Podcast
Questions and Answers
Conventional radiography effectively depicts three-dimensional structures without any overlapping tissues.
Conventional radiography effectively depicts three-dimensional structures without any overlapping tissues.
False
The term 'tomography' originates from the Greek word meaning to 'cut' or 'layer'.
The term 'tomography' originates from the Greek word meaning to 'cut' or 'layer'.
True
CT scans can differentiate between tissues of similar densities better than conventional radiographs.
CT scans can differentiate between tissues of similar densities better than conventional radiographs.
True
The term CAT scan refers solely to newer CT scanning technology.
The term CAT scan refers solely to newer CT scanning technology.
Signup and view all the answers
Spatial resolution in CT refers to the ability to define objects with distinct time intervals.
Spatial resolution in CT refers to the ability to define objects with distinct time intervals.
Signup and view all the answers
Helical scanning is a method of scanning commonly used in CT technology.
Helical scanning is a method of scanning commonly used in CT technology.
Signup and view all the answers
Topogram is a term used to refer to the initial images produced by MRI scanners.
Topogram is a term used to refer to the initial images produced by MRI scanners.
Signup and view all the answers
The thickness of the CT slice is determined by the Y-axis.
The thickness of the CT slice is determined by the Y-axis.
Signup and view all the answers
Collimators are mechanical devices that can help limit scatter radiation in CT scans.
Collimators are mechanical devices that can help limit scatter radiation in CT scans.
Signup and view all the answers
A voxel is defined as a two-dimensional square in CT imaging.
A voxel is defined as a two-dimensional square in CT imaging.
Signup and view all the answers
The common matrix size used in CT imaging is 1024x1024.
The common matrix size used in CT imaging is 1024x1024.
Signup and view all the answers
X-ray photons can either pass through, be absorbed, or be scattered by structures in the body.
X-ray photons can either pass through, be absorbed, or be scattered by structures in the body.
Signup and view all the answers
Attenuation in X-ray imaging refers to the increase in the strength of the X-ray beam as it passes through a structure.
Attenuation in X-ray imaging refers to the increase in the strength of the X-ray beam as it passes through a structure.
Signup and view all the answers
The total number of pixels in a matrix is calculated by adding the number of rows to the number of columns.
The total number of pixels in a matrix is calculated by adding the number of rows to the number of columns.
Signup and view all the answers
CT imaging processes the X-ray information to create a radiographic film.
CT imaging processes the X-ray information to create a radiographic film.
Signup and view all the answers
A pixel in CT imaging is referred to as a volume element.
A pixel in CT imaging is referred to as a volume element.
Signup and view all the answers
Hounsfield units assigned a number of -500 to air.
Hounsfield units assigned a number of -500 to air.
Signup and view all the answers
The Hounsfield unit value can range from 1000 to -1000.
The Hounsfield unit value can range from 1000 to -1000.
Signup and view all the answers
1 Hounsfield unit corresponds to a 1% difference in linear attenuation coefficient compared to water.
1 Hounsfield unit corresponds to a 1% difference in linear attenuation coefficient compared to water.
Signup and view all the answers
Polychromatic X-ray beams consist of photons with uniform energy levels.
Polychromatic X-ray beams consist of photons with uniform energy levels.
Signup and view all the answers
An object with a Hounsfield unit of 4 is likely to be fluid-filled.
An object with a Hounsfield unit of 4 is likely to be fluid-filled.
Signup and view all the answers
X-ray photons that pass through objects unimpeded are represented by a white area on the image.
X-ray photons that pass through objects unimpeded are represented by a white area on the image.
Signup and view all the answers
The linear attenuation coefficient is represented by the Greek letter α.
The linear attenuation coefficient is represented by the Greek letter α.
Signup and view all the answers
Dense elements have fewer circulating electrons compared to elements of less density.
Dense elements have fewer circulating electrons compared to elements of less density.
Signup and view all the answers
An object with high attenuation absorbs much of the X-ray beam and cannot be detected.
An object with high attenuation absorbs much of the X-ray beam and cannot be detected.
Signup and view all the answers
The amount of scatter or absorption of the X-ray beam is constant regardless of the thickness or density of the object.
The amount of scatter or absorption of the X-ray beam is constant regardless of the thickness or density of the object.
Signup and view all the answers
As the atomic number of an element increases, the attenuation coefficient generally decreases.
As the atomic number of an element increases, the attenuation coefficient generally decreases.
Signup and view all the answers
A tightly packed snowball has a lower density than a loosely packed one.
A tightly packed snowball has a lower density than a loosely packed one.
Signup and view all the answers
Bone attenuates more of the x-ray beam than lung tissue.
Bone attenuates more of the x-ray beam than lung tissue.
Signup and view all the answers
Increasing the density of an object leads to a decrease in the likelihood of photon interaction.
Increasing the density of an object leads to a decrease in the likelihood of photon interaction.
Signup and view all the answers
At a photon energy of 125-kVp, approximately 18% of the photons are absorbed or scattered when passing through 1 cm of water.
At a photon energy of 125-kVp, approximately 18% of the photons are absorbed or scattered when passing through 1 cm of water.
Signup and view all the answers
Metallic objects appear darker on a CT image than soft tissues.
Metallic objects appear darker on a CT image than soft tissues.
Signup and view all the answers
Air has a higher density than soft tissues.
Air has a higher density than soft tissues.
Signup and view all the answers
The interaction of X-ray photons with matter does not depend on the number of protons in an atom.
The interaction of X-ray photons with matter does not depend on the number of protons in an atom.
