Lecture 5 - Radiographs Flashcards
What crystal is chemically altered when stuck by an X-ray photon AND what does it create?
Silver halide
Latent image
The raised dot goes towards or away from tube head?
Towards
The larger the crystals of silver halide the ______ the film speed.
FASTER
C is slowest
D - ASA ~100
F - Fastest
Tell me about cassettes.
Contain intensifying screens
*Require less radiation to expose film
Decreased definition
Radiographic density is influenced by what?
mA
kVp
Exposure time
Focal spot to film distance
Subject density
Subject thickness
What is radiographic density?
Determined by how many photons strike the film emulsion
-This converts silver halide crystals to metallic silver
—This blocks the transmission of light thru the film
What do grids do?
Reduces scatter radiation
-Reduces scatter and fog on a radiograph
What is the developing process for in dark film processing?
Developer
Wash
Fixer
Wash
Drying
What do you have to do to keep darkroom hygiene?
Safelight
Light leakage
Chemical contamination
Infection control
For every 10 degrees Celsius in an increase, the rate of the rxn __________.
Doubles
68 F develops in 5 minutes
80 F develops in 2.5 minutes
What processing is the most time consuming, but produces best radiographs?
Manual
What is the most efficient film processing?
Auto processors
What are three waste products of film?
Chemicals
Lead
Paper
What are some advantages to digital radiology?
Lower pt exposure (usually)
-Less photons required to expose sensor
—However, temptation for more retakes
—Sensor size may need more exposures to capture all information
Faster radiographs
-No processing time
More eco friendly
- No chemicals
- No film
How much less exposure for digital compared to film?
E/F Speed film ~50-60%
PSP - 60-80%
Charge couple device - 80-88%
Other advantages of digital?
Easy storage
Easy sending
Easy retrieval
Easy to show pts
Enlarge and vary density
What are some disadvantages of digital?
COST ($10k)
Damage
Uncomfortable
Loss of image w/o back up
Film gives a better image
There are two types of digital systems. Name them.
Direct
-Sensor connects direct to a computer and provides immediate images
Indirect
-Phosphor plate is used instead of film
—Image scanned in a scanner
—Stored and read on a computer
What 4 things should you consider when selecting a sensor?
Number of pixels
Placement of cord (unless cordless)
Comfort
Cost
What part in the sensor reduces the radiation amount?
High sensitivity CSI scintillator
How are medical images sent digitally?
Sent with DICOM
-Digital Image and Communication in Medicine
*This is the standard language for the electronic communication of digital images
What is contrast resolution?
Ability to distinguish different densities in an image
Humans can only detect about 60 shades of gray ideally
What is spatial resolution?
Ability to distinguish fine detail in an image.
Humans can only detect down to 6 lp/mm - technology can do much better than that.
What is sensor latitude?
Ability to capture a range of exposures
-Ability to capture subtle differences in tissue density from gingiva to enamel
What is sensor sensitivity?
Ability to respond to small amts of radiation
*F speed film as less sensitivity
How does a sensor work?
X-ray phontons are converted to visible light as they hit the scintillator - light is channeled via the fiber optic taper to the CCD
Overexposure of a sensor leads to what?
Blooming
High res vs high contrast?
Average grayscale value of 4 adj pixels in a high res image is assigned to create one pixel in a high contrast image
Digital radiography filters are a combination of 4 things.
Optimizing grayscale
Eliminating noise thru smoothing
Sharpening image detail
Extracting features (Information)
A decrease in brightness means what?
Grayscale value of all pixels is decreased equally
How does a grayscale work?
By moving the sliders away from the opposite ends of the spectrum, dark pixels are reassigned to solid black and light pixels are reassigned as pure white
What are three ways to look at a digital radiograph?
Original
Inverted
Embossed
Infection control procedures?
Wear gloves during all radiographic procedures
Cover all non-disposable items
Sterilize non disposable items
Disinfect surfaces
