[Characteristic of the image by image reconstruction method applied to successive approximation method].

In recent years, an applied successive approximation method has emerged as a new reconstruction technique of the computed tomography (CT). The CT unit of our hospital is equipped with an adaptive statistical iterative reconstruction (ASiR) which applies this method. This time, we have investigated the feature of the images through the ASiR. A subtraction of the filtered back projection (FBP) image from the ASiR image of various phantoms took place, and the structure marginal region was evaluated by varying the blend rate of ASiR and the display field of view (DFOV). By varying the CT value difference with the surroundings (using iodinated contrast medium) the structure marginal region of the subtraction image was evaluated. Modulation transfer function (MTF) and noise power spectrum (NPS) measurements were carried out to make evaluations. The result was that the CT value of the marginal unit structure was elevated with an increase of the blend ratio of ASiR and DFOV. When the CT value difference with surroundings was high, an edge was formed in the structure near the marginal region, and when it was low, a slowdown in the peripheral zone was observed. The value of MTF and NPS showed the change. The formation of the edge and slowdown in the peripheral zone can be seen in clinical images, we fully need to understand this result and make use of it in the clinical field.