[A new method of evaluating helical artifact by image subtraction technique].

This paper proposes a new quantitative method of appraising the helical artifact generated by computed tomography (CT) images by helical scan. The quantities-appraisal method of the helical artifact uses as a sample image, the binarization image, which performs the threshold operation. Therefore, results may differ among observers and are lacking in objectivity. We devised a procedure (subtraction technique) that uses the subtraction process as a method of appraising the helical artifact that does not a perform a threshold operation, and evaluated this procedure. As compared with an area technique, a subtraction technique can divide a helical artifact into a plus CT value (Over Level) and a minus CT value (Under Level) and can evaluate them. This provides excellent repeatability and objectivity. Moreover, since CT value data are maintained, the quality of an artifact can also be evaluated, making this a very useful procedure. By using the subtraction technique, new information will be found by evaluating helical artifacts.