Factors Affecting Image Quality Flashcards
What is image quality?
The optimal features of an image that allow us to effectively interpret an image
Why does the image need to be representative of the patient’s actual anatomy?
So that we can reduce any factors that could distort the image
What does the inverse-square law say?
The further we are from the source of radiation, the less radiation we ‘re exposed to
What happens to the density as the distance increases?
The density decreases
What happens to the dose when the distance increases?
The dose decreases
What is the SID?
The source to image distance (from x-ray tube to detector)
What is the OID?
The object to image distance (from patient to detector)
What is the SOD?
Source object distance (from x-ray tube to patient)
What is the SID also known as?
FRD
What is the OID also known as?
ORD
What is the SOD also known as?
FOD
What does FRD mean?
Focus to receptor distance (from x-ray tube to receptor)
What does ORD mean?
Object to receptor distance (from patient to receptor)
What does FOD mean?
Focus object distance
What continues to happen when the OID is increased?
The x-rays continue to go in another direction as they pass through the object
Will objects further or closer to the image receptor be magnified more?
Objects further away
Should the body part being imaged be close or far from the image receptor?
As close to the image receptor as possible
Why do we have to label if an image of the chest was taken AP instead of PA?
Because in AP, the heart will be magnified more than PA, so the radiologist knows that the increased size isn’t du to abnormalities- it’s due to positioning.
When do we use AP for a chest x-ray?
If the patient can’t stand up against the wall bucky
What is the purpose of getting the patient’s chest against the wall Bucky?
So we can get the heart as close to the imaging detector as possible
What do we do to reduce the magnification?
Increase the SID
What will happen to the intensity of the x-ray beam if the SID increases?
The intensity decreases
If we change the SID, what factor do we have to change?
mAs
What happens to the intensity in the x-ray beam if we increase the distance from the source?
The intensity decreases
If you double the distance from the focus, the x-ray beam will be …. of its original intensity
1/4
How can we get the same beam intensity at double the distance?
Increase the mAs
In what direction should the object and image receptor be together?
Parallel
In what direction should the central ray and the receptor be together?
Perpendicular
What would happen if the object and receptor aren’t parallel, and if the central ray isn’t perpendicular to the receptor?
The image may be distorted
Why might image distortion be done on purpose?
To display anatomy in a certain way, e.g. an oblique hand
What are the consequences of the object not being parallel to the image receptor?
(3)
The image will be distorted
Different aspects of the image will be magnified
The object may be elongated or foreshortened, so fractures or pathologies could be missed
What is the consequence of the central ray isn’t perpendicular to the image receptor?
The image will be distorted
What factors can contribute to unsharpness in an image?
(2)
Patient movement
Focal spot size
Does this chest x-ray have movement unsharpness or no movement unsharpness?
No movement unsharpness
Does this chest x-ray have movement unsharpness or no movement unsharpness?
Movement unsharpness
Is the focal point pre-set or do we have to set it up?
It should be pre-set
What is the focus?
The area that’s bombarded by the x-rays
What can the focus be altered to be?
(2)
Broad focal spot
Fine focal spot
How many anodes does the cathode have?
2 anodes
When imaging a larger body part, do we use a broader or finer focal spot?
Broader focal spot
When imaging a smaller body part, do we use a broader or finer focal spot?
Finer focal spot
What is the issue with using a larger focal spot size?
The larger the focal spot size, the larger the area of penumbra (unsharpness)
What are the issues with using a finer focal spot size?
(2)
Finer focal spots are a more concentrated area, so more heat is produced, which could damage the anode
The image is also more susceptible to motion unsharpness
