Estimating 225Ac yield in thorium metal targets.

In this work we estimate the yield of the radioisotope [Formula: see text] in a thorium metal target geometry similar to that described by Roberston et al.. We do so in three different yet complimentary studies. In the first study, we pose a three-way coupled time-dependent model describing beam position, temperature field, and local growth of the activity of the radioisotope and solve this numerically. In the second study, we present an analytical solution of the model equations for a generalized solid target in the "beam-thin" limit, i.e. where only a small fraction of the incoming energy of the proton beam is deposited into the thorium material. In the third study, we use the insight gained from the analytical solution and describe an operating strategy to maximize yield by modulating the beam flux temporally.

Radiolysis reduction in liquid solution targets for the production of 89Zr.

Increased interest in radiometals for nuclear medicine and imaging can be hampered by radionuclide supply. 89Zr for example, is a PET imaging nuclide for which no radionuclide generator exists. One method to produce 89Zr involves irradiating aqueous solutions of yttrium nitrate salt on small medical cyclotrons. However, in irradiating these solutions the radiolysis of water can cause significant H2 and O2 gas buildup, which can eventually rupture a sealed target vessel. We examine the role of nitrate and nitrite in radiolysis. Here, we find that using copper-coated cadmium pellets to chemically reduce nitrate to nitrite in solution prior to irradiation can reduce in-target radiolysis by approximately 60% as compared to other published methods of radiolysis reduction, but only in acidic solutions. We hypothesize that during irradiation, nitrate is converted to nitrite, consuming free radicals which would otherwise be available to eliminate molecular gas species. Performing this conversion before irradiation may limit the consumption of these beneficial free radicals.

A practical solution of the Bethe equation in the energy range applicable to radiotherapy and radionuclide production.

While the dose deposition of charged hadrons has received much attention over the last decades starting in 1930 with the publication of the Bethe equation, there are still practical obstacles in implementing it in fields like radiotherapy and isotope production on cyclotrons. This is especially true if the target material consists of non-homogeneous materials, either consisting of a mixture of different elements or experiencing phase changes during irradiation. While Monte-Carlo methods have had great success in describing these more difficult target materials, they come at a computational cost, especially if the problem is time-dependent. This can greatly hinder optimal advancement in therapy and isotope targetry. Here, a regular perturbation method is used to solve the Bethe equation in the limit of small relativistic effects. Particular focus is given to incident energy level relevant to radionuclide production and radiotherapy applications, i.e. 10-200 MeV. We present a series solution for the range and dose distribution in terms of elementary functions, as opposed to special functions which will aid in uptake by practitioners.

Understanding radionuclide production in gas target systems: the effect of adsorption on the target body.

Gas target systems have been used for decades on cyclotrons to produce radionuclides for medical imaging. However, the activity recovered from such targets is often lower than its theoretically predicted value. Past research has suggested that nuclide interactions with the walls of the target body may play a key role in the loss of recoverable radionuclide activity. Here, we consider gas targets and modify the standard radionuclide production equation by adding a loss term representing radionuclides depositing on the walls of the target. We derive the form of the deposition term based on a simple adsorption model which is then linearized by solving for leading order terms. The resulting production equation uses one fitting parameter to give an estimate of the recoverable activity produced in a target system, taking adsorption into account. The model is then fit to six data series, taken in-house and reported in the literature and a parity plot compares model predictions to experimental data. The model is able to better track the data than any previous models, and points towards a phenomenological understanding of adsorption in target systems.

A forced-convection gas target for the production of [11C]CH4.

A forced-convection gas target for the production of [11C]CH4 on a 13 MeV cyclotron was constructed and tested. A small fan was incorporated into the back of the target, which mixes the target gas during irradiation. The effect of the forced convection alone on the target operation and the [11C]CH4 yield was measured. Forced convection improved the target yield by up to 16 ± 4%. In addition, improvement in heat transfer of up to 70% was observed to be a function of fan speed. Operating with forced convection allowed delivery of 21% higher beam currents while still staying in the acceptable pressure rise during irradiation, providing a 25 ± 7% greater yield.

Design and application of 3D-printed stepless beam modulators in proton therapy.

