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OBJECTIVE: To compare costs for 2 days versus 5 days of postoperative antibiotics within the antibiotics after an aPPendectomy In Complex appendicitis trial.Background:Recent studies suggest that restrictive antibiotic use leads to a significant reduction in hospital stays without compromising patient safety. Its potential effect on societal costs remains underexplored. METHODS: This was a pragmatic, open-label, multicenter clinical trial powered for noninferiority. Patients with complex appendicitis (age ≥ 8 years) were randomly allocated to 2 days or 5 days of intravenous antibiotics after appendectomy. Patient inclusion lasted from June 2017 to June 2021 in 15 Dutch hospitals. The final follow-up was on September 1, 2021. The primary trial endpoint was a composite endpoint of infectious complications and mortality within 90 days. In the present study, the main outcome measures were overall societal costs (comprising direct health care costs and costs related to productivity loss) and cost-effectiveness. Direct health care costs were recorded based on data in the electronic patient files, complemented by a telephone follow-up at 90 days. In addition, data on loss of productivity were acquired through the validated Productivity Cost Questionnaire at 4 weeks after surgery. Cost estimates were based on prices for the year 2019. RESULTS: In total, 1005 patients were evaluated in the "intention-to-treat" analysis: 502 patients were allocated to the 2-day group and 503 to the 5-day group. The mean difference in overall societal costs was - 625 (95% CI: - 958 to - 278) to the advantage of the 2-day group. This difference was largely explained by reduced hospital stay. Productivity losses were similar between the study groups. Restricting postoperative antibiotics to 2 days was cost-effective, with estimated cost savings of 31,117 per additional infectious complication. CONCLUSIONS: Two days of postoperative antibiotics for complex appendicitis results in a statistically significant and relevant cost reduction, as compared with 5 days. Findings apply to laparoscopic appendectomy in a well-resourced health care setting.
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Antibacterianos , Apendicite , Humanos , Criança , Antibacterianos/uso terapêutico , Apendicite/tratamento farmacológico , Apendicite/cirurgia , Apendicectomia/métodos , Tempo de Internação , Custos de Cuidados de Saúde , Resultado do TratamentoRESUMO
Using an 185-kg NaI[Tl] array, COHERENT has measured the inclusive electron-neutrino charged-current cross section on ^{127}I with pion decay-at-rest neutrinos produced by the Spallation Neutron Source at Oak Ridge National Laboratory. Iodine is one the heaviest targets for which low-energy (≤50 MeV) inelastic neutrino-nucleus processes have been measured, and this is the first measurement of its inclusive cross section. After a five-year detector exposure, COHERENT reports a flux-averaged cross section for electron neutrinos of 9.2_{-1.8}^{+2.1}×10^{-40} cm^{2}. This corresponds to a value that is â¼41% lower than predicted using the MARLEY event generator with a measured Gamow-Teller strength distribution. In addition, the observed visible spectrum from charged-current scattering on ^{127}I has been measured between 10 and 55 MeV, and the exclusive zero-neutron and one-or-more-neutron emission cross sections are measured to be 5.2_{-3.1}^{+3.4}×10^{-40} and 2.2_{-0.5}^{+0.4}×10^{-40} cm^{2}, respectively.
