Nonuniform angular dose distribution in digital breast tomosynthesis for increased conspicuity of small high contrast objects

Digital breast tomosynthesis (DBT) has been shown to decrease breast structural noise thus improving the detection of masses. However decreased detectability of microcalcifications was observed, and several studies have been performed to investigate the benefit of taking an additional central projection view after a DBT scan. Our study investigates the effect of variable angular dose distribution within a single DBT scan. Using a prototype DBT system with uniform angular dose distribution, several DBT scans (25 projection views over 40 degree angular range) were performed using different glandular doses. A subset of projection images was selected from each scan to form composite DBT scans (25 views each) with different angular dose distribution schemes (ADS). Two examples of ADS were: 1) seven central views with four times the dose of periphery; and 2) five central projections with six times the dose of periphery. The total dose for each ADS was the same as a reference scan with uniform dose distribution (1.5 mGy). They also had the same number of views and angular range, and were reconstructed using identical reconstruction filter settings. The detectability of calcifications, the 3D MTF and NPS of the system, and the ideal observer object detectability index for all cases were compared. The results showed that higher dose for the central views improve the detectability of calcifications. However magnitude of improvement depends on the reconstruction method and the size of the object.