A new method for the design of stepless beam modulators for proton therapy is described and verified. Simulations of the classic designs are compared against the stepless method for various modulation widths which are clinically applicable in proton eye therapy. Three modulator wheels were printed using a Stratasys Objet30 3D printer. The resulting depth dose distributions showed improved uniformity over the classic stepped designs. Simulated results imply a possible improvement in distal penumbra width; however, more accurate measurements are needed to fully verify this effect. Lastly, simulations were done to model bio-equivalence to Co-60 cell kill. A wheel was successfully designed to flatten this metric.

Automated segmentation of wood fibres in micro-CT images of paper.

A novel algorithm has been developed and validated to isolate individual papermaking fibres in micro-computed tomographic images of paper handsheets as a first step to characterize the structure of the paper. The three-step fibre segmentation algorithm segments the papermaking fibres by (i) tracking the hollow inside the fibres via a modified connected component methodology, (ii) extracting the fibre walls using a distance transform and (iii) labelling the fibres through collapsed sections by a final refinement step. Furthermore, postprocessing algorithms have been developed to calculate the length and coarseness of the segmented fibres. The fibre segmentation algorithm is the first ever reported method for the automated segmentation of the tortuous three-dimensional morphology of papermaking fibres within microstructural images of paper handsheets. The method is not limited to papermaking fibres, but can be applied to any material consisting of tortuous and hollow fibres.

3D printed plastics for beam modulation in proton therapy.

Two 3D printing methods, fused filament fabrication (FFF) and PolyJet™ (PJ) were investigated for suitability in clinical proton therapy (PT) energy modulation. Measurements of printing precision, printed density and mean stopping power are presented. FFF is found to be accurate to 0.1 mm, to contain a void fraction of 13% due to air pockets and to have a mean stopping power dependent on geometry. PJ was found to print accurate to 0.05 mm, with a material density and mean stopping power consistent with solid poly(methyl methacrylate) (PMMA). Both FFF and PJ were found to print significant, sporadic defects associated with sharp edges on the order of 0.2 mm. Site standard PT modulator wheels were printed using both methods. Measured depth-dose profiles with a 74 MeV beam show poor agreement between PMMA and printed FFF wheels. PJ printed wheel depth-dose agreed with PMMA within 1% of treatment dose except for a distal falloff discrepancy of 0.5 mm.

Estudio comparativo de la personalidad del paciente con dolor lumbar crónico y sujetos control mediante el uso del Inventario de Temperamento y Carácter / No disponible

La personalidad impacta sobre la forma en la que las personas con lumbalgia crónica enfrentan el dolor. Se ha identificado la relación entre ciertas características de la personalidad con el desarrollo y mantenimiento del dolor crónico. Los estudios sobre lumbalgia crónica y la personalidad mediante el modelo psicobiológico de la personalidad son escasos y tendrían un valor heurístico para facilitar el desarrollo de investigación en este campo. Objetivos: comparar las dimensiones de temperamento y carácter entre pacientes con lumbalgia crónica y sujetos control; y comparar las características de personalidad entre pacientes con dolor de intensidad leve y aquellos con dolor de intensidad moderada/severa. Método: se reclutaron 46 pacientes diagnosticados de lumbalgia crónica del Hospital General de México y 46 sujetos controles pareados por género y edad. Se evaluaron las características clínicas de la lumbalgia crónica. Las dimensiones de la personalidad fueron evaluadas mediante el Inventario de Temperamento y Carácter (ITC). Resultados: los pacientes mostraron una mayor puntuación en la dimensión de temperamento "búsqueda de la novedad" (NS) y menor puntuación en la "evitación al daño" (HA); así como menor puntuación en la dimensión de "cooperatividad" (CO). Los pacientes con mayor intensidad de dolor mostraron una tendencia a una mayor HA. Discusión: los resultados apoyan el modelo de atribución temor/evitación que asume que las interpretaciones catastróficas del dolor, fomentan el miedo y las conductas evitativas, empeorando el padecimiento. El estudio de la personalidad en pacientes con lumbalgia crónica brinda nuevos conocimientos sobre las áreas de intervención psicosocial requeridas por estos pacientes (AU)

