Transcript X-ray - Pharos University in Alexandria

X-Ray
Technology
By:
PROF. Dr. Moustafa Moustafa Mohamed
Faculty of Allied Medical Science
Pharos University in Alexandria
Introduction to Medical Imaging
NON Invasive
Uses of medical imaging
Obtain information about internal body
organs or the skeleton to determine a
patient’s physical
Imaging Modalities:
* X-ray (plan , Dental, Panorama, Mammo, Angio, …)
* C.T
* Ultrasound
* MRI
* Gamma Camera
* PET SPECT
Medical Image
• Generated by means of radiation
– electromagnetic (EM)
– ultrasound
– electrons
• Displayed for interpretation on
– Film
– photograph or
– computer display monitor
Types of image
1) Projections
2) Dimensional
3D & 4D
3) Slices
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•
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Trans axial - plane normal to a vector from head to toe.
Coronal - plane normal to a vector from front to back
Sagittal - plane normal to a vector from left to right.
Oblique - a slice that is not (at least approximately) one of the above.
Inside the atom
The NUCLEUS is made up
of PROTONS and NEUTRONS
PROTONS
have a positive charge.
NEUTRONS
have no electrical charge.
Inside the atom
ELECTRONS
have a negative charge.
The number of electrons in
an atom usually matches
the number of protons,
making the atom electrical
neutral.
Exactly what is an X – Ray?
• An x – ray is a form of radiation, that is
invisible
• Electromagnetic waves of short wavelength
with wavelengths between about 0.02 Å and
100 Å (1Å = 10‐10 meters).
• Very high energy
• Basically gives an “inside view”
• The energy of X‐rays, like all electromagnetic radiation, is inversely
proportional to their wavelength as given by the Einstein equation:
E = hν = hc/λ
where E = energy
h = Planck's constant, 6.62517 x 10‐27 erg.sec
ν = frequency
c = velocity of light = 2.99793 x 1010 cm/sec
λ = wavelength
Since X‐rays have a smaller wavelength than visible light, they have higher
energy.
• X‐rays can penetrate matter more easily than can visible light.
• Their ability to penetrate matter depends on the density of the matter
• X‐rays provide a powerful tool in medicine for mapping internal structures
of the human body (bones have higher density than tissue,
• and thus are harder for X‐rays to penetrate, fractures in bones have a
different density than the bone, thus fractures can be seen in X‐ray
pictures).
History
• In 1895 Wilhelm Roentgen, German Physicist, was
studying high voltage discharges in vacuum tubes,
then he noticed fluorescence of barium
platinocyanide screen lying several feet from tube
end.
• These rays where named
– X-rays--invisible penetrating radiation,
– X represent unknown in mathematics
William Conrad
Roentgen
• Wilhelm Conrad
Rontgen Won the first
Nobel Peace Prize for
physics in 1901
Early X- Ray Images
Right: Mrs. Röntgen's hand, the first X-ray
In
X-ray of Bertha Roentgen's
Hand
Types and uses of X-ray
Types and uses of X-ray
Diagnostic
Still picture
Continuous picture
Therapeutic
Still picture scan tomography
Various uses of the X - Ray
Detect malformations in bones
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Treats disorders such as various cancers
Security purposes
Alternatives for cancer detection
Annual physical exams
Pre-surgery evaluations
Electromagnetic Spectrum
Production of X-rays (1)
• X-rays are produced when rapidly moving electrons that have
been accelerated through a potential difference of order 1 kV
to 1 MV strikes a metal target.
Evacuated
glass tube
Target
Filament
Production of X-rays (2)
• Electrons from a hot element are accelerated onto a
target anode.
• When the electrons are suddenly decelerated on
impact, some of the kinetic energy is converted into
EM energy, as X-rays.
• Less than 1 % of the energy supplied is converted
into X-radiation during this process. The rest is
converted into the internal energy of the target.
Properties of X-rays
• X-rays travel in straight lines.
• X-rays cannot be deflected by electric field or
magnetic field.
• X-rays have a high penetrating power.
• Photographic film is blackened by X-rays.
• Fluorescent materials glow when X-rays are
directed at them.
• Photoelectric emission can be produced by X-rays.
• Ionization of a gas results when an X-ray beam is
passed through it.
X-ray Spectra (1)
• Using crystal as a wavelength selector, the intensity of
different wavelengths of X-rays can be measured.
X-ray Spectra (2)
• The graph shows the following features.
– A continuous background of X-radiation in which the
intensity varies smoothly with wavelength. The
background intensity reaches a maximum value as the
wavelength increases, then the intensity falls at greater
wavelengths.
– Minimum wavelength which depends on the tube voltage.
The higher the voltage the smaller the value of the
minimum wavelength.
– Sharp peaks of intensity occur at wavelengths unaffected
by change of tube voltage.
Minimum wavelength in the X-ray Spectra
• When an electron hits the target its entire kinetic
energy is converted into a photon.
• The work done on each electron when it is
accelerated onto the anode is eV.
