4. *
Our Goal
Obtain the best possible image

5. *
Best Possible Image?
What is our goal?

6. A Diagnostic Image Using the Least Radiation*
A Diagnostic Image Using the Least Radiation
A prettier picture does not provide benefit to our patient
Prettier pictures often involve additional radiation

12. Contrast difference in density between areas on radiograph
Your ability to see contrast depends on
Subject contrast
Contrast sensitivity of receptor
Scatter radiation
Monitor / Viewing conditions

13. *
Subject Contrast
difference in x-ray intensity transmitted through various parts of subject
Depends on
thickness difference
density difference
atomic number difference
radiation beam energy

14. Subject Contrast & Radiation Quality*
high energy beam = lower subject contrast
long scale contrast (less difference between areas receiving varying amounts of radiation)
low energy beam = high subject contrast
short scale contrast (more black & white; more difference between areas receiving varying amounts of radiation)
low energy beam increases patient dose

15. Photon Phates Nothing Absorbed Scattered * X Photon passes unmolested
completely removed from beam
ceases to exist
Scattered
change in direction
no useful information carried
source of noise X

16. Primary vs Scatter Primary = Good photon Scatter = Bad photon Focal
Spot
“Good” photon
Patient
“Bad” photon X
Receptor

32. Image Noise
Caution!
Image
Noise

33. Noise
covers valid information with distracting or obscuring garbage

34. Image Noise
covers valid information with distracting or obscuring garbage
Caution!
Image
Noise

35. Another Example

36. Painting Image One Dot at a Time

38. Noise makes it hard to see low contrast differences