X Ray Lecture

8/2/2019 X Ray Lecture

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X-Rays and Imaging


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The discovery of X-rays

100 years ago, Wilhelm Conrad

Roentgen, a German scientist,

discovered x-rays...


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Roentgens apparatus for

studying x-rays . He accidentally discovered X-rays in November

1895 while studying cathode rays in a low

pressure gas discharge tube. Roentgen placed various objects between the

tube and the screen, and the screen stillglowed. Finally, he put his hand in front of the

tube, and saw the silhouette of his bonesprojected onto the fluorescent screen.Immediately after discovering X-raysthemselves, he had discovered their mostbeneficial application.


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X RAYS

X rays are electromagnetic radiations having low wavelengthfrom about 10-8 m to about 10-11 m. Wavelengths of

Diagnostic x-rays: 1 to 0.1 and that ofTherapeutic x raysare 0.1 to 10-4 . They propagate with a speed of light and are unaffected by

electrical and magnetic fields.

To measure the energy of an X-ray photon we need the X-rayto give all its energy to some kind of detector. There are several classes of these detectors.They include: Proportional Counters

Microchannel PlatesSemiconductor DetectorsScintillatorsPhosphorsNEADsSingle Photon Calorimeters
http://imagine.gsfc.nasa.gov/docs/science/how_l2/proportional.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/microchannels.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/semiconductors.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_scintillators.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/phosphors.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/neads.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/calorimeters.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/calorimeters.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/neads.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/phosphors.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_scintillators.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/semiconductors.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/microchannels.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/microchannels.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/microchannels.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/proportional.htmlhttp://imagine.gsfc.nasa.gov/docs/science/how_l2/proportional.html


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Characteristic radiation

The production of"characteristic" X-rayswas first observed in1909 by Charles G.

Barkla and C.A. Sadler. If the projectile

electron interacts withan inner-shell electronof the target atomrather than an outer-shell electron,characteristic x-radiation can be

produced.
http://www.nobel.se/physics/laureates/1917/barkla-bio.htmlhttp://www.nobel.se/physics/laureates/1917/barkla-bio.htmlhttp://www.nobel.se/physics/laureates/1917/barkla-bio.htmlhttp://www.nobel.se/physics/laureates/1917/barkla-bio.html


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Bremsstrahlung Radiation As the projectile electron

passes by the nucleus, itslows down, changes itscourse, and leaves withreduced kinetic energy ina different direction.

These types of X-rays arecalled Bremsstrahlung X-rays. Heavier elements(like tungsten) are best.

In this type of

interaction, the kineticenergy of theprojectileelectron is converted intoelectromagnetic energy.


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Properties of x Rays

They are not detected by human senses (cannot beseen, heard, felt, etc.).

They travel in straight lines at the speed of light. Their paths cannot be changed by electrical or magnetic

fields. They pass through matter. They have enough energy to ionize matter and can

damage or destroy living cells. There are three distinct properties of X-rays that can be

used practically: (i) Absorption (ii) Fluorescence (iii) Diffraction


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Application of x-rays

Nondestructive testing Medical

Microcardiograohy

Skiagraphs

Diagnostic x rays

Lithography

Angiography

Abdominal studies GIT studies

Quantum mechanics


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Advantages & Disadvantages

Advantages X-rays are relatively inexpensive compared to CT scans

and other imaging studies. The equipment is readily available in most hospitals and

many doctors' offices. The examinations are painless and quick.

This destructive power is used in X-ray therapy todestroy diseased cells.Disadvantages X-rays involve exposure to radiation, which has a

cumulative damaging effect. Plain X-rays often do not provide adequate details aboutinternal organs, blood vessels, and other soft-tissue

structures. One of the dangers in the use of X rays is that they can

destroy living tissue and can cause severe skin burns on

human flesh exposed for too long a time.


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Production of x-rays


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X rays are produced in a specially constructedglass tube which basically comprise 1. A source for the production of X rays 2. A energy source to accelerate the electrons 3. A free electron path 4. A means of focusing the electron beam 5. A device to stop the electrons.


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X-ray tubes

An X-ray tube is a vacuum tube that produces X-rays. The essential components of an X-ray tube are anairtight vessel, usually of glass, and two electrodes

sealed into it.Common X-ray Tube Terminology Focal Spot Size mAs kVp Beam Coverage Duty Cycle

The tube current and exposure time affect the dose andtherefore the darkness of the image.The two processesare:

Arcing process Gettering process
http://en.wikipedia.org/wiki/Vacuum_tubehttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/Vacuum_tube


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Stationary tubes &Rotating tube

Stationary and rotating anode tubes are the twotypes of x ray tubes:

Stationary tubes: It is vacuum diode in whichthe electrons are generated by thermoionicemission from the filament of the tube.

Rotating tube:The rotating anode tube is used

in X-ray diagnostics in numerous ways. a largedisk-shaped tungsten anode is rotated at highspeed (3000 to 9000 revolutions per minute).

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X Ray Lecture