Temporal resolution of EBCT is 100 ms, an enormous improvement over mechanical CT at the time of development (1980s).
- Can be used for non-invasive coronary angiography, but is now most often used for quantification of coronary calcium.
Multi-Slice CT
- By increasing the number of detector rows, multiple channels of data can be acquired simultaneously.
- Advantage: increased longitudinal coverage that can be achieved per rotation.
- Particularly useful for cardiac acquisitions, which deal with an inherently longer scan time.
- Current state-of-the-art CT technology: simultaneously acquires 320 slices ($2.5 million) with 320 detector rows.
- Manufacturers offer 16, 32, 64, 128, and 256 detector systems, with double sampling in the longitudinal direction.
Spiral CT
- Allows for continuous tube-detector rotation and fast acquisition of data.
- Made possible using slip-ring technology.
- Unlike sequential scanning, the table moves at a constant speed through the gantry during acquisition.
- Continuous acquisition of data allows coverage of larger sections in the same amount of time.
Image Quality and Artifacts
- Image quality is primarily determined by the detector size and the number of angular projections.
- Typical resolution of clinical CT scanners: 0.2–1 mm with slice thicknesses of 0.4–5 mm.
- The focal spot of the X-ray tube is another key determinant of image quality.
- Collimators in front of the detector act as anti-scatter grids, eliminating X-ray photons that deviate from a straight source-detector path.
Artifacts
- Patient-based artifacts: motion artifact, partial volume artifact
- Physics-based artifacts: beam hardening, noise, photon starvation
- Hardware-based artifacts: ring artifacts, out of field artifacts, tube arcing
- Treatment: partial volume effects can be reduced by repositioning the patient or increasing resolution.
Dual-Source CT
- Equipped with two X-Ray tubes rotating at a 90o angle to each other.
- Advantage: improvement of the temporal resolution.
- Application: dual-energy CT, which improves tissue differentiation by operating with different tube voltages (kV).### Image Quality and Artifacts
- Image quality is primarily determined by detector size and number of angular projections
- Typical resolution of clinical CT scanners is 0.2–1 mm with slice thicknesses of 0.4–5 mm
- Higher slice thickness can reduce radiation dose and improve Signal to Noise Ratio (SNR) at the expense of axial resolution
- Focal spot of the X-ray tube is a key determinant of image quality; a larger focal spot blurs the image
- Collimators in front of the detector act as anti-scatter grids, eliminating X-ray photons that deviate from a straight source-detector path
- Collimators in front of the X-ray tube reduce beam size and limit beam thickness, creating a small apparent focal spot
Artifacts
- Streaking artifacts can occur due to photon starvation or metallic materials
- Beam hardening, metallic material, patient motion, and uncalibrated detectors can cause artifacts
- Ring artifacts can occur when detectors are not centered with respect to the source or are not calibrated
- Metal artifacts can cause streaking artifacts due to block parts of projection data
- Patient motion can cause motion blur, which cannot be corrected but can be reduced with shorter acquisition times and helical scanning principle
CT Scanner Development
- Originally, CT scanners sequentially acquired axial slices according to the stop-and-shoot principle
- Spiral CT scanners allow for continuous tube-detector rotation and fast acquisition of data
- Electron beam CT (EBCT) was developed to image the heart
- Multi-slice CT scanners allow for increased longitudinal coverage and improved spatial resolution
- Dual-source CT scanners are equipped with two X-ray tubes rotating at a 90o angle to each other, improving temporal resolution
Performance Characteristics of CT
- EBCT generates and directs electrons along a stationary tungsten ring, eliminating rotating parts
- EBCT has an enormous improvement of temporal resolution (100 ms) compared to mechanical CT
- EBCT is often used for quantification of coronary calcium
Types of CT Scanners
- First generation detectors: one type of beam, pencil-like x-ray beam, translate-rotate movement, duration of scan (average): 25-30 minutes
- Second generation detectors: multiple, fan-shaped x-ray beam, translate-rotate movement, duration of scan (average): less than 90 seconds
- Third generation detectors: multiple, arranged in an arc, fan-shaped x-ray beam, rotate-rotate movement, duration of scan (average): approximately 5 seconds
- Fourth generation detectors: multiple, arranged in an outer ring, fan-shaped x-ray beam, rotate-fixed movement, duration of scan (average): few seconds
Learn about the engineering aspects of CT scanners, including how image quality is affected and how to distinguish between patient and machine caused artefacts. Understand the different generations of CT scanners and their detectors. Test your knowledge with this quiz!
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