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 [Formula: see text] 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., [Formula: see text]) combinations was considered. Results: The optimal setting was 120[Formula: see text]kVp, 300[Formula: see text]mAs, 0.641 pitch, 320[Formula: see text]mm FOV and 1.0[Formula: see text]s of rotation time of CT scan. The minimal MDD was 2.65[Formula: see text]mm under 0.39[Formula: see text]mm of the slit depth from the revised Student’s [Formula: see text]-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[Formula: see text]mm and 2.93[Formula: see text]mm for 0.43[Formula: see text]mm and 0.41[Formula: see text]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.
The CT scan protocol optimization for peripheral arterial occlusive disease (PAOD) syndrome was performed by organizing seven CT factors [kVp, mAs, pitch, field of view (FOV) (mm), time of rotation (s), slice thickness (mm), and matrix size] into Taguchi unique [Formula: see text] orthogonal array. The minimum detectable difference (MDD) in the optimizing process was quantified by adopting a customized line group gauge. Besides, three qualified experts in radiology examined by the double-blind criterion the gauge scanned images and ranked them, yielding the optimal setting of CT scan protocols. The latter setting for PAOD included the kVp of 100, mAs of 240, pitch of 0.513, FOV of 320[Formula: see text]mm, rotation time of 0.75[Formula: see text]s, slice thickness of 4.0, and matrix size of [Formula: see text]. The ANOVA and revised Student’s [Formula: see text]-test verified the smallest MDD as 1.43[Formula: see text]mm at a 0.45-mm gauge depth. The ranking process, which makes it possible to magnify and emphasize the imaging correlation among groups, was found to be preferable to grading in the optimization process. The comparative analysis of various MDDs obtained from different medical facilities and literary sources was performed, which revealed that the cardiac X-ray provided the finest spatial resolution according to the quantified MDD. Meanwhile, the CT scan protocol for PAOD adopted in this study had finer MDD than that for the abdomen due to comparatively low kVp or/and mAs.
BACKGROUND: Radiologists widely use the minimum detectable difference (MDD) concept for inspecting the imaging quality and quantify the spatial resolution of scans. OBJECTIVE: This study adopted Taguchi’s dynamic algorithm to optimize the MDD of cardiac CT angiography (CTA) using a V-shaped line gauge and three PMMA phantoms (50, 70, and 90 kg). METHODS: The phantoms were customized in compliance with the ICRU-48 report, whereas the V-shaped line gauge was indigenous to solidify the cardiac CTA scan image quality by two adjacent peaks along the V-shaped slit. Accordingly, the six factors A-F assigned in this study were A (kVp), B (mAs), C (CT pitch), D (FOV), E (iDose), and F (reconstruction filter). Since each factor could have two or three levels, eighteen groups of factor combinations were organized according to Taguchi’s dynamic algorithm. Three welltrained radiologists ranked the CTA scan images three times for three different phantoms. Thus, 27 (3 × 3 × 3) ranked scores were summed and averaged to imply the integrated performance of one specific group, and eventually, 18 groups of CTA scan images were analyzed. The unique signal-to-noise ratio (S/N, dB) and sensitivity in the dynamic algorithm were calculated to reveal the true contribution of assigned factors and clarify the situation in routine CTA diagnosis. RESULTS: Minimizing the cross-interactions among factors, the optimal factor combination was found to be as follows: A (100 kVp), B (600 mAs), C (pitch 0.200 mm), D (FOV 280 mm), E (iDose 5), and F (filter XCA). The respective MDD values were 2.15, 2.32, and 1.87 mm for 50, 70, and 90 kg phantoms, respectively. The MDD of the 90 kg phantom had the most precise spatial resolution, while that of the 70 kg phantom was the worst. CONCLUSION: The Taguchi static and dynamic optimization algorithms were compared, and the latter’s superiority was substantiated.
The minimum detectable difference (MDD) at various beats/min (BPM) of CT angiography (CTA) was evaluated using an oblique V-shape line gauge and poly methyl methacrylate (PMMA) phantom in this study. The customized phantom with the size of [Formula: see text][Formula: see text]cm3 was made from a 1[Formula: see text]cm-thick PMMA. The reciprocating mechanism in the phantom was run by a step motor with an eccentric gear connected to a crank rod to provide a stable harmonic motion, simulating the cardiac beats. The MDD has a unique feature in defining the quality characteristic of CT-scanned images and provides more information than simple line pair/cm in the previous studies. The derived MDD was quantified according to various BPM, and the CTA factor combination was preset following either the conventional recommendation or the optimal one. In doing so, the performance was substantiated by the Taguchi-based signal-to-noise ratio and integrated by another index, namely, figure of merit (FOM). The MDD and corresponding [Formula: see text] (dB) changed from [Formula: see text][Formula: see text]mm to [Formula: see text][Formula: see text]mm and from 16.7[Formula: see text]dB to 14.2[Formula: see text]dB, respectively, for conventional settings; while those obtained for the optimal preset changed from [Formula: see text][Formula: see text]mm to [Formula: see text][Formula: see text]mm and from 12.2 dB to 16.4 dB, respectively of CTA at 0–90 BPM. The integrated FOM values for conventional or optimal cases were 1240 and 1337, respectively. The MDD proved to be a useful technique in justifying the CTA-scanned images. For compliance with previous studies, MDD results can be converted to the line pair/cm results, but it is more informative than the quantized number of line pairs.
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