What is pixels and voxels?

Two dimensional slice section are composed of pixels which are the smallest picture elements.

  • The more the pixels in a certain distance the better the resolution.
  • Currently the highest resolution available for both CT and MRI is 512×512 pixels per image. In  a field that is 30×30 cm, this gives a low resolution.
  • The image resolution is stated by the number of pixels in the x any y axis only and the size of the image field will not be actually defined.
  • Each pixel in the CT scan has the value ranging from 1000 to 3096. This is often referred to as hounsfield unit (HU)
  • CT scan are calibrated such that the value 0 = the density of water.
  • High pixel values are displayed white. Lower pixel values – lower the density of tissue → darker.
  • Pixel are 2D but it is possible to convert those pictures element into a 3 D block.
  • This 3D block is referred to as a voxel or a volumetric picture element. Depending on the inter slice distance, voxel can be:
    • a cube
    • cuboid
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