Digital Imaging Flashcards
What are the advanatges of digital x ray imaging?
Negates the need for chemical processing
*reduces processing errors
Enhancement of the imagine obtained
What is resolution?
Counting the number of pixels in a given linear unit
Measured in lp/mm
How are images produced?
outputting pixels in lines
What is the resoltuion of a conventional film?
22lp/mm
What colour are pixels in a digital image?
Grey
They are assigned a shade of grey depending on the amount of radiation reaching the sensor
T/F
The Digitial imaging receptor film based?
False
What are the advanatges of digital imaging?
Lower radation dose (40-80%) reduction Elmination of film processing Sensors maybe re used Manipulation so image can be improved Stored on computer Images can be transmitted electrically Subtraction techniques may be used
What type of receptors are used in digital imaging?
Digital which can be either direct action or indirect action
What type of image does a direct action rimage receptor produce?
Instant image
What type of image does an indirect image recpetor produce?
image needs to be processed in a laser scanner
How does Direct Digitial imagine work?
this used a charged couple device (CCD) or a CMOS complimentary metal oxide semiconductor
What are CCD’s? What are the advantages and diasadvantes?
A photodiode absorbs photons and produces charge representing pixels
Converts light into electrons
Expensive to manufacture as they have to transport charge across the chip without distortion
What kind of image to CCD’s produce?
High quality and low noise
How do CMOS work?
Convert light to an electrical charge and then process into electrical signals
WHat are the features ofCMOS?
Lowe power
Easter to manufacture same Process as microprocessors
Cheap or manufacture
Light sensitivity lower than CCD
Image noisier than CCD
Active area small compared to size of sensor
More flexible since each pixel can be read individually
How do wireless sensors work?
They use radio frequency transmission
What method do Phostimuable Phosphor plates use?
They are a method of indirect digital imaging
What type of plate is used in the PSPs?
Plastic plate Coated with a phosphor material which is sensitive to X-rays
What does the phosorh plate to with the X-ray energy?
It stores it
How is the image generated in the PSP?
Indirect
The PSP plate is then placed in a laser reader which releases the photon energy as light
What are the advantages of PSP over CCD?
Larger variety of imaging areas
No bulky connecting cable
Slimmer imaging plate
Variations in exposure potentially correctable
More unform response across plate
Trasmission cable from CCD may cause noise
What are the disadvantages of PSP?
Plates must be processed within 8 hours
Requires separate processing therefore adds timing
Need to ensure plate is cleared before re using
Careful handling to prevent scratches
How can you manipulate digital images?
Altering brightness by lowering or raising all grey levels together
How can you change the contrast of the image?
Altering the contrast multiplies or divides all the grey level numbers by the same amount so that the relative grey level ratios are maintained
