IEM - Xray Production

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59 Terms

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X-ray Production

Conversion of projectile-electron kinetic energy into heat, infrared radiation, and x-rays at the anode target.

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Projectile Electron

Electron accelerated from the cathode that strikes the anode target and produces heat and x-rays.

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Electron-Target Interaction

Encounters between projectile electrons and the orbital electrons or nuclear field of target atoms that generate x-ray photons and heat.

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Thermionic Emission

Release of electrons from a heated filament on the cathode side of the x-ray tube.

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Space Charge Effect

Self-limiting build-up of electrons around the filament that restricts further thermionic emission.

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Focusing Cup

Negatively charged cathode component that confines the electron cloud into a narrow beam toward the anode.

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Tube Current

Stream of electrons traveling from cathode to anode during exposure; measured in milliamperes (mA).

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Anode Heat

Thermal energy generated when 99 % of projectile-electron kinetic energy interacts with outer-shell electrons of the target.

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Characteristic Radiation

X-rays emitted when an outer-shell electron fills an inner-shell vacancy created by a projectile electron; energy is discrete and element-specific.

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K-Characteristic X-Ray

Characteristic photon produced from a K-shell vacancy; requires ≥ 69 kVp in tungsten targets.

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Bremsstrahlung Radiation

‘Braking’ x-rays produced when projectile electrons are decelerated by the nuclear field of target atoms; continuous energy spectrum.

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Emission Spectrum

Graphic display of x-ray beam energies showing discrete characteristic peaks superimposed on a continuous Bremsstrahlung curve.

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X-Ray Quantity (Intensity)

Number of x-ray photons in the useful beam; measured in milligray in air (mGya) or exposure.

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Milliampere-Seconds (mAs)

Product of tube current and exposure time; x-ray quantity is directly proportional to mAs.

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Kilovolt Peak (kVp)

Peak tube potential that controls beam energy and affects quantity as the square of the kVp ratio.

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Inverse Square Law

X-ray intensity is inversely proportional to the square of the distance from the source (I ∝ 1/d²).

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Square Law

mAs must be changed by the factor (SID₂)²/(SID₁)² to maintain beam intensity when source-to-image distance changes.

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Filtration

Use of metal (usually 1–5 mm Al) to remove low-energy photons, reducing patient dose and beam quantity while hardening the beam.

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Inherent Filtration

Permanent filtration from the glass envelope, insulating oil, and mirror inside the collimator.

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Added Filtration

Filtration that is added to the part of the x-ray tube. Sheets of aluminum placed at the tube port to absorb low-energy x-rays.

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Total Filtration

Sum of inherent and added filtration; must be ≥ 2.5 mm Al for tubes operating above 70 kVp.

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Compensating Filter

Accessory filter (e.g., wedge, bow-tie) that evens out non-uniform anatomy by differentially attenuating the beam.

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Wedge Filter

Most common type of compensating filter; thick edge is aligned with thinner anatomy to equalize exposure.

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Bow-Tie Filter

Curved compensating filter used in CT to match the rounded shape of the head or body.

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Bilateral Wedge (Trough) Filter

Double-wedge filter commonly used for AP thorax to balance exposure between lungs and mediastinum. Performs similar function to the wedge filter.

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X-Ray Quality (Penetrability)

Ability of x-rays to pass through tissue; increases with higher kVp and added filtration.

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Coherent (Classical) Scattering

Low-energy (< 10 keV) interaction in which x-ray excites an atom and is re-emitted with equal energy but different direction.

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Diffraction X-ray

<10 kVp; used in research for structural and molecular analysis

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Grenz rays

10–20 kVp; used in dermatology for medical purposes.

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Superficial X-ray

50–100 kVp; used in therapy of superficial tissues.

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Diagnostic X-ray

30–150 kVp; used in medical imaging of anatomical structures and tissues.

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Orthovoltage X-ray

200–300 kVp; used in therapy of deep-lying tissues.

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Supervoltage X-ray

300–1000 kVp; used in therapy of deep-lying tissues.

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Megavoltage X-ray

>1000 kVp (1 MV); used in therapy of deep-lying tissues and in industry for checking integrity of welded metals.

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Compton Scattering

Interaction of diagnostic-range x-rays with outer-shell electrons, producing a scattered photon of lower energy and a Compton (recoil) electron.

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Compton Electron

Ejected outer-shell electron resulting from Compton scattering. Most of the energy is divided between scattered x-ray and Compton electron.

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Recoil electron

The ejected electron; Other term for Compton electron

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Photoelectric Effect

Total absorption of an x-ray by an inner-shell electron, which is ejected as a photoelectron; dominant at low kVp/high-Z materials.

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Photoelectron

Inner-shell electron ejected during a photoelectric interaction.

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Pair Production

High-energy (≥ 1.02 MeV) interaction near the nucleus where the x-ray converts to a positron–electron pair.

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Annihilation Radiation

Process where a positron combines with an electron, converting their mass to two 0.511 MeV photons at 180° apart.

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Photodisintegration

Absorption of an x-ray (> 10 MeV) by the nucleus, followed by emission of a nuclear fragment.

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Compton Scattering and Photoelectric Effect

The only important X-ray Interaction to Radiology

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Effective Atomic Number

Composite atomic number that expresses overall electron density of a compound or mixture (e.g., bone 13.8, soft tissue 7.4).

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Emission Button (Exposure Switch)

Control that applies high voltage across the tube, driving electrons to the anode and producing x-rays and heat.

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Rotor/Prep Button

Switch that heats the filament for thermionic emission and accelerates the rotating anode to operational speed.

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Electron Cloud (Space Charge)

Collection of electrons around the filament prior to exposure.

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Penetrability

Depth to which x-ray photons can travel in tissue; synonymous with beam quality.

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Outer-Shell Interaction

Collision of projectile electrons with outer-shell electrons in the target that produces heat, not useful x-rays.

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Bremsstrahlung Continuous Spectrum

Range of photon energies from zero up to the maximum kVp, characteristic of Bremsstrahlung production.

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Characteristic Peak

Discrete spike in the x-ray spectrum corresponding to energy differences between specific electron shells (e.g., Kα, Kβ).

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Aluminum (Z = 13)

Material chosen for filtration because it is inexpensive, readily available, and easily shaped while effectively absorbing low-energy photons.

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99 % Heat / 1 % X-Rays

Approximate distribution of projectile-electron kinetic energy at the anode

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kVp–Quantity Relationship

X-ray quantity changes proportional to (kVp₂/kVp₁)²; doubling kVp increases quantity fourfold (factor of 4).

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mAs–Quantity Relationship

X-ray quantity is directly proportional to mAs; doubling mAs doubles quantity.

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Distance–Quantity Relationship

X-ray intensity decreases with the square of the distance per the inverse square law.

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Filters and Beam Quality

Adding filtration removes low-energy photons, increasing average beam energy (quality) while decreasing quantity.

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Diagnostic Range

X-ray energy spectrum of approximately 30–150 kVp used for medical imaging.

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Positron Emission Tomography (PET)

Nuclear medicine technique relying on pair production and annihilation radiation to detect metabolic activity.