After the production of the gradient coil of the magnetic resonance imaging system, electromagnetic field testing is required to verify whether the assembly accuracy meets the electromagnetic field requirements. Since the passive magnetic field B _z satisfies the Laplace ^,s equation and is a harmonic function, and according to the extreme value principle of harmonic function, the maximum or minimum values of B _z can only appear on the boundaries, so the observation points of the magnetic field are generally selected on the surface of the spherical imaging area. For superconducting magnets used for human body magnetic resonance imaging, a spherical area with a center diameter of 40~50 cm is generally selected as the shimming target area. Only the field value of the target area needs to be measured, and the spherical harmonic coefficients obtained after data processing are used to determine the magnetic field performance of the gradient coil. There are many testing principles and methods for electromagnetic fields, so there is no unified way and method in the field of commercial applications. This article is based on the Gauss-Legendre numerical integration, measures and analyzes the magnetic field performance of gradient coils by building a data acquisition system, and this article applies numerical analysis methods to calculate the spherical harmonic coefficients of the magnetic field using discrete test data, providing a feasible method for the production and testing of gradient coils.
Magnetic Resonance Imaging/methods* ; Magnetic Fields ; Electromagnetic Fields ; Equipment Design

Objective:To study the effects of the alternate rapid maxillary expansion and constriction(Alt-RAMEC)with maxillary protraction on different parts of upper airway by CBCT.Methods:20 Angle Class Ⅲ patients aged 9-12 years were included,and CBCT images were taken before treatment and after Alt-RAMEC with maxillary protraction,the total volume of the upper airway,the volume of each part of the nasopharynx,palatopharynx,linguopharynx and laryngopharynx,the cross-sectional area of the division in-terface,and the minimum cross-sectional area were measured after 3D reconstruction using Dolphin software,the data were analyzed using SPSS 26.0 software.Results:The total upper airway volume,nasopharyngeal volume,and palatopharyngeal volume were in-creased by the average of 1 385.39 mm3(P=0.013),546.74 mm3(P=0.011)and 768.03 mm3(P=0.035)respectively after Alt-RAMEC with maxillary protraction treatment;the area of the nasopharyngeal and palatopharyngeal division interface increased by 73.79 mm2(P=0.002),the cross-sectional diameter by 1.41 mm(P=0.037),and sagittal diameter by 1.52 mm(P=0.022)respectively;however,there was no statistically significant change in the volume,minimum cross-sectional area,partition area,and partition transverse and sagittal diameters of the linguopharynx and laryngopharynx(P＞0.05).Conclusion:Alt-RAMEC with maxil-lary protraction can significantly increase nasopharyngeal and palatopharyngeal volumes,with no significant effect on the linguopharyn-geal and laryngopharyngeal segments of the airway.

Objective:To investigate the effect of head model in improving the photographic ability of interns during the photographic training of oral facial image in pediatric dentistry.Methods:A total of 60 interns of stomatology school affiliated to Xinjiang Medical University were randomly divided into head model training group, mutual training group and clinical probation group for photographic training. After the training, the interns in the three groups were evaluated for the photographic time, the level of photos, etc., by the training test and satisfaction level of volunteers. Besides, the head model training group was conducted by questionnaire survey. One-way analysis of variance and least significant difference analysis were used to analyze the data between groups by SPSS 17.0 software.Results:There was no statistical difference between the head model training group and the mutual training group in photographic time and level of photos, while both of them were much better in the head model training group and mutual training group than in the clinical probation group ( P<0.05). There was no statistical difference between the head model training group and the mutual training group in the satisfaction level, while that was lower in the head model training group than in the clinical probation group ( P<0.05). According to the questionnaire survey, most interns in the head model training group acknowledged its effects. Conclusion:The use of head model can help improve the oral photographic ability, and promote the teaching effect and efficiency in photographic training.