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This work focused on exploring whether the long intergenic non-protein coding RNA LINC00958 is associated with the prognosis of head and neck squamous cell carcinoma (HNSCC). Associations of the LINC00958 expression level with clinicopathological features of HNSCC were investigated by logistic regression and Wilcoxon signed-rank test. The Kaplan-Meier method was applied to evaluate patient survival. Clinical data and expression profiles were obtained from The Cancer Genome Atlas (TCGA). Associations of patient clinical characteristics with overall survival (OS), progression-free interval (PFI), and disease-specific survival (DSS) were assessed by univariate and multivariate analysis using the Cox proportional hazard model. Immune cell infiltration analysis and gene set enrichment analysis (GSEA) were applied to determine any significant effects of LINC00958. High LINC00958 expression was related to early pT stage (P < 0.01), primary therapy outcome (P < 0.01), HPV status (P < 0.001), lymphovascular invasion (P < 0.001), and perineural invasion (P < 0.01). The receiver operating characteristic curve showed strong prognostic power for LINC00958 (area under curve = 0.886). High LINC00958 expression predicted poor OS (P = 0.007), DSS (P = 0.036), and PFI (P = 0.040). LINC00958 was related to signalling pathways and the infiltration of certain immune cells. miR-27b-5p was significantly associated with LINC00958, and downstream NT5E predicted poor survival in HNSCC cases. LINC00958 may affect the prognosis by regulating NT5E via miR-27b-5p, and could serve as a possible factor to predict the prognosis of HNSCC, especially oral squamous cell carcinoma.
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OBJECTIVE: Major depressive disorder (MDD) is the second-most prevalent mental health condition in Vietnam. This study aims to validate the Vietnamese versions of the self-reported and clinician-rated Quick Inventory of Depressive Symptomatology (QIDS-SR and QIDS-C, respectively) and the Patient Health Questionnaire (PHQ-9), and to assess the correlations between the QIDS-SR, QIDS-C, and PHQ-9. METHODS: 506 participants with MDD (mean age, 46.3 years; 55.5% women) were assessed using the Structured Clinical Interview for DSM-5. The internal consistency, diagnostic efficiency, and concurrent validity of the Vietnamese versions of QIDS-SR, QIDS-C, and PHQ-9 were determined using the Cronbach's alpha, receiver operating characteristic curve, and Pearson correlation coefficient, respectively. RESULTS: The Vietnamese versions of QIDS-SR, QIDS-C, and PHQ-9 demonstrated acceptable validity, with an area under the receiver operating characteristic curve of 0.901, 0.967, and 0.864, respectively. Sensitivity and specificity, respectively, were 87.8% and 77.8% for QIDS-SR and 97.6% and 86.2% for QIDS-C at the cut-off score of 6, and were 82.9% and 70.1% for PHQ-9 at the cut-off score of 4. Cronbach's alphas for QIDS-SR, QIDS-C, and PHQ-9 were 0.709, 0.813, and 0.745, respectively. The PHQ-9 highly correlated with the QIDS-SR (r = 0.77, p < 0.001) and the QIDS-C (r = 0.75, p < 0.001). CONCLUSION: The Vietnamese versions of the QIDS-SR, QIDS-C, and PHQ-9 are valid and reliable tools for screening of MDD in primary healthcare settings.
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Transtorno Depressivo Maior , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Transtorno Depressivo Maior/diagnóstico , Transtorno Depressivo Maior/psicologia , Questionário de Saúde do Paciente , Escalas de Graduação Psiquiátrica , Psicometria , Reprodutibilidade dos Testes , Autorrelato , População do Sudeste Asiático , VietnãRESUMO
The COHERENT Collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220 MeV/c^{2} using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9 keV_{nr}. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6 kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants α_{D}<0.64, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.
