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The prescribed convergence time control issue of spacecraft with parametric uncertainty in inertia and disturbance is investigated. An adaptive sliding mode control solution is given. As a stepping stone, a new practical predefined-time stability theorem is established for a class of nonlinear systems. Its maximum convergence time is independent of initial states and explicitly prescribed via a gain given by the users. An adaptive predefined-time sliding-mode manifold is then developed. A chattering-free and nonsingular predefined-time controller is finally designed. The spacecraft attitude dynamics' states are governed into a tiny neighborhood with arbitrary small radius after the prescribed time. The performance of this control solution is validated through two simulation examples. [ABSTRACT FROM AUTHOR]

Objective: To investigate the occurrence rate of the prelacrimal recess (PLR) and its medial bony wall dimensions based on the radiological analysis to help surgeons enhance the understanding of anatomic structures for the endoscopic prelacrimal recess approach. Methods: Cone-beam computed tomography images of 255 patients were evaluated retrospectively. The prevalence of the PLR in maxillary sinus was investigated and the thickness of its medial bony wall was measured and statistically assessed. Meanwhile, the width of the PLR was measured. The correlation between the width of the PLR and its medial bony wall thickness was assessed. The data were compared between the left side and right side, male and female. Results: The PLR was present in 82.5% of the maxillary sinus, with no significant differences between the left and right sides, as well as different gender groups. The mean thickness of the medial bony wall of the PLR was 2.84 ± 1.41 mm, without statistical difference between the left and right sides but significantly larger in males than in females. The mean width of the PLR was 4.62 ± 1.74 mm and it had a significant negative correlation with the thickness of the medial bony wall of the PLR. Conclusion: A large individual variation exists in the anatomy of PLR, including its prevalence and dimensions of its medial bony wall. When considering the intranasal endoscopic prelacrimal recess approach, the surgeons should carefully evaluate the anatomical structure of the PLR preoperatively so as to minimize the risks of surgical complications. [ABSTRACT FROM AUTHOR]

Purpose: Cone-beam CT dacryocystography (CBCT-DCG) is a newly developed lacrimal passage imaging technique. This pilot study aimed to determine the effect of reducing tube current on image quality and radiation dose of CBCT-DCG in healthy volunteers. Materials and methods: Thirty volunteers were randomly divided into three groups of ten. Each group of subjects underwent CBCT-DCG using a tube current of 13 mA, 10 mA, and 7 mA respectively. The image quality of CBCT-DCG was assessed independently by two observers using three different scoring methods and compared among the groups. The effective dose was estimated and compared among the three different tube current groups. Results: The CBCT-DCG images provided a high spatial and contrast resolution of the bony structures and the contrast medium. No significant differences were found in the image quality between different tube current groups. Compared with the 13 mA group (49.44 μSv), the effective dose for 10 mA group (38.40 μSv) and 7 mA group (27.12 μSv) decreased by 22.33% and 45.15%, respectively. Conclusion: By decreasing the tube current, CBCT-DCG can be performed with a significant reduction of effective dose without loss of image quality in healthy volunteers. [ABSTRACT FROM AUTHOR]

Objectives: Cone beam CT dacryocystography (CBCT-DCG) is a new imaging technique for assessing the lacrimal drainage system (LDS). The purpose of this pilot study is to compare the diagnostic capability and radiation dose of CBCT-DCG in different scanning fields of view (FOV) to evaluate the possibilities of the reduction of radiation dose. Methods: Fifteen healthy volunteers underwent CBCT-DCG in an upright position. The first five subjects were scanned using the scanning FOV of 11 × 10 cm (Group A), then 8 × 8 cm (Group B), and the last five subjects 5 × 5.5 cm (Group C). The image quality and diagnostic validity of different groups were evaluated by two experienced otolaryngologists. The effective dose of each group was calculated and compared. Results: All images showed good delineation of the LDS and its surrounding structures. With regard to the image quality and diagnostic validity, no differences were found among different groups. Compared with Group A, the effective radiation dose for Group B (38.40 μSv) was 38.54% lower and that for Group C (17.12 μSv) was 72.60% lower. Conclusions: A substantial reduction of the effective dose for CBCT-DCG in healthy volunteer by decreasing FOV is possible without compromising the diagnostic capability. CBCT-DCG is a potential valid first-line imaging test for the evaluation of LDS, and it permits functional assessment of lacrimal drainage. [ABSTRACT FROM AUTHOR]

Background: The intranasal endoscopic prelacrimal recess approach (PLRA) to the maxillary sinus (MS) has been reported to treat many MS and skull base diseases. However, previous studies revealed that the width of the prelacrimal recess (PLR) shows a large individual variation. The purpose of this study was to ascertain the prevalence of the PLR in MS according to gender and age. Methods: A series of 701 maxillofacial cone beam computed tomography (CBCT) scans from adult patients were analyzed retrospectively. Patients were divided into five age groups (18–24 years, 25–34 years, 35–44 years, 45–54 years, and ≥ 55 years) and by sex. The frequencies of occurrence of the PLR in the MS were calculated and compared. Results: According to the findings obtained from our study, PLR was present in 81.5% of maxillary sinuses. No differences were found when the data distributions of right and left sides were compared. For individuals, the right and left sides were not always symmetrical. The probability of PLR was lesser among women than among men, but this differences was not significant. Another finding of our study was that the percentage of PLR decreased with increasing age among patients aged < 55 years, however, increased again among patients aged ≥ 55 years. Conclusion: The anatomy of PLR varies among individuals. Careful analysis of individual anatomical structure characteristic is recommended when considering intranasal endoscopic PLRA to the MS. Besides, the age variation of PLR should be considered in order to avoid complications. [ABSTRACT FROM AUTHOR]