RESUMEN
This study investigated the possibility of using low-cost, handheld, retinal imaging devices for the automatic extraction of quantifiable measures of retinal blood vessels. Initially, the available handheld devices were compared using a Zeiss model eye incorporating a USAF resolution test chart to assess their optical properties. The only suitable camera of the five evaluated was the Horus DEC 200. This device was then subjected to a detailed evaluation in which images in human eyes taken from the handheld camera were compared in a quantitative analysis with those of the same eye from a Canon CR-DGi retinal desktop camera. We found that the Horus DEC 200 exhibited shortcomings in capturing images of human eyes by comparison with the Canon. More images were rejected as being unevaluable or suffering failures in automatic segmentation than with the Canon, and even after exclusion of affected images, the Horus yielded lower measurements of vessel density than the Canon. A number of issues affecting handheld cameras in general and some features of the Horus in particular have been identified that might contribute to the observed differences in performance. Some potential mitigations are discussed which might yield improvements in performance, thus potentially facilitating use of handheld retinal imaging devices for quantitative retinal microvascular measurements.
RESUMEN
The optic disc (OD) in retinal fundus images is widely used as a reference in computer-based systems for the measurement of the severity of retinal disease. A number of algorithms have been published in the past 5 years to locate and measure the OD in digital fundus images. Our proposed algorithm, automatically: (i) uses the three channels (RGB) of the digital colour image to locate the region of interest (ROI) where the OD lies, (ii) measures the Shannon information content per channel in the ROI, to decide which channel is most appropriate for searching for the OD centre using the circular Hough transform. A series of evaluations were undertaken to test our hypothesis that using the three channels gives a better performance than a single channel. Three different databases were used for evaluation purposes with a total of 2,371 colour images giving a misdetection error of 3% in the localisation of the centre of the OD. We find that the area determined by our algorithm which assumes that the OD is circular, is similar to that found by other algorithms that detected the shape of the OD. Five metrics were measured for comparison with other recent studies. Combining the two databases where expert delineation of the OD is available (1,240 images), the average results for our multispectral algorithm are: TPR = 0.879, FPR = 0.003, Accuracy = 0.994, Overlap = 80.6% and Dice index = 0.878.
RESUMEN
OBJECTIVE: To describe the functioning and participation of people with disabilities seen in Haiti Team Canada Healing Hands clinics before and after the 2010 earthquake. DESIGN: Cross-sectional survey. SETTING: Rehabilitation clinics. PARTICIPANTS: A convenience sample of individuals attending Team Canada Healing Hands clinics (N=194): individuals who completed the survey before the 2010 earthquake (n=72) and individuals who completed the survey after the 2010 earthquake (n=122). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0). RESULTS: Overall WHODAS 2.0 scores before and after the 2010 earthquake were in the top 10th percentile of population normative data, where higher scores reflect greater disability. A median increase (6.6 points) in disability was reported after the earthquake (Mann-Whitney U, P=.055). There was a significant increase (Mann-Whitney U, P<.001) in WHODAS 2.0 scores related to mobility (18.8 points), life activities (30 points), and participation (16.7 points) domains after the earthquake. CONCLUSIONS: Persons in Haiti with a disability attending Team Canada Healing Hands clinics reported a low level of functioning. The increase in WHODAS 2.0 scores related to mobility, life activities, and participation domains suggests that the 2010 earthquake had a negative impact on functioning of this population and provides additional information on the responsiveness of the WHODAS 2.0 in limited resource settings. Future work can include using WHODAS 2.0 to monitor the impact of rehabilitation service and advocacy initiatives in Haiti and similar locations.
Asunto(s)
Actividades Cotidianas , Personas con Discapacidad/psicología , Personas con Discapacidad/rehabilitación , Terremotos , Calidad de Vida , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Estudios Transversales , Evaluación de la Discapacidad , Femenino , Haití , Estado de Salud , Humanos , Relaciones Interpersonales , Masculino , Salud Mental , Persona de Mediana Edad , Limitación de la Movilidad , Centros de Rehabilitación , Reproducibilidad de los Resultados , Participación Social , Adulto JovenRESUMEN
The morphology of the retinal blood vessels can be an important indicator for diseases like diabetes, hypertension and retinopathy of prematurity (ROP). Thus, the measurement of changes in morphology of arterioles and venules can be of diagnostic value. Here we present a method to automatically segment retinal blood vessels based upon multiscale feature extraction. This method overcomes the problem of variations in contrast inherent in these images by using the first and second spatial derivatives of the intensity image that gives information about vessel topology. This approach also enables the detection of blood vessels of different widths, lengths and orientations. The local maxima over scales of the magnitude of the gradient and the maximum principal curvature of the Hessian tensor are used in a multiple pass region growing procedure. The growth progressively segments the blood vessels using feature information together with spatial information. The algorithm is tested on red-free and fluorescein retinal images, taken from two local and two public databases. Comparison with first public database yields values of 75.05% true positive rate (TPR) and 4.38% false positive rate (FPR). Second database values are of 72.46% TPR and 3.45% FPR. Our results on both public databases were comparable in performance with other authors. However, we conclude that these values are not sensitive enough so as to evaluate the performance of vessel geometry detection. Therefore we propose a new approach that uses measurements of vessel diameters and branching angles as a validation criterion to compare our segmented images with those hand segmented from public databases. Comparisons made between both hand segmented images from public databases showed a large inter-subject variability on geometric values. A last evaluation was made comparing vessel geometric values obtained from our segmented images between red-free and fluorescein paired images with the latter as the "ground truth". Our results demonstrated that borders found by our method are less biased and follow more consistently the border of the vessel and therefore they yield more confident geometric values.