• Hence hf = eV and the maximum frequency
f max
eV

h
Therefore,
min
hc

eV
Continuous (Bremsstrahlung) X-Ray
Production
Characteristic X-ray Spectra
• Different target materials give different wavelengths
for the peaks in the X-ray spectra.
• The peaks are due to electrons knock out inner-shell
electrons from target atoms.
• When these inner-shell vacancies are refilled by free
electrons, X-ray photons are emitted.
• The peaks for any target element define its
characteristic X-ray spectrum.
Characteristic X-Ray Production
Anode Heating
• This occurs when projectile electrons excite an atoms outer
shell electrons but do not eject them from the atom.
• For most X-ray machines, about 99% of the projectile electrons
lose energy this way.
• Infrared EM radiation (observed as heat energy) is produced
when the excited electrons relax and fall back into the original
energy level
• The amount of anode heating can be reduced by increasing
the energy of the projectile electrons so that they cause more
ionization rather than excitation.
Uses of X-rays
•
In medicine
To diagnose illness and for
treatment.
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In industry
To locate cracks in metals.
X-ray crystallography
To explore the structure of
materials.
Conditions for x ray production
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Separation of electrons
Production of high speed electrons
Focusing of electrons
Sopping of high speed electrons in target
COLD GAS CATHODE TUBE
• glass tube with partial vacuum with small
amount of gas,
• two electrodes, one negative (cathode)
• & another positive (Anode).
Hot Cathode Diode tube
• In 1913 W.D. Coolidge invented new type of
tube on Edison principal called
• Hot Cathode Diode tube.
• It made possible the control of mA and kV
independently and there by controlling the
quantity and quality of x-rays.
PARTS OF X RAY TUBE
• Glass Tube
• Cathode
– Filament
– Supporting wires
– Focusing cup
• Anode
– Stationary
– Rotating
Main components of x-ray unit
are:
•·
X-ray tube
•·
X-ray electrical power generator
•·
Control unit
•·
Film or digital system
In addition to:
•·
Table unit
•·
Bucky film tray and grid system
•·
Suspension system
Introduction
X-ray image is a shadow picture produced by x-rays
emitted from a point source
Image contrast is (((proportion
with)))
1- Mass attenuation coefficient of the
imaged part
2- Density
3- Thickness
Principles of X-ray tube
Battery
Main components of a modern xray tube
• A heated filament releases electrons that are accelerated across a
high voltage onto a target.
• The stream of accelerated electrons is referred to as the tube
current.
• X rays are produced as the electrons interact in the target.
• The x rays emerge from the target in all directions but are restricted
by collimators to form a useful beam of x rays.
• A vacuum is maintained inside the glass envelope of the x-ray tube
to prevent the electrons from interacting with gas molecules.
X-Ray Tubes
X‐ray Absorption
• When the x‐rays hit a sample, the oscillating electric field of the
electromagnetic radiation interacts with the electrons bound in an atom.
• Either the radiation will be scattered by these electrons, or absorbed and
excite the electrons.
• A narrow parallel monochromatic x‐ray beam of intensity I0 passing
through a sample of thickness x will get a reduced intensity I according
to the expression:
• I = I0 e‐μ x or Ln (I0 /I) = μ x
• where μ is the linear absorption coefficient, which depends on the types
of atoms and the density ρ of the material.
How X‐ray Lose Energy within
Matter?
• • Photoelectric effect
• X‐ray interacts with an electron by giving all its
energy to the electron near the nucleus.
• It is the most probable way of losing energy
• X‐ray energy must be greater than or equal to
the electron binding energy to the nucleus
• Compton effect
• X‐ray (of energy at least 511 KeV)
colloids with a loosely bound outer
electron.
• The electron receive part of the energy
and the rest goes in different direction
as a scattered photon radiations each
of 511 KeV
Pair production
• X‐ray (of energy at least 1.02 MeV)
penetrates the intense electric field of
nucleus. It is converted to an electron and a
positron each of 511 KeV.
• The positron will then colloids with one
electron and results in the production of two
annihilation
Bragg's Law
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According to Bragg, X‐ray diffraction can be viewed as a process similar to
reflection from planes of atoms in the crystal.
In Bragg's construct, the planes in the crystal are exposed to a radiation source at a
glancing angle θ and X rays are scattered with an angle of reflection also equal to
θ. The incident and diffracted rays are in the same plane as the normal to the
crystal planes.
Bragg reasoned that constructive interference would occur only when the path
length difference between rays scattered from parallel crystal planes would be an
integral number of wavelengths of the radiation.
When the crystal planes are separated by a distance d, the path length difference
would be 2d sin θ. Thus, for constructive interference to occur Bragg’s law must be
fulfilled.
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For constructive interference: nλ = 2a
From trigonometry:
a = d sin θ
or
2a = 2 d sin θ
thus,
nλ = 2d sin θ
What it says is that if we know the wavelength ,λ , of the X‐rays going in to
the crystal, and we can measure the angle θ of the diffracted X‐rays
coming out of the crystal, then we know the spacing (referred to as
d‐spacing) between the atomic planes.
d = nλ /2 sin θ
Checkpoint Question 1
What are x-rays?
