12 Questions
What is the primary function of the collimators in a CT scanner?
To narrow the x-ray beam width and reduce scatter
Which component of a CT scanner converts x-rays into light and energy?
Radiation detectors
What is the typical range of the high-frequency power supply used for the x-ray tube in CT scanners?
80 to 140 kilovolts
What is the purpose of the beam shaping filters in CT scanners?
To remove low-energy x-rays, reduce patient dose, and minimize beam hardening artifacts
How is the slice width adjusted in CT scanners?
By adjusting the detector width by combining adjacent detectors
What is the average energy of x-rays used in CT imaging?
75 keV
What does spatial resolution in CT imaging measure?
Ability to distinguish small objects close together
How do filters in CT imaging affect spatial resolution?
Trade off spatial resolution for noise reduction or contrast improvement
What unit are CT images composed of, measured in Hounsfield units?
Linear attenuation coefficients
What is the purpose of dual-source CT scanners?
Faster imaging and lower radiation doses
Which technique is commonly used in CT scans for stone composition analysis?
Virtual non-contrast imaging
What is a key factor in minimizing radiation exposure in CT fluoroscopy?
Tube current
Study Notes
- CT scanners have four main components: x-ray tube, filtration devices, collimators, and radiation detectors arranged around the patient in the center.
- The x-ray tube in CT scanners has a larger focal spot compared to mammography, typically around 1mm, made of tungsten, and requires a high-frequency power supply ranging from 80 to 140 kilovolts.
- CT beam shaping filters, often made of Teflon, are used to remove low-energy x-rays, reduce patient dose, and minimize beam hardening artifacts.
- Collimators in CT scanners, typically made of lead, are located under the filter and help reduce scatter by narrowing the x-ray beam width.
- Radiation detectors in CT scanners are devices like scintillators that convert x-rays into light, then into energy, which is processed by the computer to create grayscale images.
- To adjust slice width in CT scanners, detector width is adjusted by combining adjacent detectors to achieve the desired slice thickness.
- Modern CT scanners with multiple detectors allow for the acquisition of multiple slices per rotation, offering high temporal resolution and the ability to create multi-planar reformats.- CT scanners can range from 64-slice to 1000 projections per turn, allowing for multiple slices and manipulation of slice width.
- X-rays in CT are highly filtered and have an average energy of 75 keV, with intensity depending on tissue attenuation.
- Linear attenuation coefficient (LAC) measures how well x-rays move through tissue in CT imaging.
- CT images are created using processes like back projection and filtered back projection to determine linear attenuation coefficients for each pixel.
- Spatial resolution in CT imaging refers to the ability to distinguish small objects close together, measured in line pairs per centimeter.
- Filters in CT imaging, like bone or soft tissue filters, trade off spatial resolution for noise reduction or contrast improvement.
- CT images are maps of linear attenuation coefficients, measured in Hounsfield units based on arbitrary definitions of air and water.
- Pixel size in CT is determined by the field of view over matrix size, with smaller pixels improving spatial resolution.
- Voxel is a 3D unit representing average attenuation of tissues, while a pixel is a 2D unit displaying grayscale values.
- Dual-source CT scanners have two x-ray tubes operating at different kV settings, allowing for faster imaging and lower radiation doses.- Stone composition analysis in CT scans has implications for clinical use, allowing for efficient protocols and potential diagnosis of conditions like adrenal nodules.
- Techniques like virtual non-contrast imaging and iodine overlays are used in CT scans for various purposes.
- The process of CT scanning involves initial steps like scout imaging to determine the area to scan and setting parameters like tube current modulation, kV, and mAs.
- Gated CT is commonly used for cardiac imaging, with options for prospective or retrospective gating depending on the diagnostic needs and radiation dose considerations.
- CT fluoroscopy involves continuous tube rotation to obtain multiple images per second, with tube current being a key factor in minimizing radiation exposure.
- Factors affecting spatial resolution in CT scans include detector width, slice thickness, and reconstruction filters, impacting image clarity and detail.
- Contrast resolution in CT scans is influenced by factors like the number of x-rays (controlled by current, kV, etc.) and slice thickness, affecting visibility of structures in the image.
- Artifacts in CT images can arise from issues like partial volume averaging, motion, beam hardening, metal artifacts, and out of field artifacts, each requiring specific strategies for mitigation.
- Specific artifacts like ring artifacts caused by faulty detectors and photon starvation artifacts in high attenuating areas have characteristic appearances and fixes in CT imaging.
- Radiology board exam questions often focus on comparing CT to digital radiography in terms of spatial and contrast resolution, highlighting the differences between the modalities.
Test your knowledge on the components of CT scanners such as x-ray tubes, filters, collimators, and detectors, as well as imaging techniques like slice width adjustment, spatial resolution, contrast resolution, and artifact mitigation.
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