Alex Vargas

Sensitivity analysis of geometric errors in additive manufacturing medical models.

Additive manufacturing (AM) models are used in medical applications for surgical planning, prosthesis design and teaching. For these applications, the accuracy of the AM models is essential. Unfortunately, this accuracy is compromised due to errors introduced by each of the building steps: image acquisition, segmentation, triangulation, printing and infiltration. However, the contribution of each step to the final error remains unclear. We performed a sensitivity analysis comparing errors obtained from a reference with those obtained modifying parameters of each building step. Our analysis considered global indexes to evaluate the overall error, and local indexes to show how this error is distributed along the surface of the AM models. Our results show that the standard building process tends to overestimate the AM models, i.e. models are larger than the original structures. They also show that the triangulation resolution and the segmentation threshold are critical factors, and that the errors are concentrated at regions with high curvatures. Errors could be reduced choosing better triangulation and printing resolutions, but there is an important need for modifying some of the standard building processes, particularly the segmentation algorithms.

Tratamiento y prevención de la mucositis oral asociada al tratamiento del cáncer

One of the most common and troublesome complications of modern intensive anticancer treatments is oral mucositis. The purpose of this review is to summarize current evidence and clinical guidelines regarding its prevention and therapy. The use of keratinocyte growth factor-1, supplementary glutamine and other recently developed treatment modalities are discussed. The injury of the oral mucosa caused by antineoplastic agents promotes the local expression of multiple pro-inflammatory and pro-apoptotic molecules and eventually leads to the development of ulcers. Such lesions predispose patients to several infectious and nutritional complications. Also, they lead to modification of treatment schedules, potentially affecting overall prognosis. Local cryotherapy with ice chips and phototherapy with low energy laser may be useful as preventive measures. Mouthwashes with allopurinol and phototherapy with low energy laser can be used as treatment. In radiotherapy, special radiation administration techniques should be used to minimize mucosal injury. Pain control should always be optimized, with the use of patient controlled analgesia and topical use of morphine. Supplemental glutamine should not be used outside of research protocols. Lastly, thorough attention should be paid to general care and hygiene measures.

Quantitative assessments of geometric errors for rapid prototyping in medical applications

Purpose – In medical applications, it is crucial to evaluate the geometric accuracy of rapid prototyping (RP) models. Current research on evaluating geometric accuracy has focused on identifying two or more specific anatomical landmarks on the original structure and the RP model, and comparing their corresponding linear distances. Such kind of accuracy metrics is ambiguous and may induce misrepresentations of the actual errors. The purpose of this paper is to propose an alternative method and metrics to measure the accuracy of RP models.Design/methodology/approach – The authors propose an accuracy metric composed of two different approaches: a global accuracy evaluation using volumetric intersection indexes calculated over segmented Computed Tomography scans of the original object and the RP model. Second, a local error metric that is computed from the surfaces of the original object and the RP model. This local error is rendered in a 3D surface using a color code, that allow differentiating regions where...

Anatomía y Neuroanatomía, Disciplinas Perjudicadas por la Reforma Curricular

En los ultimos tiempos, la docencia en Morfologia ha debido enfrentar un escenario cambiante, producto de: a) un cambio curricular que ha llevado a la reduccion de las horas destinadas a los cursos de Anatomia y Neuroanatomia; b) la dificultad creciente de obtener material cadaverico para las actividades practicas de dichos cursos; c) el incremento en el numero de alumnos de los cursos de pregrado; y, d) la reduccion alarmante de los cultores de estas ciencias basicas del curriculo de Medicina. Como resultado de lo anterior, es dable esperar, que esta situacion -que tiene un alcance mundial-, mas temprano que tarde tenga un efecto en el conocimiento morfologico de los medicos recien formados. En este estudio se analiza el rendimiento obtenido en pruebas diagnosticas de reconocimiento de estructuras en Anatomia y Neuroanatomia, aplicadas a medicos residentes de primer ano de la especialidad de Radiologia, formados bajo este nuevo paradigma curricular. Los resultados mostraron que la nota promedio (escala 1 a 7) de la prueba diagnostica fue 3,14 + 0,99. Es interesante notar que para una evaluacion similar, los alumnos de primer ano de la carrera de medicina obtienen una nota promedio de 5,75 +0,55. Luego de aplicar a los mismos residentes del estudio un curso teorico-practico de nivelacion en Anatomia, se aprecia un mejoramiento en el reconocimiento de estructuras anatomicas, con nota promedio de 4,79 + 0,96; detectandose una mejora sustantiva en la identificacion de elementos en secciones anatomicas de tronco. En las evaluaciones de temas neuroanatomicos, las diferencias son aun mas notorias (1,53 v/s 3,97). Estos datos reposicionan a las actividades practicas de Anatomia, en especial el trabajo con material cadaverico , como un quehacer central en el proceso de aprendizaje de estos temas. Esta situacion de olvido y/o desconocimiento observada en los nuevos medicos, ha generado una gran demanda por cursos de apoyo morfologico para las distintas especialidades