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BACKGROUND: The appropriate duration of postoperative antibiotics for complex appendicitis is unclear. The increasing global threat of antimicrobial resistance warrants restrictive antibiotic use, which could also reduce side-effects, length of hospital stay, and costs. METHODS: In this pragmatic, open-label, non-inferiority trial in 15 hospitals in the Netherlands, patients with complex appendicitis (aged ≥8 years) were randomly assigned (1:1) to receive 2 days or 5 days of intravenous antibiotics after appendicectomy. Randomisation was stratified by centre, and treating physicians and patients were not masked to treatment allocation. The primary endpoint was a composite endpoint of infectious complications and mortality within 90 days. The main outcome was the absolute risk difference (95% CI) in the primary endpoint, adjusted for age and severity of appendicitis, with a non-inferiority margin of 7·5%. Outcome assessment was based on electronic patient records and a telephone consultation 90 days after appendicectomy. Efficacy was analysed in the intention-to-treat and per-protocol populations. Safety outcomes were analysed in the intention-to-treat population. This trial was registered with the Netherlands Trial Register, NL5946. FINDINGS: Between April 12, 2017, and June 3, 2021, 13 267 patients were screened and 1066 were randomly assigned, 533 to each group. 31 were excluded from intention-to-treat analysis of the 2-day group and 30 from the 5-day group owing to errors in recruitment or consent. Appendicectomy was done laparoscopically in 955 (95%) of 1005 patients. The telephone follow-up was completed in 664 (66%) of 1005 patients. The primary endpoint occurred in 51 (10%) of 502 patients analysed in the 2-day group and 41 (8%) of 503 patients analysed in the 5-day group (adjusted absolute risk difference 2·0%, 95% CI -1·6 to 5·6). Rates of complications and re-interventions were similar between trial groups. Fewer patients had adverse effects of antibiotics in the 2-day group (45 [9%] of 502 patients) than in the 5-day group (112 [22%] of 503 patients; odds ratio [OR] 0·344, 95% CI 0·237 to 0·498). Re-admission to hospital was more frequent in the 2-day group (58 [12%] of 502 patients) than in the 5-day group (29 [6%] of 503 patients; OR 2·135, 1·342 to 3·396). There were no treatment-related deaths. INTERPRETATION: 2 days of postoperative intravenous antibiotics for complex appendicitis is non-inferior to 5 days in terms of infectious complications and mortality within 90 days, based on a non-inferiority margin of 7·5%. These findings apply to laparoscopic appendicectomy conducted in a well resourced health-care setting. Adopting this strategy will reduce adverse effects of antibiotics and length of hospital stay. FUNDING: The Netherlands Organization for Health Research and Development.
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Antibacterianos , Apendicite , Humanos , Apendicite/tratamento farmacológico , Apendicite/cirurgia , Encaminhamento e Consulta , Resultado do Tratamento , TelefoneRESUMO
We measured the cross section of coherent elastic neutrino-nucleus scattering (CEvNS) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source at Oak Ridge National Laboratory. New data collected before detector decommissioning have more than doubled the dataset since the first observation of CEvNS, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT Collaboration determined the cross section to be (165_{-25}^{+30})×10^{-40} cm^{2}, consistent with the standard model, giving the most precise measurement of CEvNS yet. The timing structure of the neutrino beam has been exploited to compare the CEvNS cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino nonstandard interactions while testing lepton flavor universality and measures the weak mixing angle as sin^{2}θ_{W}=0.220_{-0.026}^{+0.028} at Q^{2}≈(50 MeV)^{2}.
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OBJECTIVES: Traffic-related air pollution (TRAP) negatively impacts children's health. Self-protective measures are available, but population uptake is variable. It is essential to understand human beliefs and behaviours related to air pollution in order to understand the lack of self-protection in communities. As a prelude to undertaking a comprehensive assessment of children's attitudes and beliefs on the health effects of TRAP exposure, we sought to develop and validate an appropriate instrument. STUDY DESIGN: This study used exploratory sequential mixed methods. METHODS: This instrument, based on the constructs of the health belief model (HBM), aimed to determine factors predicting wearing a mask to protect against TRAP exposure. An initial literature-based questionnaire was modified using in-depth interviews, focus group discussions, and a quantitative survey pilot. This study included 121 school students and nine professional experts in Vietnam. The questionnaire was tested for content validity, agreement, test-retest reliability, and internal consistency. RESULTS: The concordance of questionnaire items between two repeated assessments ranged from 47.2% to 78.3%, intraclass correlation coefficients ranged from 0.16 to 0.87 and Cronbach's internal reliability coefficient for the instrument was 0.60. CONCLUSION: The self-administered instrument, based on the HBM, is suitable to understand health attitudes and beliefs related to self-protective behaviours to reduce TRAP exposure.
