Podcast
Questions and Answers
What year was the first clinical prototype CT brain scanner installed at Atkinson Morley's Hospital?
What year was the first clinical prototype CT brain scanner installed at Atkinson Morley's Hospital?
1971
What is the primary advantage of the pencil beam geometry used in 1st generation CT scanners?
What is the primary advantage of the pencil beam geometry used in 1st generation CT scanners?
What does the term 'FOV' stand for?
What does the term 'FOV' stand for?
What is the primary difference between 1st generation and 2nd generation CT scanners?
What is the primary difference between 1st generation and 2nd generation CT scanners?
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What is the main advantage of 3rd generation CT scanners over 1st and 2nd generation scanners?
What is the main advantage of 3rd generation CT scanners over 1st and 2nd generation scanners?
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3rd generation CT scanners were the first to use slip-ring technology for power and data transmission.
3rd generation CT scanners were the first to use slip-ring technology for power and data transmission.
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What is the primary advantage of 4th generation CT scanners over 3rd generation scanners?
What is the primary advantage of 4th generation CT scanners over 3rd generation scanners?
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What is the primary disadvantage of 4th generation CT scanners?
What is the primary disadvantage of 4th generation CT scanners?
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What type of CT scanner is specifically designed for cardiac imaging and is capable of acquiring scan data in milliseconds?
What type of CT scanner is specifically designed for cardiac imaging and is capable of acquiring scan data in milliseconds?
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Spiral/Helical CT scanners use slip-ring technology to enable continuous data acquisition while the table is moving.
Spiral/Helical CT scanners use slip-ring technology to enable continuous data acquisition while the table is moving.
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What is the primary function of the algorithm used in Spiral/Helical CT scanners?
What is the primary function of the algorithm used in Spiral/Helical CT scanners?
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What is the main difference between single-slice CT (SSCT) and multislice CT (MSCT)?
What is the main difference between single-slice CT (SSCT) and multislice CT (MSCT)?
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Which of the following is NOT an advantage of multislice CT (MSCT) over single-slice CT (SSCT)?
Which of the following is NOT an advantage of multislice CT (MSCT) over single-slice CT (SSCT)?
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Dual Source CT scanners are primarily used for which of the following applications?
Dual Source CT scanners are primarily used for which of the following applications?
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Which of the following is NOT a significant advantage of dual-energy CT compared to MSCT?
Which of the following is NOT a significant advantage of dual-energy CT compared to MSCT?
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Advanced CT scanners can help decrease the risk of contrast media reactions in patients.
Advanced CT scanners can help decrease the risk of contrast media reactions in patients.
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What is the primary benefit of CT over conventional radiography in terms of image manipulation?
What is the primary benefit of CT over conventional radiography in terms of image manipulation?
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Which of the following is NOT a key advantage of CT over MRI?
Which of the following is NOT a key advantage of CT over MRI?
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Which of the following is a significant disadvantage of CT compared to ultrasound?
Which of the following is a significant disadvantage of CT compared to ultrasound?
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What is the primary reason why CT is more commonly used for trauma scans than ultrasound?
What is the primary reason why CT is more commonly used for trauma scans than ultrasound?
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Study Notes
Introduction to Computed Tomography (CT)
- HSMI 3314 course
- Presented by Asst. Prof. Dr. Ummi Farhana
Learning Outcomes (W1)
- Historical development of the CT scanner
- Advantages of advanced CT vs. previous generations
- Limitations of conventional radiography and linear/conventional tomography
- Characteristics of various CT technologies/generations (1st-5th Generation, Spiral/Helical CT (MSCT/MDCT), Dual Source CT)
- Advantages and disadvantages of CT over other imaging modalities
Historical Perspective
- 1967: X-ray beam passed through an object in all directions. Measurements of X-ray transmission could provide information about internal structure. Collaboration with radiologists evaluated the machine using human brain specimens. Showed ability to differentiate tumor tissues and grey/white matter.
- 1971: First clinical prototype CT brain scanner developed at Atkinson Morley's Hospital. Processing time reduced to 20 minutes using minicomputers. Reduced further to 4.5 minutes.
- 1972: First patient scan using the clinical prototype. Image used to distinguish between normal and diseased tissue.
- 1973: First whole-body CT scanner. Introduction of 3rd generation CT scanner.
- 1974: Introduction of 4th generation CT scanner.
- 1975: Introduction of Dynamic Spatial Reconstructor (DSR) allowing dynamic volume scanning of cardiovascular and pulmonary systems with high temporal resolution.
1980 to 1998
- 1980: Electron Beam Computed Tomography (EBCT) introduced for cardiovascular imaging without motion artifacts. Capable of acquiring multi-slice images in 50ms and 100ms.
- 1988: Research and development of Multislice CT (MSCT)
- 1990: Introduction of single-slice Spiral/Helical CT scanners that allow continuous volume scanning.
- 1992: Introduction of dual Spiral/Helical CT scanners.
- 1998: Introduction of Multislice Spiral/Helical CT scanners.
Terminologies
- Coronal, Axial, Sagittal: Anatomical planes used to view images.
- Hyperdense, Isodense, Hypodenses: Different densities of tissues shown on CT images.
Limitations of Conventional Radiography
- Superimposition: All structures appear on the film at once, making distinction difficult.
- Heterogeneity: Difficult to differentiate between homogenous and heterogenous tissues of varying thickness.
- Qualitative: Not quantitative.
Limitations of Linear Tomography
- Limited to Single Plane: Images only in one plane, hindering detailed analysis.
- Image blurring: Persistence image that cannot be removed.
- Image degradation: Reduced image contrast due to scattered x-ray radiation.
