OPTIMIZING THE MINIMUM DETECTABLE DIFFERENCE OF COMPUTED TOMOGRAPHY SCANNED IMAGES VIA THE TAGUCHI ANALYSIS: A FEASIBILITY STUDY WITH AN INDIGENOUS HEPATIC PHANTOM AND A LINE GROUP GAUGE

Objective: The minimum detectable difference (MDD) of computed tomography (CT) scanned images was quantified and optimized according to an indigenous hepatic phantom, line group gauge and Taguchi L-18 optimization analysis in this work. Methods: Optimal combinations of CT scan factors in every group with the level organization were judged using the Taguchi analysis, in which every factor was organized into only 18 groups, creating evaluated outcomes with the same confidence as if every factor was analyzed independently. The five practical factors of the CT scan were (1) kVp, (2) mAs, (3) pitch increment, (4) field of view (FOV) and (5) rotation time for one loop of CT scan. Insofar as each factor had two or three levels, the total number of 162 (i.e., 2 x 3 x 3 x 3 x 3) combinations was considered. Results: The optimal setting was 120 kVp, 300 mAs, 0.641 pitch, 320 mm FOV and 1.0 s of rotation time of CT scan. The minimal MDD was 2.65 mm under 0.39 mm of the slit depth from the revised Student's t-test with a 95% confidence level. In contrast, the MDD of conventional and the best one (no. 7) among all original 18 groups were 3.27 mm and 2.93 mm for 0.43 mm and 0.41 mm slit depths, respectively. Conclusion: The Taguchi analysis was found very lucrative for the design of imaging analysis in practical diagnosis. The indigenous line group gauge and hepatic phantom also proved to be suitable in simulating the human body in real hepatic carcinoma examination.