Medical Imaging Notes

X-Rays

X-Rays

Produced by energetic electrons interacting with matter, converting kinetic energy into electromagnetic radiation.

Cathode

The source of electrons in an x-ray tube, where electrons are thermionically emitted.

Anode

The electrode in an x-ray tube that receives electrons from the cathode, generating x-rays.

Bremmstrahlung Spectrum

The probability distribution of x-ray photons based on their energy produced by electron interactions.

Characteristic Radiation

Discrete peaks of x-ray energy emitted when inner-shell vacancies in atoms are filled by outer-shell electrons.

Half-Value Layer (HVL)

Thickness of material required to reduce the intensity of an x-ray or gamma-ray beam to half its original value.

Attenuation

The removal of photons from a beam as it passes through matter, caused by absorption and scattering.

Compton Scattering

The predominant interaction of x-ray photons with matter in diagnostic energy range, where photons scatter and lose energy.

Photoelectric Effect

Interaction where all incident photon energy is absorbed by an electron, which is then ejected from the atom.

Mammography

A radiographic examination aimed at detecting breast pathology, including cancer.

Tube Filtration

The process of removing low and high energy x-rays from the beam to optimize patient safety and image quality.

Bow Tie Filter

A beam shaping filter used in CT scans to equalize radiation dose across different body thicknesses.

Rayleigh Scattering

A scattering process where the incident photon excites the total atom, primarily occurring with low energy x-rays.

Mass Attenuation Coefficient

A normalized measure showing how many photons are absorbed per unit density of material.

Exposure Time

The duration during which the x-ray tube is activated and producing x-rays.

Filtration

The process of selectively removing lower energy x-rays to reduce patient dose and improve image quality.

Grid-Biased Tube

A type of x-ray tube that uses a focusing cup maintained at a different voltage to improve image quality.

Fluoroscopy Applications

Used for catheter positioning, GI tract visualization, and other medical applications requiring real-time x-ray feedback.

Anode Target Material

The atomic composition of the anode affects the efficiency of x-ray production.

Linear Attenuation Coefficient (µ)

Measures the fraction of x-ray photons removed from a beam per unit thickness of material.

Characteristic X-ray Spectrum

Produced when electrons from higher energy shells fill vacancies in lower energy levels, leading to emission of x-rays.

X-ray Interaction Types

Includes Rayleigh scattering, Compton scattering, photoelectric absorption, and pair production.

Space Charge-Limited Operation

Occurs in x-ray tubes when the tube current is limited by the space charge around the cathode.

Effective Focal Spot Size

The projected size of the focal spot on the image receptor, which varies with anode angle and filament lengths.

Computed Tomography (CT)

A medical imaging technique using x-ray technology to create detailed images of the body's internal structures.

Helical CT

A type of CT imaging where the x-ray tube rotates in a spiral manner around the patient, providing rapid image acquisition.

CT Scan

An imaging procedure that uses x-rays to take pictures of slices of the body, which are then compiled to create cross-sectional images.

Contrast Medium

A substance used in CT scans to enhance the visibility of certain tissues or blood vessels in the images.

Slice Thickness

The width of the individual slices taken during a CT scan, influencing image detail and radiation dose.

CT Reconstruction

The process of creating a 3D representation from the 2D images produced by a CT scan.

Radiation Dose

The amount of ionizing radiation absorbed by the patient during a CT scan, which is a consideration in patient safety.

CT Angiography

A specialized type of CT imaging that visualizes blood vessels by using contrast agents and CT technology.

Multi-slice CT

A CT technology that allows for the simultaneous acquisition of multiple slices, enhancing speed and image quality.

Image Artifact

An error in the imaging process that can distort the final CT image, often caused by movement or hardware issues.

What is Mammography?

A radiographic examination aimed at detecting breast pathology, including cancer.

How does mammography help in breast cancer detection?

Mammography can detect tumors that are too small to be felt and can identify microcalcifications that may indicate cancer.

What are the two types of mammograms?

Screening mammograms, which are routine exams, and diagnostic mammograms, which are used when problems are suspected.

What is a 3D Mammogram?

Also known as digital breast tomosynthesis, it creates a 3D image of the breast, improving detection rates.

What is the purpose of breast compression in mammography?

Compression reduces the thickness of the breast tissue, improving image quality and minimizing radiation exposure.

What does a suspicious mammogram result mean?

It indicates that further evaluation, such as a diagnostic mammogram or biopsy, may be necessary.

What types of interactions do x-rays have with matter?

X-rays can interact with matter through Rayleigh scattering, Compton scattering, photoelectric effect, and pair production.

What is Rayleigh Scattering?

A scattering process where low-energy x-rays are scattered elastically by atoms without energy loss.

What is Compton Scattering?

An interaction where x-ray photons collide with electrons, leading to a change in direction and energy loss of the photon.

What is the Photoelectric Effect?

A process where an x-ray photon is completely absorbed by an electron, leading to the ejection of the electron from the atom.

What is Pair Production?

An interaction where a photon with a high enough energy creates a particle-antiparticle pair, typically an electron and a positron.

How does x-ray energy affect interaction types?

Lower energy x-rays are more likely to undergo photoelectric effect, while higher energy x-rays are more likely to scatter via Compton scattering.

What is the significance of the mass attenuation coefficient?

It quantifies how easily x-rays are absorbed or scattered by a material, influencing image contrast in CT scans.

How does material density affect x-ray interactions?

Increased density typically leads to greater absorption of x-rays, impacting the quality and contrast of the resulting images.

What is the role of anode target material in x-ray production?

The atomic composition of the anode affects the efficiency of x-ray production and influences the characteristic radiation spectrum.

What is the impact of x-ray interactions on image artifacts in CT?

X-ray interactions that are not uniform can lead to image artifacts, affecting the clarity and accuracy of CT images.