###### Abstract  
This study optimized the ultrasound image of carotid artery stenosis using Taguchi dynamic analysis and an indigenous water phantom. Eighteen combinations of seven essential factors of the ultrasound scan facility were organized according to [PERSON]'s L\({}_{\mathrm{IS}}\) orthogonal array. The seven factors were assigned as follows: (1) angle of probe; (2) signal gain; (3) resolution vs. speed; (4) dynamic range; (5) XRES; (6) zoom; (7) time gain compensation. An indigenous water phantom was customized to satisfy the quantified need in [PERSON]'s analysis. Unlike the conventional dynamic Taguchi analysis, an innovative quantified index, the figure of merit (FOM), was proposed to integrate four specific quality characteristics, namely (i) average difference between the practical scan and theoretically preset area (78.5, 50.2 and 12.6 mm\({}^{2}\)) of stenosis, (ii) standard deviation of the average, (iii) practical scan's sensitivity \(\beta\) to various stenosis diameters (10, 8, and 4 mm), and (iv) correlation coefficient \(r^{2}\) of the linear regressed sensitivity curve. The highest value (\(FOM=0.413\)) was furnished by the optimal combination of factors on 18 groups under study, yielding high \(r^{2}\) and low \(\beta\) or standard deviation values and the best quality of ultrasound images for the further clinical diagnosis. The comparison between FOM and the conventional signal-to-noise (S/N) ratio in [PERSON]'s analysis revealed that FOM compiled more quality characteristics that were superior by nature to fulfill the practical need in clinical diagnosis. The alternative choice in ultrasound scan optimization can be based on stenosis diameter variation from a different perspective to be explored in the follow-up study. carotid artery stenosis; ultrasound image quality; [PERSON]'s dynamic analysis; orthogonal arrays; figure of merit (FOM); signal-to-noise (S/N) ratio; water phantom +
Footnote †: journal: Applied Sciences  
to monitor patients after endarterectomy or stenting [3,4]. Meanwhile, the grayscale B-mode is widely used in the routine ultrasound examination of carotid arteries to detect abnormalities and flow-limiting artery stenosis for revealing cranial and external carotid artery disease in clinical diagnosis. It is essential to optimize the ultrasound scan images in routine diagnosis since its noninvasive nature always prioritizes for medical staff to catch the general idea of stenosis syndrome. Several researchers have noted the importance of acquiring high-quality ultrasound scanned images and proposed solutions via various approaches. [PERSON] et al. [5] adopted computer-aided analysis, while [PERSON] [6] and [PERSON] et al. [7] proposed new algorithms to improve the resolution of scanned images by their postprocessing. Alternatively, [PERSON] et al. [8] developed a tissue-like phantom for imaging optimization from a practical survey approach, while [PERSON] et al. [9] applied a customized silicone-rubber tube phantom to optimize the carotid arterial wall image. [PERSON] et al. [10] combined polyvinyl alcohol cryogel phantoms with optimization of ultrasound scans based on carotid plaque geometries in MRI images. Finally, [PERSON] et al. [11] created a simplified five-tissue-like phantom, effectively simulating various diseased plaque segments. However, optimizing image quality of grayscale B-mode carotid ultrasound scans of carotid artery stenosis patients remains a challenging problem, for which a solution would significantly enhance the diagnostic accuracy. A narrow profile of carotid artery stenosis (in contrast to the cardiac one) is often ignored by radiologists. Based on previous findings of our research group [12; 13; 14; 15], this study attempts to solve it by using an indigenous water phantom and dynamic Taguchi analysis based on the figure of merit (FOM) approach, in contrast to the earlier applied static one based on signal-to-noise (S/N) ratio [12].