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How is CR different from DDR and IDR?
- Cr uses a casstte with a photostimuable phosphor image
- IDR uses a phosphor but converts x-rays to light and then to a signal
- DDR does not use a phosphor, it converts x-rays directly to a signal
What does the H & D curve represent?
- It represents the difference btwn Digital and F/S with their relatiion to amount of exposure to optical density
- F/S has a sigmoid curve
- Digital has a linear
- Digital provides more information at the low and high exposure levels
- Digital has a higher dynamic range than film
Describe how a CR cassette captures an image.
When struck with x-rays, outer shell electrons in the photstimuable phosphor plate become excited and hold that state of excitement (the latent image) for a period of time
What is the purpose of the europium-doped barium fluorohalide crystals in CR?
Europium acts as a catalyst to help speed up processing (Kyle)
Europium is an activator that allows the electrons to store the energy (image) for a period of time (Bushong)
Where is the latent image stored in a CR plate?
In outer shell electrons of the photostimuable phosphor plate
Besides x-ray interactions what can cause the LGM value to increase?
Degradation of the imaging plate by light or heat
How long can a latent image be stored?
What are the steps the image reader takes to process an image
- 1. Infrared laser scans image plate.
- 2. Electrons emit a faint light (proportional to remnant radiation)
- 3. photomultiplier amplifies light and converts to a digital signal (ADC)
- 4. signal sent to computer and DAC takes place
What kind of relationship does the signal and IR exposure have?
What is the purpose of the photomultiplier tube?
amplifies the faint light emitted by the phosphor electrons, before they are converted to a signal
What parts of the plate emit light when scanned by the laser?
The stimulated outer shell electrons of the phosphor
Which has a greater latitude with different techniques, CR or F/S? How can this be a problem?
- CR has a greater latitude
- Pt. may be overdosed because a diagnostic quality image will appear with a wide range of techniques.
In CR what is the controlling factor to Density and Contrast?
- mAs controls IR exposure, LGM (density)
- kVp controls visibility of detail (contrast)
What are short term database functions?
they allow the user to locate time, create lists of images, image interpretation and maintain teaching files
What is Gradation processing?
gradation processing- controls the range of densities used to display structures on the image, allows for and limits the range of windowig and leveling
What is dynamic range control?
provides a wide diagnostic field, allows for visualization of bone and soft tissuein a single image display
What type of post processing allows us to fade superimposing structures and enhance areas of interest?
Why is it so important they we stay within LGM range?
To provide diagnostic quality images while following ALARA principles
In CR what are the controlling factors of resolution?
- - Image reading matrix
- - Size of the laser reader (100 or 400 speed)
- - Size of phosphor crystals (fixed)
- - spatial frequency (controls sharpness of boundaries between structures of different densities)
Which has a greater contrast resolution F/S or DR?
CR/DR have superior contrast resolution with over 10,000 shades of grey compared to 30 with F/S
Whichhas an increased spatial resolution?
Is there more penumbra using 100 or 400 speed?
What are the advantages of using DR over CR?
- 1. Do not need a cassette = faster
- 2. Higher heat capacity, in excess 1 MHU
What is the diffeence between Direct and Indirect Digital Radiography?
Indirect uses a phosphor to create light which creates a signal
Direct converts x-rays dierectly into a signal
In indirect radiography what do the x-rays interact with?
And what is the light caoptured by to then create a signal?
- Cesium Iodide phosphor
- Amorphous Silicon
What has taken the place of amorphous silicon?
A charge coupled device
How is spatial resolution improved in DR? What do x-rays interact with?
eliminates the spread of light, the decrease in penumbra allows for a better spatial resolution
What are the two principles of every medical image?
spatial resolution and contrast resolution
What is the relationship between size and spatial frequency?
The smaller the size of pixels the higher the spatial frequency
What is modulation transfer function?
- The ability of the DR to display images that vary insize to the actual object without losing any information.
- Relationship between spatial frequnecy of the object to that of the image.
What is contrast resolution?
- The ability of DR to portray shades of grey in relation to black and white
- AKA dynamic range for DR
What is 100% contrast?
Black and White
What is the relationship between bit capacity and contrast resolution?
- Bit capacity is the amount of shades of grey each pixel can hold.
- The higher the bit caoacity the greater the contrast resolution.
Describe signal: noise ratio.
The higher the signal the less noise, they are inversly proportional
What are the optimal viewing conditions?
Straight on and not too far away
What is DQE?
- Detective Quantum Efficiency
- - absorbtion coefficient: ratio absorbed by the IR to the amount of remnant radiation
- - spatial frequnecy of the remnant radiation
A higher DQE means more remnant radiation is being absorbed by the IR, which means lower techniques are required for creating an image and lowers patient dose.
DR has highest DQE > CR > F/S
What are some examples of preprocessing?
The algorithms in the computer or processor
Name 3 components of the PACS system?
Display system, Network, Storage System
Do imaging systems have a higher or lower spatial resolution compared to film?
List the different types of imaging systems from least to greatest amount of dose.
DRR, F/S, CR
What are thethree types of digital artifacts?
- - Image Receptor
- (dust, dirt, scratches, malfunction of pixels, Ghost images, double exposure)
- - Software
- (image compression, failure of flat fielding, failuer to electronically preprocess the image)
- - Object
- (Pt. positioning, improper collimation, partioning, backscatter, Fog)
- - Object
What does a histogram represent?
It is a plot graph of the frequency of the appearance of an object is seen, in this case, the value of each pixel (or shade of grey)