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Questions and Answers
The focal spot size does not affect the resolution of an x-ray image.
The focal spot size does not affect the resolution of an x-ray image.
False
The tube current can only be increased by adjusting the filament temperature.
The tube current can only be increased by adjusting the filament temperature.
True
The focusing cup is negatively charged to help focus the electron stream to the target.
The focusing cup is negatively charged to help focus the electron stream to the target.
True
The heel effect causes increased intensity of the x-ray beam on the anode side.
The heel effect causes increased intensity of the x-ray beam on the anode side.
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Most x-ray tubes have three filaments which allow the use of multiple focal spots simultaneously.
Most x-ray tubes have three filaments which allow the use of multiple focal spots simultaneously.
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The half value layer represents the thickness of a material required to reduce the intensity of an x-ray beam to one-third of its initial value.
The half value layer represents the thickness of a material required to reduce the intensity of an x-ray beam to one-third of its initial value.
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A small target angle optimizes heat ratings but limits field coverage.
A small target angle optimizes heat ratings but limits field coverage.
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The apparent focal spot can appear larger from the patient's perspective compared to its actual size.
The apparent focal spot can appear larger from the patient's perspective compared to its actual size.
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A collimator is used in x-ray radiography to increase the patient dose.
A collimator is used in x-ray radiography to increase the patient dose.
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The target angle in an x-ray tube is typically between 0 and 5 degrees.
The target angle in an x-ray tube is typically between 0 and 5 degrees.
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Higher kilovoltage can help overcome the space charge effect in x-ray tubes.
Higher kilovoltage can help overcome the space charge effect in x-ray tubes.
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The anti-scatter grid is used to increase the contribution of scattered X-rays to the image.
The anti-scatter grid is used to increase the contribution of scattered X-rays to the image.
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At saturation voltage, all electrons liberated by the filament reach the anode regardless of further increases in kilovoltage.
At saturation voltage, all electrons liberated by the filament reach the anode regardless of further increases in kilovoltage.
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The basic components of a planar x-ray radiography system include a collimator, an anti-scatter grid, and a detector.
The basic components of a planar x-ray radiography system include a collimator, an anti-scatter grid, and a detector.
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Reducing the thickness of copper in a beam can increase the total linear attenuation coefficient for x-rays.
Reducing the thickness of copper in a beam can increase the total linear attenuation coefficient for x-rays.
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Electrons become positive after leaving the filament in an x-ray tube.
Electrons become positive after leaving the filament in an x-ray tube.
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Study Notes
Medical Imaging: X-Ray Radiography
- X-rays are used in medical imaging.
- A graphic shows an X-ray tube that produces X-rays to penetrate a body part.
Half Value Layer (HVL)
- HVL is the material thickness needed to halve X-ray/gamma-ray beam intensity.
- The formula for HVL calculation is: HVL = 0.693/μ (where μ is the linear attenuation coefficient)
- A 2000 monoenergetic photon beam reduced to 1000 photons by a 0.01m thick copper slab example is given, in which the linear attenuation coefficient (μ) of the copper for these photons is calculated as 69.3 m⁻¹
Planar Radiography/Projection Imaging
- It produces a 2D image of a patient's 3D anatomy.
- The diagram shows an X-ray source, patient, and detector, illustrating the principles.
Instrumentation of Planar Radiography
- Basic components of a planar X-ray radiography system include:
- X-ray tube: emits X-rays.
- Collimator: restricts the beam to the area of interest.
- Anti-scatter grid: reduces scattered X-rays.
- Detector: converts X-ray energy into light.
Space Charge
- Negative electrons stay close to the filament.
- Electron cloud surrounds filament, making it more difficult to release additional electrons.
Kilovoltage and Space Charge
- Gradually increasing kilovoltage overcomes space charge.
- At high enough kilovoltage, saturation occurs, releasing all possible electrons.
Saturation Voltage
- The kilovoltage at which increasing it further doesn't increase tube current.
- Tube current is emission limited at this point.
Focal Spot
- The area of the anode struck by the electron stream.
- Focal spot size affects image resolution.
Focusing Cup
- It is negatively charged to focus the electron stream to the target.
- It prevents electron spread due to mutual repulsion.
Focal Spots (Further Details)
- Most X-ray tubes have multiple filaments and focal spots.
- Typically, only one is active at a time.
- Small focal spots provide better resolution.
- Large focal spots enhance heat capacity.
Cross-Section of X-Ray Tube
- Illustration displays the internal anatomy of an X-ray tube, including the horn, filaments, and focal spots.
- Also illustrates the stinger, the target, and highlights of GTS products.
Line Focus Principle
- Focal spots are angled / slanted.
- When viewed from the target, the spot appears much smaller compared to the filament.
- The larger apparent size at the filament allows for a better heat capacity.
Target Angle
- The angle between the target and the perpendicular to the X-ray tube axis.
- Typically ranges from 7 to 15 degrees.
- Its affect on heat capacity is highlighted, and smaller angles have greater field coverage, and larger target angles have a poorer heat distribution.
Line Focus (continued)
- The apparent focal spot is calculated from the actual focal spot's value, according to the angle.
Target Angle (continued)
- Larger target angles have greater heat capacities.
- Smaller target angles decrease heat capacity, but offer greater field coverage.
Heel Effect
- The intensity of the X-ray beam is significantly reduced on the anode side.
- The beam passes through more material when exiting the anode.
X-Ray Detectors
- Traditional X-ray film uses screen-film radiography.
- Digital detectors use computed and/or digital radiography.
Screen-Film Cassette
- Composed of a cassette, intensifying screens, and a film sheet.
- The film is a thin plastic sheet with a photosensitive emulsion on one or both sides.
X-ray Film
- Darker films indicate higher X-ray exposure.
- Optical density (OD) quantifies the film's darkness (quantifying the film's light transmittance).
- The densitometer is the tool calculating OD values, and the formula given illustrates this calculation.
Example: Contrast Calculation
- Contrast between regions on a radiograph can be calculated using optical densities. For example a contrast of 0.176 equates to regions with 1.0 and 1.5 corresponding optical densities, respectively.
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Description
This quiz explores the fundamentals of X-ray radiography, including the principles of X-ray production and the concept of the half value layer (HVL). It also covers the instrumentation used in planar radiography and how 2D images are created from 3D anatomical structures. Test your understanding of these critical aspects of medical imaging.
