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BMET X-ray.pdf
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4. The inner-shell electron is tightly bound to the nucleus. Thus, K-shell
electrons or inner-shell electrons have a higher binding energy than
outer-shell electrons. Tungsten is a large atom with 74 orbiting
electrons. As atomic complexity increases, the electrons in any given
shell are more tightly bound than in a less complex atom.
When the projectile electron ionizes a target atom by removing a K-
shell electron, a temporary electron void is produced in the K-shell. This
is a highly unnatural state for the target atom and is corrected by an
outer-shell electron falling into the void in the K shell. Tungsten, for
example, has electrons in shells out to the P shell, and when a K-shell
electron is ionized, its position can be filled with electrons from any of
the outer shells. The transition of an orbital electron from an outer shell
to an inner shell is accompanied by the emission of an X-ray.
X-ray Basics
5.
6.
7. The production of heat and characteristic X-rays involves interactions between the
projectile electrons and the electrons of target atoms. Another type of interaction in
which the projectile electron can lose its kinetic energy is an interaction with the nucleus
of a target atom. In this type of interaction the kinetic energy of the projectile electron is
converted into electromagnetic energy.
A projectile electron that completely avoids the orbital electrons as it passes through a
target atom may come sufficiently close to the nucleus of the atom to come under its
influence. Because the electron is negatively charged and the nucleus is positively
charged, there is an electrostatic force of attraction between them. The closer the
projectile electron gets to the nucleus, the more it is influenced by the electrostatic field
of the nucleus. This field is very strong because the nucleus contains many protons and
the distance between the nucleus and the projectile electron is very small. As the
projectile electron passes by the nucleus, it slows down, changes its course, and leaves
with reduced kinetic energy in a different direction. These types of X-rays are called
Bremsstrahlung X-rays. Bremsstrahlung is a German word for slowing down or braking.
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17. No feedback of generated KV, mA/
open loop
High Skin Dose
Inferior image quality
21. DC
AC
DC
AC
DC
AC
Line Input
EMI Filter
Inverter High Voltage
Transformer
400 V ยป UDC = 566 V
IGBT: fres
= 30 - 100 kHz
U T
= 40 - 150 kV
I T
= 0,1 - 1000 mA
P Puls = 4 W - 100 kW
P 60s ยฃ 40 kW
P 10min ยฃ 10 kW
U Tube
ITube
IF
Tube Rotating Anode
Control
fan = 4 - 300 Hz IGBT
S = 10 - 20 kVA
PWM
fres
= 20 - 100 kHz
PH = 100 - 150 W
IGBT
3 ยป
UDC
77. ๏จ A Crossed grid has two grids sandwiched together
with the result that the strips are usually both
parallel to and at right angles to the long
dimension of the grid.
78. ๏จ A focused grid is one in which the lead strips
are tilted progressively as they move away
from center. Lines through each of these strips
would converge at a point known as the grid
focus.
79.
80.
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82. Grid Primary Transmission
The useful X-Rays which pass straight from
the X-Ray tube to the film are known as
Primary transmission is basically the
percentage of primary X-Rays which pass
through the grid and hit the film, and is thus
measured by using the same apparatus with
and without the grid in place.
83.
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89. Grid cutoff is an undesirable absorption of
primary x-ray beams by grid strips, which
prevents the useful x-rays from reaching the
image receptor. It is caused by improper
grid positioning and most often occurs with
parallel grids.
90.
91.
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93. ๏จ The quantity of scattered radiation in an x-ray beam reaching a
receptor can be reduced by separating the patient's body and
receptor surface, as shown below. This separation is known as
an air gap. Scattered radiation leaving a patient's body is more
divergent than the primary x-ray beam. Therefore, scattered
radiation spreads out of the primary beam area. The reduction of
scattered radiation in proportion to primary radiation increases
with air-gap distance. Several factors must be considered when
using this method of scatter reduction. Patient exposure is increased
because of the inverse-square effect. The use of an air gap
introduces magnification. Therefore, a larger receptor size is
required to obtain the same patient area coverage. If the air gap is
obtained by increasing the tube-to-receptor distance, the x-ray
equipment must be operated at a higher output to obtain adequate
receptor exposure.
94.
95. ๏จ A bucky is typically used for table or wall
mounted x-raysystems and holds the x-
ray cassette and grid. A bucky, is a device
found underneath the exam table, a drawer like
device that the cassette and grid is slid into
before shooting x-ray.
113. Oil in x-ray tube and HV Transformer
for cooling and Insulation
That is stable at high temperatures and has
excellent electrical insulating properties Its
functions are
To insulate,
suppress corona ,
Supress arcing, and to serve as a coolant.
116. An AEC system uses a physically thin
radiation
An AEC system uses a physically thin radiation ionization
detector "AEC detector" which is positioned between the
patient being x-rayed and the x-ray film cassette. X-rays
passing through the patient also pass through this "AEC
detector" before they strike the x-ray film.
A weak ionization signal from the AEC detector is
integrated as a ramp shaped voltage waveform. This ramp
signal rises until it matches a pre-set threshold. At this
point the x-ray exposure is terminated. AEC devices are
calibrated to ensure that similar exams have linearity in
exam densities. This is due to the fact that a milliamperage
station is no longer selected and instead relies upon the
ionization within the selected chambers
