金属アーチファクト低減処理画像に対する逐次近似応用再構成の影響

抄録

Purpose: This study aimed to evaluate the effect of adaptive iterative dose reduction 3D (AIDR 3D) on the computed tomography (CT) image quality by using single energy metal artifact reduction (SEMAR). Materials & Methods: A water phantom (22 cmφ) with the stem for total hip arthroplasty made of titanium was scanned. The volume CT dose index (CTDI_vol) was set to 8.9 and 5.0 mGy. The reconstruction was performed using filtered back projection and AIDR 3D by soft kernel (FC13) and SEMAR. The averaged profile method was used for the quantitative evaluation of artifacts. We placed a rectangular region-of-interest on the artifact part, and obtained the x-direction averaged profile (Profile A). Profile B was obtained using a water phantom without metal. Profiles A and B were normalized as Profiles A′ and B′ using the mean value calculated from Profile B. Based on the standard deviation (SD) calculated from Profile B′, the background variation level was defined as ±2SD, and subtracted from Profile A′ (Profile A″). Finally, the area of Profile A″ was calculated and defined as Artifact_total. Artifact_over, and Artifact_under, respectively, the positive- and negative-side components of Artifact_total. Results: Both Artifact_total and Artifact_under increased according to the strength of AIDR 3D. The variations of Artifact_over and Artifact_under, due to the AIDR 3D strength, were small and large, respectively. Further, in comparison with a high dose, the effect of artifact emphasis increased at low dose. Therefore, it should be noted that stronger AIDR 3D can emphasize the residual metal artifact.