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Poluição do Ar , Conhecimentos, Atitudes e Prática em Saúde , Poluição do Ar/prevenção & controle , Criança , Humanos , Psicometria , Reprodutibilidade dos Testes , Inquéritos e QuestionáriosRESUMO
We report the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer CEvNS over the background-only null hypothesis with greater than 3σ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2±0.7)×10^{-39} cm^{2}-consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the CEvNS process and provides improved constraints on nonstandard neutrino interactions.
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Feto Abortado/anormalidades , Cardiopatias Congênitas/diagnóstico , Perinatologia/educação , Traqueia/embriologia , Ultrassonografia Pré-Natal , Feto Abortado/irrigação sanguínea , Autopsia , Feminino , Coração Fetal/diagnóstico por imagem , Coração Fetal/embriologia , Cardiopatias Congênitas/embriologia , Humanos , Gravidez , Traqueia/diagnóstico por imagemRESUMO
BACKGROUND: Resorbable biomaterials have been developed to reduce the amount of foreign material remaining in the body after hernia repair over the long-term. However, on the short-term, these resorbable materials should render acceptable results with regard to complications, infections, and reoperations to be considered for repair. Additionally, the rate of resorption should not be any faster than collagen deposition and maturation; leading to early hernia recurrence. Therefore, the objective of this study was to collect data on the short-term performance of a new resorbable biosynthetic mesh (Phasix™) in patients requiring Ventral Hernia Working Group (VHWG) Grade 3 midline incisional hernia repair. MATERIALS AND METHODS: A prospective, multi-center, single-arm trial was conducted at surgical departments in 15 hospitals across Europe. Patients aged ≥18, scheduled to undergo elective Ventral Hernia Working Group Grade 3 hernia repair of a hernia larger than 10 cm2 were included. Hernia repair was performed with Phasix™ Mesh in sublay position when achievable. The primary outcome was the rate of surgical site occurrence (SSO), including infections, that required intervention until 3 months after repair. RESULTS: In total, 84 patients were treated with Phasix™ Mesh. Twenty-two patients (26.2%) developed 32 surgical site occurrences. These included 11 surgical site infections, 9 wound dehiscences, 7 seromas, 2 hematomas, 2 skin necroses, and 1 fistula. No significant differences in surgical site occurrence development were found between groups repaired with or without component separation technique, and between clean-contaminated or contaminated wound sites. At three months, there were no hernia recurrences. CONCLUSION: Phasix™ Mesh demonstrated acceptable postoperative surgical site occurrence rates in patients with a Ventral Hernia Working Group Grade 3 hernia. Longer follow-up is needed to evaluate the recurrence rate and the effects on quality of life. This study is ongoing through 24 months of follow-up.
