Study on RF Heating of Implants in Different Conductivity Medium / 中国医疗器械杂志

In MRI examination, RF heating of implants will affect the safety of implant wearers. The conductivity of various tissues in the human body is significantly different, and the medium conductivity will affect the distribution of the RF electric field. Therefore, it is necessary to study the RF heating of different medium conductivity. Based on the analysis of the principle of MRI RF heating, this study build the model of the bird cage coil, ASTM standard phantom and lead, and the conductivity of several typical human tissues is selected as the conductivity in the experiment. Then calculate the power deposition of the lead at 64 MHz. The results show that the medium conductivity has no effect on the distribution of electric field and power deposition, and the hot spot distribution remains unchanged under different conductivity; The smaller the conductivity is, the larger the power deposition of the lead is, and the greater the temperature rise of the lead caused by RF heating is; The change of conductivity and power deposition is approximately linear. At the limit of 2 W/kg whole body specific absorption rate(SAR), the conductivity decreases, and the wire power deposition increases sharply.

Safety Study of Implant Wearers in MRI RF Field Environment / 中国医疗器械杂志

The complex electromagnetic field environments in magnetic resonance imaging system(MRI) can have a significant impact on patients carrying implants, the RF heating problems being particularly important. To ensure the safety of the patients, it is necessary to understand the distribution of tissue temperature in the MRI environment and its changes over time. Based on the analysis of tissue temperature rise in MRI, this paper constructs a bird cage coil for generating RF field in MRI system, and constructs ASTM standard/improved phantom and single-cavity pacemaker finite element models, use time-domain finite difference (FDTD) to simulate. Firstly, the correctness of the simulation software and simulation method was validated according to the method of ISO. Then the distribution of the electric field, SAR and temperature field and the temperature change with time were calculated in the environment of 64 MHz, 2 W/kg. The difference in temperature rise with blood heat exchange and no blood heat exchange (standard/improved phantom) was specifically compared. The simulation results show that there are electric field and SAR hotspots near the electrode tip, the wire tail and the case of pacemaker. There are high SAR values on both sides of the phantom, and the shorter the distance from the coil, the higher the SAR. The temperature field distribution is similar to the SAR distribution; the temperature is higher in the area around the end of the wire and the case of pacemaker because the heat accumulation is higher around this area. At the same time, blood heat exchange can reduce the temperature rise to a certain extent.

Pharmacoeconomic Evaluation of Peramivir versus Oseltamivir in the Treatment of Influenza Complicated with Febrile Seizures for Children / 中国药房

ABSTRACT OBJECTIVE：To compare the effectiveness and economics of peramivir and oseltamivir in the treatment of influenza complicated with febrile seizures in children. METHODS：In retrospective study，152 children with influenza complicated with febrile seizures were collected from our hospital during Dec. 2018 to Mar. 2019.They were divided into peramivir group（81 cases） and oseltamivir group （71 cases）. Fever remission time， medication duration， hospital duration， clinical efficacy （determined by convulsion，cough，nasal obstruction，runny nose，sore throat，etc.），the incidence of rash，the number of children with combined antibiotic and TCM were compared between 2 groups. Cost-effectiveness analysis was used to evaluate cost-effectiveness ratio（CER）and incremental cost-effectiveness ratio（ICER）of medication regimen in 2 groups. The sensitivity analysis of the effect and total cost were carried out with Logistic regression and multiple linear regression respectively through CER and ICER calculated by reducing 15％ drug price. RESULTS：There was no statistical significance in fever remission time， medication duration，hospitalization duration，the incidence of rash and proportion of children with combined antibiotics between 2 groups（P＞0.05）. There was statistical significance in proportion of children with combined TCM and clinical effect，and the proportion of children with combined TCM in peramivir group was significantly lower than oseltamivir group（P＜0.001）. Clinical effect of peramivir group was significantly better than that of oseltamivir group（P＝0.021）. Total cost of peramivir group and oseltamivir group were 5 442.84 yuan/person and 5 571.71 yuan/person（P＝0.795）；CER of them were 54.47 and 56.51；ICER of peramivir group was － 89.38. The results of sensitivity analysis were consistent with those of basic analysis.CONCLUSIONS： Compared with oseltamivir，peramivir is more effective and less costly for children with influenza and febrile seizures.