Abstract: In order to remove the stripes and ring artifacts caused by the defects of the detector and to improve the reconstructed image quality from flat panel detector in dental CT， a new gain correction method based on threshold was proposed.The air images were collected under the same radiation conditions as the normal scan to calculate the gain coefficient matrix by the normalization method. What’s more，the attenuation of the object was taken into account. With the matrix of the gain coefficient and the result of the threshold judgment， the gain correction was performed on each pixel of the image one by one according to the calculated gain coefficient matrix. Experimental result showed that a large number of stripes and ring artifacts in the image were effectively removed after the correction， with no stripes introduced again. The quality of the reconstructed image was improved significantly.

Key words: dental CT, flat panel detector, gain correction, ring artifact