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X-ray Imaging System (Midterms)
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Three Principal Parts of X-ray Imaging System
X-ray tube
Operating console
High-voltage generator
Operating Console
allows RT to control the
x-ray tube current
and
voltage
so useful x-ray beam is of proper quantity and quality
provides for control of line compensation, kVp, mA, and exposure time
located in an adjoining room with a protective barrier separating the two (most systems)
X-ray tube
located in the examination room
High-voltage generator
housed in an equipment cabinet positioned against a wall
always close to the x-ray tube, usually in the examination room
responsible for
increasing
the output voltage from the autotransformer to the kVp necessary for x-ray production
Radiation quantity
number
of x-rays or the
intensity
of the x-ray beam
expressed in
milligray
(mGya) or
milligray/milliampere-second
(mGya/mAs)
Radiation quality
penetrability
of the x-ray beam
expressed in
kilovolt peak
(kVp) or
half-value layer
(HVL)
Meters
provided for monitoring
kVp
,
mA
, and
exposure time
220
V power
V power that most x-ray imaging systems are designed to operate
some are
110
V or
440
V
5%
voltage provided to an x-ray unit may vary by as much as this percent
Line Compensator
measures the voltage provided to the x-ray imaging system and adjusts that voltage to precisely
220
V
Autotransformer
has a
single winding
and is designed to supply a
precise voltage
to the filament circuit and to the high-voltage circuit of the x-ray imaging system
where power supplied to the x-ray imaging system is first delivered
works on the principle of
electromagnetic induction
but is very different from the conventional transformer
can be designed to step up voltage to approximately twice the input voltage value
Primary
connections
A and A' conduct the input power to the autotransformer
Secondary
connections
C allows autotransformer to
increase
voltage
D and E allow a
decrease
in voltage
Primary voltage
voltage it
receives
operated by
autotransformer
Secondary voltage
voltage it
provides
operated by
induction device
Autotransformer
Law
same as
transformer
law
Minor
kilovolt peak Selection
"fine tunes"
represent two separate series of connections on the autotransformer
Major
kilovolt peak Selection
represent two separate series of connections on the
autotransformer
kVp
determines the
quality
of the x-ray beam
220
V Primary voltage
controllable from about
100
to
400
kVp Meter
placed across the output terminals of the autotransformer and therefore actually reads
voltage
, not kVp
Scale
of the kVp meter
registers kilovolts because of the known
multiplication factor
of the turns ratio
Pre-reading
kVp Meter
kVp meter registers, even though
no exposure
is being made and the circuit has
no current
allows the voltage to be monitored
before
an exposure
Milliamperes (mA
)
measure of x-ray tube
current
, crossing from cathode to anode
Temperature of the filament
determines the
number of electrons
emitted by the filament
Filament temperature
controlled by the
filament current
measured in
amperes
(A)
3
to
6
A
currents of
normally
operated filaments
Thermionic emission
release of
electrons
from a heated filament
Filament circuit
separate circuit that controls x-ray tube current
Connections
provide voltage for the
filament
circuit
Precision resistors
used to
reduce
this voltage to a value that corresponds to the selected milliamperage
result in fixed stations that provide tube currents of 100, 200, or 300 mA, and higher
mAs
product of x-ray tube
current
(mA) and
exposure time
(s)
also "
electrostatic charge
(C)"
mA meter
connected at the center of the
secondary
winding of the high-voltage step-up transformer
how x-ray tube current is monitored
Secondary
voltage
alternating at
60 Hz
such that the center of this winding is always at
zero
volts
Filament Transformer
"
Filament heating isolation step-down transformer
"
steps down the voltage to approximately
12
V and provides the current to
heat
the filament
Primary windings
thin copper and carry a current of
0.5 to 1 A
and approximately
150 V
Secondary
windings
thick and approximately
12 V
electric potential and carry a current of
5 to 8 A