Ch 5 The X-Ray Imaging System Flashcards
fluoroscopic couches tilt ___ to the foot side and ___ to the head side
90; 30
3 parts of the x-ray system:
x-ray tube, operating console & high-voltage generator
radiation quantity:
the number of x-rays or intensity of the x-ray beam, mGya or mGya/mAs
radiation quality:
penetrability of the beam, kVp or half-value layer (HVL)
most x-ray imaging systems operate on ___ of power
220V
voltage can vary by as much as ___
5%
line compensator:
measures the voltage provided to the x-ray imagining system and adjusts that voltage to 220V
the power supplied to the x-ray system is first delivered to the _____
autotransformer
*the autotransformer has a ____ and is designed to ___
single winding and is designed to deliver precise voltage to the filament circuit
in the autotransformer the voltage it receives (primary) and the voltage is provides (secondary) are:
directly proportional to the number of turns in the transformer
minor kilovolt peak:
“fine tunes” the selected technique
*kVp determines the:
quality of the x-ray beam
pre-reading kVp meter:
allows the voltage to be monitored before an exposure
*thermionic emission:
the release of electrons from a heated filament
x-ray tube current if controlled through:
filament circuit
in a falling load generator exposure; the result is:
begins at the maximum mA and the mA drops as the anode heats, the result is minimum exposure time
*mAs aka _____
electrostatic charge (C)
guard timer will:
terminate an exposure after a prescribed time, usually 6s
in synchronous timers the minimum exposure time is ___
1/60s
*most exposure timers are:
electronic and are controlled by a microprocessor & are accurate to milli seconds (.001s)
*mAs timers are used on:
falling load and capacitor discharge imaging systems
AEC:
automatic exposure control, measures the quantity of radiation that reaches the IR and terminates the exposure when it receives the required radiation
*high-voltage generator has 3 primary parts:
high-voltage transformer, filament transformer & rectifiers
turns ratio is the:
number of secondary windings to the number of primary windings
voltage is ____ proportinal to the number of turns
directly
current is ____ proportional to the number of turns
indirectly
the turns ratio of high-voltage transformers are:
500:1 or 1,000:1
*transformers will only operate on ___
AC
the only difference between primary and secondary wavelengths is ____
amplitude
primary voltage is ___
secondary voltage is ___
primary current is ___
secondary current is ____
V
kV
A
mA
a common wall plug is ___ Hz and ___ changing direction ____
60 Hz and AC changing direction 120 times a second
an x-ray tube is ____
DC
*rectification is:
the process of converting AC to DC
a rectifier is:
a electronic device that allows current flow in only one direction
*voltage rectification is required:
to ensure that electrons flow from x-ray tube cathode to anode only
rectification is accomplished with _____
diodes
a diode contains:
two electrodes
n-type semiconductors have:
loosely bound electrons that are relatively free to move
p-type semiconductors have:
spaces or “holes” where there are no electrons
half-wave rectification is ______; the result is ______; uses ___ diodes
the inverse voltage is removed from the supply of the x-ray tube by rectification; the result is a series of positive pulses separated by gaps; only half the AC waveform appears in the output; has 0, 1, or 2 diodes
during the positive portion of AC waveform ______; during negative portion of AC waveform ______
the rectifier allows electric current to pass; the rectifier does not conduct (no current)
full-wave rectification is ______; the output voltage is ____; exposure time is _____
the negative half of the AC waveform is reversed so the anode is always positive, current is shown during both the positive and negative phases; output voltage is positive with no gaps; exposure times halved
single-phase power results in:
a pulsating beam
three-phase power has:
multiple waveforms superimposed on each other resulting in a waveform that maintains nearly a constant high voltage
three-phase power has __ pulses per ____ sec
6; 1/60
*with 3 phase power the voltage applied across the x-ray tube is:
nearly constant, never dropping to 0 during exposure
SCR’s:
silicon-controlled rectifiers
*full wave rectification or high-frequency voltage generation is used in:
almost all stationary x-ray imaging systems
*during capacitor discharge the voltage:
falls approximately 1kV/mAs
single-phase power has ___ voltage ripple
100%, voltage varies from 0 to the maximum value
3 phase 6 pulse power has ___ voltage ripple
14%, the voltage never falls below 86% of the maximum value
3 phase 12 pulse power has ___ voltage ripple
4%, the voltage supplied never falls below 96% the maximum value
high-frequency power generators have ___ voltage ripple
1%, they have greater radiation quality and quantity
*less voltage ripple results in:
greater radiation quality and quantity
x-rays are performed with:
3 phase power
fluoroscopy is performed with:
single-phase power
transformers and high-voltage generators power is measured in ___
kilo watts (kW)
high-voltage generators provide power to the x-ray tube in 3 ways:
single-phase power, 3 phase power & high-frequency power
X-ray systems usually operate on voltages of ______ and currents of ______
25-150kVp, 100-1200mA
when using the fluoro table for fluoro not for x-ray:
move the bucky to the foot of the table
3 phase generators are found:
on the wall
photodiodes are:
below the IR, shuts off based on density
ionization chambers are:
above the IR
the back up timer is always:
1.5 times longer than the needed exposure time
electrons travel from ____ to ____ in the tube
cathode to anode
peak x ____ = average voltage
peak x .707 = average voltage (keV)
average x ____ = peak voltage
average x 1.41 = peak voltage (kVp)
the autotransformer is found:
in the control console
the control console is aka:
primary circuit
high-voltage section is aka:
secondary circuit
going from the primary to the secondary circuit there is a ____ in voltage because there is a _____ in current
step down, step up
