Tissue Projection Errors – The second category of technical errors in panoramic radiography are tissue projection errors or those due to tissue superimposition. There are two errors possible:
- Hard Tissue Projection Errors
- Spine – The first hard tissue error can occur when the patient assumes the “head extended” position. One of the final instructions to patients before panoramic exposure is that they should move their feet slightly forward into the machine – a sort of “panoramic shuffle”. This has the effect of straightening the cervical spine of the patient. If the patient is not instructed to do this they will often assume a head projected position. This is because of the natural tendency of patient’s is to put their head forward into the panoramic head holding apparatus rather than physically moving their head and their body. The positioning effect of this is that the spine assumes a more oblique position with respect to the x-ray beam and attenuates (absorbs) more x-rays.