Optimization of dual slot antenna using floating metallic sleeve for microwave ablation.

Backward heating reduction is vital in power distribution optimization in microwave thermal ablation. In this study, we optimized dual slot antenna to yield reduction in backward heating pattern along the antenna shaft with the application of floating metallic sleeve. Finite element methods were used to generate the electromagnetic (EM) field and thermal distribution in liver tissue. The position of the sleeve from the tip of the probe (z = 0 mm) was varied within the range 14 ≤ z ≤ 22 mm while sleeve length was varied within 16 ≤ z ≤ 48 mm at 2 mm interval using operating frequency of 2.45 GHz. The best optimized design has reflection coefficient of -20.87 dB and axial ratio of 0.41 when the sleeve position was at 17 mm and sleeve length was 18 mm. Experimental validation shows that inclusion of a floating metallic sleeve on dual slot antenna for hepatic microwave ablation averagely increased ablation diameter and aspect ratio by 17.8% and 33.9% respectively and decreased ablation length by 11.2%. Reduction in backward heating and increase in power deposition into liver tissue could be achieved by using this antenna to provide greater efficiency and localization of specific absorption rate in delivering microwave energy for hepatic ablation.

Potential health risks due to telecommunications radiofrequency radiation exposures in Lagos State Nigeria.

BACKGROUND: The global system mobile telecommunications system (GSM) which was recently introduced in Nigeria is now being used by over 40 million people in Nigeria. The use of GSM is accompanied with exposure of the users to radiofrequency radiation (RFR), which if significant, may produce health hazards. This is the reason why many relevant national and international organizations recommended exposure limits to RFR and why it is made compulsory for GSM handsets to indicate the maximum power output as a guide to potential consumers. OBJECTIVE: This study was conducted to measure the RFR output power densities (S) from the most commonly used GSM handsets used in Lagos State and compare with the limit recommended for safety assessment. METHODS: Over 1100 most commonly used handsets of different makes and models as well as wireless phones were sampled and studied in all over the local government areas of the State. An RFR meter, Electrosmog from LESSEMF USA was used for the measurements. The handsets were assessed for health risks using the reference value of 9 Wm(-2) as recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). RESULTS: The range of the S-values obtained varied from a minimum of 1.294 0.101 Wm(-2) with Siemens model R228 to a maximum of 16.813 +/- 0.094 Wm(-2) with Samsung model C140*. The results from wireless telephones showed very low S-values ranging from a minimum of 0.024 +/- 0.001 Wm(-2) with HUAWEI and ST CDMA 1 to a maximum of 0.093 +/- 0.002 Wm(-2) with HISENSE. CONCLUSION: The results showed that the population in Lagos State may be at risk due to significant RFR exposures resulting principally from the use of GSM. Quite a number of handsets emit power above the ICNIRP recommended value. Measured RFR power close to Radio and Television masts and transmitters are within tolerable limits in most cases, only that the public should not reside or work close to RFR installations. Phone calls with GSM should be restricted to essential ones while youths and children that are more susceptible to RFR hazards should be supervised in their use of GSM. Wireless phones are quite safe.

Assessment of pre-operational radiological conditions at the Linac Centre of the Lagos University Teaching Hospital, Nigeria.

