RESUMO
Background and objective: With the development of image processing techniques, it has become possible to measure the changes in retinal vessels of hypertensive patients by means of eye fundus photographs. Patients and method: In this paper we aim to classify retinal vessels automatically into arterioles and venules. In order to do so, we have compared three different strategies based on the colour of the pixels in images through an analysis of 78 hypertensive patients' eye fundus images. The first strategy classifies all the vessels by applying a clustering algorithm. The second divides the retinal image into four quadrants and classifies the vessels that belong to the same quadrant independently from the rest of the vessels. The third strategy classifies the vessels by dividing the retinal image into four quadrants that are rotated inside the mentioned image. Results: The third strategy was the one that obtained the best results, since it minimizes the number of unclassified vessels. In the initially analysed set of 20 images, we correctly classified 86.53% of the vessels, and this percentage remains similar in a set of 58 images examined by three medical experts. This confirms the validity of the method that automatically calculates the arteriovenous ratio (AVR).Conclusion: Our results are an improvement on those previously described in the bibliography, reducing the number of non-classified vessels. Furthermore, the method entails low computational costs.
Fundamento y objetivo: El desarrollo de técnicas de procesado de imágenes ha devuelto interés para poder medir de una forma objetiva los cambios en la estructura microvascular del hipertenso a través de las fotografías digitales del fondo de ojo. Pacientes y método: Para clasificar de forma automática los vasos de la retina en arteriolas y vénulas, con una elevada precisión, hemos comparado tres estrategias diferentes basadas en la información del color de los pixeles de la imagen del fondo de ojo, analizando 78 imágenes de fondo de ojo de hipertensos. La primera estrategia clasificaría todos los vasos aplicando un algoritmo de agrupamiento. La segunda divide la retina en cuatro cuadrantes y clasifica los vasos que pertenecen al mismo cuadrante independientemente del resto de los vasos. La tercera estrategia clasifica los vasos dividiendo la retina en cuadrantes que son rotados. Resultados: La mejor estrategia resultó la tercera porque minimiza el error y el número de vasos no clasificados. La característica vectorial más determinante está basada en la media o la mediana del componente gris del espacio de color RGB. Para las 20 imágenes inicialmente analizadas hemos clasificado correctamente el 86.53% de los vasos, y este porcentaje permanece similar en el grupo de 58 imágenes examinadas por tres expertos, lo que confirma la validez del método, para el cálculo del índice arteriovenoso de forma automática. Conclusión: Nuestros resultados son superiores a los descritos previamente, reduciendo además el número de vasos no clasificados. Por otro lado, el costo computacional del método es bajo
Assuntos
Humanos , Vasos Retinianos , Retinopatia Hipertensiva , Fundo de Olho , Hipertensão , MicrocirculaçãoRESUMO
In a sample comprising 51 normotensive subjects and 51 subjects with in-clinic arterial hypertension [blood pressures (BPs) > or = 140/90 mmHg), we investigated the prevalence of target organ damage [left ventricular hypertrophy (LVH) and retinal vasculopathy] in white coat hypertension (WCH) groups defined using: (a) the "optimal ambulatory BP" criterion of the Seventh International Consensus Conference (in-clinic BPs >140/90 mmHg, daytime mean BPs < 130/80 mmHg) and (b) the "normal ambulatory BP" criterion proposed in 1997 by Verdecchia and co-workers (in-clinic BPs >140/ 90 mmHg, daytime mean BPs < 135/85 mmHg), and we compared the results with those obtained for the normotensive group and for a WCH group defined as in a 1996 study of the same data. We found that the newer criteria did not alter the conclusions reached in 1996: namely, that WCH constitutes a state of risk intermediate between normotension and sustained hypertension, which demands in-depth evaluation and active monitoring, if not immediate therapy. We also found that when the WCH group was defined as those patients with in-clinic BPs > or = 140/90 mmHg and 24-h mean BPs < 121/78 mmHg, the prevalence of target organ damage was similar to that found in the control group. We conclude that if WCH status is to imply absence of elevated risk of target organ damage, then the ambulatory BP threshold defining WCH should be lower than the upper limit of ambulatory BPs among subjects who are normotensive in the clinic. The desirability of predicting target organ damage in both hypertensive and normotensive subjects using criteria combining in-clinic BPs, daytime mean ambulatory BPs and night-time mean ambulatory BPs is suggested.
