Performance of three-photon PET imaging: Monte Carlo simulations

We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered. Three-photon imaging requires high energy resolution detectors. Parameters currently attainable by CdZnTe semiconductor detectors, the technology of choice for the future development of radiation imaging, are assumed. Spatial resolution is calculated as a function of detector energy resolution and size, position in the field of view, scanner size, and the energies of the three gamma annihilation photons. Possible ways to improve the spatial resolution obtained for nominal parameters: 1.5 cm and 3.2 mm FWHM for human and small animal scanners, respectively, are indicated. Counting rates of true and random three-photon events for typical human and small animal scanning configurations are assessed. A simple formula for minimum size of lesions detectable in the three-gamma based images is derived. Depending on the contrast and total number of registered counts, lesions of a few mm size for human and sub mm for small animal scanners can be detected

An investigation of tooth loss factors in elderly patients using panoramic radiographs

Objectives The aim of this study was to observe the dental condition in a group of elderly patients over a period of 10 years in order to clarify important risk factors. Materials and methods Participants were elderly patients (in their eighties) who took panoramic radiographs between 2015 and 2016, and for whom panoramic radiographs taken around 10 year earlier were also available. The number of remaining and lost teeth, the Eichner Index, the presence or absence of molar occlusion, the respective condition of dental pulp, dental crowns, alveolar bone resorption, as well as periapical lesions were investigated through the analysis of panoramic radiographs. Additionally, other important variables were collected from patients' medical records. From the obtained panoramic radiograph sets, the patients' dental condition was investigated, and a systematic comparison was conducted. Results The analysis of the panoramic radiographs showed that the number of remaining teeth decreased from an average of 20.8-15.5, and the percentage of patients with 20 or more teeth decreased from 69.2 to 26.9%. A factor analysis investigating tooth loss risk suggested that tooth loss was associated with the bridge, P2 or greater resorption of the alveolar bone, and apical lesions, and gender (with males having a higher risk compared to females). Conclusions Teeth showing P2 or greater alveolar bone resorption, bridge, and apical lesions on panoramic radiographs are most likely to be lost in an elderly patient's near future. Consequently, this group should be encouraged to visit their dental clinics regularly and receive comprehensive instruction on individual self-care methods

Electronic Structures of N-doped Graphene with Native Point Defects

Nitrogen doping in graphene has important implications in graphene-based devices and catalysts. We have performed the density functional theory calculations to study the electronic structures of N-doped graphene with vacancies and Stone-Wales defect. Our results show that monovacancies in graphene act as hole dopants and that two substitutional N dopants are needed to compensate for the hole introduced by a monovacancy. On the other hand, divacancy does not produce any free carriers. Interestingly, a single N dopant at divacancy acts as an acceptor rather than a donor. The interference between native point defect and N dopant strongly modifies the role of N doping regarding the free carrier production in the bulk pi bands. For some of the defects and N dopant-defect complexes, localized defect pi states are partially occupied. Discussion on the possibility of spin polarization in such cases is given. We also present qualitative arguments on the electronic structures based on the local bond picture. We have analyzed the 1s-related x-ray photoemission and adsorption spectroscopy spectra of N dopants at vacancies and Stone-Wales defect in connection with the experimental ones. We also discuss characteristic scanning tunneling microscope (STM) images originating from the electronic and structural modifications by the N dopant-defect complexes. STM imaging for small negative bias voltage will provide important information about possible active sites for oxygen reduction reaction.Comment: 40 pages, 2 tables, 16 figures. The analysis of Clar sextets is added. This version is published on PHYSICAL REVIEW B 87, 165401(2013

Pickoff and spin-conversion quenchings of ortho-positronium in oxygen

The quenching processes of the thermalized ortho-positronium(o-Ps) on an oxygen molecule have been studied by the positron annihilation age-momentum correlation techinique(AMOC). The Doppler broadening spectrum of the 511 keV gamma-rays from the 2gamma annihilation of o-Ps in O_2 has been measured as a function of the o-Ps age. The rate of the quenching, consisting of the pickoff and the spin-conversion, is estimated from the positron lifetime spectrum. The ratio of the pickoff quenching rate to the spin-conversion rate is deduced from the Doppler broadening of the 511 keV gamma-rays from the annihilation of the o-Ps. The pickoff parameter ^1Z_eff, the effective number of the electrons per molecule which contribute to the pickoff quenching, for O_2 is determined to be 0.6 +- 0.4. The cross-section for the elastic spin-conversion quenching is determined to be (1.16 +- 0.01) * 10^{-19} cm^2.Comment: 4 pages with 5 eps figures, LaTeX2e(revtex4

The effectiveness of mouthwashes in alleviating radiation-induced oral mucositis in head and neck cancer patients: A systematic review

Objective The aim of the study was to perform a systematic literature search and meta-analysis to reveal the most effective mouthwash for head and neck cancer patients who are experiencing radiation therapy-induced mucositis. Methods Using two electronic databases, a literature search and data interpretation were systematically performed as follows: (i) problem specification, (ii) devising of a literature search plan, (iii) literature search and retrieval of publications, and (iv) meta-analysis and data interpretation. The main problem was specified as follows: what mouthwash is effective in alleviating oral mucositis for head and neck cancer patients who are undergoing radiotherapy? Results The literature search yielded 354 titles and abstracts. After reviewing the extracted literature, 25 publications met the inclusion criteria for this study and 17 of 25 were eventually evaluated in the meta-analysis. Conclusion The results of the meta-analysis indicated that the use of a mouthwash that includes anti-inflammatory properties contributes the most to alleviating oral mucositis in patients who are undergoing radiotherapy to treat head and neck cancer

