2. Digital Imaging Flashcards
What is the main difference between analog and digital signals?
Analog signals have continuous electrical signals but digital signals have non-continuous electrical signals
The greater the number of pixels, the higher the spatial resolution
True 😊
Pixel =
Voxel =
Picture element
Volume element
What is dynamic range?
The range of grey scale values that can be assigned to each pixel
NB: It is inherent to the machine so cannot be changed
For LCDs, passive screens use what type of light?
Active screens use what type of light?
Fluorescent light
Light emitting diodes (LEDs)
What advantages do LEDs have over fluorescent light?
- Brighter
- Superior contrast resolution
- Better viewing angle
What is the full name for DICOM?
Digital Imaging and Communication in Medicine
What is DICOM?
This is a standard that describes how to format and exchange medical images and associate information
NB: DICOM protocol is used to produce, manipulate, exchange, and store imaging data
T or F. DICOM uses the Gray Scale Display Function (GSDF) which allows for display on any DICOM compatible device with consistent gray scale appearance
True
What are the 5 objectives of DICOM in RT?
- RT image (DRRs, sim images, kV images
- RT plan (geometric and diametric data for EBRT and brachytherapy
- RTSS (structure sets-patient anatomy,ie. structures, markers and isocenters as defined on treatment planning systems
- RT dose (dose distributions, volume, histograms, isodose curves and dose matrices
- RT treatment record (data from treatment sessions)
What is the full name for PACS?
Picture Archiving and Communication Systems
What is PACS?
The system that is used for the storage and transfer of radiological images (it is the network)
NB: DICOM is the universal language across PACS systems
Name the 4 principle components of PACS
- Image acquisition system
- Display system
- Network
- Storage system
What are the two classes of digital imaging systems?
- Indirect digital radiography
- Direct digital rdiography
What is Indirect digital radiography?
Phosphors react with x-rays to produce light photons, light creates the signal
NB: Light is the middleman
What is Direct digital radiography?
Sensors detect radiation leaving the patient and send data to a computer in digital format
What is the intermediate step between analog and full digital?
Computed radiography (CR) Indirect radiography
What is commonly used for fluoroscopy or small field of view applications like dentistry?
Charged-Coupled Devices (CCDs)
What is the function of a scintillator?
To convert photon to light
T or F. As you gain spatial resolution, you lose contrast resolution
True
NB: Ideal detector element is a compromise between spatial and contrast resolution
What is the math formular for Fill Factor?
Fill factor =
light sensitive area/area of detector element
What is the Fill Factor?
The portion occupied by the light sensitive image receptor
A high fill factor:
Has a larger light sensitive area which is good for CONTRAST resolution
What type of material is used in direct detection panels?
Amorphous selenium (A-Se)
Which detection method is more accurate. Direct or Indirect?
Direct
Name the 3 advantages of digital fluoroscopy
- Reduced patient dose
- Faster image acquisition
- Enhanced contrast resolution
What is pulse progressive fluoroscopy
An X-ray imaging technique which uses pulsed radiation to reduce dose while maintaining real-time visualization of moving structures.
Name the 3 events in the timing of pulses in a PPF
- Interrogation time
- Extinction time
- Duty cycle
Why do we use contrast in fluoroscopy?
To help improve visibility of soft tissue structures via photoelectric effect
What are the two standard mammography views?
- Craniocaudal (CC)
- Mediolateral Oblique View (MLO)
What are the differences between pre- and post-processing?
Pre-processing:
1. Automatic using algorithms
2. Reduces noise and distortion
3. Improves contrast (reduces noise)
4. Eg. image lag, line noise, defective pixel
Post-processing:
1. User driven
2. Image enhancement for viewer display
What view is the most important projection for breast mammography?
Mediolateral Oblique View
What is image inversion?
When the grey scale values are reversed (Dark becomes white and white becomes dark)
What is subtraction?
When select ranges of brightness are removed from the image
What is window width?
It is the range of CT numbers displayed on a projected image
A wide window width and high level is appropriate for ______
Bone
Mid-range WW and level is appropriate for ____
Mediastinum and blood vessels
A narrow window width and lower level is appropriate for _____
Lung alveoli and branching bronchi
What is dose optimization?
Finding the balance between patient exposure and image quality
What is subject contrast?
Differential absorption through tissue based on exposure settings
T or F. Higher kVp with reduced mA reduces patient dose
True
What is Exposure Index?
It relates to the amount (quantity) of radiation reaching the image receptor
Window width and level values
