Digital Imaging Receptors Flashcards
Film screen radiology (FSR)
Also called “flat films”
Flat panel detectors
What are reasons film is being replaces with digital? (5)
- Less retakes
- Lower long term costs
- Storing images is easier & less costly
- Electronically send images
- Images can be manipulated to show other pathology
Two types of digital imaging receptors
- CR - Computed radiography
- DR - Direct digital radiography
What is the difference with DR and film?
It’s the image receptor!
Computer radiography (CR): Cassette info
- CR contains a phosphor plate in it’s cassette instead of a film sheet like analog.
- The CR receptor includes a cassette w/imaging plate (IP)
- IP absorbs transmitted x-rays to produce the latent image
- During absorption, a luminescence is released as part of the photoelectric effect
- Phosphor layer is composed of barium fluorohalide crystals doped with europium
- This layer receives transmitted x-rays & holds the latent image until it’s processed
Photoelectric effect (3)
- X-ray photons usually carry enough energy to ionize an atom in their path.
- Ionization means that an atom has temporarily released an orbiting electron.
- This atom is now a positive ion. The ejected electron is held in a higher energy state until it’s released through processing.
What is PACS as an acronym?
PACS
- Picture - viewing at workstations
- Archiving - images short/long term
- Communication - local or wide area networks
- System - use with HIS, other equipment
What does PACS do? (3)
- Once an image is made, it’s sent to PACS
- Image is also sent elsewhere as offsite storage - Then image can be pulled up & viewed
- Method that allows storing, retrieving, distributing throughout your hospital or the internet
What is DICOM acronym?
Digital Imaging and Communications in Medicine
What does DICOM do?
- Imaging standard that allows multiple pieces of medical equipment to communicate
- Essentially all PACS and almost all equipment speak to DICOM now
- DICOM doesn’t effect image quality!
Computed radiology:
Once a scan is complete from the cassette, how does it get “wiped?”
- The imaging plate (IP) is exposed to a bright light before it’s returned into the cassette and ready for more services
- This erases any excess energy left in the IP after the previous exposure
T/F: Digital rad has a wide latitude
True!
T/F: kVp has no effect on image quality with DR
True
T/F: DR can get both bone and soft tissue in the same exposure
True
What does scatter do to the image?
FOGS IT and exposes anyone in proximity
What is Compton’s effect?
AKA “scatter”
- When the xray beam interacts with the patient, some of the beams are deflected
- Photons that were directed toward the patient interact with outer shell electrons and change directions
Four ways to reduce scatter?
- Collimate the light to reduce the area of exposure
- Reduce kVp by 15% and double the mAs to reduce scatter. As kVp increases, so will the scatter.
- Add a grid to the exam
- Air gap techniques: works better in human med than vet med
What are grids?
- They are composed of tiny lead lines embedded in either plastic or aluminum.
- The lines are positioned so that X-ray beams pass between the lines
- Scatter will be impacted by the lead lines
Should the mAs be slightly increased when using a grid?
Yes, they can absorb some of the primary beam
What are some examples of digital artifacts? (5)
- Look up table/image processing errors
- Exposure artifacts
- CR & DR artifacts
- Interference artifacts
- Display artifacts
Artifacts (digital or not) (5)
- Mis-positioning
- Motion
- Incorrect patient ID
- Double exposures
- Grid cut off
Common grid errors
CR Artifacts (7)
- Fading
- Light leak
- Physical damage
- cracks, scuffs, scratches
- contamination
- dust/dirt - Dirt in reader
- Highly sensitive to scatter radiation
- Upside down in bucky
- Overtime if image not read then electrons fall back to ground energy state
- Several days of fading req for significant fading to occur
Uberschwinger Artifact
“Overshoot”
- Image may have black halo in certain objects (nail in a foot)
- Can be mistaken as infection when this happens
- Or loosening of orthopedic device
Exposure artifact (5)
- VERY high exposures
- Maximum detector response reached
- No response to increased dose
- Uniformly dark
- Cannot be windowed/leveled
Film vs Digital
Film:
- Latitude is narrower
- Minor under/over exposure will fail to provide diagnostic image
- Bone and soft tissue cannot be detailed in the same view
Digital:
- Wider latitude
- kVp no effect on image quality
- Detail of both bone and soft tissue in one image