Personality has an important role in the way patients with chronic low back pain face pain. Some personality features have been associated to the development and the maintenance of chronic pain. Studies of chronic low back pain and personality according to the psychobiological model of personality are scarce and will have a heuristic value to promote research in this field. Objectives: to compare temperament and character dimensions between patients with chronic low back pain and control subjects; ant to compare personality features between patients with low intensity pain and those with pain of moderate/severe intensity. Method: a total of 46 patients with chronic low back pain were recruited from the Hospital General de México and were matched by age and gender with 46 control subjects. Clinical features of the disorder were assessed. Personality dimensions were evaluated with the Temperament and Character Inventory (TCI). Results: patients exhibited higher scores on the temperament dimension "novelty seeking" (NS) and lower scores on "harm avoidance" (HA), also, lower scores were found on the character dimension "cooperativeness" (CO). Patients with moderate/severe pain reported a tendency to a higher HA. Discussion: our results support the attribution fear/avoidance model which presumes that catastrophic interpretations of pain give rise to fear and avoidant behaviors which worsens the pain problem. The study of personality in patients with chronic low back pain gives new information related to the psychosocialinterventions required for these patients (AU)

[Asthma phenotype during the first six years of life]. / Fenotipos de asma durante los primeros seis años de vida.

UNLABELLED: Asthma is one of the main wheezing causes during the first years of life. In our country it is a common respiratory chronic illness but insufficient studies still exist on the asthma phenotypes during the first years of life. OBJECTIVE: To know the phenotype of asthma in a group of children younger than 6 years old. MATERIAL AND METHODS: 185 children of both sexes were studied with antecedent of having presented wheezing (tree episodes or more) and it registered data about the antecedents of family and personal allergy, dietary habits during the first year of life, infections, data on the beginning and the evolution of the condition, and they were practiced determinations of peripheral eosinophilia, total serum IgE and gastric gammagram to discard illness for gastroesophageal reflux. All were carried out skin tests for foods and aeroallergens. RESULTS: In the group of 185 patients of both sexes, they had data that supported the allergic process, in 137. It was correlated the atopy antecedents significantly, positive skin tests, eosinophilia (more than 300), with elevated IgE for the age (p < 0.05). The gastric gamagrama was carried out in 144 patients, of which were positive results for gastroesophageal reflux in 64 (44%) and in 79 (54%) it was reported doubtful or negative. It was related the gastroesophageal reflux presence and the positive skin tests significantly (p < 0.05). CONCLUSIONS: The more common phenotype of asthma in our patients corresponds to a wheezing pattern that persist after the 3 years old, in relation to an allergic component. Furthermore in most of those children a positive gastroesophageal reflux was an important finding.

Fenotipos de asma durante los primeros seis años de vida / The asthma phenotypes during the first six years of life

El asma es una de las primera causas de sibilancias durante los primeros años de vida. En nuestro medio es una enfermedad crónica cada vez más frecuente; sin embargo, aún existen insuficientes estudios sobre los fenotipos de asma durante los primeros años de vida. Objetivo. Conocer el fenotipo del asma en un grupo de niños menores de seis años. Material y métodos. Se estudiaron 185 niños de uno y otro sexo con antecedentes de haber presentado sibilancias (tres ocasiones o más) en quienes se recabaron datos sobre los antecedentes familiares y personales de alergia, hábitos dietéticos durante el primer año de vida, infecciones, datos sobre el inicio y la evolución del padecimiento, y se les practicaron determinaciones de eosinófilos periféricos. IgE sérica total y gamagrama gástrico para descartar enfermedad por reflujo gastroesofágico. A todos se les realizaron pruebas cutáneas para alimentos e inhalables. Resultados. Del grupo de 185 pacientes se encontraron datos que apoyaban el proceso alérgico en 137. Se correlacionaron significativamente los antecedentes de atopia, positividad en las pruebas cutáneas, elevación de eosinófilos periféricos (más de 300) con nivel de IgE por arriba de los esperados para la edad (p<0.05). El gamagrama gástrico se realizó en 144 pacientes, de los cuales se encontraron resultados positivos para reflujo gastroesofágico en 64 (44 por ciento) y en los restantes 79 (54 por ciento) se reporto dudoso o negativo. El reflujo se relacionó significativamente y las pruebas cutáneas positivas (p<0.05). Conclusiones. El fenotipo de la mayoría de nuestros pacientes corresponde a un patrón de sibilancias que persisten después de los tres años, y se relacionan con un componente alérgico, además de que una proporción importantes de ellos se relaciona con datos de reflujo gastroesofágico

Alergia a alimentos en niños con hiperrespuesta de la vía aérea / Food allergy in children with airway hiperresponsiveness

