R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

2.9 Close up of noise.
Medical imaging for rapid prototyping 19
of increasing image noise. Smoothing fi lters reduce noise content in images
but also decrease edge sharpness.
In general, when building medical models, smooth fi lters tend to give
better results and are easier to work with. The effect of sharp versus smooth
fi ltering is illustrated in Figs. 2.11 and 2.12 where the arrow represents a
density profi le, which is shown as the graph on the right.
Although the smooth image contrast appears poor on screen (Windows
computers can only show 256 shades of grey), taking a density profi le shows
that the actual contrast is good and that the smooth data allows a much
lower threshold to be used.
2.3 Magnetic Resonance (MR)
2.3.1 Background
Magnetic Resonance (MR) imaging exploits the phenomenon that all atoms
have a magnetic fi eld that can be affected by radio waves. Atoms have a