RESUMO
Objective:To fundamentally solve the problems of valve dysfunction caused by limited size of artificial valve, high requirements for implantation technology, destruction of subvalvular structure and proliferation of fibrous endothelial tissue. We have developed a prosthetic valve with zero left ventricular occupancy. The valve frame is appropriately higher than the existing products, slightly chimney shaped, fully accommodates the movement of the valve leaves in the valve frame, and completely supraannular surgical implantation. This study uses this valve for preclinical animal test.Methods:Seven sheep underwent the replacement of the artificial valve under the direct vision of cardiopulmonary bypass. Warfarin was used for anticoagulation for 6 months 24 hours after operation. The blood biochemistry, anticoagulation and cardiac color Doppler ultrasound were detected after operation. The sheep were killed 180 days later for autopsy to observe whether the artificial valve caused thromboembolism. The efficacy and safety of valve were observed.Results:Two of the seven sheep died within 24 hours after operation, and five survived for a long time. Later, they were killed at 180 days. The mechanical properties of the artificial valve were good, and there was no thromboembolism around the artificial valve and important organs. The tissue layer of suture ring has been completely organized and endothelial cells, and the thickness of tissue layer is about 0.6-1.0 mm. The mitral valve of experimental animals can be opened and closed freely, with smooth surface and no abnormal echo. The follow-up of color Doppler ultrasound showed that the left ventricular ejection fraction was normal (0.60-0.70) before and 6 months after operation. The results of cross valve pressure difference and blood flow velocity of artificial valve were good (vmean was far lower than 5 mmHg(1 mmHg=0.133 kPa) and pmean was lower than 1 m/s) , suggesting that the hemodynamic performance of artificial valve was good. Left ventricular retrograde angiography showed that the artificial valve was completely located in the left atrium with good position and normal opening and closing. There was no obvious perivalvular leakage and other abnormalities. Within 7 days of blood test, the indexes of surgical stress were more abnormal than those before operation. At 12 and 24 weeks, there were no obvious abnormalities in blood routine test, liver and kidney function and other blood test indexes of animals in each group.Conclusion:The new chimney shaped mechanical valve implanted completely above the mitral annulus has good wear resistance, histocompatibility, antithrombotic and hemodynamic performance.
RESUMO
Objective To investigate the role of dual-source parallel radio frequence (RF) and single-source excitation in liver imaging at 3.0 T MR.Methods This study was a retrospective analysis.One hundred and seven subjects underwent a 3.0 T TX MR scanning including axial spectrally selective attenuated inversion recovery (SPAIR) T2WI,axial DWI and coronal balanced-fast field echo( Balanced FFE).Each sequence was carried out with both single-source and dual-source RF excitation.Student＇s t test was used to compare the differences between single-source and dual-source RF excitation in the image uniformity,signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR).Wilcoxon signed rank test was used to determine whether there was difference between conventional and parallel transmission in the score of image quality.Reader agreement was assessed using the Cohen＇s Kappa test.Results For the image uniformity,there was significant difference between single-source and dual-source excitation (418.40 ± 66.75 for single-source vs.416.26 ± 50.61 for dual-source,t =2.524,P ＜ 0.05 ).There also existed significant difference between single-source and dual-source excitation in SNR and CNR,respectively.The SNR and CNR of parallel transmission (22.03 + 12.16 and 18.33 ± 10.01,respectively) were both higher than those of single transmission (20.36 ± 11.21 and 15.22 ± 8.95,respectively) ( t =- 2.630,P ＜ 0.05 for SNR and t =- 4.238,P ＜ 0.05 for CNR).Image quality comparisons revealed significantly better results with dual-source than single-source RF excitation at SPAIR T2 WI ( 1.40 + 0.42 vs.1.81 ± 0.27 ),DWI ( 1.08 ± 0.40 vs.1.63 ± 0.36 ) and Balanced FFE sequence ( 0.95 ± 0.45 vs.1.65 ± 0.37,Z =- 5.894,- 5.801 and - 6.985,respectively,P ＜ 0.01 ).In the comparison of image quality,the agreement between the two readers was very good ( Kappa ＞ 0.8,P ＜ 0.05 ).Conclusion Dual-source parallel RF excitation MR imaging in liver enables reducing dielectric shading,improving homogeneity of the RF magnetic induction field,and increasing SNR and CNR at 3.0 T.