Unit 4 + 5 + 6

primary factors

mA, kVp, exposure time, distance

mAs

measurement of tube current, quanitity

exposure time

controls duration of exposure, quantity

kVp

sped of electrons move in tube, quantity and quality

how can energy of electron affect quality

higher energy means higher penetrability

distance, inverse square law

distance of tube to image receptor, quanitity

secondary factors

contrast, receptor exposure, spatial resolution, distortion

contrast definition and its purpose

degree of differentiation between light and dark areas in radiograph, make anatomy more visible

scales of contrast

long/low and short/high

air gap technique

increased OID to decrease scatter

grids purpose

absorbed scatter and unwanted radiation

beam restriction (collimation)

reducing area leads to less scatter and better contrast

patient factors that affect contrast

pathology, patient habits, tissue type and density

destructive pathology affect on contrast

short/high

additive pathology affect on contrast

low/long, more technique

anode heel effect

intensity is greater on cathode side (120) compared to anode (75)

generator output on receptor exposure

single phase, triple phase, high frequency (less technique, better radiation efficiency)

spatial resolution

sharpness and quality of anatomical structural lines from attenuation

receptor exposure factors (8)

mAs, kVp, SID, grids, tube filtration, beam restriction, anode heel effect, patient factors

focal spot blur/ penumbra

area of UNsharpness

umbra

area of sharpness

contrast factors (6)

kVp, OID, grids, tube filtration, beam restriction, patient factors

affects of unsharpness and spatial resolution on a LARGE focal spot size

unsharpness increases, spatial resolution decreases

affects of unsharpness and spatial resolution on a SMALL focal spot size

unsharpness decreases, spatial resolution increases

spatial resolution factors (6)

OID, SID, focal spot size, motion, patient factors, angle

how can SID affect focal spot blur

large SID, decrease blur or small SID, increases blur

OID affect on focal spot blur

increase OID, increase blur or decrease OID, decrease blur

distortion factors (3)

magnification, foreshortening, elongation

mAs distance compensation formula

mAs1/mAs2= (d1)2/(d2)2

magnification factor

MF= SID/SOD

15 % rule

increasing kvp is the same thing as doubling mas or decreasing kvp is the same thing as dividing your mas

object size

object size = image size/MF

focal spot blur formula

focal spot size/SOD = focal spot blur/OID

double focus tube

tube with two filaments and focal spots

fractional focus tube

tube with smaller focal spot and anode angle less that 5 degrees

focal spot/track

region of the anode target where electrons interacts to produce x rays

properties of x ray (13)

no mass, invisible, electrically neutral, travel at speed of light, not optically focused, polyenergetic, range of energies, travel in straight lines, fluoresces substances, penetrate body, absorption or scatter in body, produce secondary radiation, cause damage to tissue

photon

bundle of energy

wavelength

distance between two corresponding points on a sine wave, measured in angstroms

frequency

number of wavelength that pass through a point, measured in Hertz

energy

measured in units of eV (10 kEV to 100 kEV)

short to long waveforms

high energy/frequency (short), low energy/frequency (long)

conditions necessary for x ray production (4)

separation, focusing, acceleration, sudden stop or break

components of x ray tube (5)

glass/metal enclosure, cathode, anode, induction motor, protective housing

cathode side and contains what?

negative side of tube, contains filament and focusing cup

anode

positive side of tube, stationary and rotating

purpose of anode (4)

receive and conduct electrons, mechanical support, dissipate heat

induction motor

powers rotating tube, stator on outside and rotor on inside of enclosure, works through electromagnetic induction

protective housing

guards against excessive radiation exposure and electric shock, contains oil

leakage radiation

any radiation that exits the protective housing (less than 1 mgy /hr at 1m)

glass/metal enclosure

withstands heat temperatures (glass), longer lifespan (metal), vacuum allows efficient x ray production and life

atomic number and melting point of Tungsten

#74, 3400 degrees C

motor that runs the tube

energy converted into head and x ray (%)

99% heat, 1% x ray

different focal spot size

thin areas use small filament (<200 mA), thick areas use large filament (>200 mA)

anode heel effect

intensity on cathode side is greater than anode, 120 to 75

causes of tube failure (9)

pitting, crazing, cracking, bearing damage, prolonged rotoring, filament breakage, arcing, oil overheating, physical abuse

different method to prevent tube failure (5)

tube/anode rating chart, warm x ray tube, high kvp, low mas, dont rotor long

different factors to consider when using a radiographic rating chart (6)

filament size, anode speed, target angle, number of exposures, tube design, cold vs hot tube, power supply, rectification

electromagnetic spectrum (EMS)

composed of different electromagnetic energies and radiations grouped by wavelength and frequency

how does the cathode work

low voltage circuit causes thermionic emission bunching up electrons to space charge, ejects to anode target

how does anode work

anode rotates during exposure, electron stream spread over a larger area

heat units

amount of heat produced from exposure, HU= mA x time x kVp x generator factor

generator factors from heat units

single phase (1), three phase (1.35), high frequency (1.40)

radiographic rating chart

shows unsafe for x ray tube, any combination of time mAs or kvp under mA curve is unsafe