X-ray Production Flashcards

Question

What does the metal shielding do?

Answer 1

usually lead absorbs x-rays window where x-ray beam exits

Answer 2

dissipates heat produced by x-ray tube by thermal convection

Answer 3

Removes lower energy (non-diagnostic) X-rays from beam * Low energy photons would all be fully absorbed by patient’s tissues & increase patient dose but not contribute to image Aluminium (of adequate thickness) is able to absorb these photons so that the resulting X-ray beam contains mostly diagnostic X-ray photons

Answer 4

* <70kV→1.5mm * ≥ 70 kV → 2.5mm (modern equipment operates in the range of 60-70 kV)

Answer 5

Dictates distance between focal spot (of target) & patient * “Focus to skin distance” (fsd) * Altering fsd will affect degree of divergence of X-ray photons in X-ray beam (& affect intensity of X-ray beam) * Increasing fsd reduces divergence of X-ray beam & therefore reduces magnification of image (but also reduces intensity of X-ray beam) * A set distance helps ensure a consistent radiographic technique

Answer 6

* <60kV→100mm * ≥ 60 kV → 200mm (ie. modern equipment)

Answer 7

attenuated by lead shielding attenuated by aluminium filtration exit tubehead to form x-ray beam

Answer 8

Lead diaphragm attached to end of spacer cone * Reduces patient dose Crops X-ray beam to match size & shape of X-ray receptor * Tubeheads inherently create a circular beam * Collimators typically change circular cross-section to a rectangular cross-section

Answer 9

advantage - can reduce effective dose to patient by approximately 50% disadvantage - increases risk of collimation errors (but this can be minimised using good radiographic technique)

Answer 10

* On/off switch & light * Electronic timer * Exposure time selector & presets * Warning light & noise (for when X-rays are being generated) * (Kilovoltage selector)

Answer 11

- heat production (involve outer shell electrions of tungsten atoms at target) - x-ray production (involve inner shell electrons and nuclei of tungsten atoms at target, less than 1% of interations)

Answer 12

Bombarding electron reaches tungsten outer shell electron & either: - Comes into close proximity & is then decelerated & deflected - both negatively charged - Collides & is deflected Bombarding electron loses kinetic energy which is converted to heat Heat energy dissipated Tungsten target > copper block >oil in tubehead > air

Answer 13

Continuous radiation interactions (majority) Characteristic radiation interactions

Answer 14

Bombarding electron passes close to target nucleus, causing it to be rapidly decelerated & deflected → lost kinetic energy released as X-ray photons

Answer 15

Photons produced over wide range of energies * increase in proximity of electron to nucleus → increase in deceleration + deflection → increase in energy released * Greater proportion of lower energy photons

Answer 16

when electron collides directly with nucleus & stops completely * Rare * Numerically identical to the potential difference (ie. voltage) across the X-ray tube * eg. 70 kV → 70 keV photon produced

Answer 17

Bombarding electron collides with an inner-shell electron & either displaces it into a more peripheral shell (excitation) or removes it completely (ionisation) The remaining orbiting electrons rearrange themselves to re-fill the innermost shells * When an electron “drops” to a lower shell it loses energy which is emitted as a photon of specific energy * Values depend on the element involved (eg.tungsten)

Answer 18

Photon energy equals the difference in the binding energies of the 2 shells involved (which are specific to that element) Target made up of tungsten atoms * K shell binding energy = 69.5 keV * L shell binding energy = 10.2 keV * M shell binding energy = 2.5 keV

Answer 19

dental X-ray tubes often operate at 70 kV so that bombarding electrons have sufficient energy (70 keV) to displace K shell electrons

Answer 20

**Continuous** * Produces a continuous range of X-ray photon energies * Maximum photon energy matches the peak voltage * Bombarding electron interacts with nucleus of target atom **Characeristic** * Produces specific energies of X-ray photon, characteristic to the element used for the target * Photon energies depend on the binding energies of electron shells * Bombarding electron interacts with inner- shell electrons of target atom

Answer 21

continuous radiation (-low energy photons) + characteristic radiation

X-ray Production Flashcards

(45 cards)