A finite element-based machine learning approach for modeling the mechanical behavior of the breast tissues under compression in real-time.

This work presents a data-driven method to simulate, in real-time, the biomechanical behavior of the breast tissues in some image-guided interventions such as biopsies or radiotherapy dose delivery as well as to speed up multimodal registration algorithms. Ten real breasts were used for this work. Their deformation due to the displacement of two compression plates was simulated off-line using the finite element (FE) method. Three machine learning models were trained with the data from those simulations. Then, they were used to predict in real-time the deformation of the breast tissues during the compression. The models were a decision tree and two tree-based ensemble methods (extremely randomized trees and random forest). Two different experimental setups were designed to validate and study the performance of these models under different conditions. The mean 3D Euclidean distance between nodes predicted by the models and those extracted from the FE simulations was calculated to assess the performance of the models in the validation set. The experiments proved that extremely randomized trees performed better than the other two models. The mean error committed by the three models in the prediction of the nodal displacements was under 2 mm, a threshold usually set for clinical applications. The time needed for breast compression prediction is sufficiently short to allow its use in real-time (<0.2 s).

A complete software application for automatic registration of x-ray mammography and magnetic resonance images.

PURPOSE: This work presents a complete and automatic software application to aid radiologists in breast cancer diagnosis. The application is a fully automated method that performs a complete registration of magnetic resonance (MR) images and x-ray (XR) images in both directions (from MR to XR and from XR to MR) and for both x-ray mammograms, craniocaudal (CC), and mediolateral oblique (MLO). This new approximation allows radiologists to mark points in the MR images and, without any manual intervention, it provides their corresponding points in both types of XR mammograms and vice versa. METHODS: The application automatically segments magnetic resonance images and x-ray images using the C-Means method and the Otsu method, respectively. It compresses the magnetic resonance images in both directions, CC and MLO, using a biomechanical model of the breast that distinguishes the specific biomechanical behavior of each one of its three tissues (skin, fat, and glandular tissue) separately. It makes a projection of both compressions and registers them with the original XR images using affine transformations and nonrigid registration methods. RESULTS: The application has been validated by two expert radiologists. This was carried out through a quantitative validation on 14 data sets in which the Euclidean distance between points marked by the radiologists and the corresponding points obtained by the application were measured. The results showed a mean error of 4.2 ± 1.9 mm for the MRI to CC registration, 4.8 ± 1.3 mm for the MRI to MLO registration, and 4.1 ± 1.3 mm for the CC and MLO to MRI registration. CONCLUSIONS: A complete software application that automatically registers XR and MR images of the breast has been implemented. The application permits radiologists to estimate the position of a lesion that is suspected of being a tumor in an imaging modality based on its position in another different modality with a clinically acceptable error. The results show that the application can accelerate the mammographic screening process for high risk populations or for dense breasts.

Segmentation of the breast skin and its influence in the simulation of the breast compression during an X-ray mammography.

A novel method of skin segmentation is presented aimed to obtain as many pixels belonging to the real skin as possible. This method is validated by experts in radiology. In addition, a biomechanical model of the breast, which considers the skin segmented in this way, is constructed to study the influence of considering real skin in the simulation of the breast compression during an X-ray mammography. The reaction forces of the plates are obtained and compared with the reaction forces obtained using classical methods that model the skin as a 2D membranes that cover all the breast. The results of this work show that, in most of the cases, the method of skin segmentation is accurate and that real skin should be considered in the simulation of the breast compression during the X-ray mammographies.

MRI skin segmentation for the virtual deformation of the breast under mammographic compression.

Breast Magnetic Resonance Image skin has similar intensity levels than dense tissue, and may produce segmentation errors if not managed correctly. In this work a novel skin segmentation method is presented and validated by experts, aimed to obtain as many pixels belonging to the real skin as possible. Segmented skin will be used to build a breast biomechanical model to register X-Ray Images with Magnetic Resonance Images in the future, using a virtually deformed Magnetic Resonance Image.

[Thymectomy in myasthenia gravis: long-term evolution and predictive factors]. / Timectomía en la miastenia gravis: evolución a largo plazo y factores pronósticos.

INTRODUCTION: Thymectomy is a surgical procedure which is generally accepted for treatment of myasthenia gravis. OBJECTIVE: To describe the long-term evolution of 217 myasthenic patients who had had thymectomies in the Hospital Clinico Quirurgico Hermanos Ameijeiras in La Habana, Cuba. PATIENTS AND METHODS: We determined the stage of evolution of 217 patients, followed-up periodically, with an average observation time of 83.4 months and an interval of between 5 and 155 months. We also studied the frequency of remission and the influence of a group of variables on this, as well as the mortality and its causes. RESULTS: The clinical state of the patients was: remission 77 (35.4%); pharmacological remission 45 (20.7%); significant improvement 70 (32.2%); the same or worse 5 (2.3%); deaths 11 (5%), and unknown 9 (4.1%). The cases with thymomas had a more unsatisfactory course than the other patients, with fewer remissions and greater mortality. Over the first five years of the evolution of the disease, there was a 30% rate of remission; after five years this rose to 35-40% and after ten years reached 47%. The age of the patient, duration of symptoms, histology of the thymus, age of onset of the disease and duration of follow-up did not have any significant effect (p < 0.05) on the long-term evolution of the thymectomy, in contrast to the gravity of the condition according to Osserman's scale. CONCLUSION: The results of thymectomy, in our study were good and similar to the results reported in the international literature.

