Mean Glandular Dose and Figure of Merit of 2 Dimensional and 3 Dimensional Imaging in Digital Breast Tomosynthesis

Abstract

Studies of Mean Glandular dose (MGD) and Image quality for 3D imaging are still relatively new compared to 2D imaging. Therefore the objective of this research is to compare mean glandular dose (MGD) and figure of merit (FOM) obtained using ionization chamber between 2D and 3D breast imaging. This experimental study was conducted at the National Cancer Society using the Hologic Selenia Digital Breast Tomosynthesis. Three types of CIRS phantom with 50/50, 30/70 and 20/80 glandularity were exposed with an Auto - Filter mode in the Cranio-caudal projection. The ionization chamber (IC) was used to measure the Entrance Surface Air Kerma (ESAK) and Half Value Layer (HVL). The MGD value was calculated using Euref protocol and finally the image quality was assessed qualitatively by two radiologists and quantitatively by figure of merit (FOM). The results of the experiment showed that the MGD value obtained from the experiment increased with thickness and the MGD value for 3D projection is consistently higher than 2D projection. The spectrum W/Rh has a higher FOM value compared to spectrum W/Al for all phantoms. For 3D imaging the FOM value decreased when the depth of the object increased and the object is clearer in the center compared with other slices. In summary, it is estimated the MGD value for combined 2D and 3D increased by 1.5 - 2.5 times than single 2D mammography. The combined 2D and 3D imaging MGD value for 50% was 2.27 mGy, for 30% was 3.07 mGy and for 20% was 4.09mGy. *The combined 2D and 3D imaging for 50% glandularity is less than FDA limit for single projection and resulted in superior image quality compared to 2D imaging alone.