image processing

Question 1

what is flat field compensation

Answer 1

known irregularities within the digital image being compensated for before the image signal arrives from the detector

Question 2

what is dynamic range/bit depth

Answer 2

ability to display a number of discreet values/ shades of grey

Question 3

why does a ‘raw’ image have low contrast

Answer 3

as it has a wide dynamic range of digital detectors in a linear function

Question 4

what does the LUT do

Answer 4

converts digital pixel values into grey-scale intensities

(they give contrast characteristics for a particular examination)

Question 5

what is edge enhancement/ unsharp mask/ spacial filter

Answer 5

algorithm identifies sharp edge boundaries in image

increases image contrast immediatly around edges

creates subtle bright and dark highlights on either side of any edges in image

Question 6

what is an adv and dis of edge enhancement

Answer 6

adv: improves visibility of clonal structure

dis: enhances noise if no further algorithms applied

Question 7

how do you filter noise/ smooth an image

Answer 7

reduce quantum mottle (quantum noise) and increase SNR by increase dose/mAs or using image-processing algorithm which filterers the signal

Question 8

what are adv and dis with filtering noise

Answer 8

adv: patient dose can be lowered

dis: image may become more blurred

Question 9

what does a virtual grid do

Answer 9

filters image by removing unwanted signals made by scattered radiation when not using a grid

Question 10

how does a virtual grid remove scatter

Answer 10

increases contrast

reduces noise/granularity

Question 11

what are some post processing functions

Answer 11

• resize
• invert (black to white)
• adjust collimation
• annotate
• flip rotate

Question 12

what are the 3 image storage areas an image is sent to

Answer 12

1. DICOM image (digital imaging and communications in medicine)
2. PACS (picture archiving and communication system)

3, post-processed further on workstations (reformatted in 3D, measurements taken etc)

Question 13

what is the difference between lossy and lossless compression

Answer 13

lossy is irreversible compression of and image

lossless is reversible compression of an image

Question 14

what is dual energy subtraction

Answer 14

multiple images within milliseconds at different energy levels

Question 15

what is auto image paste

Answer 15

multiple images in one automated exam