Ch. 8 Digital Imaging Flashcards
acquiring images using x-rays & digitally displaying them on computer files
Digital imaging
digital images that can be sent through a computer network to numerous computers inside and outside the medical facility
conventional radiography
“cassette-based” digital imaging
- photostimuable phosphor plate that stores the latent image
- thick phosphor made of barium flurohalide with europium
-high resoultion IPs produce greater image resolution
Computed Radiography
IP is exposed
CR reader scans the IP with a laser beam turning the energy into light
IP is erased with a white light
Process of viewing an image with Computed radiography
CR reader unit, computer workstation, computer system, computer storage, printer
required items for Computed Radiography
“Cassetteless” digital imaging
- uses flat-panel detectors made of a scintillation screen or a photoconductor to convert photons into electrical signals
- 2 conversion systems: indirect vs. direct
Digital Radiography
2-step process where xray energy is converted into light and then into an electrical signal using a scintillator made of cesium iodide
Digital Radiography-Indirect Conversion
collects the electric charges as a matrix of pixel size elements (Detector Elements)
Amorphous Silicon
Takes the stored charge and converts it into digital values that are sent to the computer for processing/viewing
Analog-to-Digital Converter (ADC)
no photodiode, but instead converts the light from the scintillator to the electric signal
Charged Coupled Device (CCD)
converts light into electrons that are stored in capacitors
-most common semiconductor is silicon
Complementary Metal Oxide Semiconductor (CMOS)
1-step process where detectors convert the xray energy directly into an electric signal through an amorphous selenium detector without light conversion
Digital Radiography- Direct Conversion
how fast can DR images be processed?
3-5 seconds
defects that cause a loss in information
-dust, scratches, interactions between materials can occur
dead pixels
amount of detail/sharpness available
-larger matrix with smaller pixels = greater resolution
Spatial resolution
ability to distinguish anatomical structures of similar subject contrast
contrast resolution
the responce of the detector to different levels of radiation exposure
dynamic range
the ability of the digital system to convert input electric signal into a useful image
Signal-to-noise ratio
noise that occurs when there are not enough photons to provide a high-quality image
quantum mottle
Histogram
Look-up table (LUT)
Window Level
Window Width
Electronic Cropping
Image Stitching
Image annotation
Edge Enhancement
Smoothing
Subtraction
Contrast Enhancement
Functions of the processing system (“editing” images)
controls density (brightness)
Window level
controls contrast
Window Width
a graph of the minimum & maximum signals in the image
Histogram
images are produced with uniform density & contrast regardless of the amount of exposure
-problems occur when too little/too much exposure is used resulting in loss of contrast & detail
rescaling