Timectomía en la miastenia gravis: evolución a largo plazo y factores pronósticos / thymectomy in myasthenia gravis: long-term evolution and predictive factors

Introduction. Thymectomy is a surgical procedure which is generally accepted for treatment of myasthenia gravis. Objective. To describe the long-term evolution of 217 myasthenic patients who had had thymectomies in the Hospital Clinico Quirurgico Hermanos Ameijeiras in La Habana, Cuba. Patients and methods. We determined the stage of evolution of 217 patients, followed-up periodically, with an average observation time of 83.4 months and an interval of between 5 and 155 months. We also studied the frequency of remission and the influence of a group of variables on this, as well as the mortality and its causes. Results. The clinical state of the patients was: remission 77 (35.4%); pharmacological remission 45 (20.7%); significant improvement 70 (32.2%); the same or worse 5 (2.3%); deaths 11 (5%), and unknown 9 (4.1%). The cases with thymomas had a more unsatisfactory course than the other patients, with fewer remissions and greater mortality. Over the first five years of the evolution of the disease, there was a 30% rate of remission; after five years this rose to 35-40% and after ten years reached 47%. The age of the patient, duration of symptoms, histology of the thymus, age of onset of the disease and duration of follow-up did not have any significant effect (p< 0.05) on the long-term evolution of the thymectomy, in contrast to the gravity of the condition according to Osserman’s scale. Conclusion. The results of thymectomy, in our study were good and similar to the results reported in the international literature (AU)

Introducción. La timectomía es un procedimiento quirúrgico ampliamente aceptado en el tratamiento de la miastenia gravis. Objetivo. Describir la evolución a largo plazo de 217 pacientes miasténicos a quienes se efectuó timectomía en el Hospital Clínico Quirúrgico Hermanos Ameijeiras de La Habana, Cuba. Pacientes y métodos. Se determinó el estado evolutivo de 217 pacientes, seguidos periódicamente, con un tiempo de observación promedio de 83,4 meses y un intervalo de entre 15 y 155 meses. Asimismo, se estudió la frecuencia de remisión y la influencia de un grupo de variables sobre ella, así como la mortalidad y sus causas. Resultados. El estado clínico de los pacientes fue: remisión 77 (35,4%); remisión farmacológica 45 (20,7%); mejoría significativa 70 (32,2%); igual o peor 5 (2,3%); fallecidos 11 (5%), y desconocido 9 (4,1%). Los casos con timoma evolucionaron menos favorablemente que el resto de los pacientes, pues pudo observarse una menor frecuencia de remisiones y una mayor mortalidad. En los primeros cinco años de evolución la frecuencia de remisiones fue del 30%; después de los cinco años aumentó hasta un 35-40%, y después de diez años alcanzó un 47%. La edad del paciente, la duración de los síntomas, la histología del timo, la edad de debut de la enfermedad y el tiempo de seguimiento no tuvieron una influencia significativa (p< 0,05) sobre la evolución a largo plazo de la timectomía, a diferencia de la gravedad de la enfermedad de acuerdo con la escala de Osserman. Conclusión. Los resultados de la timectomía en nuestro estudio fueron favorables y similares a los publicados internacionalmente (AU)

[Dual-chamber pacemakers in obstructive hypertrophic cardiomyopathy: gradient variation with stress echocardiography]. / Marcapasos bicameral en la miocardiopatía hipertrófica obstructiva: variación del gradiente con ecocardiografía de estrés.

INTRODUCTION: Permanent cardiac pacing with a dual chamber pacemaker has become a valid alternative in treatment of patients with obstructive hypertrophic cardiomyopathy and refractory symptoms to pharmacological treatment, with a significant decrease of left ventricular outflow tract gradient. AIM: To assess any modification of the gradient with dobutamine stress echocardiography. PATIENTS AND METHODS: We study 10 patients with obstructive hypertrophic cardiomyopathy and angina and/or dyspnea refractory to customary pharmacological treatment. A dual chamber pacemaker had been implanted 3-6 months previously. A dobutamine stress echocardiography was performed, beginning with a 10 microgram/kg/min infusion, with increases of 10 micrograms each 3 minutes until a maximum of 40. Modification of subaortic gradient, severity of systolic anterior motion of mitral valve (SAM, degree 0-3/3) and severity of mitral regurgitation (degree 0-4/4) were assessed. RESULTS: Subaortic gradient decreased in all patients after pacemaker implantation (90 +/- 15 vs 20 +/- 10 mmHg; p < 0.001). With stress echocardiography the gradient increased in all patients (20 +/- 10 to 101 +/- 13 mmHg; p < 0.001). After implant there were only two patients with a +1 SAM, while during stress echocardiography SAM developed in all patients in +2 or +3 degree. Three patients had +1 mitral regurgitation after pacemaker implantation but during stress echocardiography 2-4/4 mitral regurgitation developed in all patients. CONCLUSIONS: Permanent dual chamber pacing decreased left ventricular outflow tract gradient in patients with obstructive hypertrophic cardiomyopathy, but during dobutamine stress echocardiography obstruction echocardiographic signs appeared.

[Continuing education in health. Possibilities and limitations]. / Educación permanente en salud. Posibilidades y limitaciones.

The author starts with a definition of continuing education as a system of educational activities organized with some continuity over extended periods and directed at in-service health personnel for the chief purpose of complementing their initial training and thereby improving or extending health coverage. This definition encompasses all categories of health personnel. It is noted that education today faces two challenges: attainment of the goals of health for all by the year 2000 through the strategies of primary care, and the revolution in information technology. Continuing education is a possible response from the education field. It is stated, however, that in many cases the socioeconomic and health systems of countries hamper the development of continuing education programs.