A comparative study of thermal effects of 3 types of laser in eye: 3D simulation with bioheat equation

The application of laser in ophthalmology and eye surgery is so widespread that hardly can anyone deny its importance. On the other hand, since the human eye is an organ susceptible to external factors such as heat waves, laser radiation rapidly increases the temperature of the eye and therefore the study of temperature distribution inside the eye under laser irradiation is crucial; but the use of experimental and invasive methods for measuring the temperature inside the eye is typically high-risk and hazardous. In this paper, using the three-dimensional finite element method, the distribution of heat transfer inside the eye under transient condition was studied through three different lasers named Nd:Yag, Nd:Yap and ArF. Considering the metabolic heat and blood perfusion rate in various regions of the eye, numerical solution of space–time dependant Pennes bioheat transfer equation has been applied in this study. Lambert–Beer's law has been used to model the absorption of laser energy inside the eye tissues. It should also be mentioned that the effect of the ambient temperature, tear evaporation rate, laser power and the pupil diameter on the temperature distribution have been studied. Also, temperature distribution inside the eye after applying each laser and temperature variations of six optional regions as functions of time have been investigated. The results show that these radiations cause temperature rise in various regions, which will in turn causes serious damages to the eye tissues. Investigating the temperature distribution inside the eye under the laser irradiation can be a useful tool to study and predict the thermal effects of laser radiation on the human eye and evaluate the risk involved in performing laser surgery.     

A numerical evaluation of SAR distribution and temperature changes around a metallic plate in the head of a RF exposed worker

The 1998 International Commission for Non-Ionising Radiation (ICNIRP) Guidelines for human exposure to radiofrequency (RF) fields contain a recommendation to assess the potential impact of metallic implants in workers exposed up to the allowable occupational field limits. This study provides an example of how numerical electromagnetic (EM) and thermal modelling can be used to determine whether scattered RF fields around metallic implants in workers exposed to allowable occupational ambient field limits will comply with the recommendations of relevant standards and guidelines. A case study is performed for plane wave exposures of a 50 mm diameter titanium cranioplasty plate, implanted around 5-6 mm under the surface of the forehead. The level of exposures was set to the ambient power flux density limits for occupational exposures specified in the 1998 ICNIRP guidelines and the current 1999 IEEE C95.1 standard over the frequency range 100-3000 MHz. Two distinct peak responses were observed. There was a resonant response for the whole implant at 200-300 MHz where the maximum dimension of the implant is around a third of the wavelength of the RF exposure. This, however, resulted in relatively low peak specific energy absorption rate (SAR) levels around the implant at the exposure limits. Between 2100-2800 MHz, a second SAR concentrating mechanism of constructive interference of the wave reflected back and forth between the air-scalp interface and the scalp-plate interface resulted in higher peak SARs that were within the allowable limits for the ICNIRP exposures, but not for the IEEE C95.1 exposures. Moreover, the IEEE peak SAR limits were also exceeded, to a lesser degree, even when the implant was not present. However, thermal modelling indicated that the peak SAR concentrations around the implant did not result in any peak temperature rise above 1 degrees C for occupational exposures recommended in the ICNIRP guidelines, and hence would not pose any significant health risk.     

Statistical analysis of the gamma evaluation acceptance criteria: A simulation study of 2D dose distributions under error free conditions

