ABSTRACT
A Monte Carlo simulation has been developed for neutron stimulated emission computed tomography (NSECT) using the GEANT4 toolkit. NSECT is a new approach to biomedical imaging that allows spectral analysis of the elements present within the sample. In NSECT, a beam of high-energy neutrons interrogates a sample and the nuclei in the sample are stimulated to an excited state by inelastic scattering of the neutrons. The characteristic gammas emitted by the excited nuclei are captured in a spectrometer to form multi-energy spectra. Currently, a tomographic image is formed using a collimated neutron beam to define the line integral paths for the tomographic projections. These projection data are reconstructed to form a representation of the distribution of individual elements in the sample. To facilitate the development of this technique, a Monte Carlo simulation model has been constructed from the GEANT4 toolkit. This simulation includes modeling of the neutron beam source and collimation, the samples, the neutron interactions within the samples, the emission of characteristic gammas, and the detection of these gammas in a Germanium crystal. In addition, the model allows the absorbed radiation dose to be calculated for internal components of the sample. NSECT presents challenges not typically addressed in Monte Carlo modeling of high-energy physics applications. In order to address issues critical to the clinical development of NSECT, this paper will describe the GEANT4 simulation environment and three separate simulations performed to accomplish three specific aims. First, comparison of a simulation to a tomographic experiment will verify the accuracy of both the gamma energy spectra produced and the positioning of the beam relative to the sample. Second, parametric analysis of simulations performed with different user-defined variables will determine the best way to effectively model low energy neutrons in tissue, which is a concern with the high hydrogen content in biological tissue. Third, determination of the energy absorbed in tissue during neutron interrogation in order to estimate the dose. Results from these three simulation experiments demonstrate that GEANT4 is an effective simulation platform that can be used to facilitate the future development and optimization of NSECT.
Subject(s)
Image Interpretation, Computer-Assisted/methods , Models, Biological , Neutrons , Radiometry/methods , Tomography, Emission-Computed/methods , Computer Simulation , Models, Statistical , Monte Carlo Method , Radiation Dosage , Scattering, RadiationABSTRACT
INTRODUCTION: Neurotoxoplasmosis (NTX) is one of the commonest opportunist infections in patients infected by the human immunodeficiency virus. It presents with a variety of clinical features in the immunocompromised patient. PATIENTS AND METHODS: We made a horizontal retrospective descriptive study of 88 patients with a diagnosis of NTX treated in the Pedro Kour Institute during a three years period. Our aim was to find which were the most common forms of clinical presentation in our setting and to evaluate the use of paraclinical examinations in reaching the presumptive diagnosis. The patients had clinical examinations, CSF studies, detection of indirect immunofluorescence titres (IFI) for Toxoplasma, imaging studies (CAT) and lymphocyte counts. RESULTS: The commonest symptoms were: headache in 79%, fever in 55.68%, motor defect in 44.31% and disorders of consciousness in 29.54% of the patients. The IFI titres were negative in 31.54% of the patients, between 1/16 and 1/32 in 38.34% and between 1/64 and 1/1,024 in only 30.07% of cases. The T CD4+ lymphocyte count was less than 200 cells in 66.7% of the patients; 72% of imaging studies showed typical lesions, in association with other disorders in 38% of the cases (lymphomas, cryptococcosis, tuberculous meningoencephalitis and cytomegalovirus encephalitis). CONCLUSIONS: NTX in a patient with AIDS often presents in our setting with headache and fever, motor deficit and alterations of consciousness. The diagnosis should be confirmed by immunological or imaging studies since in this disease serology and CSF studies are less specific.
Subject(s)
Acquired Immunodeficiency Syndrome/epidemiology , Toxoplasmosis, Cerebral/epidemiology , Adult , Animals , Consciousness Disorders/diagnosis , Consciousness Disorders/epidemiology , Cuba/epidemiology , Enzyme-Linked Immunosorbent Assay , Female , Fever/diagnosis , Fever/epidemiology , Fluorescent Antibody Technique, Indirect , Headache/diagnosis , Headache/epidemiology , Humans , Male , Middle Aged , Psychomotor Disorders/diagnosis , Psychomotor Disorders/epidemiology , Retrospective Studies , Severity of Illness Index , Toxoplasma/isolation & purification , Toxoplasmosis, Cerebral/diagnosis , Toxoplasmosis, Cerebral/parasitologyABSTRACT
Introducción. La neurotoxoplasmosis (NTX) es una de las infecciones oportunistas más frecuentes en el paciente infectado por el virus de inmunodeficiencia humana y se presenta con diversidad de manifestaciones clínicas en el huésped inmunoafectado. Pacientes y métodos. Realizamos un estudio descriptivo horizontal, retrospectivo, en 88 pacientes atendidos en el Instituto Pedro Kourí, durante un período de 3 años, con el diagnóstico clínico de NTX, con el propósito de describir qué formas clínicas de presentación en nuestro medio son las más frecuentes, así como evaluar la utilidad de los exámenes paraclínicos en el diagnóstico presumible. Se les realizó examen clínico, estudio del LCR, detección de los títulos de la inmunofluorescencia indirecta (IFI) para Toxoplasma, estudios imaginológicos (TAC), así como recuento de poblaciones linfocitarias. Resultados. Los síntomas que se presentaron con mayor frecuencia fueron: cefalalgia en un 79 por ciento, fiebre en un 55,68 por ciento, defecto motor en el 44,31 por ciento y trastornos de la conciencia en el 29,54 por ciento de los pacientes. Los títulos de IFI estaban negativos en el 31,54 por ciento de los pacientes, entre 1/16 y 1/32 en el 38,34 por ciento, y entre 1/64 y 1/1.024 en sólo el 30,07 por ciento de los casos. El recuento de linfocitos T CD4+ se encontraba por debajo de 200 células en el 66,7 por ciento de los pacientes; el 72 por ciento de los estudios imaginológicos evidenciaron lesiones típicas, y se asociaron a otras entidades en el 38 por ciento de los casos (linfomas, criptococosis, meningoencefalitis tuberculosa y encefalitis por citomegalovirus). Conclusiones. La NTX en el paciente con sida se presenta frecuentemente en nuestro medio con cefalalgia, asociada a fiebre, déficit motor y trastornos de conciencia, y su diagnóstico debe complementarse con el estudio inmunológico e imaginológico, pues los resultados de los estudios serológicos y del LCR son más inespecíficos en esta enfermedad (AU)
Subject(s)
Middle Aged , Animals , Adult , Male , Female , Humans , Toxoplasma , Toxoplasmosis, Cerebral , Fluorescent Antibody Technique, Indirect , Retrospective Studies , Psychomotor Disorders , Cuba , Consciousness Disorders , Acquired Immunodeficiency Syndrome , Fever , Headache , Severity of Illness Index , Enzyme-Linked Immunosorbent AssayABSTRACT
Rapid withdrawal of short to intermediate half-life benzodiazepines may be hazardous, particularly in the elderly. The use of carbamazepine to facilitate withdrawal has been reported in younger patients. We describe four elderly patients (average age, 72.5 years) who had each experienced at least one unsuccessful attempt at alprazolam withdrawal and who were subsequently successfully withdrawn via the use of carbamazepine over a period ranging from 2 to 6 days. These geriatric patients experienced no major withdrawal symptoms, but mild symptoms were common. There was no correlation between dose or duration of alprazolam use and extent of withdrawal symptoms. We recommend use of this treatment regimen in a hospital setting only, where close monitoring can occur.