La etiología de la hiperrespuesta de la vía aérea es variada. Algunos autores mencionan la participación de la alergia a alimentos en los pacientes con procesos crónicos del aparato respiratorio. Se estudiaron a 26 niños con diagnóstico de hiperrespuesta de la vía aérea y alergia a alimentos diagnosticada por: pruebas cutáneas positivas a diversos alimentos y reto simple ambulatorio a alimentos. Se les indicó dieta de restricción alimentaria, principalmente la leche de vaca, que fue sustituida por semihidrolizado de proteínas, durante 12 semanas. Se registraron la intensidad de los síntomas: rinorrea, obstrucción nasal, tos y sibilancias durante el periodo de estudio. Se realizaron pruebas cutáneas a diversos alimentos y reto simple ambulatorio con leche de vaca. Se aplicó la prueba de Chi cuadrada para el análisis estadístico. El 23 por cinto de los pacientes fueron del sexo femenino, el 76.9 por ciento del sexo masculino, de seis meses a tres años de edad, con un promedio de 19.5 meses de edad. El 76 por ciento de los pacientes tenían antecedentes heredo-familiares de alergia. La alimentación con leche materna sólo se ofreció hasta el 5o. mes de vida al 38.4 por ciento. Para el 6o. mes de vida el 100 por ciento ya había iniciado ablactación. La mayoría de los pacientes tenían intensidad 4-5 de los síntomas al inicio del estudio: 96.2 por ciento de los niños con rinorrea y obstrucción nasal y 88.5 por ciento con tos y sibilancias. En 45 por ciento se reportó IgE elevada. El reto ambulatorio a alimentos fue positivo en 42.3 por ciento de los niños. La intensidad de los síntomas mejoró al final del periodo de la dieta de restricción en la mayoría de los niños (88.5 por ciento) con una p<0.0001. De nuestro estudio concluimos que la dieta de restricción de alimentos es un recurso que demostró efectividad en el tratamiento de los niños con hiperrespuesta de la vía aérea y alergia a alimentos

Persistent trigeminal artery as a cause of dizziness.

Complaints of vertigo and dizziness are common problems referred to otolaryngologists for evaluation. Awareness of uncommon causes of dizziness increases the physician's ability to diagnose and treat these patients. We present the case of a middle-aged woman who presented with episodes of vertigo and symptoms suggestive of vertebrobasilar insufficiency. These symptoms were the result of a persistent trigeminal artery (PTA) and occlusive carotid artery disease. A PTA is a carotid-basilar anastomosis that has been reported to be demonstrated on 0.1% to 0.6% of all cerebral angiograms. Persistence of this vessel usually leads to hypoplasia or agenesis of the ipsilateral posterior communicating artery, and leaves the internal carotid artery as the main source of blood supply to the region of the upper brainstem. The appearance and clinical significance of this unusual condition will be discussed.

Advances in vertebral artery surgery at the skull base.

Between July 1975 and May 1985, 219 procedures were performed on the vertebral system; two were intracranial, 118 were at the skull base and 99 were at the neck base. Of the 108 patients operated on at the skull base, procedures were multiple in five and bilateral in two. Bypass to the vertebral artery between the transverse process of C1 and C2 was performed 91 times. The blood supply for the bypass was the common carotid (70), the external carotid (9), the internal carotid (9), the subclavian (3), and the occipital artery (3). Decompression was performed in three patients, segmental resection in seven, and ligation in two. The primary objective was to increase the flow capacity of the vertebral artery. This flow to the Circle of Willis supplies the forebrain and the hindbrain if the internal carotid artery is obstructed and the posterior communicating artery is patent, or it may supply only the hindbrain when no communication exists. The pathologic processes include atherosclerosis, thrombosis, dissection, compression, and vasospasm. The male:female ratio is 2:3. Long-term mortality is 19% for the male and 4.6% for the female. Hindbrain symptoms in the male predates cardiac symptoms by 2 to 4 years. Operative mortality and stroke rate is less than 3% combined. Long-term graft patency is 87%. Vertebral artery surgery at the skull base produces results superior to those following proximal segment reconstruction when measured by dynamic computerized tomographic scanning, neurofunctional testing, and symptom relief. Success following reconstruction depends on careful patient selection and surgical expertise. The techniques of reconstruction are well established and results have been durable for over a decade.

Mediastinal and subcutaneous emphysema in labor.

The recent world literature on mediastinal emphysema has been reviewed and two cases added. This condition is relatively benign, and the supportive treatment is discussed. Subsequent pregnancies have been uncomplicated.