General introduction

The visualization of three dimensional data can be accomplished with sections. The regular sections:

• Transverse (also transaxial, axial, horizontal),
• Coronal (also frontal),
• Sagittal,
• Inclined.

 
The examination of spatial connections in a direction which is not in a regular section raises serious difficulties, so other visualization methods are used as well.

The information required to be represented could belong to a surface, as our casual observations, or be diffused in a volume, such as colored liquid not entirely mixed with water.

If the information belongs to a surface and the shape of the surface is not so important, then the surface can transform into a plane. This method is used visualizing bull’s eye during an examination of the myocardium’s blood supply.

If the surface's shape is of importance, the methods used in graphics are helping us (surf rendering). For example, surface presentation with grid structure or creating a three-dimensional image which contains transparent and opaque elements.

Three-dimensionality is composed of the following things:

• Two eyes see two slightly different pictures which are synthesized in the brain (stereo vision). This sensory method only can work with close objects. If the objects are far away, the difference is so small between them that the brain can no longer differentiate them.
• Size constancy: The closer things seem to be larger. We are conscious of the size of known objects. For instance, we observe a person who seems to be small as a distant person. Painters use this method for the illustration of distance.
• Lightening:
  • Coming from one point, the objects close to the light source are more lightened.
  • With parallel lightening using point source, the object perpendicularly lightened seem to be more bright than ones from another direction. {DIV}

 
In the case of surface visualization, generally techniques are applied from computer graphics. In the course of this, the surface’s reflectivity can be set. It could be reflective (smooth, shiny surface) and diffuse (rough surface).

• In the case of diffuse light reflection, closer things are more bright.
• The light source and the point of view can be the same. Its realization is quite simple.
• The light source and the point of view can be different (more than one source): appearance of shadows

 
An image can be constructed with the consideration of multiple reflections (ray tracing).

The image on the computer’s screen could move, rotate, which helps, moreover, assures on its own three-dimensional view.

Visualizing three dimensional medical images, generally parallel projection is applied and it can be supposed that the source and the point of view overlap, which makes the algorithm required for visualization much more simple. Another simplification is that the surface is considered to be monochromatic.

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