SU-E-I-02: Effects of Projection View Sampling On CT Numbers and Noise Level in Cone Beam Breast CT

Abstract

Purpose: To investigate and optimize the effects of the number of projection views for minimal noise level in cone bream breast CT. Methods: An Anrad flat panel detector was used on a bench top experimental CBCT system with fixed exposure. A wax phantom simulating a breast was used to study the reconstruction artifacts. A Lucite phantom with uniform structure was used to study the variation of the noise level with the number of views. The phantoms were scanned with 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 and 1400 evenly spaced projection views over 360° while keeping the total exposure at a level corresponding to a mean glandular dose (MGD) of 7.2 mGys. Each image set was reconstructed with Feldkamp's backprojection algorithm using a ramp filter. Two regions of interest (ROIs) were selected in the reconstructed images, one at the center and the other near the edge. Mean values and standard variations were measured in ROIs and plotted as the function of the number of projection views. Results: The mean values for the wax phantom were found to peak at 300 projection views. The standard variation was lowest with 400 projection views for both Lucite and wax phantoms. Conclusion: For the detector and exposure level used, 400 projection views resulted in lowest noise level, indicating optimal combination of reconstruction artifacts from projection view sampling and image noises, which tend to decrease and increase with the number of projection views, respectively. This work was supported in part by grants CA139830, CA138502 and CA124585 from the NIH‐NCI.