Exam 2- Factors selected at control panel Flashcards
mA-
quantity of electrical current flowing in a circuit
cathode contains-
filament
when current is applied to the filament circuit-
-flow through filament
-heat up filament circuit
-electrons will be boiled off
filament-
coil of wire where electrons are going to be boiled off
Thermionic emission-
boiling off of electrons at filament
focusing cup-
place on cathode where electrons are boiled off of filament & held in place
space charge/electron cloud-
collection of electrons boiled off filament in focusing cup
the lower the mA-
the lower quantity/amount of electrons boiling off the filament
as more circuit is applied to the filament, the circuit-
gets hotter
intensity/quantity of the x-ray beam is directly proportional to-
mA
exposure time-
amount of time in which beam is activated & exposure occurs
when using a breathing technique, use a _____ exposure time-
longer
want exposure time as short as possible to-
eliminate motion
2 types of motion-
voluntary & involuntary
eliminate voluntary motion-
good patient instructions
eliminate involuntary motion-
-short exposure time
-immobilization devices
mAs-
total quantity of x-rays produced at exposure
penumbra-
blur
mA directly proportional to-
beam intensity & exposure
time/exposure time directly proportional to-
quantity/intensity/exposure of x-rays produced bec it is directly proportional to electrons
mAs directly proportional to-
receptor exposure
quantum model referred to as-
mottle
causes mottle to appear on radiograph-
insufficient exposure/mA, s, or mAs
mottle-
grainy appearance in image
low exposure (low mA & short exposure time) results in-
mottle
exposure index-
when you make an exposure & a # pops up it represents the amt. of exposure to IR
exposure index ranges-
1500-1700
law of reciprocity-
states as long as product remains the same, mA & time can be altered & still produce same total exposure (mAs)
mA, s, or mAs increases-
receptor exposure (they’re directly proportional
kVp-
measure of force behind a current of electricity that causes it to flow
direction of electron flow-
when potential diff. in x-ray tube, electrons flow from C(-)–A (+) side
kVp determines-
how fast electrons will travel from cathode side to anode side
kV-
measures quality of x-rays produced at exposure
higher energy electrons result in-
higher energy x-ray photons that will be more penetrating
kVp affects-
quantity of x-ray beam bec higher energy electrons have more interactions at anode & produce more x-ray photons
higher energy electrons have-
more energy @ anode & produce more x-ray photons
2 types of x-rays produced-
Brimstrung & Characteristic
high kVp is used for-
thicker parts (chest)
w: low energy you’re going to have-
higher contrast between adjacent structures
scale of contrast refers to-
the entire image
interactions w: matter-
1.) Compton Scattering/Effect
2.) Coherent Scattering
3.) Photoelectric Effect
4.) Pairproduction
5.) Photodisintegration
6.) X-ray photon
interactions w: matter that occur in diagnostic range (3)-
1.) Compton Scattering/Effect
2.) Coherent Scattering
3.) Photoelectric Effect
compton scatter/effect-
interactions account for 99% of scatter that reaches IR
photoelectric effect-
-x-ray photon is completely absorbed & doesn’t reach IR
-results in subj. contrast in img
____ & ____ primarily affect img. quality-
compton & PE
kVp increases, what decreases-
photoelectric effect decreases & produces more Compton scattering
scatter-
-unwanted exposure
-should use a grid to reduce it
-also called fog sometimes
kVp increases, any scatter produced x-ray photons will have-
higher energy produced
if scattered photons have a higher energy-
it is more likely to penetrate patient & go straight to IR
3 ways increasing the kVp can increase receptor exposure-
1.) quantity of x-rays will also increase because of interactions at anode
2.) x-ray photons with higher energy are more likely to penetrate through patient & get to IR
3.) energy of Compton Scattering is more likely to increase/have higher energy & penetrate patient & strike IR
minimum kVp required to-
-penetrate anatomy of interest adequately
-produce desired scale of contrast
kVp that is too low will not-
penetrate anatomy & increase patient dose
higher kVp reduces-
patient dose because as kVp increases, mAs can decrease
optimal kVp-
setting will be similar, but vary among manufacturer’s processing systems
If kVp doesn’t penetrate part (too low), what will result for that?
Insufficient exposure to IR (MOTTLE IN IMAGE)
If you use a kVp that is too hot/high, what will happen to image?
Darker because it’s over-penetrating part
wide exposure latitude-
-increased kVp, wider exposure latitude
-Optimal kVp for proj. may be 100, w: range of 95-105
Narrow Exposure Latitude-
-decreased kVp, narrow exposure latitude
-Optimal kVp for proj. may be 52, w; range of 50-54
if the kVp is too penetrating-
more of the beam will penetrate the anatomy than it should, thus increasing receptor exposure
too much receptor exposure from excessive kVp-
negatively affects image quality
increasing kVp by 15% change will-
double receptor exposure
increase kVp by 15% to maintain-
RE, cut your mAs in half
kVp increases-
receptor exposure
kVp decreases-
contrast
no practical amount of mAs can compensate-
for insufficient kVp
purpose of AEC-
produce more consistent exposure & reduce repeats
optimum mA-
maximum mA setting for a given focal spot size, which doesn’t overload anodes capacity
AEC acts as-
back up timer when exposure is made
AEC location-
after the patient, but before the IR
density control setting-
-each setting represents 25% change in beam intensity
-N- means normal, could be from 1-8 & -1 to -8
mAs readout-
when mA is set & use AEC, the AEC will multiply mA by AEC time & get mAs readout
limitations of AEC (4)-
1.) anatomy must completely cover detector
2.) detector must be covered with anatomy of interest
3.) failure to collimate will result in more scatter production
4.) AEC shouldn’t be used if prosthetic/surgical device over detector
APR-
preset technical factors
APR allows tech. to-
choose exam & utilizes electronically stored technical factors
2 types of technique charts-
-fixed kVp
-variable kVp
fixed kVp-
uses optimal kVp for that body part & mAs varies depending on part thickness
variable kVp-
kVp changes with part thickness & mAs remains constant
if you change the kVp, kVp varies by-
2 for every cm of part thickness
exposure standardization-
elimination of variation as much as possible in as many as possible factors which affect optimum exposure time
exposure standardization reduces-
patient exposure
