Patient Interactions

1. Patient Interactions • Photoelectric • Classic Coherent Scatter • Compton Scattering • Pair Production • Photodisintegration

3. Interaction in The body begin at the atomic level Atoms Molecules Cells Tissues Organ structures

4. X-ray photons can change cells

5. Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous to living tissue. 1913

6. EM Interactions with Matter • General interactions with matter include • scatter (w or w/o partial absorption) • absorption (full attenuation)

7. No interaction: X-ray passes completely and get to film Complete absorption: no x-rays get to film Partial absorption with scatter Interactions of X-rays with matter

8. Photoelectric effect • Low energy (low kVp) x-ray photon ejects inner shell electron (energy absorbed) • Leaving an orbital vacancy. As vacancy is filled a photon is produced • More likely to occur in absorbers of high atomic number (eg, bone, positive contrast media) • Contributes significantly to patient dose, • As all the photon energy is absorbed by the patient (and for the latter reason, is responsible for the production of short-scale contrast).

10. CASCADE

11. Photoelectric – Absorption

12. PHOTOELECTRIC ABSORBTION IN THE PATIENT (CASCADE OF ELECTRONS)

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

14. 8 p+ + 8e- = neutral atom CLASSICAL SCATTER IN PATIENT INCOMING PHOTONS FROM TUBE Pass by the ELECTRONS IN THE PATIENT Do not interact with e– Causes them to VIBRATE – RELEASING SMALL AMOUNTS OF HEAT

15. Classical (Coherent) Scattering • Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photon • No ionization takes place • Electrons in shells “vibrate” • Small heat is released • The photon is scattered in different directions • Energies below 10K keV

16. Coherent / Classical Scatter

17. Classic Coherent Scatter

20. Compton scatter • High energy (high kVp) x-ray photon ejects an outer shell electron. • Energy is divided between scattered photon and the compton electron (ejected e-) • Scattered photon has sufficient energy to exit body. • Since the scattered photon exits the body, it does not pose a radiation hazard to the patient. • Can increase film fog (reduces contrast) • Radiation hazard to personnel

23. Compton Scatter

24. COMPTON SCATTERING – OUTER SHELL ELECTRON IN BODY – INTERACTS WITH X-RAY PHOTON FROM TUBE

26. (WAVY LINE IN = PHOTON MUST BE INTERACTION IN THE BODY)

27. During Fluoro – the patient is the largest scattering object

28. XXXXX

29. Differential Absorbtion • Results from the differences between xrays being abosorbed and those transmitted to the image receptor • Compton Scattering • Photoelectric Effect • X-rays transmitted with no interaction

30. Compton and Differential Absorbtion • Provides no useful info to the image • Produces image fog, a generalized dulling of the image by optical densities not representing diagnostic information • At high energies

31. Photoelectric and Differential Absorbtion • Provides diagnostic information • X-rays do not reach film because they are absorbed • Low energies (more differential absorbtion) • Gives us the contrast on our image

32. No interactions with Image Receptor and Differential Absorbtion • No interaction • Usually high kVp • Goes through body • Hits image receptor • Usually represents areas of radiolucency (low atomic numbers) • Results in dark areas on the film

33. The probability of radiation interaction is a function of tissue electron density, tissue thickness, and X-ray energy (kVp). • Dense material like bone and contrast dye attenuates more X-rays from the beam than less dense material (muscle, fat, air). • The differential rate of attenuation provides the contrast necessary to form an image.

35. Pair Production

37. Photodisintegration

39. Remember….When reviewing diagrams What is coming in (e or photon? Where is it occurring (the tube or body?) Keep practicing – you will get it