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Hérnia Ventral/cirurgia , Herniorrafia/métodos , Hérnia Incisional/cirurgia , Telas Cirúrgicas , Adulto , Idoso , Materiais Biocompatíveis , Feminino , Herniorrafia/efeitos adversos , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Seroma/epidemiologia , Telas Cirúrgicas/efeitos adversos , Infecção da Ferida Cirúrgica/epidemiologiaAssuntos
Diabetes Mellitus Tipo 2 , MicroRNAs/genética , Hepatopatia Gordurosa não Alcoólica , Adamantano/análogos & derivados , Diabetes Mellitus Tipo 2/complicações , Diabetes Mellitus Tipo 2/tratamento farmacológico , Dipeptídeos , Humanos , Hepatopatia Gordurosa não Alcoólica/complicações , Hepatopatia Gordurosa não Alcoólica/tratamento farmacológicoRESUMO
BACKGROUND: While HIV infection is associated with increased cardiovascular risk, benefit from statin is not well established in HIV-infected adults. We assessed whether statins are associated with a decrease in carotid artery intima-media thickness (cIMT) progression and all-cause mortality in HIV-infected adults who are at elevated ASCVD risk and recommended for statins. METHODS: Carotid IMT was measured at baseline and follow-up in 127 HIV-infected adults who meet ACC/AHA criteria to be on statins. Inverse probability of treatment weighting (IPTW) was used to address selection bias. Multivariable models were used to control for baseline characteristics. RESULTS: 28 subjects (22%) were on statins and 99 subjects (78%) were not. Mean cIMT at baseline was 1.2 mm (SD = 0.34) in statin users and 1.1 mm (SD = 0.34) in non-users, and the multivariable adjusted difference was 0.05mm (95%CI -0.11, 0.21 p = 0.53). After 3.2 years of follow-up, average cIMT progression was similar in statin users and non-users (0.062mm/yr vs. 0.058 mm/yr) and the multivariable adjusted difference over the study period was 0.004 mm/yr (95% CI -0.018, 0.025, p = 0.74). All-cause mortality appeared higher in non-statin users compared with statin users, but the difference was not significant (adjusted HR = 0.74, 95%CI 0.17-3.29, p = 0.70). CONCLUSION: In a HIV cohort who had elevated ASCVD risk and meet ACC/AHA criteria for statins, treatment with statins was not associated with a reduction in carotid atherosclerosis progression or total mortality. Future studies are needed to further explore the impact of statins on cardiovascular risk in the HIV-infected population.
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Doenças das Artérias Carótidas/epidemiologia , Causas de Morte , Infecções por HIV/complicações , Inibidores de Hidroximetilglutaril-CoA Redutases/uso terapêutico , Doenças das Artérias Carótidas/diagnóstico , Doenças das Artérias Carótidas/prevenção & controle , Espessura Intima-Media Carotídea , Estudos de Coortes , Progressão da Doença , Feminino , Seguimentos , Infecções por HIV/mortalidade , Humanos , Masculino , Pessoa de Meia-Idade , Medição de Risco , Fatores de RiscoRESUMO
Zirconate systems having the composition 3HfO2·15SiO2·xY2O3·(82 - x)ZrO2, where x = 2, 7 and 12â mol% Y2O3, were synthesized by a sol-gel method. The analysis of X-ray diffraction data showed the presence of the t-ZrO2, m-ZrO2, m-HfO2, Y2SiO5 and Y2Si2O7 crystalline phases in a ceramic nanomixture. Spectroscopic data show that the increase of the Y2O3 content of samples determines the increase of the t-ZrO2, m-HfO2 and silicate crystalline phases. Gap energy values decrease almost linearly with increasing Y2O3 content of samples. A detailed study of XANES data does not show a significant difference with increasing Y2O3 content of the samples suggesting an appreciable stability of the hafnium ions +4 oxidation state and their microvicinity. EXAFS results show that the local structure around the Hf cation is similar to that from the monoclinic crystalline HfO2 where the Hf-O coordination number tends to 7. The bond lengths of Hf-O shells show small deviations from â¼2.12â Å and the Hf-metal paths become more structured by increasing the Y2O3 content of the samples.
