Lecture 4: Imaging processing

Question 1

What problems are there with displaying images on workstations and how do more expensive systems compensate for this? (3 marks)

Answer 1

• We need to ensure that images look the same on different systems.
• Our visual system does not have a linear response (it is harder to see contrast in dark parts of the image).
• High end displays use a standardised curve to compensate for this.

Question 2

What pre-processing is performed on images in CR and DR systems? (3 marks)

Answer 2

• CR systems, shading is performed to compensate for variations in the sensitivity of the light guide
• DR systems, flat fielding is performed to compensate for differences in sensitivities in different pixels and defective pixel compensation.

Question 3

Give 6 different ways in which images can be processed? (6 marks)

Answer 3

• change the window and level to show different ranges of intensities.
• grid line suppression from anti-scatter grid
• look up table for intensity standardisation, apply a function to the pixel values
• edge enhancement
• noise reduction
• image subtraction like coronary angio

Question 4

What QA can be performed on digital imaging systems? (4 marks)

Answer 4

• Modulation transfer function (ability to record a range of different spatial frequencies)
• noise power analysis (power of the noise at different frequencies)
• CNR, spatial res…