Panniculus carnosus, remanentes vestigiales en la región axilar

Las variaciones anatomicas de los elementos musculares de la region axilar son poco frecuentes y, generalmente, se encuentran olvidadas en los textos modernos de anatomia. Sin embargo, cuando existen, presentan un serio escollo para el cirujano, ya que alteran los hitos anatomicos de referencia para el abordaje de los importantes elementos vasculares y neurales de la region. Desde el siglo XIX algunos autores han descrito una variedad de pequenos fasciculos musculares originados en el Panniculus carnosus, que se disponen en relacion con los elementos neurovasculares de la axila. En esta ocasion presentamos un hallazgo efectuado en un cadaver, de sexo masculino, utilizado con fines docentes en el Departamento de Anatomia de la Escuela de Medicina de la Pontificia Universidad Catolica de Chile. En la region axilar derecha, se observa un fasciculo muscular que se extiende desde la apofisis coracoides, dispuesto por delante del musculo subescapular y pasando por detras del paquete neurovascular de la axila. En su trayecto, este fasciculo toma intima relacion con el nervio axilar y con la porcion distal de la arteria subescapular. El musculo aberrante termina como una expansion aponeurotica, dispuesta ventral al tendon del latisimo del dorso, que se funde con la fascia axilar.

El papiro de Edwin Smith y su trascendencia médica y odontológica

BACKGROUND The historical bases of occidental medicine precede the Hippocratic corpus. Between the third and first millennium B.C. Egyptian medicine developed a model of medical practice that was a reference horizon for other Mediterranean cultures. There are a great number of papyri of that time, which gathered the medical and surgical skills and that are matter of study. The Edwin Smith papyrus (PES) is one of them. We analyzed the PES in its historical context, its history, its structure and its medical and dental significance. Finally, we analyzed the relevance of PES as a sign of a change in the medicine study method in the ancient Egypt. PES is an insight into how medicine was practiced in ancient Egypt. Historically, it is also the first medical document based on objective observations, excluding all magical and religious perceptions, as well as the underlying cultural framework. The similarity between the current clinical method and that described in the Smith papyrus, strongly suggests the idea that part of the origin of medicine, can be found in ancient Egypt.Background: The historical bases of occidental medicine precede the Hippocratic corpus. Between the third and first millennium B.C. Egyptian medicine developed a model of medical practice that was a reference horizon for other Mediterranean cultures. There are a great number of papyri of that time, which gathered the medical and surgical skills and that are matter of study. The Edwin Smith papyrus (PES) is one of them. We analyzed the PES in its historical context, its history, its structure and its medical and dental significance. Finally, we analyzed the relevance of PES as a sign of a change in the medicine study method in the ancient Egypt. PES is an insight into how medicine was practiced in ancient Egypt. Historically, it is also the first medical document based on objective observations, excluding all magical and religious perceptions, as well as the underlying cultural framework. The similarity between the current clinical method and that described in the Smith papyrus, strongly suggests the idea that part of the origin of medicine, can be found in ancient Egypt.

Análisis del Paladar Oseo como Zona Dadora de Injerto

El paladar oseo podria ser una zona favorable como dadora de injertos, siempre que se pueda determinar con seguridad su grosor. El objetivo de este estudio fue evaluar la correlacion entre la altura facial superior y el grosor del paladar oseo. En 29 craneos secos se midio la altura facial superior, ubicando los puntos craneometricos nasion y prostion. Luego se midio el grosor del paladar oseo de todas las muestras a los 6 y 9 mm a dorsal del conducto incisivo, en la zona paramediana (3 y 6 mm. de la linea media en ambas antimeras). Se realizo el Test de Correlacion de Pearson, para establecer si la altura facial puede predecir el grosor del paladar oseo. Existe una gran variabilidad en el grosor del paladar oseo entre los craneos, con un rango de 0,1 a 1,1 cm. El mayor grosor se presento a los 6 mm. hacia dorsal del conducto incisivo, con un promedio de 0,71 ± 0,20 cm. No se determino una correlacion estadisticamente significativa entre la altura facial superior y el grosor del paladar. Para definir ajustadamente el grosor del paladar oseo y, asimismo, su utilidad como zona dadora de injerto, sera necesario confrontar la craneometria con estudios imagenologicos avanzados

Adhesivos de cianoacrilato en cirugía oral y maxilofacial

The cyanoacrylate adhesives (ACA) are synthetic materials with adhesive properties. When is applied in tissues, it polymerizes and bonds with the underlying tissue. Since the 70s’ have been explored their surgical applications for closing wounds, fistulas, bleeding control, and graft fixation, among others. Its use as an alternative for closing wounds in skin and mucous is one of the most studied. The ACA have a limited absorption degree, with no evidence of systemic toxic effects. They have the advantage of being applied quickly, painlessly, with antibacterial effect and hemostatic according to the report of literature, but with reduced tensile strength. The objective of this literature review is to describe the use and applications of ACA, with focus on oral and maxillofacial surgery, with a critically evaluation of their applications.

Generation of mineral density distribution maps from subject‐specific models of mandibles – a preliminary study

Determination of the mineral content of bone and its distribution by computed tomography (CT) enables one to define the insertion points for prosthetic devices, or determine the degree of healing in cases of fracture or surgical intervention. The use of subject‐specific models allows mapping of the spatial structure and the mineral content of the bone graphically and quantitatively.