Chapter 1 (pages 38-47) Flashcards
When making an image, exposure factors must be picked with what variables?
Density of part/anatomic number
Thickness of the anatomical part
Pathology
Technology being used
What are technique factors?
kVp and mA
Image Quality Factors (analog)
Density
Contrast
Spatial Resolution
Distortion
What is the primary controlling factor for RE?
mAs
What is the secondary controlling factor for RE?
SID
Relationship between RE and mAs
Direct Proportional
If you double the mAs, you double the amount of x-rays
Other factors that affect the RE (analong)
kV, part thickness, chemical time, chemical temp, grid ratios, and film screen speed
What is the Anode Heel Effect?
Cathode side of the tube has more xrays being projected than the anode side, so the thicker side of the patient should go to the cathode side
FATCAT - fat side to cathode
Diaphragm is the thickest part of the abdomen
What are examples of compenstating filters?
Boomerang (shoulder)
Ferlic filter (hips)
Wedge filters (chest, foot)
What does a compensating filter do?
Filters out a portion of the primary beam toward the thin or less dense part of the body
What causes an image to be underexposed and what will it look like?
Too little mAs - image will be very light
What causes an image to be overexposed and what will it look like?
Too much mAs, image will be very dark
What is contrast?
The difference in receptor exposure between adjacent areas
What does long gray scale contrast look like?
Many, many shades of grey - hard to tell the difference between them (think of a paint strip)
What does low contrast look like?
a large amount of adjacent grays. Difficult to tell the difference from one gray to the next. Needs a kVp # like 110
In productions, what is the main controlling factor for contrast?
kVp
Digital images use kVp and LUT (look up tables)
A high kVp will give what type of contrast?
Low contrast image - more gray colors
A low kVp will give what type of contrast?
High contrast - more black and white
What is the relationship between kVp and receptor exposure?
Direct - as you increase kVp, RE increases
4 causes of grid cutoff
Off center - the center of your IR must be the same as the center of your focused grid
Off level - means your central ray is not at a good 90 degrees to the center of the grid
Off focus - this has to do with distance. Some grids only work for certain distances
Upside down focus - x-rays must be going in the same direction as the grid lines
What is grid frequency?
The number of lead strips per inch or centimeter
What is spatial resolution?
defined as the recorded sharpness of structures on an image
Geometric controlling factors for spatial resolution (analog)
Focal spot size, SID and OID
A small focal spot results in less penumbra
The higher the SID, the better the spacial resolution
As OID decreases, spatial resolution increases
What is motion on an image?
Blurring effect
Can be voluntary or involuntary
What is the best way to control motion?
Short exposure time
Communication to the patient
Patient immobilization and controlled breathing
What is distortion?
A misrepresentation of an object shape or size
What has the least amount of beam divergence?
Central ray
What are the 4 controlling factors of distortion?
SID - magnfication
OID - magnification
Object-image alignment - foreshortening
CR alignment - elongated
What are the 5 different tissue types from least dense to most
Air
Fat
Water
Muscle
Bone
Current technology has a broader:
Exposure latitude (can edit pictures now that they are digital)
What is short gray scale contrast?
Looks like very few shades of white, black, and gray
What is high subject contrast?
A certain black and white look of an image.
What is the kVp range for all body parts?
60-120. 130 will degrade the image
What is foreshortening?
The object is not lined up correctly with the IR. Incorrect placement causes the object to look smaller.
Ex. both joints of long bones need to be on IR.
How does central ray alignment affect distortion?
Central ray must be aligned with the object. The more beam divergance, the more distortion. Body part will look elongated
Types of distortion
Magnification
Elongation
Foreshortening
Another word for distortion?
Misrepresentation
How much does SID need to increase for every 1” of OID
By a factor of 7
How to fix grays when RE is optimal?
15% rule
How to fix overpenetrated and overexposed
Decrease kVp
How to fix underpenetrated and underexposed
Increase kVp
How to fix overexposure or underexposure
Double or half mAs
What is Air Gap Technique theory?
Increasing OID, reduces scatter - no need for a grid
A 40” SID is how many cm?
100 cm
What is needed in the filament cup to burn off electrons?
mA and current
