18 Questions
What is the primary factor that determines the spatial resolution of a CT imaging system?
The detector spacing and measurement capability
If a CT system has detectors that are larger than the imaged object, how will this affect the spatial resolution of the system?
It will decrease the spatial resolution
How does the alignment of the detectors in a CT system affect the spatial resolution?
Improper alignment may result in less resolving power than predicted by detector size and spacing alone
Which of the following is NOT a characteristic of the CT imaging system that contributes to image degradation?
Attenuation of the x-ray beam
Which of the following statements about the relationship between focal spot size and spatial resolution is correct?
Smaller focal spot size results in better spatial resolution
How does the use of a regular geometric structure with a sharp interface help to measure the spatial resolution of a CT imaging system?
The blurring of the image at the sharp interface is a measure of the spatial resolution
What is the primary source of soft-tissue contrast in CT imaging?
Differences in physical densities of tissues
How does windowing in CT contribute to visualizing different tissues?
It maps small differences in density to large differences in grayscale
What is the primary factor that determines the absorption of x-rays in tissue during CT imaging?
The linear attenuation coefficient of the tissue
Which of the following factors contributes the least to the absorption of x-rays in CT imaging?
X-ray energy level
In the context of CT imaging, what is the primary reason for using a high peak kilovoltage and relatively high beam filtration (beam hardness)?
To maximize Compton scatter events
Based on the information provided, which of the following tissues would have the highest linear attenuation coefficient in CT imaging?
Bone (density = 1.85 g/cm^3)
Which of the following factors contributes the most to improving contrast resolution in CT imaging?
Scatter radiation rejection by pre-patient and pre-detector collimators
What is the primary factor that limits the ability to image low-contrast objects with CT?
Size and uniformity of the object being imaged, and noise in the CT system
What is the effect of increasing the tube current in CT imaging?
Reduces noise in the image
Which of the following statements about contrast in CT imaging is correct?
The difference in linear attenuation coefficients of adjacent structures determines their contrast.
In CT imaging, what is spatial resolution defined as?
The ability to distinguish small, closely spaced objects on an image
Which of the following is NOT a factor that contributes to image quality in CT imaging?
Type of detector used in the CT scanner
Study Notes
CT Imaging System Characteristics
- The CT imaging system's characteristics, including collimation, detector size, mechanical and electrical gantry control, and the reconstruction algorithm, contribute to image degradation.
Factors Affecting Spatial Resolution
- Spatial resolution is determined by the x-ray tube focal spot size and blurring in the image detector.
- A smaller focal spot size results in better spatial resolution.
- Detector size and spacing are crucial factors in determining spatial resolution, with smaller detectors and closer spacing resulting in better resolution.
- Detectors must be the same size or smaller than the imaged object and close together to resolve objects near each other.
- Improper detector alignment can reduce resolving power.
CT Imaging Principles
- CT imaging is based on differences in tissue electron density, which are primarily due to differences in physical density.
- Soft-tissue contrast in CT is mainly due to differences in physical density.
- The 2-dimensional image of a 2-dimensional slice in CT enables visualization of small differences in soft-tissue density.
- Windowing can map small differences in density to large differences in grey levels, making CT visualization of various tissues possible.
X-ray Absorption and Contrast
- X-ray absorption in tissue is characterized by the x-ray linear attenuation coefficient, which is a function of x-ray energy and atomic number of the tissue.
- In CT, absorption of x-rays by the patient is also determined by the mass density of the body part.
- The CT imaging system amplifies differences in subject contrast, resulting in high image contrast.
- The range of CT numbers for tissues is approximately 0-1000 Hounsfield Units (HU).
Contrast Resolution
- Contrast resolution in CT is limited by noise, tube current, inherent tissue properties, and beam kilovoltage.
- A higher tube current reduces noise, while a higher beam energy reduces contrast between objects.
- The use of contrast media can enhance contrast in CT imaging.
Test your knowledge on CT scans and soft-tissue contrast, focusing on the main factors that contribute to subject soft-tissue contrast in CT imaging.
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