- Diagnostic issues: Limited resolution and contrast differentiation.
- Radiation exposure: Multiple exposures required for different angles and planes can result in high radiation dose.
Limitations of Conventional Radiography and Linear Tomography
- Both fail to adequately demonstrate slight tissue differences in subject contrast.
- Linear attenuation coefficients of different tissues (e.g., fat, water, CSF, plasma, red cells) are also shown.
- Conventional method is qualitative rather than quantitative.
Goals of Computed Tomography
- Overcome image limitations.
- Reduced Superimposition: X-ray beam focused onto a specific cross-section to minimize overlapping issues.
- Improved Image Contrast: Precise beam collimation to reduce scatter radiation, resulting in improved image contrast.
- Quantitative Measurement: Digital signal analysis that measure minute differences in tissue contrast.
1st Generation CT
- Parallel beam geometry with highly collimated parallel x-rays.
- Pencil beam system uses 180 translations separated by 1º rotation.
- Collected 180 x 160 = 28800 rays.
1st Generation CT Advantages/Disadvantages
- Advantages: Very efficient scatter reduction.
- Disadvantages: Data acquisition takes 5 minutes per image, patient motion causes image quality degradation, constraints for cardiac and respiratory motion, only practical for head scans.
2nd Generation CT
- Translate/rotate data acquisition.
- The tube and detector rotate each by a large increment depending on the detector number and translate to collect data in different directions (180⁰)
- This method is known as rectilinear multiple pencil beam scanning. Reduction in acquisition time, inversely proportional to the number of detectors.
3rd Generation CT
- Fan-shaped beam geometry, rotating X-ray tube and fixed detector array.
- Continuous rotation of 360⁰.
- Simultaneous data acquisition.
3rd Generation CT Advantages/Disadvantages
- Advantages: Reduced scan times, reduced artifacts from patient motion. High collimation reduces scatter, thereby improving image quality.
- Disadvantages: Frequent ring artifacts due to repeated use of detectors; if one detector shows a slight misaligment, the artifacts appear in the image.
4th Generation CT
- Wide fan-shaped rotating X-ray tube and fixed detector array. Continuous rotations.
- Number of detectors controlled by the width of beam.
- Continuously rotating beam scanning.
4th Generation CT Advantages/Disadvantages
- Advantages: Higher sampling density eliminates aliasing, artifact-free. Reduced scanner stability requirements, reduced scanning time.
- Disadvantages: Increased patient dose due to over-scanning and excessive scatter radiation from the detector array. High cost due to the high number of detectors.
5th Generation CT (Electron Beam CT - EBCT)
- High velocity scanning system.
- Acquire data in milliseconds.
- Useful for cardiac applications (motion freezing)
- Electron beam technology generates a 130kV electron beam.
- Electron beam collides with the target ring resulting in x-ray beam generation
- The sweeping motion of the electron beam (by deflection coil) provides rotation.
Spiral/Helical CT
- Continuous x-ray tube rotation
- Patient moves through the gantry aperture while the scanning is being performed.
- Continuous data acquisition using slip-ring technology.
- Rotary movement around the patient longitudinal axis (Z).
Single Slice CT (SSCT)
- First design of spiral tomography devices using X-ray detectors arranged in a row.
- Continuous 360° rotation of fan-shaped beam geometry.
Multi Slice CT (MSCT)
- Adds more rows of detectors (between 4/ 320 rows).
- Simultaneous acquisition of projections for subsequent reconstruction (up to 4 slices).
- Reduces scanning time and improves resolution, reducing image noise.
Dual CT
- Dual Energy Dual Detector: Uses two X-ray tubes positioned 90 degrees apart for different kVp operation. Allows using low and high kVp in the same acquisition.
- Dual Energy single Source: Uses one X-ray tube and quick kVp switching to capture two projections at different energies in a single rotation. Permits reasonable imaging quality, but with potential trade-offs in speed.
- Dual Layer: Uses a single source with a two layer detector and kVp switching to distinguish between high and low energy photons for detailed imaging contrast.
Dual Source CT Advantages
- Increased scan speed
- Elimination of beam hardening artifacts
- Automatic segmentation for example automatic bone removal
- Retrospective images at any possible energy.
- Tissue characterization.
- Virtual unenhanced images
Advantages (Advanced CT)
- Faster scan times and elimination of start-stop
- Overlap and missed areas reduced
- More diagnostic information
- Improved clinical applications and section thickness
Advantages of CT over Conventional Radiography
- Excellent low contrast resolution
- Capability to manipulate window width and level for better visualization
- Volume scanning (spiral) for enhanced image analysis
- Advanced techniques like dynamic, perfusion, PET CT
- Image manipulation for comprehensive analysis
Advantages of CT over MRI
- Speed, better for emergency.
- Bone imaging.
- Less sensitive to motion.
- Cost effective.
- Better for patients with implants.
Advantages of CT over Ultrasound
- Better penetration and resolution for deeper structures
- Less operator dependency, more consistent and reproducible results.
- Imaging through gas and bone: CT penetrates gas and bone, unlike ultrasound.
- Comprehensive whole-body scans
Disadvantages of CT
- High radiation exposure.
- Higher cost
- Limited soft tissue contrast compared to MRI.
- No functional imaging (compared to MRI).
- Potential safety issues with contrast media (compared to MRI).
Disadvantages of CT over Ultrasound
- Cost and accessibility: Ultrasound is generally cheaper and more portable.
- Radiation exposure: Ultrasound is radiation-free.
- Real-time imaging: Ultrasound provides real-time data useful for guiding biopsies and fetal monitoring, which CT doesn't.
- Imaging superficial and dynamic structures: Ultrasound better suited for superficial structures and dynamic images.
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