-
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?
24 hours
-
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?
Direct
-
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?
subtraction
-
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?
Film Screeen
-
Is there more penumbra using 100 or 400 speed?
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.
Ideakly 1:1
-
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?
lower
-
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)
|
|
