Background filtering for accuracy improvement in computed tomography with iterative region-of-interest reconstruction

Two methods for preventing the deterioration of the accuracy of iterative region-of-interest (ROT) reconstruction are proposed. Both methods apply filters; the first one applies them to the whole region the outside the region of interest (outside ROT) without distinguishing objects ("method 1", hereafter); and the second one applies them to only the air and patient-table regions while masking other objects outside the ROT ("method 2"). The effectiveness of both methods was evaluated in terms of simulated CT values by using two different phantoms. Method 1 reduced the artifact intensity level by 86% (at most) compared with that obtained with the conventional method. In the case of an object with high attenuation coefficient, method 2 decreases the level more than method 1. In other words, method 2 improves reconstruction accuracy without causing deterioration by the filters. By selecting either method 1 or 2 in accordance with the attenuation coefficient in regions of objects to be imaged, it is possible to reduce the error level compared with the conventional method.