Applying Radiographic Technique to Digital Imaging Flashcards
What are the fundamental differences between digital and screen/film technology?
- Image displayage display is independent of image acquisition
What is the primary goal of radiographic technique?
To ensure adequate signal (SNR) reaches the detector system to allow computer algorithms can make corrections to the image
What is one rule for kVp in digital technology?
There needs to be enough kVp to penetrate the part, otherwise it will be underexposed
Why is DR better than CR?
Because DR goes through direct conversion vs CR which is indirect
What is scatter associated with in imaging?
Part thickness and collimation, with kVp only being limitedly associated
What is a benefit of increased kVp, despite the increase in scatter?
It leads to a slight reduction in contrast (longer grayscale) to allow more visibility of tissues
What adjustment of kVp can be done to save patient dose?
Increase of 15% kVp and cutting mAs in half
How much skin exposure is reduced by an increase of 15% kvP?
67% net reduction in patient skin exposure without noticiable mottle
What does a higher kvp allow in terms of penetration?
Higher kvp allows for a better penetration, which allows for a rescale of contrast with less mottle
What is one exception to the 15% increase kVp rule?
Chest radiography which already uses a higher kVp and low mAs
Does kVp still control image contrast?
Yes, because the intensity of the remnant beam is altered by kVp, which will affect the penetration/contrast
Which imaging type allows for a much greater range of exposure?
DR - Digital imaging
What is the exposure latitude of Digital imaging?
-50% to +400%
What does the large range of exposure latitude make difficult in digital imaging?
Makes it difficult to create an overexposure that will need a repeat image (saturated image)
What are the 4 factors leading to unaccpetable levels of patient exposure?
- 200 speed systems, which are highly utilized, require more radiation than higher speed systems
- Use of lower kVps
- Fear of mottle from underexposure
- Over-reliance on digital system corrections
What is the tradeoff of using a higher speed system?
Can create more likelihood of noise
Which systems are better at reducing scatter?
CR cassettes due to the high kVp
How can the efficiency of CR be reduced?
By background radiation or scatter prior to actual exposure
What do AEC systems need to be calibrated with?
Need to be calibrated to coincide with CR EI and DI numbers
What does the calibration between AEC and CR DE/EI allow?
Utilization of kVp properly, avoidance of mottle and creating technique charts
What attention needs to be paid to when using AEC?
Proper positioning, alignment and selection of detector cells
What should be used rarely in AEC?
Density setting
What is the 30% rule in CR?
Exposure indicator errors are likely unless at least 30% of the imaging plate is exposed
How was the use of grids increased in digital imaging?
They’re now built into DR rooms and can even be used on smaller parts