Signup and view all the answers
Positive contrast agents typically have a lower density than the surrounding structures.
Positive contrast agents typically have a lower density than the surrounding structures.
Signup and view all the answers
A contrast agent permanently changes the physical properties of the structures it fills.
A contrast agent permanently changes the physical properties of the structures it fills.
Signup and view all the answers
Soft tissues have a linear attenuation coefficient roughly proportional to their physical density.
Soft tissues have a linear attenuation coefficient roughly proportional to their physical density.
Signup and view all the answers
Contrast agents can only be administered orally.
Contrast agents can only be administered orally.
Signup and view all the answers
The image contrast in x-ray imaging is influenced by density differences among tissues.
The image contrast in x-ray imaging is influenced by density differences among tissues.
Signup and view all the answers
Lung tissue will appear lighter than bone on a CT image.
Lung tissue will appear lighter than bone on a CT image.
Signup and view all the answers
Low-density contrast agents are often used to enhance imaging results.
Low-density contrast agents are often used to enhance imaging results.
Signup and view all the answers
Signup and view all the answers
Study Notes
Computed Tomography (CT) Basics
- Conventional radiographs show a 3D object as a 2D image, causing overlapping tissues.
- Computed Tomography (CT) overcomes this limitation by scanning thin body sections with a rotating X-ray beam, producing cross-sectional images.
- CT's unique physics allows differentiation between tissues with similar densities, unlike conventional radiography.
Advantages of CT over Conventional Radiography
- Eliminates superimposed structures.
- Enables differentiation of small density differences in anatomical structures and abnormalities.
- Provides superior image quality.
Terminology
- Tomography comes from the Greek word "tomo," meaning to cut, section, or layer.
- In CT, a sophisticated computer method produces cross-sectional slices of the human body.
- Older scanning systems are often referred to as computerized axial tomography (CAT) scan.
CT Image Terminology
- The preliminary images produced are sometimes called "topograms," "scouts," or "scanograms", depending on the vendor.
- "Continuous acquisition scanning," "spiral," "helical," or "isotropic" scanning refer to methods for continuous image acquisition.
CT Image Quality
- Spatial resolution describes the ability to distinctly locate small objects.
- Low-contrast resolution refers to a system's ability to differentiate objects with similar densities.
- Temporal resolution refers to the speed of data acquisition. Faster acquisition reduces artifacts from motion, like heart imaging.
CT Slice Thickness
- Each CT slice represents a specific plane in the body.
- The slice thickness is determined by the Z-axis.
- Limiting the X-ray beam to the chosen slice thickness reduces scatter radiation and overlapping structures.
- Collimating (using small shutters) controls the X-ray beam path.
Pixels and Voxels
- CT slice data is organized into elements: pixel (picture element)
- A matrix (grid) of pixels (X and Y axes) creates the image. Adding the Z-axis creates a voxel (volume element)
- A common CT matrix size is 512x512, with a total of 512 x 512 pixels.
- Each pixel contains information on the scanned area.
Beam Attenuation
- An X-ray beam consists of photons, which can pass through, be redirected (scattered), or absorbed by a structure.
- The amount of reduction in the X-ray beam due to interaction with the body is called attenuation.
- The degree of attenuation depends on the X-ray beam strength, structure characteristics, and the structure’s path.
- In CT, the X-ray beam passes through the body and the detected photons are used to create an image.
- The number of photons that either pass through the body or are absorbed/scattered determines the shades of gray in the image.
Density and Attenuation
- Density is the degree of concentration of an object's mass per unit volume.
- High-attenuation structures have a strong effect on the X-ray beam, showing up bright in the image (e.g., bone).
- Low-attenuation structures have less effect on the X-ray beam, showing up dark in the image (e.g., air).
- Linear attenuation coefficient (μ) quantifies the amount of attenuation per unit thickness.
Hounsfield Units (HU)
- In CT, measurements are expressed in Hounsfield units, named after Godfrey Hounsfield.
- These units are also called CT numbers or density values.
- HU quantify the degree to which a structure attenuates an X-ray beam.
- Water is assigned 0 HU, bone 1000 HU, and air -1000 HU
- Helps in identifying characteristics of different tissues and structures.
Artifacts
- Artifacts are objects on the image that are not present in the actual scanned area.
- Beam-hardening artifacts occur with preferential absorption of low-energy photons, resulting in dark streaks or a cupping effect, mainly seen with dense structures.
- These artifacts reduce image quality.
Contrast Agents
- Used to create temporary artificial density differences in the body.
- Increase the difference in densities between different structures, enabling better visibility of structures.
- Positive contrast agents (such as barium sulfate and iodine) have higher densities than the surrounding tissues, producing white areas on the images.
- Low-density contrast agents are used to highlight lower density structures, reducing their appearance to dark areas.
Polychromatic X-ray Beams
- CT and conventional radiography use polychromatic x-ray energy (photons with varying energies).
- Low-energy photons are absorbed more effectively than high-energy photons.
- This difference affects the image, potentially leading to artifacts.
Filtering the X-ray Beam
- Filtering the beam with materials like Teflon, Aluminum can improve image quality by reducing the range of X-ray energies and creating a more homogenous beam, eliminating artifacts.
- Reducing softer (lower energy) photons also reduces radiation dose to the patient.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers the fundamental concepts of CT imaging, including terminology, techniques, and the principles behind spatial resolution and imaging layers. Dive into terms like tomography, voxel, and collimation to enhance your understanding of CT technology.