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BACKGROUND: The objective of this study was to assess whether a zinc-impregnated polypropylene mesh (ZnMesh) has better antibacterial properties in a contaminated environment compared with a regular polypropylene mesh. MATERIALS AND METHODS: Thirty-eight Wistar Han rats underwent cecal ligation and puncture to induce peritonitis 24 h before implantation of an intraperitoneal ZnMesh or a regular polypropylene mesh. Primary outcome was the number of colony forming units (CFU) per sample (mesh and abdominal wall). Secondary outcomes were macroscopic (incorporation of mesh, abscesses, and adhesions on mesh surface) and histological (inflammatory cell reaction, mesh-specific parameters, and collagen deposition) parameters. All outcomes were evaluated after 30 and 90 d. RESULTS: After 30 d, no significant difference in CFU per sample was present between the ZnMesh and control groups. After 90 d, a lower number of CFU per sample was present in the ZnMesh group compared with the control group (trypticase soy agar with 5% sheep blood: 0 log10 CFU/sample IQR: 0-1.40 versus 1.58 log10 CFU/sample IQR: 0-4.30, P = 0.012; MacConkey: 0 log10 CFU/sample IQR: 0-2.65 versus 1.18 log10 CFU/sample IQR: 0-4.04, P = 0.438). After 90 d, the percentage of adhesions on mesh surface was significantly higher in the ZnMesh group (95% IQR: 60%-100% versus 50% IQR: 23%-75%, P = 0.029). No differences were seen in other macroscopic outcomes or histology. CONCLUSIONS: A significantly lower number of CFU per sample was found in the ZnMesh group after 90 d. After 30 d, no statistically significant differences in CFU per sample were seen. This result suggests that the ZnMesh group has better antibacterial properties in a contaminated environment. However, this is at the cost of a significantly higher percentage of adhesions.
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Hérnia Ventral/prevenção & controle , Peritonite/cirurgia , Telas Cirúrgicas , Infecção da Ferida Cirúrgica/prevenção & controle , Aderências Teciduais/epidemiologia , Zinco/administração & dosagem , Parede Abdominal/cirurgia , Animais , Bactérias/isolamento & purificação , Contagem de Colônia Microbiana/estatística & dados numéricos , Modelos Animais de Doenças , Humanos , Masculino , Teste de Materiais , Peritonite/complicações , Peritonite/microbiologia , Polipropilenos , Ratos , Ratos Wistar , Infecção da Ferida Cirúrgica/diagnóstico , Infecção da Ferida Cirúrgica/microbiologia , Aderências Teciduais/etiologia , CicatrizaçãoRESUMO
BACKGROUND: Incisional hernia (IH) is one of the most frequent complications after abdominal surgery. Follow-up with regard to IH remains challenging. Physical examination and imaging to diagnose IH are time-consuming and costly, require devotion of both the physician and patient, and are often not prioritized. Therefore, a patient-reported diagnostic questionnaire for the diagnosis of IH was developed. Objective of this study was to validate this questionnaire in a consecutive sample of patients. METHODS: All patients above 18 y of age who underwent abdominal surgery with a midline incision at least 12 mo ago were eligible for inclusion. Included patients visited the outpatient clinic where they filled out the diagnostic questionnaire and underwent physical examination. The questionnaire answers were compared with the physical examination results. The diagnostic accuracy of the entire questionnaire was assessed by multivariable logistic regression. RESULTS: In total, 241 patients visited the outpatient clinic prospectively. 54 (22%) patients were diagnosed with IH during physical examination. The area under the receiver operating characteristic curve of the diagnostic questionnaire was 0.82. Sensitivity and specificity were respectively 81.5% and 77.5%. The positive and negative predictive values were 51.2% and 94%, respectively. Ten (19%) patients with IH were missed by the questionnaire. CONCLUSIONS: The patient-reported diagnostic questionnaire as currently proposed cannot be used to diagnose IH. However, given the high negative predictive value, the questionnaire might be used to rule out an IH. Long-term follow-up for the diagnosis of IH should be performed by clinical examination.
