X-Rays Flashcards
what are the three essential components for the x-ray?
- source of x-ray (uniform distribution)
- object (attenuation by object)
- image receptor (spatial distribution of x-rays on image receptor)
what led to the discovery of x-rays?
Wilhem Roentgen noticed a barium screen fluorescing while generating cathode rays
what are the features of X-ray tube?
- mobile (enables x-rays production at different angles and positions)
- uniform (to provide image contrast)
- collimated (adjustment of size)
which factors in uniform distribution of x-rays control the image appearance?
controls image appearance by
- x-ray energy (kVp)
- amount of x-rays (mAs)
- penetration -> contrast
- image density -> blackening
what does the x-ray interaction with matter (attenuation) result in?
- alters properties of incident beam
- attenuation (absorption and scatter)
- magnification and distortion of objects
what are the features of an image receptor?
- converts x-rays into image - influences image appearance
- consists of film and film-screen - chemical reaction
- computed radiography - scanning laser
- direct-digital radiography - computing
what are the two types of DDR?
- solid state detectors
2. flat panel detectors
name four factors on the basis of which image is evaluated and interpreted?
- centring and collimation
- exposure factors
- processing
- artefacts
name the SEVEN essential components in x-ray?
- tube
- collimator
- light beam diaphragm
- generator
- casette
- bucky
- couch
LGBT CCC
what are the characteristics of x-rays?
- penetrate matter
- interact with matter
- cause certain material to fluorescence
- cause certain materials to produce electric charge
how are x-rays produced?
produced by a side deceleration of electrons in target
what is the protective role of tube housing?
provides
- physical protection
- radiation protection
- electrical protection
- filled with oil for
a. heat dissipation (excess)
b. electrical insulation
what are the features of cathode?
- source of electrons - negatively charged to focus the electrons towards anode and stop spatial spreading
it consists of - filament (wire filament for small and large focal spot)
- focusing cup - surrounds the cathode which consists of the two wire filaments
why is tungsten used as filament?
- good thermionic emitter (emission of electrons from heat source)
- high melting point - 3140 degree C
- high atomic number (Z=74, higher attraction property)
- can be manufactured into thin wires
what causes the heating in thermionic emission and how much current is supplied?
- electric current causes heating
2. above 4As electrons are boiled off
what are the features of anode?
- Positively charged to attract electrons
- Target made of tungsten for same reasons as for filament (in cathode)
- Rhenium added to tungsten to prevent cracking of anode target at high temperatures and usage
- Set into an anode disk of molybdenum with stem
- Set at an angle to direct x-ray photon beam down towards patient. Usual angle is 5º - 15º
what are the three functions of anode?
- support target material
- electrical conductor
- thermal conductor
what are the two types of anode?
- stationary - consists of an anode fixed in position with the electron beam constantly streaming onto one small area
- rotating - consists of a disc with thin tungsten around the circumference that rotates. Due tot he rotation it overcomes heating by having different areas exposed to the electron stream over time
X-rays are electromagnetic waves?
A. True
B. Fasle
True
what is an X-ray tube and what does it consists of?
- The X-ray tube is a vacuum tube that converts electrical input power into X-rays, it’s composed by a glass envelope with a cathode (filaments) and an anode (target) inside
- It consists of collimator, light beam diaphragm, filtration and ionisation chamber. They are movable (x,y,z).
in which year did Rongten discovery x-ray accidentally?
1895
how are x rays formed?
- electrons produced at the filament of X-ray tube
- accelerated towards the anode target of tube and collide with target atoms
- electrons then lose energy and decelerate, then energy released in the form of x-rays
what are three ways electrons might collide with target atom?
- interaction b/w them and outer electrons in the atom = no x-rays, heat
- interaction b/w them and the nuclei of the atom - x-rays + heat (Bremsstahlung)
- interaction b/w them and individual electron in the inner orbits = X-rays + heat (characteristic)
why is x-ray production an inefficient process?
95-99% of energy produced in x-rays is heat and the rest 5-1% is x-rays
what are the two famous ways of x-ray production?
- bremstrahlung
2. characteristic
what is bremstrahlung radiation?
energetic electrons from the filament interact with the nuclei of target atoms and are slowed down thus giving off energy in the form of x-rays. It is also called braking radiation.
what is characteristic radiation?
energetic electrons remove electrons from the inner orbital and the vacancies created are filled by electrons from outer orbitals, giving off energy in the form of x-rays
what is atomic number and melting point of tungsten?
atomic number - 74
melting point - 3370 degree C
why is tungsten used an ideal target material or anode in X-ray tubes?
- high atomic number has higher attractive property
2. high melting point will prevent the excess heart production damage
name an alloy used with tungsten
rhenium
which atoms are used in mammography as anodes?
- molybdenum - atomic number 42
2. rhodium - atomic number 45
what are the features of stationary anode?
- used in low output tubes
2. 99.5% of electron energy is converted to heat
what are the features of rotating anode?
- typically glass envelope insert
- increase heat dissipation
- increase anode load
what is anode pitting/ cracking?
It is line formed by the hitting of electrons on the rotating anode from prolonged use
what is anode angle?
it is a spectrum of angle with varying intensity to create effective x-rays via small focus
what is anode heel effect?
refers to the lower field intensity towards the anode in comparison to the cathode due to lower x-ray emissions from the target material at angles perpendicular to the electron beam
what does a large focus and small focus result in terms of images obtained?
- large focus - blurred image
2. small focus - sharp image
why dual filaments are used? and state three usual combinations
dual filaments offer two effective spot sizes the common combinations are 1. 0.6mm and 1.2mm 2. 0.3mm and 1.2mm 3. 0.4mm and 0.8mm
what is an ideal x-ray source?
point source