PurposeTo investigate the statistical distribution of the gamma value under error-free conditions, in order to study the relation between the gamma evaluation failure rate and statistically significant deviations in the general situation.MethodsThe 2D absorbed dose distribution for 30 clinical head-and-neck IMRT fields were calculated in a QC phantom. For the same fields, dose measurements were simulated by assuming that the calculated value represented the expectation value, and by adding a random spatial uncertainty of 1–9 mm (1SD) and a random dose uncertainty of 1%–3% (1SD). The simulated measurements were then compared to the calculated dose using the gamma evaluation, and the distribution of the failure rate (i.e. the probability of gamma values above unity) was analysed.ResultsFor a wide range of the random measurement uncertainty, a distinct peak in the failure rate distribution was observed. The presence of higher failure rates was associated with large values of the second order derivative of the dose distribution. For spatial uncertainties larger than or equal to the resolution of the dose matrix, and for reasonable dose uncertainties, the median value of the failure rate distribution was fairly constant.ConclusionsSimulations showed, in the general case, that the probability of having a gamma value above unity under error-free conditions was not spatially uniform. We believe that this shortcoming may be partly responsible for the limited ability of the gamma evaluation method to detect errors in clinically relevant situations.     

A double blind randomized controlled trial to evaluate the efficacy of green tea in gingivitis

Gingivitis is the most common form of oral disease especially among patients undergoing fixed orthodontic treatment. Green tea, which is extensively used in Asian countries, can help to improve the overall gingival health, which can be assessed by using the gingival indices. Evaluation of the effectiveness of green tea on the gingival health of patients undergoing Orthodontic treatment is of interest. 40 otherwise healthy patients undergoing fixed orthodontic treatment were randomly divided in two groups namely (1) study group and (2) control group. Gingival indices were scored for all the patients. Study group was given mouth rinse with green tea extract and control group was given placebo with no green tea extract. Gingival indices were measured for all the patients after 21 days. Mann Whitney U test and Wilcoxon test was used for statistical analysis. The gingival indices scoring in which the values before and after the use of mouthwash were compared. The p value was found to be statistically significant (p<0.05) in study group. But in control group statistical significant could not be reached.     

Role of chronic infection and inflammation in the gastrointestinal tract in the etiology and pathogenesis of idiopathic parkinsonism. Part 2: response of facets of clinical idiopathic parkinsonism to Helicobacter pylori eradication. A randomized, double-blind, placebo-controlled efficacy study

BACKGROUND: Links between etiology/pathogenesis of neuropsychiatric disease and infection are increasingly recognized. AIM: Proof-of-principle that infection contributes to idiopathic parkinsonism. METHODS: Randomized, double-blind, placebo-controlled efficacy study of proven Helicobacter pylori eradication on the time course of facets of parkinsonism. Intervention was 1 week's triple eradication therapy/placebos. Routine deblinding at 1 year (those still infected received open-active), with follow-up to 5 years post-eradication. Primary outcome was mean stride length at free-walking speed, sample size 56 for a difference, active vs. placebo, of 3/4 (between-subject standard deviation). Recruitment of subjects with idiopathic parkinsonism and H. pylori infection was stopped at 31, because of marked deterioration with eradication failure. Interim analysis was made in the 20 who had reached deblinding, seven of whom were receiving antiparkinsonian medication (long-t(1/2), evenly spaced) which remained unchanged. RESULTS: Improvement in stride-length, on active (n = 9) vs. placebo (11), exceeded size of effect on which the sample size was calculated when analyzed on intention-to-treat basis (p = .02), and on protocol analysis of six weekly assessments, including (p = .02) and excluding (p = .05) those on antiparkinsonian medication. Active eradication (blind or open) failed in 4/20, in whom B-lymphocyte count was lower. Their mean time course was: for stride-length, -243 (95% CI -427, -60) vs. 45 (-10, 100) mm/year in the remainder (p = .001); for the ratio, torque to extend to flex relaxed arm, 349 (146, 718) vs. 58 (27, 96)%/ year (p < .001); and for independently rated, visual-analog scale of stance-walk videos (worst-best per individual identical with 0-100 mm), -64 vs. -3 mm from anterior and -50 vs. 11 lateral (p = .004 and .02). CONCLUSIONS: Interim analysis points to a direct or surrogate (not necessarily unique) role of a particular infection in the pathogenesis of parkinsonism. With eradication failure, bolus release of antigen from killed bacteria could aggravate an effect of ongoing infection.