DR: Image display

Question 1

In digital imaging, what is meant by the ‘bit-depth’?

Answer 1

Bit-depth refers to the number of grey-levels that can be assigned to a pixel. A 12-bit image will allow 212 discrete grey levels (ie 4096).

Question 2

For a given image area, what is the effect of using a smaller pixels?

Answer 2

Improved image resolution and increased image size (in terms of MB). (Applies less to nuclear medicine as resolution is not limited by display equipment but by the fundamental limitations to imaging)

Question 3

Why does a raw image require pre-processing?

Answer 3

Detector has a very wide dynamic range and has captured the whole range of exposure levels – processing required to select the clinically relevant range. Flat field correction and bad pixel map also applied to correct for missing pixels and detector non-uniformities.

Question 4

What is the effect on the displayed image of reducing the display window width?

Answer 4

The image will be displayed at higher contrast – a small range of stored pixel values is mapped to cover the whole black-white range in the displayed image. Stored pixel data outside the window width will be displayed as either black or white.

Question 5

How does a reporting workstation differ from a standard PC?

Answer 5

Higher luminance monitor, higher bit-depth, often higher resolution, built in calibration curves, stable luminance

Question 6

Why is the registration of PET and CT images useful?

Answer 6

Allows clinician to see both the functional and anatomical information