3. Terminologies
Radiology is a specialized field of medicine.
Radiography is the science of using radiation to
provide images of the tissues, organs, bones, and
vessels that comprise the human body.
Radiologists, physicians who have had special training in
interpreting diagnostic images, read or diagnose these
images.
4. X-Ray
In 1895 Rontgen discovered unknown
type of radiation called X-Ray.
They are electromagnetic waves (1)
with high frequency(2), high energy(3)
and short wavelength(4).
7. Interactions producing X-rays
X-rays are produced in the X-ray tube by two
interactive processes between incoming
electrons and the atoms of the target:
1. Characteristic radiation
2. Bremsstrahlung
9. Interactions between incoming electrons and the nucleus of the
atom (Bremsstrahlung X-ray production)
This interaction process occurs when
the incoming electron from the
filament with its small negative
charge) and large kinetic energy is
deflected by a second charged mass
(the nucleus of the tungsten atom
which has a mass many thousands of
times greater than the mass of the
incoming electron, and a much greater
(positive) charge also)
11. X-Ray Production
Bremsstrahlung (braking/deceleration) x-rays are produced when a
projectile electron is slowed by the nuclear field of a target atom
nucleus
In the diagnostic range, most x-rays are bremsstrahlung x-rays
Characteristic x-rays are emitted when an outer-shell electron fills an
inner-shell void
This type of x-radiation is called characteristic because it is
characteristic of the target element
Approximately 99% of the kinetic energy of projectile electrons is
converted to heat (Anode heat)
12. Quantity and Quality of X-ray Beam
General shape of an emission spectrum is always the
same, but its relative position along the energy axis
can change
The farther to the right a spectrum is, the higher the
effective energy or quality of the x-ray beam
The larger the area under the curve, the higher is the
x-ray intensity or quantity
13. Effect of mA and mAs
A change in mA or mAs results in a proportional change in the amplitude of the x-ray
emission spectrum at all energies
(Tube current)
14. Effect of kVp (Voltage between Cathode& Target )
As kVp is raised, area under curve increases by approximating the square of the
factor by which kVp was increased
Accordingly, x-ray quantity increases with the square of this factor
Change in kVp affects both amplitude and position of x-ray emission spectrum
In diagnostic range, 15% increase in kVp is equivalent to doubling mAs
15. Effect of Added Filtration
Adding filtration to the useful x-
ray beam reduces x-ray beam
intensity while increasing the
average energy .
The result of added filtration is
an increase in the average
energy of the x-ray beam with
an accompanying reduction in
x-ray quantity .
16. Effect of Target Material ………heavy metal
The atomic number of the target
affects both the number (quantity)
and the effective energy (quality) of
x-rays
As the atomic number of the
target material increases, the
efficiency of the production of
bremsstrahlung radiation
increases, and high-energy x-rays
increase in number to a greater
extent than low-energy x-rays.
17. Effect of Voltage Waveform …
Both quantity and quality decrease by ripples
Because of reduced ripple, operation with three-phase power or
high frequency is equivalent to an approximate 12% Increase in
kVp, or almost a doubling of mAs over single phase power.
20. Half-Value Layer (HVL)….How to describe the quality of x-ray
beam (how this beam can penetrate inside the body)
In radiography, quality(energy of x-ray penetration) of x-
rays is measured by the HVL
Exponential
decrease
21. X-Ray Exponential Attenuation
Total reduction in number of x-rays remaining in x-ray
beam after penetration through a given thickness of
tissue is called attenuation
When broad beam of x-rays is incident on any tissue,
some x-rays are absorbed, and some are scattered
Attenuation is the combined effect of both absorption
and scattering
Tissue
22.
23.
24. X-Ray Interaction with Matter
Coherent scattering (energy < 10 keV)
Compton scattering
Photoelectric effect
Pair production (energy > 1.02 MeV)
Relevant to x-ray imaging
25. Coherent scattering (energy < 10 keV) Pair production (energy > 1.02 MeV)
Two Interactions not relevant to X-Ray imaging
30. The higher the energy of the X-
ray, the more penetrating it is,
and vice versa.
Also, the higher the atomic
number of the element, the less
the ability of X-rays to penetrate,
and then the absorption
increased.
Also, the density and thickness
determine the ability of the rays
to penetrate, the more they
increase, penetrating X-rays are
less. This is why lead is used as
a shield against X-rays because
it has a large atomic number.
