* Our Goal Obtain the best possible image

* Best Possible Image? What is our goal?

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

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

* 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

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

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

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

Image Noise Caution! Image Noise

Noise covers valid information with distracting or obscuring garbage

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

Another Example

Painting Image One Dot at a Time

Noise makes it hard to see low contrast differences