Intraoral ultrasonographic features of tongue cancer and the incidence of cervical lymph node metastasis

Purpose: The purpose of this study was to investigate the relationship between the visual characteristics of tongue lesion images obtained through intraoral ultrasonographic examination and the occurrence of late cervical lymph node metastasis in patients with tongue cancer. Patients and Methods: This study investigated patients with primary tongue cancer who were examined using intraoral ultrasonography at Hiroshima University Hospital between January 2014 and December 2017. The inclusion criteria were squamous cell carcinoma, curative treatment administration, lateral side of tongue, surgery or brachytherapy alone, no cervical lymph node or distant metastasis as primary treatment, and treatment in our hospital. The exclusion criteria were carcinoma in situ, palliative treatment, dorsum of tongue, and multiple primary cancers. The follow-up period was more than 1 year. The primary endpoint was the occurrence of late cervical lymph node metastasis, and the primary predictor variables were age, gender, longest diameter, thickness, margin or border shapes of the lesion, and treatment methods. The relationship between the occurrence of late cervical lymph node metastasis and the longest diameter, thickness, margin types, and border types as evaluated through intraoral ultrasonography were assessed. The data were collected through a retrospective chart review. Results: Fifty-four patients were included in this study. The analysis indicated that irregular lesion margins were significantly associated with the occurrence of late cervical lymph node metastasis (P < .0001). The cutoff value for late cervical lymph node metastasis was 21.2 mm for the longest diameter and 3.9 mm for the thickness. Conclusions: The results of this study indicates that the irregular lesion margin assessed using intraoral ultrasonography may serve as an effective predictor of late cervical lymph node metastasis in N0 cases. (C) 2020 American Association of Oral and Maxillofacial Surgeon

Nonpolar optical scattering of positronium in magnesium fluoride

We report the results of the analysis of the temperature broadening of the momentum distribution of delocalized Positronium (Ps) in Magnesium Fluoride in terms of optical deformation-potential scattering model (long-wavelength optical phonons). The Ps optical deformation-potential coupling constant $D_{o}$ in MgF$_{2}$ has been determined to be $(1.8\pm0.3)\times10^{9}$ eV/cm. We also show that the Ps momentum distribution is sensitive to second-order phase transitions in those crystals where optical deformation-potential scattering is allowed in one and forbidden in another crystalline phase

An evaluation of a refresher training intervention for HIV lay counsellors in Chongwe District, Zambia

To address a severe shortage of human resources for health, the Zambian Ministry of Health has begun to make use of lay counsellors for HIV counselling and testing. However, their skills and knowledge rarely have been reviewed or refreshed. We conducted a two-day refresher workshop for lay counsellors to review their performance and refresh their skills and knowledge. The objective of this study was to evaluate the refresher training intervention for HIV lay counsellors in the rural district of Chongwe in Zambia. The two-day refreshertraining workshop was held in November 2009. Twenty-five lay counsellors were selected by District Health Office and participated in the workshop. The workshop included: the opening, a pre-training exercise, lectures on quality assurance with regard to testing and safety precautions, lectures on counselling, filling the gap/Q&amp;A session, and a post-training exercise. In both the pre- and post-trainingexercise, participants answered 25 true/false questions and tested 10 blood panel samples to demonstrate their knowledge and skill on HIV counselling and testing. The average overall knowledge test score&#160; increased from 79% to 95% (p&lt;0.001). At the baseline, knowledgetest scores in topic of standard precaution and post-exposure prophylaxis were relatively low (58%) but rose to 95% after the training (p&lt;0.001). The per cent agreement of HIV testing by lay counsellors with reference laboratory was 99.2%. Participants&#8217; knowledge was improved during the workshop and skill at HIV testing was found to remain at a high level of accuracy. Relatively weak knowledge of standard precautions and post-exposure prophylaxis suggests that lay counsellors are at risk of nosocomial infections, particularly in the absence of refresher training interventions. We conclude that the refresher training was effective for improving the knowledge and skills of lay counsellors and provided an opportunity to monitor their performance

Abnormal positioning of the common carotid artery clinically diagnosed as a submandibular mass

The common carotid artery (CCA) usually runs along the long axis of the neck, although it is occasionally found in an abnormal position or is displaced. We report a case of an 86-year-old woman in whom the CCA was identified in the submandibular area. The patient visited our clinic and reported soft tissue swelling in the right submandibular area. It resembled a tumor mass or a swollen lymph node. Computed tomography showed that it was the right CCA that had been bent forward and was running along the submandibular subcutaneous area. Ultrasonography verified the diagnosis. No other lesions were found on the diagnostic images. Consequently, the patient was diagnosed as having abnormal CCA positioning. Although this condition generally requires no treatment, it is important to follow-up the abnormality with diagnostic imaging because of the risk of cerebrovascular disorders