X-Ray Radiography Basics

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson
Download our mobile app to listen on the go
Get App

Questions and Answers

What effect does increasing the filament temperature have on tube current?

  • It decreases the tube current.
  • It allows for an increase in tube current. (correct)
  • It has no effect on tube current.
  • It permanently limits the tube current.

What is the primary function of the focusing cup in an x-ray tube?

  • To focus the electron stream to the target. (correct)
  • To increase the tube current.
  • To increase the size of the focal spot.
  • To negatively charge the filament.

What is a benefit of using a small focal spot in an x-ray tube?

  • Improved heat ratings.
  • Greater electron beam energy.
  • Improved resolution. (correct)
  • Increased field coverage.

What is typically the angle of the target in an x-ray tube?

<p>7 to 15 degrees (D)</p> Signup and view all the answers

What does the line focus principle describe?

<p>The relationship between actual and apparent focal spot size. (B)</p> Signup and view all the answers

How does the heel effect impact the intensity of the x-ray beam?

<p>It decreases intensity on the anode side. (C)</p> Signup and view all the answers

Which characteristic defines a focal spot that requires better heat ratings?

<p>Larger actual focal spot. (D)</p> Signup and view all the answers

What is the effect of a larger target angle on field coverage?

<p>Increases field coverage. (A)</p> Signup and view all the answers

What does the half value layer (HVL) represent in the context of x-ray radiography?

<p>The thickness of material required to reduce the intensity of an x-ray beam to one-half of its initial value. (D)</p> Signup and view all the answers

Which component of a planar x-ray radiography system is responsible for converting the energy of transmitted x-rays into light?

<p>Detector (B)</p> Signup and view all the answers

What effect does increasing kilovoltage have on the flow of electrons from the cathode to the anode?

<p>It has no effect on the number of electrons reaching the anode at saturation. (D)</p> Signup and view all the answers

What does the anti-scatter grid do in an x-ray radiography system?

<p>Reduces the contribution of scattered x-rays to the image. (C)</p> Signup and view all the answers

What occurs when the kilovoltage is raised too high in relation to the electron flow?

<p>All electrons liberated by the filament reach the target without any losses. (B)</p> Signup and view all the answers

In the context of x-ray radiography, what is a primary function of the collimator?

<p>To reduce the patient dose and minimize scattered x-rays. (C)</p> Signup and view all the answers

How does the space charge effect influence the x-ray tube's performance?

<p>It limits the flow of electrons from cathode to anode when excessive charge builds up. (D)</p> Signup and view all the answers

What is the significance of the total linear attenuation coefficient in the context of x-ray transmission through materials?

<p>It quantifies how easily x-rays are absorbed or scattered by a material. (D)</p> Signup and view all the answers

Flashcards

Half-Value Layer (HVL)

The thickness of material required to reduce the intensity of an X-ray or gamma-ray beam to half its initial value.

Planar Radiography

A method of creating a 2-dimensional image of a 3-dimensional patient anatomy using X-rays.

X-ray Tube

The component in an X-ray system that generates X-rays.

Collimator (in X-ray)

A device used to reduce the area of the X-ray beam, limiting radiation exposure to the patient.

Signup and view all the flashcards

Anti-scatter grid

A device placed in the X-ray path to reduce the amount of scattered X-rays in the image.

Signup and view all the flashcards

Space Charge

A phenomenon in X-ray tubes where electrons from the cathode repel each other, limiting the flow.

Signup and view all the flashcards

Kilovoltage (kVp)

The voltage applied across the X-ray tube, impacting the energy of the emitted X-rays.

Signup and view all the flashcards

Saturation Voltage

High enough Kilovoltage where all liberated electrons reach the target.

Signup and view all the flashcards

Kilovoltage & Tube Current

A point at which increasing kilovoltage doesn't increase tube current, determined by the saturation of electrons at the target.

Signup and view all the flashcards

Focal Spot

The area of the anode where the electron beam strikes, affecting x-ray resolution.

Signup and view all the flashcards

Focusing Cup

A negatively charged component of the x-ray tube that directs the electron beam toward the focal spot.

Signup and view all the flashcards

Line Focus Principle

Technique used to create a small apparent focal spot while having a larger, more robust actual focal spot, improving heat dissipation.

Signup and view all the flashcards

Actual Focal Spot

The true size of the focal spot, as seen from the filament.

