Xray physics & positioning

• fast moving electrons collide with matter= xrays produced
• in a tube this is done by directing electrons against a metal target.
• 1% of their energy is in radiation, the other energy is given up in the form of heat
• the tube is lined with lead protection
• 2 electrodes: cathode and anode

• large filament
• small filament
• focusing cup

• source of the electrons
• made of tungsten

• current applied to the filament- coil becomes hot
• boiling off electrons

• QUANTITY of elecrons (mA)
• number of electrons determines number of xrays created

• part of the cathode, encaes 2 filaments
• where the thermionic emission occurs

• positive electrode in the xray tube
• most xray consist of a rotating anode
• rotating target receives electrons as they move from cathode to anode

• dissipate heat generated
• exposes are of tungsten called focal spot

better

• effect of making the actual focal spot smaller
• smaller target angle, smaller effective spot

heats the filament causing boiling off of electrons

more current=more electrons produced= more xrays= greater radiograph density (darker)

blackness on film

structures that produce blackness on film

structures that produce whiteness on film

directly proportional

primary method to control blackness

more mAs= more film exposure

• force applied to accelerate electrons
• greater force= greater photons

inversely related

high kvp= high energy= strong penetration

shorter wavelengths with ability to penetrate tissue

difference between structures, makes detail visible

inversely related

• high contrast= short scale
• long wavelengths, weak penetration
• black and white film
• less scatter, increased exposure

• low contrast= long scale
• more shades of grey (soft tissue film)
• more scatter, decreased exposure

lower contrast- longer scale- more greys: increase kvp by 15% and decrease mAs by 50%

high contrast- short scale-b&w: decrease kvp by 15% and increase mAs by 50%

• mAs is the prime method to control density
• relationship between kvp and density is not proportional
• 15% increase in kVp by 15% will double the density on the film

• denser tissue absorbs xrays
• gas/fat= black
• mm, water, ST= gray
• bone, metal= white

intensity of the xray is greater at the cathode side than the anode side

• less xray
• smaller effective focal spot
• more detail
• use on thinner body part

• more xray
• larger effective focal spot
• less detail
• thicker body part

length of space from focal spot (tube) to the recording medium (film)

as you increase FFD- image gets smaller and more clear. decreases magnification and distortion

as you decrease FFD- image gets bigger and blurrier

explains the intensity of the beam affected by changes in the FFD

intensity of radiation varies inversely with the square of the distance from the source

40 inch FFD: doubled to 80 in FFD

80 inch FFD the mAs must be 4x amount for blackness maintained

• lateral cervical
• flex/ext
• obliques
• pa chest/lat chest

• flourescent crystals- the salt changes the xray photons into visible light photons
• *decrease pt exposure*

• claritiy and sharpness of an image
• umbra is the picture made by the beam
• penumbra is the blury halow parts

• distance b/n patient and film
• increased ofd: image becomes bigger/blurrier (more penumbra)

decreased ofd: image becomes smaller/clearer

*object as close as possible for better detail*

• pressure between the film holder ont he xray film
• should be evenly distributed
• *wire mesh test is best for testing*

reduces the sharpness of the image

• size and magnification
• OFD and FFD

• reduced by:
• grid
• air gap
• collimator
• filter

• alternating strips of lead and spacer material
• placed betweeen the patient and the film
• sole purpose of the grid is to improve the quality of the radiograph by absorbing scatter
• increases patient dose of radiation

height of the lead strips to the distance between the strips

chiros use 12:1

• 6-10" gap between patient and film
• lateral cervical view
• distance between body part and film: scatter radiation diverge
• reduces patient dose but distorts/magnifies the image

• limits the size of the beam to the size of the body part
• best way to reduce scatter radiation

• removal of low energy photons
• made of aluminum
• stops weak photons from entering patients body- reducing scatter radiation

• used to identify irratiation of patients
• measures radiation energy absorbed

• occupationally exposed people
• identifies the effectivness of radiation absormed
• badge worn on collar
• 1 RAD= 1 REM

• the number of REMS a person can get in a lifetime w/o getting rad posioning
• MPD= 5 (age-18)/ yr
• 5 REMS is the safe limit per year

• majority of the useful beam
• interacts with the target nucleus

• high intensity electron hits an inner shell electron, knocked off position
• outer shell then fills its spot

• primary form of scatter
• moderate energy knocks an outer shell
• causes a loss of energy

• low energy xray changes direction w/ no energy loss
• contributes to film fog

low energy photon absorbed by the subject creating a leatent image

• mottle caused by fluctuation of number of photons absorbed by the intensifying screens
• faster screens produce more quantum mottle
• use hight MAS low KVP decreases radiographic noise

• solutions that are too hot= increase density
• solutions that are too low= insufficient density

• 1) developer: brings out latent image developing silver halide
• 2) rinse:
• 3) fixer: hardens the image, making it permanant
• 4) washing: removes developer and fixer

produces shades of grey (phenidone/hydroquione)

• swelling of emulsion
• na+ carbonate

• controls oxidation
• na+ sulfite, K sulfite

• protects unexposed crystals
• potassium bromide/iodine

• controls swelling of emulsion
• glutaraldehyde

• nuetralizes the developer/ stop bath
• acetic acid

removes undeveloped ag halide/ hypo solution

• stiffens/shrinks the emulsion
• potassium alum

maintains ph of fixer

light leak, developer too hot, overexposure

developer treatment low, chemicals need replacing

inadequate fixer

inadequate fixer

insufficient washing

old film, hot developer, contaminated chemicals

insufficient fixing

vertically to avoid pressure damage

• produces when removing film quickly
• black and branching lightening lines

changes AC to DC

steps up or down the power

one form of energy to another

beam of radiation loses energy

added tot he base of film to reduce glare

black and branching

• appear as creases
• MC reason for creases

sella turcica best seen here

• frontal sinus
• 15 * caudal

• foramen magnum
• 35* caudad

maxillary sinuses

air gap technique, 72" FFD

15* caudad tilt

• dens and atlas best viewed
• used for jefferson burst frx

IVFs

• articular processes and apophyseal jts
• pt is PA

standing, arm closest to bucky is raised overhead, other arm at pt's side

• PA
• deep breath in and hold
• 72" FFD

IVFs

• 25* cephalic
• dont breath dont move

• pars
• 40 FFD

15* tube tilt

10* tube tilt caudal

no tub e tilt

tube 30*/35* cephalic

• tube 5* cephalad
• AP

views greater tuberosity

views lesser tuberosity

tube tilt 15* caudal for PA position, 15* cephalic for AP position

hand supinated

fat pad sign

scaphoid and lunate

supine or standing, feet turned in 15 *

• intercondylar fossa, osteochondritis desicans
• tube tilt 45* caudal
• prone patient w/ knee flexed to 45*

patella and patellofemoral jt space

tube tilt 10* cephalic