1 / 42

x-ray interaction with matter human biology

IMAGE CREATION. ATOMSINTERACTION WITH

oshin
Télécharger la présentation

x-ray interaction with matter human biology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. X-Ray Interaction with Matter & Human Biology

    4. Patient Interactions **Photoelectric** Classic Coherent Scatter **Compton Scattering** Pair Production Photodisintegration

    9. Coherent Scattering The wavelength is equal to the incident x-ray or equal energy. The only difference is the direction of travel Energy in = Energy out - Only changes is direction

    11. Compton Effect or Compton Scattering Occurs throughout the diagnostic imaging range The incident x-ray interacts with the outer electron shell on an atom of matter, removing it. It not only causes ionization but scatters the incident x-ray causing a reductions in energy and the change of direction.

    12. Compton scatter A fairly high energy (high kVp) x-ray photon ejects an outer shell electron. Though the x-ray photon is deflected with somewhat reduced energy (modified scatter), it retains most of its original energy and exits the body as an energetic scattered photon. A Compton e- is also released Since the scattered photon exits the body, it does not pose a radiation hazard to the patient. It can, however, contribute to film fog and pose a radiation hazard to personnel (as in fluoroscopic procedures).

    15. Compton scatter Both the scattered x-ray and the Compton electron have enough energy to cause more ionization before loosing all their energy In the end the scattered photon is absorbed photoelectrically

    16. Compton Effect The Compton electron looses all of its kinetic energy by ionization and excitation and drops into a vacancy in an electron shell previously created by some other ionizing event The probability of Compton effect increases as photon energy increases, however the atomic number does not affect the chances of the Compton effect

    17. Compton Scatter Compton is just as likely to occur with soft tissue as bone. Compton can occur with any given photon in any tissue Compton is very important in Radiography, but not in a good way. Scattered photons provides no useful diagnostic information

    18. Compton Effect Scattered radiation produces a uniform optical density on the radiograph that reduces image contrast Scattered radiation from Compton contributes to the majority of technologists exposure, especially during fluoroscopy STAY AWAY FROM YOUR PATIENT !

    19. Scatter from the Patientduring Fluoroscopy

    20. ISOEXPOSURE CURVES

    21. Photoelectric Effect or Absorption Inner-shell ionization The photon is not scattered it is totally absorbed The e- removed from the atom of matter is called a photoelectron, with an energy level equal to the difference between the incident photon and the e- binding energy.

    22. Binding Energy is very important Table 10-2

    28. Photodisintegration

    29. PHOTOELECTRIC ABSORBTION IS WHAT GIVES US THE CONTRAST ON THE FILM

    31. Compton scatter Contributes to no useful information Is independent of the atomic number of tissue. The probability of Compton is the same for bone atoms and for soft tissue atoms The probability for Compton is more dependent on kVp or x-ray energy

    32. Compton Scatter Results in image fog by optical densities not representing diagnostic information Photon are Photons IR is does not know the difference

    33. Photoelectric Absorption Provides information to the IR because photons do not reach the IR This represents anatomic structures with high x-ray absorption characteristics; radiopaque structures; tissue with high atomic number; or tissue with high mass density

    34. Attenuation – The total reduction in the # of photons remaining in an x-ray beam after penetration through tissue Absorption = x-ray disappears (Photoelectric, Pair production & Photodisintegration) Scattering = partially absorbed, x-ray emerges from the interaction traveling in a different direction (sometimes with less energy) Absorption + Scattering = Attenuation

    35. 3 Types of x-rays are important for IMAGE FORMATION DIFFERENTIAL ABSORPTION = the difference between those x-rays absorbed and those transmitted to the IR Compton scatter (no useful information) Photoelectric absorption (produces the light areas on the image) Transmitted x-rays (produces the grey/dark areas on the image)

    38. Differential Absorption The difference in x-ray interactions Fundamental for image formation Occurs because of Compton Scattering, Photoelectric absorption, and X-ray transmission

    39. Differential Absorption

    40. Compton vs. Photoelectric Below 60 kVp Photoelectric absorption is predominant above 60 kVp Compton scatter begins to increase. Dependent on the tissue attenuation properties Table 10-13

    41. Differential absorption factors High atomic number = larger atoms Mass Density = how tightly the atoms of tissue are packed Z # for air and soft tissue are about the same the OD changes are due to mass density difference Table 12–3 & 12-5

    42. Radiation Protection Producing high-quality radiographs require careful technique selection, reducing kVp improves differential absorption and image contrast However, patient dose is increased because more photons are absorbed by the body

More Related