• X-rays are high-energy waves that travel at the
speed of light. X-rays can penetrate fairly
dense objects, such as the human body. They
cannot be seen, heard, felt, tasted, or smelled.
Checkpoint Question 2
• Why is it important to schedule a barium
enema before an upper GI or barium swallow?
Answer
• Barium enemas involve filling only the large intestine
with barium. Because the large intestine is the last
part of the GI tract, this barium can be eliminated
more quickly. If an upper GI examination is
performed first, it may be days later before barium
can be eliminated, thus delaying other examinations.
Radiation Safety
• X-rays have potential to cause cellular or
genetic damage
• At highest risk
– Pregnant women
– Children
– Reproductive organs of adults
1.
2.
3.
4.
5.
Radiation Safety Procedures
for Patients
Reduce exposure amounts as much as
possible
Avoid unnecessary examinations
Limit area of body exposed
Shield sensitive body parts
Evaluate potential pregnancy status
Radiation Safety Procedures
for Clinical Staff
1.
2.
3.
4.
5.
6.
Limit amount of time exposed to x-rays
Stay far away from x-rays
Use available shielding
Avoid holding patients during exposure
Wear individual dosimeters
Ensure proper working condition of equipment
Diagnostic Procedures
• Routine radiographic examinations
• Named for part of body involved
• Performed for viewing bone structure or
abnormalities
Mammography
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Specialized x-ray examination of the breast
Screening tool for breast cancer
Breast compressed in specialized device
Has become vital adjunct to biopsy
procedures
Contrast Media Examinations
• Radiographic contrast media helps
differentiate between body structures
• Used to evaluate structure and function
Contrast Media
• Introduced into body in several ways
– Swallowing
– Intravenously
– Through a catheter
• Medical assistant must ensure that patients
understand preparation instructions
Checkpoint Question 3
• How do contrast media help in
differentiating between body structures?
Answer
• Contrast media help differentiate between
body structures by artificially changing the
absorption rate of a particular structure so
that it can be seen clearly instead of blending
in with adjacent structures. For example,
barium sulfate absorbs radiation and shows
up as white areas on a radiograph.
Fluoroscopy
• Use x-rays to observe movement within the
body
– Barium sulfate through the digestive tract
– Iodinated compounds showing the beating of the
heart
Computed Tomography
(CT, CAT scan)
• Tomography
– X-ray tube and film move in relation to one
another, blurring all structures except those in
focal plane.
• CT uses x-rays from a tube circling the patient,
analyzed by computers to create crosssectional images
Checkpoint Question 4
• How does fluoroscopy differ from
computed tomography and sonography?
Answer
• Fluoroscopy uses x-rays to show movement
within the body. CT uses a combination of xrays and computers to create cross-sectional
images of the body. Sonography uses highfrequency sound waves to create crosssectional still or real-time (motion) images of
the body.
Radiation Therapy
• High-energy radiation is used to destroy
cancer cells
• Treatments must be planned carefully by
radiologist
• Most patients have some side effects
Transfer of Radiographic Information
• Radiographic images remain part of permanent
record
• Digital images saved on disk
• X-ray films belong to site where study was
performed
• Examining physician or radiologist writes summary
of the examination
• Medical assistant obtains patient’s permission to
have summary sent to office physician
Teleradiology
• Use of computed imaging and information
systems
• Provides new benefits in medicine
• Digital images can be transmitted via
telephone lines to distant locations
• Allows for consultation with experts on
difficult cases
Dental X- Rays
• What is the purpose of dental x- rays
• What does the assistant giving the x- ray look
for
• What is the educational requirements of the
person giving the x- ray
• Specific shots that are taken when in the
“chair”
Purpose of dental x - rays
• To help the dentist reach a
correct diagnosis.
• Help to provide the patient with
proper care and treatment.
What is found through x – rays?
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Tooth Decay
Periodontal disease
Extra Teeth
Bone cancer (cysts)
Osteoporosis
Root fragments( configuration)
Abscesses of the teeth or gums
Tooth position
Tatar below the gum line
Jaw joint irregularities
Facial bone composition
Reported problems
• Table systems
- mechanical system for positioning tabletops
-Wires and cables may break ---- tabletop to jam
• Control unit
-Control levers jam (MA, KV, Time, …)
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Collimator (Levers)
Light Localizer
Tube
PCB Control
Mechanical jam of film tray
Collimator loss from its x-ray tube
****** LOSS X-RAY TUBE SUSPENSION ******
Purchase Considerations
Tube
(focal spot of the tube determine the resolution of images)
Generator
(High frequency generator needs less space and smaller HV cables)
Table
(Fixed, floating top, tilting, or elevating which is suitable for
traumatic and emergency patients).
Digital radiography
Image quality, storage space,
Digital Imaging and Communication in Medicine (DICOM),
remote control,