RAD 120.01: Exposure 1 Theory | Chapter 23 Technical Considerations in Digital Imaging

What is the universal exposure indicator?

Deviation Index (DI)

What is the range for DI?

-3 to +3

What is the targeted range for DI?

-0.5 to 0.5+

What happens when DI shows +1 to +3 what does that mean?

Indicates Overexposure

• Repeat only if anatomy is clipped or burned out.

What happens when DI shows >+3 what does that mean?

Excessive Radiation Exposure

• Repeat only if anatomy is clipped or burned out.

• Requires immediate management follow.

What happens when DI shows -1 to -3 what does that mean?

Underexposure

What happens when DI shows <-3 what does that mean?

Repeat

What is low contrast resolution artifact?

Digital has a wide dynamic range to detect all levels/radiation (low to high)

• It then assign a unique shade of grey.

• It gives us the ability to see subtle differences between shades of gray.

What results from low contrast resolution artifact?

Visibility of Artifacts

• Clothing

• Tattoos

• Positioning Sponges

These were not visible with film/screen imaging.

How does data drop occur?

The DEL is overwhelmed with x-ray photon energy and when the image is reconstructed, these data points are dropped from the image.

What can result in Data Drop?

Over-Exposure

What is the data drop in an area called?

Saturation

What will the resulting image due to data drop look like?

Bony anatomy that has very little soft tissue over it.

What is the solution to data drop?

Solutions:

• Compensating Filter

• Bolus Material: such as…

  • Rice

  • IV Bag

  • Filter Boomerang

These can absorb some of the photons and prevent saturation.

What are the areas of which data drop can occur?

• AC Joints

• Lungs

• Lateral Hips

• Perineum of Pelvis

• C-Spine

Why are dirty or damaged imaging plates a problem in CR?

• This may appear as lucency (white spot) or line on an image.

• This can mimic hairline fractures or cause artifacts.

What should you do about dirty/damaged IP in CR?

Clean or replace if necessary

How does incomplete erasure occur?

When the IP isn’t completed erased by the CR reader.

What can cause incomplete erasure?

• Saturation

• Improperly functioning CR reader erasure cycle.

What can result from incomplete erasure?

• Ghosting

• Low Contrast Images

When should IPs be erased before using?

If an IP hasn’t been used in 48 hours, it should be erased before using.