Demonstration of dual resolution cone beam CT technique with an a-Si/a-Se flat panel detector

Abstract

In this study, we demonstrated volume of interest (VOI) scanning technique in dual resolution cone beam CT (CBCT) breast imaging. A paraffin cylinder with a diameter of 130 mm was used to simulate breast. A wire phantom with a diameter of 15 mm was constructed as VOI. The phantom contains 8 vertically aluminum wires of various diameters surrounded by paraffin. The wire phantom was inserted into the breast phantom 45 mm away from the center. The phantoms were first scanned with a bench top experimental CBCT system at a low exposure level with the detector operated in a binning mode. Then a VOI mask was placed between the x-ray source and the phantoms. The phantoms were scanned again with high exposure level and the detector operated in the non-binning mode. The VOI mask was moved to follow the wire phantom during the whole CT scan to limit the exposures to cover the VOI only. The low resolution and high resolution images were then combined together for reconstruction with FDK algorithm. Visual review of the regular and dual resolution CBCT images shows that thinnest resolvable wire in the dual resolution CBCT images has a diameter of 152 μm. The thinnest resolvable wire in regular CBCT images has a diameter of 254 μm. The estimated dose to the phantom for dual resolution CBCT is 123% of that with regular CBCT at low exposure level. The dual resolution CBCT technique greatly enhances the CT image quality while still remains a low exposure level to the phantom.