Disadvantages of helical scanning

• Broadening of slice profile

  • e.g. 5mm using pitch 1, 360° interpolator gives 6.3 mm slice
  • problem overcome by using 180° interpolator, at expense of image noise (~15% higher than axial)

• Helical interpolation artefacts

  • Worse at high pitches
  • Axial still choice for some examinations (e.g. head)
    • With multi-slice scanners, helical may be preferred