Objective To investigate the effect of flipped classroom model in the theory teaching of urology,and to provide a reference for promoting teaching methods.Methods The clinical medicine classes 1 and 2 of 2014 in the five-year undergraduate program,with 120 students in each class,were enrolled,with class 1 as teaching reform class and class 2 as traditional teaching class.The flipped classroom model was applied in class 1,and the traditional teaching method was applied in class 2.Tests and questionnaires were used at the end of the class to evaluate teaching effect.All the data were analyzed by Graphpad Prism 6.1,t test and Chi-square test were used for stabistical analysis.Results There were significant differences between the teaching reform class and the traditional teaching class in the mean score of chapter test [(80.78± 9.02) vs.(75.03 ± 7.98),P ＜0.05] and the mean score of comprehensive quality [(82.09 ± 8.89) vs.(76.34 ± 6.45),P＜0.05].The questionnaire survey showed an overall degree of satisfaction of 98.5％ among students;81.67％ of all students actively participated in learning,91.67％ were willing to participate in the teaching with flipped classroom model,75.84％ thought this model improved learning enthusiasm,65％ thought it improved the ability of self-study,73.33％ thought it improved their understanding of the learning content,and 84.17％ thought it strengthened the communication between teachers and students.Conclusion The flipped classroom model has a better effect than the traditional teaching model in the theory teaching of urology and is easily accepted by students.Therefore,it holds promise for clinical application.

Objective:To investigate the effects of bone morphogenetic protein 2(BMP-2)expression in the related periodontal tissue on bone remodeling under different distracting force during rapid tooth movement by resistance reduction and distraction. Methods:1 2 Beagle dogs were randomly divided into 4 groups as follows:5 d distraction,1 5 d distraction,1 5 d distraction and 1 0 d retaining and 1 5 d distraction and 90 d retaining.4 4 were distalized.6 teeth in each group were randomly assigned to re-sistance and distracting method,resistance and conventional method and conventional method,and there were 2 teeth in each group.Moving teeth models were prepared regularly.BMP-2 expression was examined by immunohistochemistry.Results:The BMP-2 positive expression of the 3 groups of different distraction schedule showed similar distribution area,and it reached peak at the end of 1 5-day distration,but the group of resistance and distracting method showed the maximum peak(P <0.05)and maximum tooth movement(P <0.01 ).In different stages of distraction,the positive expression in the group of resistance reduc-tion and conventional method was higher than in the group of conventional method but lower than the group of resistance reduction and extraction method(P <0.05).There was no significant difference in BMP-2 positive expression among 3 groups when retai-ning was 90 d(P >0.05).Conclusion:Resistance reduction with sustained strong distracting force can significantly increased the positive expression of BMP-2 and effectively accelerate new bone formation in periodontal tissue.

BACKGROUND:To make a better preparation for orthodontic tooth, we investigate the changes in the localization of the anterior wal of the maxilary sinus and maxilary tuberosity, analyze the development of the maxila, and detect the bone mass of the maxila and development timing. However, the use of Auto-CAD software has not been reported to localize the anterior wal of the maxilary sinus and maxilary tuberosity. OBJECTIVE: To investigate the localization and growth of the anterior wal of the maxilary sinus and maxilary tuberosity in 300 children aged 4-14 years from the Han ethic group in Urumqi, Xinjiang Uygur Autonomous Region, China. METHODS: Totaly 300 children, 4-14 years of age, admitted at the Stomatological Hospital of Urumqi, Xinjiang Uygur Autonomous Region, China, were enroled. According to Helman’s dental developmental staging, these children were divided into five groups: groups IIA, IIC, IIIA, IIIB, IIIC. Auto-CAD software was used to analyze the panoramic radiographs of the maxila and mandible. The tracing of each radiograph was digitized by translating the reference points onto an X-Y coordinate system. The straight line that passed the point where the nasal septum intersected with the hard palate (point O) and the point where the medial wal of maxilary sinus intersected with the hard palate (point PA) was designated as the X axis. The straight line that was vertical to the X axis and passed through the point O at a right angle was designated as the Y axis. The X and Y coordinate values of reference point were calculated. And then O point was set as (0, 0), and the point where the posterior wal of maxilary tuberosity intersected with the hard palate (PP) was set as (PPX, PPY). Colected data were analyzed statisticaly to understand the changes in the localization of PA and PP at different stages of dental development. RESULTS AND CONCLUSION:The change of point PA had on significant differences between the five groups (α > 0.05). Point PP grew obviously in a horizontal rearward and vertical downward manner from stage IIA to IIIA; this point only presented a horizontal rearward growth from stage IIIA to IIIB and only a vertical downward growth from stage IIIB to IIIC. This period was the time of the second molar eruption, indicating that the second molar eruption is helpful to the vertical growth of the maxila.

