LXMO Concepts Flashcards
inverse square law
the intensity of an X-ray beam decreases proportionally to the square of the distance from the source
low-voltage circuit
subcircuit between the alternating current (AC) power supplyand the primary side of the high-voltage (step-up) transformer
control console
where operator sets all exposure techniques
autotransformer
single-coil transformer that serves three functions. 1. provides means for kVp selection, 2. compensation for fluctuations in incoming line voltage, and 3. supplies power to other parts of the x-ray circuit. PRIMARY FUNCTION IS TO VARY VOLTAGE TO THE PRIMARY SIDE OF STEP-UP TRANSFORMER
exposure switch
closes the circuit, allowing current to flow through primary side of step-up transformer.
exposure timer
device that terminates the exposure
filament circuit
subcircuit of the main x-ray circuit. PRIMARY PURPOSE IS THE FILAMENT CIRCUIT IS TO SUPPLY A LOW CURRENT TO HEAT THE X-RAY TUBE FILAMENT FOR THERMIONIC EMISSION OF ELECTRONS
mA selector
controls the amperage in the filament circuit
high-voltage circuit
includes x-ray tube and the rectifier, current only flows in this circuit during an exposure
step-up/high voltage/high-tension transformer
increases the incoming voltage by the value of the transformer ratio
high voltage transformer
primary purpose is to supply the x-ray tube with high enough voltage to create the x-rays
rectification
the process of changing alternating current into direct current so it flows in one direction only
rectifier
changes the AC into direct current. ensures that current flows in the correct direction. goes from the filament to the target
self-rectification
inefficient way, no longer used
half-wave rectification
uses diodes to convert the circuit from AC to DC. uses 2 diodes. in half-wave the negative phase of the electrical cycle is eliminated and a gap remains
full-wave rectification
4 diodes, current can be redirected during the negative half of the electrical cycle so the current will flow in the same direction in both positive and negative halves of the cycle
half-wave
60 pulses per second and hz
full-wave
120 times per second
single-phase x-ray generators
powered by single source of AC current. creates a pulsating current that alternates from positive to negative. results in a single x-ray beam. 120 pulses of electricity per second = 120 pulses of x-rays per second
three-phase generator
powered by 3 separate sources of AC current at the same time. wave form has the appearance of a ripple w/ no real low points. 360 pulses of electricity per second = 360 pulses of x-rays per second
three-phase
more efficient and produces approx. 40% more x-rays than single-phase current. decreases exposure times by 40%
high-frequency generators
most commonly used. uses single source of AC current. 60 hz wave is converted to 6000hz when rectified. some can convert the frequency to as high as 10,000hz
AEC
automatic exposure control, terminates exposure time when a certain amount of radiation has been detected by IR
APR
automatically programmed radiography (APR). processor controls the exposure factors and sets exposure techniques using presets
single phase heat unit formula
HU = mA x time x kVp
three phase HU formula
HU = mA x time x kVp x 1.35
high frequency HU formula
HU = mA x time x kVp x 1.4
mAs formula
mA x time = mAs
what setting for x-rays impacts density in radiographs?
mA, by varying them and increasing/decreasing exposure time
what setting for x-ray impacts contrast in radiographs?
kVp, decrease increases contrast, increase reduces contrast
penetrometer
solid piece of aluminum that acts as a scale to simulate different densities
short-scale contrast
short range of densities (high contrast)
long-scale contrast
long scale of densities (low contrast)
subject contrast
affected by kVp and subject density, range of differences in the intensity after attenuation through the patient
fog
unwanted exposure to the radiographic image
SID
source to image receptor distance
OID
object to image receptor distance
umbra
actual anatomic area, body part, or structure
penumbra
“unsharp edges” of the umbra
4 prime factors of exposure are?
mA, time, kVp, and SID
four basic types of body habitus?
sthenic, hyposthenic, asthenic, and hypersthenic
sthenic
“average” 50% of population, “text book descriptions”
hyposthenic
“slender normal” 35% of population, organs tend to be longer/narrower, and in more vertical position
asthenic
very slender, organs long and narrow, 10% of the population
hypersthenic
massive and stocky, 5% of the population, thorax is short, broad, and deep. organs are high and more horizontal in position
