86. Origin of X-rayrename
yaboiemil's version from 2016-02-06 19:16
Section1. Roentgen invented x-rays
2. X-rays are PHOTONS of very high energy. They are electromagnetic radiation
specifically from ATOMIC ELECTRON SHELLS.
Passage of X-rays through the body3. X-rays are created from a beam of electrons accelerated between the hot cathode
(a.k.a the filament) and the cold anode (tungsten).
4. The electrons are suddenly decelerated by the anode, and the result is that a
small part of the liberated energy is transformed into high-energy photons.
5. Low energy photons are absorbed by the primary filter (before they reach patient)
6. These high energy photons pass through the body, being unequally attenuated by
the tissue and the bones. This mean that different numbers of high-energy photons
reach the imaging area (fluorescent screen or photographic film), creating varying
shades of grey.
7. Before they reach the film, the photons are filtered one more time through a Bucky
Grid (a grid of lead) to remove any x-rays not travelling in a straight line.
Radiography/Fluoroscopy8. Radiography uses photography film to create a stable image
9. Fluoroscopy uses a fluorescent screen to create a real-time image
Importance of Collimators10. X-rays that are not going straight towards the screen will cause blurring. Therefore
a grid (Bucky grid after patient) is used to catch any deflected/slanted x-rays before
they reach the film/screen.
11. The primary grid is used to catch any low-energy photons that would not aid in imaging.
Image blur and how to reduce it12. Image blur is caused for many reasons:
|Reason for Blur||How to diminish|
|Movement of Patient||Shorter exposure time (but more radiation needed)|
|Geometric Penumbra||Diminish focus area on anode (cool it more), Shorter distance btwn patient and film|
|Diffraction and Scattering||Buckey Grid should absorb most|
|Light emitted from luminescent foil attached to film||???|
Contrast Agents13. Soft tissues can be almost indistinguishable on an x-ray. Contrast agents are therefore used to
visualize spaces (e.g. vessels). There are POSITIVE and NEGATIVE contrasting agents:
|Positive||BaSO4, substances with heavy atoms|