Signup and view all the flashcards

Apparent Focal Spot

The size of the focal spot as projected onto the image receptor or patient. It is smaller than the actual focal spot due to the line focus principle.

Signup and view all the flashcards

Target Angle

The angle between the target and a line perpendicular to the tube axis, influencing both heat capacity and beam coverage.

Signup and view all the flashcards

Heel Effect

The uneven intensity of the x-ray beam across the image, with reduced intensity on the anode side.

Signup and view all the flashcards

Study Notes

X-Ray Radiography

  • X-rays are used in medical imaging.
  • Half-value layer (HVL) is the thickness of material required to reduce the intensity of an x-or gamma-ray beam to one-half its initial value.
  • HVL = 0.693/μ
  • A narrow beam of 2000 monoenergetic photons reduced to 1000 photons by a 0.01 m thick copper slab has a linear attenuation coefficient (μ) of approximately 69.3 m⁻¹.

Planar Radiography/Projection Imaging

  • Planar radiography acquires a 2D image of a patient's 3D anatomy.
  • X-rays travel from a source through the patient to a detector.

Instrumentation of Planar Radiography

  • Key components of an X-ray radiography system include and X-ray tube, a collimator, anti-scatter grid, and a detector.
  • A collimator reduces patient dose and Compton scattered X-rays.
  • An anti-scatter grid further reduces scattered X-rays.
  • A detector converts the energy of transmitted X-rays into light.

Space Charge

  • Electrons leaving the filament create a positive charge.
  • A cloud of negative electrons surrounds the filament.
  • This cloud repels new electrons, limiting electron flow from cathode to anode.

Kilovoltage & Space Charge

  • Increasing kilovoltage gradually overcomes space charge.
  • Higher kilovoltage allows more electrons to reach the anode.
  • At a high enough kilovoltage, saturation occurs, meaning all electrons liberated from the filament reach the target.
  • Further increasing kilovoltage doesn't increase the number of electrons reaching the anode.

Saturation Voltage

  • Saturation voltage is the kilovoltage at which increasing it further does not increase tube current.
  • At this point, all electrons that can be generated are already traveling to the target.
  • Tube current is emission-limited; increasing it only happens by increasing filament temperature.

Focal Spot

  • Focal spot is the area on the anode where electrons strike, affecting resolution and heat capacity.
  • Smaller focal spots improve resolution.
  • Larger focal spots allow for better heat capacity, but reduce resolution.

Focusing Cup

  • A focusing cup uses a negative charge to control and focus the electron stream, overcoming the natural repulsion between electrons.

Focal Spots (cont.)

  • Most X-ray tubes have two filaments and thus two focal spots.
  • Only one filament is used at a time.
  • Small focal spot - improved resolution.
  • Large focal spot - improved heat capacity, but lower resolution.

Cross-Section of X-Ray Tube

  • An X-ray tube has various components, including filaments, focal spots, a target, a cathode and anode, and other hardware.

Line Focus Principle

  • Focal spot is angled to create a smaller apparent focal spot, improving resolution from the patient's perspective.
  • The actual focal spot appears larger from the filament than it appears from imaging areas.

Target Angle

  • The target angle is the angle between the target and the perpendicular to the tube axis, typically 7-15 degrees.
  • A smaller target angle leads to a smaller apparent focal spot, better heat ratings, but reduced field coverage.
  • A larger target angle leads to a larger apparent focal spot, better heat capacity, and improved field coverage.

Heel Effect

  • The intensity of the X-ray beam is reduced on the anode side of the beam, because the beam travels through more material exiting from that side.

X-Ray Detectors

  • Traditional X-ray film (screen-film radiography)
  • Digital detectors (Computed and digital radiography)

Screen-Film Cassette

  • Screen-film detectors consist of a cassette, intensifying screens, and film.
  • Film is a thin plastic sheet with photosensitive emulsion on one or both sides.

X-ray Film

  • X-ray film is a negative recorder.
  • Increased X-ray exposure results in darker film.
  • Optical density (OD) quantifies the darkness of the film.

Example: Contrast

  • Contrast is calculated by comparing the log of ratios of the optical densities of two regions, as compared. An example uses optical densities of 1.0 and 1.5

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

More Like This

Use Quizgecko on...
Browser
Browser