BACKGROUND: The Lagos University Teaching Hospital, Nigeria has acquired a 6 - 15 MeV ELEKTA linear accelerator for clinical teletherapy. The 15 MeV is a sufficient energy to activate photonuclear interactions of the type (h(nu), n) and (h(nu), e), in some materials found within the locality, thereby enhancing the background radiation exposure levels in the environments. OBJECTIVE: The objective of this study is to conduct a pre-operational assessment of the radiological conditions of the new LINAC Centre and its environments which is required for future uses in the assessment of the environmental impacts due to the applications of the facility. The results of this study are to provide a baseline data needed for such assessments and the impact of eventual LINAC accidents. METHODS: Radiation exposure levels due to natural background radioactivity in the controlled and supervised areas and offices in the LINAC localities have been measured. The environmental radiation survey around the Centre was conducted according to the requirements prescribed by the ICRP, IAEA Basic Safety Standards etc. The specific radioactivity contents of 100 building, furna and flora material samples have been determined using a Gamma Well Scintillation Counter. RESULTS: The mean exposure rates all over the LINAC Centre varied from 2.0 muSvh(-1) to 3.3 muSvh(-1). In the controlled areas, the mean value was 2.4 muSvh(-1) and it was 2.7 muSvh in the supervised areas, while in the adjacent offices, it was 2.5 muSvh(-1). The means of the measured specific activities in the cement concrete, soil, plant and grass samples were 42.7299 Bqkg(-1), 39.9592 Bqkg(-1), 23.9010 Bqkg(-1) and 20.8940 Bqkg(-1) respectively. CONCLUSION: A database for the assessment of the environmental impacts of the clinical LINAC and the impacts of its eventual accidents has been generated for future periodic uses.

Safety Awareness in Selected X-ray Diagnostic Centres in Surulere and Ikeja Local Government Areas of Lagos State; Nigeria

Background: Health hazards are associated with exposure to ionizing radiations such as x-rays. Many private x-ray diagnostic clinics in Lagos State operate with inadequate safety and protection devices; which make the conditions unsafe to patient and environment. Objective: To assess the working conditions; protection measures put in place; safety awareness and attitudes of both employees and employers to safety and protection in radiodiagnostic centers in Surulere and Ikeja Local Government Areas.Methodology: Questionnaires were used for collecting information on socio-demographic data; occupational history; activities; working conditions; knowledge and experience of radiation hazards in x-ray centers. Interviews were conducted with Heads of Departments and Radiologists using the checklist adapted from the International Atomic Energy AgencyResults: 88.9 of the participating centers had adequate space and some safety assessment performed prior to installation of the facility. 81.5 had few basic protection devices. Only 40.7employed adequate and qualified staff while 25.9 provided personnel training and 22.2 had quality control programme. 14.8 had radiation protection programme. 60.2of respondents were aware of health hazards associated with radiation exposures; 57.8 of which were males. Conclusion : Operation conditions in most private diagnostic centers are below standard due to grossly inadequate provision of safety and protection devices. Employment of qualified staff and continuous education need be emphasized and enforced

Effects of 2.45 GHz microwave exposures on the peroxidation status in Wistar rats.

One of the consequences of exposures to microwave (MW) radiations is the enhanced production of free O2, free radicals, peroxides and superoxides. The effects on the lipid peroxidation status (LPS) of whole body irradiation of 120 Wistar rats with 2.45 GHz MW at a power density of 6mWcm(-2) have been studied using the MW generator model ER6660E from Toshiba UK Ltd. The LPS in the rats was monitored for a period of 8 weeks post irradiation using thiobarbituric acid (TRA) method. The MW exposures caused an increase in the LPS from the mean control value of 4.18 x 10(-6)g 1(-1)to a maximum of 6.50 x 10(-6) g 1(-1) within the first 24 hrs, and then gradually reduced to control value after about a week. 1mg kg(-1) of ascorbic acid administered before irradiation caused a decrease in the LPS from the control value to a minimum of 2.86 x 10(-6)g 1(-1) within the first week. The value then gradually rose to a maximum of 3.96 x 10(-6)g 1(-1) within the monitoring period. 1 mg kg(-1) of a-tocopherol also administered before irradiation also caused a decrease in the LPS from the control value to a minimum of 2.10 x 10(-6) g 1(-1) within the first week. The value then gradually rose to a maximum of 3.94 x 10(-6) g 1(-1) within the monitoring period. The results obtained from this study demonstrate that MW exposures cause significant increase in the LPS and there are protective effects of the anti-oxidants ascorbic acid and alpha-tocopherol.