Dose saving and scatter reduction in Volume-of-interest (VOI) cone beam CT- Work in progres

In this study, we investigated the magnitude of scattered radiation and beam quality on the low contrast performance in cone beam breast CT imaging with applying volume-of-interest (VOI) imaging technique. For experiments, we used our bench-top cone beam CT (CBCT) system with a flat-panel digital detector. A cylindrical polycarbonate phantom of 11 cm in diameter was used to simulate breasts to measure radiation dose, scatter-to-primary-ratio (SPR), and contrast-tonoise ratio. To implement the VOI scanning technique, a lead filter with a rectangular opening was placed between the x-ray source and the breast phantom. The x-ray tube voltage setting was 80 kVp. The breast phantom was imaged without and with the VOI filter for open filed and VOI field, respectively. Dose measurement was performed using TLD dosimeters. Slot scanning technique with varying slot width was used to measure SPR values. The image quality assessment was performed based on figure of merit (FOM). The results showed that dose can be reduced by a factor of 3 or more outside the VOI and by a factor of 1.6 at the center of the phantom. The SPR value could be reduced by a factor of 9 inside the VOI, and the FOM was improved by a factor of 1.8 at the center of the phantom.