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Assistência ao Convalescente/métodos , Hérnia Incisional/diagnóstico , Medidas de Resultados Relatados pelo Paciente , Exame Físico , Ferida Cirúrgica/complicações , Idoso , Estudos de Viabilidade , Feminino , Humanos , Hérnia Incisional/etiologia , Masculino , Pessoa de Meia-Idade , Curva ROC , Estudos RetrospectivosRESUMO
Dual-phase xenon detectors lead the search for keV-scale nuclear recoil signals expected from the scattering of weakly interacting massive particle (WIMP) dark matter, and can potentially be used to study the coherent nuclear scattering of MeV-scale neutrinos. New capabilities of such experiments can be enabled by extending their nuclear recoil searches down to the lowest measurable energy. The response of the liquid xenon target medium to nuclear recoils, however, is not well characterized below a few keV, leading to large uncertainties in projected sensitivities. In this work, we report a new measurement of ionization signals from nuclear recoils in liquid xenon down to the lowest energy reported to date. At 0.3 keV, we find that the average recoil produces approximately one ionization electron; this is the first measurement of nuclear recoil signals at the single-ionization-electron level, approaching the physical limit of liquid xenon ionization detectors. We discuss the implications of these measurements on the physics reach of xenon detectors for nuclear-recoil-based WIMP dark matter searches and the detection of coherent elastic neutrino-nucleus scattering.
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Abstract Positron emission tomography (PET) is one of the most important diagnostic tools in medicine, allowing three-dimensional imaging of functional processes in the body. It is based on a detection of two gamma rays with an energy of 511 keV originating from the point of annihilation of the positron emitted by a radio-labeled agent. By measuring the difference of the arrival times of both annihilation photons it is possible to localize the tracer inside the body. Gamma rays are normally detected by a scintillation detector, whose timing accuracy is limited by a photomultiplier and a scintillator. By replacing a photo sensor with a microchannel plate PMT (MCP-PMT) and a scintillator with Cherenkov radiator, it is possible to localize the interaction position to the cm level. In a pioneering experimental study with Cherenkov detectors using PbF 2 crystals and microchannel plate photomultiplier tubes MCP-PMT a time resolution better than 100 ps was achieved. In this work a DRS4 digital ring sampler chip was used to read out single photon output signals from two different MCP-PMTs (Hamamatsu R3809 and Burle 85001) with a sampling rate of 5×109 samples/s. The digitized waveforms were analyzed and a comparison between the two detectors timing response was made. The time resolutions achieved were (161 ± 2.21) ps and (220 ± 2.63) ps FWHM for the Hamamatsu and Burle MCP-PMT respectively. No significant variances were observed in the study of the behavior of the FWHM when both MCP-PMT were scanned.
Resumen La tomografía por emisión de positrones (PET) es una importante herramienta en el diagnóstico médico ya que permite la obtención de imágenes tridimensionales de los procesos funcionales en el cuerpo. La técnica está basada en la detección de los dos cuantos gamma de 511 keV originados en la aniquilación del positrón emitido por el radiofármaco administrado al paciente. Midiendo la diferencia en la llegada de los dos cuantos gamma es posible determinar la posición en la que ocurrió la aniquilación. En los equipos convencionales son utilizados detectores centellantes cuya respuesta temporal está limitada por el fotomultiplicador y el cristal centellante. Remplazando el fotomultiplicador por un PMT (MCP-PMT) y el cristal centellante por un detector Cherenkov, es posible localizar la posición en la que ocurrió la aniquilación con una exactitud a nivel de pocos centímetros. En previos resultados experimentales utilizando detectores Cherenkov con cristales de PbF 2 y MCP-PMT se alcanzó una respuesta temporal de menos de 100 ps. En este trabajo fue utilizado un chip DRS4 con una velocidad de procesamiento de las señales de 5×109 samples/s para la lectura de la salida de fotones únicos de los dos MCP-PMT estudiados (Hamamatsu R3809 y Burle 85001). Las señales digitalizadas fueron analizadas y se realizó una comparación entre la respuesta temporal obtenida para ambos MCP-PMT. El tiempo de respuesta obtenido en términos de FWHM fue de (161 ± 2.21) ps y (220 ± 2.63) ps para los MCP-PMT Hamamatsu y Burle respectivamente. No se detectaron variaciones significativas en el FWHM al escanearse la superficie activa de ambos MCP-PMT .