Radiography Flashcards
Where does x-ray production occur?
X-ray tube head
How does the cathode differ between sophisticated and portable x-ray machines
Sophisticated machine - much higher current (mA) which causes more heating of the filament and releases more x-rays.
Portable machine - low mA so the filament is heated to a lower temperature and less electrons are released.
Briefly explain Potential Difference
A high voltage is applied to the anode side so that there is a voltage differential between the cathode and anode
The positive side of the tube head is the?
Anode
The negative side of the tube head is the?
Cathode
What does kV control?
Voltage
What does increasing kV do to the electrons?
Increases voltage - increases speed of electrons - increases energy of the x-rays - increases the penetrating power of the beam
Which type of rectification is preferable?
3 phase (electrons are hitting the anode continuously rather than in bursts) - reduced kV fluctuation
What is rectification?
How often during the exposure time the voltage is applied to the anode and therefore how often electrodes are flowing.
In what way is a rotating anode beneficial?
Gives a larger surface area for heat to dissipate
Which effect allows us to see different shades of gray in x-rays and why?
The photoelectric effect - differential absorption
What is the effect of Compton Scattering?
X-rays scatter away from the primary source to other people in the room or may fog the x-ray film.
What will increase scatter?
Higher kV, increased thickness, increased density, decreased collimation
What does mA affect?
current to the cathode - electron cloud - the number of x-rays
What does the seconds control affect?
How long the electrons flow
What does increase in kV do to the x-ray?
Increased penetration, decreased contrast, increased scatter
Define radiographic density and list which factors contribute to it
The blackness of the film - determined by the number of photons reaching the plate - all factors (kV, mA, s) contribute
Describe the contrast of an image with few shades of grey
High contrast
Describe the contrast of an image with many shades of grey
Low contrast
Which exposure factor controls contrast?
kV
What are the main things to assess a radiograph for in practice?
positioning, density, detail and distortion
What factors affect contrast?
kV, object thickness and density, scattered radiation, film processing
What is radiographic detail?
the degree of definition or clarity
What factors affecat radiographic detail?
focus to film distance, object to film distance, movement blur, focal spot size, film screen combination, scatter
How can you control the area exposed?
Collimation
What is a grid?
a device placed between the patient and the film to absorb scatter
What are the 3 functions of a cassette?
light proof box, ensures intimate contact between the film and screens, transforms x-rays to light
Where are intensifying screens found and what are they made up of?
inside the cassette, made of layers of phosphor crystals that adsorb x-ray energy and convert it to visible light