BACKGROUND: Palatal implant could be an effective type of anchorage that can afford long-term stress, and bone thickness and bone density of the implant placement will affect the success of the implant stability. Presently, actinoscopy commonly used in stomatological clinic cannot provide the precise information of palatal bone thickness and bone mineral density such as toroidal slide plate photograph and skull lateral projection. OBJECTIVE: To measure the thickness and density of median palatine suture, and to provide the consultation for implant anchorage using spiral CT. DESIGN, TIME AND SETTING: A measurement study was performed at the Medical Imaging Center, First Affiliated Hospital of Xinjiang Medical University from July to December in 2008 PARTICIPANTS: The sample consisted of 194 cases undergoing 64 slice CT at the Medical Imaging Center of First Affiliated Hospital of Xinjiang Medical University, including the scope of the hard palate and maxillary dentition. They were aged from 18 to 50, and divided into three groups by age, 18-30-year-old group, 31-40-year-old group, and 41-50-year-old group. METHODS: Measurement of palatal raphe area first three-dimensional reconstruction of images at up to nasion plane centerline, whichever was determined as a reference surface plane, selection one point on incisor cervix in this line, to measurement of the available palatal bone height; sagittal views were selected at 6 mm dorsally from the incisive canal. The available bone height was defined as the distance from the palatal baseline (lower cortical border of the palate) to the nasal cavity (upper cortical border of the nasal cavity). Bone mineral density can also be measured at the same site, take the average of the cortical and cancellous bone. MAIN OUTCOME MEASURES: The palatal bone thickness and bone thickness density were measured at 6 mm dorsally from the incisive canal. RESULTS: Male in the palatal bone thickness and bone mineral density were significantly higher than female (P < 0.05); there were no significant difference between Han and Uygur (P>0.05). In different age's group of men and women, the palatal bone thickness and bone mineral density showed no statistical difference (P > 0.05). Age, palatal bone thickness and palatal bone mineral density had no significant correlation. CONCLUSION: Spiral CT can be used in different parts of mandible thickness and density measurement and analysis. The palate raphe can be implant as orthodontic anchorage if it measured exactly.

Objective To investigate the expression and clinical significance of survivin and PTEN in bladder transitional cell carcinoma(TCC).Methods The expression of survivin and PTEN was studied by S-P immunohistochemisty in 10 cases of normal urinary bladder tissues and 62 cases of the bladder TCC. Results All the normal urinary bladder tissues showed positive staining pattern of PTEN protein, negative staining pattern of survivin protein, positive rate of PTEN in 62 cases of the bladder TCC is 46.8%,the difference of positive rate between grade Ⅰ and grade Ⅲ was significant(P＜0.05),the difference of positive rate between Tis～T_1 and T_2～T_4 showed a trend of decreasing, but there was no statistically significant difference(P＞0.05);positive rate of survivin in 62 cases of the bladder TCC is 56.5%,the difference of positive rate between grade Ⅰ and grade Ⅲ was significant(P＜0.05),the difference of positive rate between Tis～T_1 and T_2～T_4 was significant too(P＜0.05).The expression of PTEN protein and survivin protein was reversely correlated(P＜0.05).Conclusion The abnormal expression of PTEN protein and survivin protein play an important role in the occurrence and progress of the bladder TCC.It can be regarded as a useful diagnostic marker in the bladder TCC.