Room: AAPM ePoster Library
Purpose: Heel effect is a known phenomenon in x-ray imaging. However, the effect of kVp on the Heel effect in the mammographic energy range is relatively unknown. The Heel effect should be investigated for different kVp values and different target/filter combinations.
Methods: Using a Hologic Selenia Dimensions mammography unit, a Radcal AGMS-DM+ solid-state detector was positioned at 0cm, 6cm, 12cm, and 18cm from the chest edge. For these positions, different target/filter combinations (W/Rh, W/Ag, and W/Al) were used to find the exposure for various kVp (20-39kVp for W/Rh and W/Ag; 20-49kVp for W/Al). The ratio was found for the exposures at the different positions to exposure at the 0cm, and compared across the different kVp.
Results: The relative exposures were plotted for all target/filter combinations and for various kVp values. For W/Rh and W/Ag, the relative exposure increases for the increasing kVp values, peaks around 25kVp, and decreases past 25kVp when looking at a fixed distance (6cm, 12cm, and 18cm) from the chest edge. For W/Al, the relative exposure increases with kVp until 35kVp, where it dips, and then begins increasing again past 40kVp for a fixed distance.
Conclusion: The Heel effect was found to have a dependence on the kVp for various mammography target/filter combinations. For W/Rh and W/Ag, the relative exposure peaked at 25kVp for a fixed distance for all distance measurements. For the W/Al, there is a dip in relative exposure at 35kVp. It is also unclear why there is this dip at this kVp. It is suspected to be caused by the k-edge of the filter material, however further investigation should be done.