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The effect of source to image-receptor distance on effective dose for some common X-ray projections

¹ Unitec New Zealand, Private Bag 92025, Auckland, New Zealand, ² School of Medical Radiation Science, Cumberland Campus, University of Sydney and ³ Medical Physics Department, Westmead Hospital, Sydney, Australia

View larger version (35K): [in a new window]   Figure 1. The three cases considered by Welander and Wickman, collimation to (a) image receptor, (b) central region of interest (ROI) and (c) entrance surface. The arrows indicate the size and position of the beam area.

View larger version (17K): [in a new window]   Figure 2. Theoretical normalized energy imparted as source-to-image distance (SID) is changed, for collimation to image receptor, central region of interest (ROI) and entrance surface.

View larger version (11K): [in a new window]   Figure 3. (a) Dependence of effective dose on source to image distance (SID) for the lateral chest projection for three collimation cases. (b) Dependence of effective dose on SID for the lateral lumbar-spinal joint (LSJ) projection for extended SID up to 10.0 m. Collimation is to a central ROI. The line of best fit is for SID of 2.0–10.0 m.

View larger version (33K): [in a new window]   Figure 4. Collimation to a fixed beam size at the entrance surface, showing the cut-off of tissue at greater source-to-image distances (SIDs). In practice, if the SID is increased, the light-field dimensions have to be increased also so as to avoid this cut-off.