Is digital image compression acceptable within diabetic retinopathy screening?

AIMS: The National Screening Committee (NSC), whilst recommending the use of digital mydriatic retinal photography for diabetic retinopathy screening, has not yet accepted the use of digitally compressed images for grading. By greatly reducing the file size, however, compression of images is invaluable for storage and for its rapid transmission across computer networks. We undertook a study to compare the different levels of JPEG compression with the original bit-mapped image to determine whether there was any loss of clinical detail following compression. METHODS: Three hundred and thirty images were analysed in this study. These images had been captured from 66 eyes consecutively photographed in a diabetic retinopathy screening programme, using a Sony DXC-950 P 3CCD colour video camera mounted on a Canon CR6-45NMf fundus camera. Single 45 degrees macula-centred images were taken from each eye. The images were compressed using the JPEG algorithm within Adobe Photoshop (version 4.0) and then displayed with a Sony Trinitron colour monitor. Four different levels of compression were used, JPEG-1, JPEG-2, JPEG-3, JPEG-4, and an objective analysis was undertaken using 'lesion counts'. The compressed images were assessed separately and blindly and the results compared with their original BMP images. RESULTS: Eight BMP images could not be evaluated (five right eye and three left eye). A total of 290 images were therefore used in the final evaluation. All the JPEG-1 images with file sizes between 16 and 24 kb were found to be 'pixelated', while the JPEG-4 images (66-107 kb) appeared similar to the original BMP (1.3 Mb) images. Both JPEG-2 and JPEG-3 images had significantly lower counted lesions than the BMP images. CONCLUSIONS: From our findings we can conclude that only some degree of image compression (compression ratios of 1 : 20 to 1 : 12) with file sizes of 66-107 kb is permissible using JPEG format, whereas the images obtained after higher compression ratios may not be suitable for diabetic retinopathy screening.

Service use and needs of people with motor neurone disease and their carers in Scotland.

A national study of patients with motor neurone disease (MND) and their carers was conducted in Scotland in late 1996. A questionnaire covering areas such as: use of medical, social and voluntary services; use of or waiting for specialised equipment; satisfaction with provided services; and standard demographic data was used in face-to-face interviews conducted by the four Scottish Motor Neurone Disease Association care advisers. The care advisers also assessed the respondent's level of impairment, using a standard instrument: the Amyotrophic Lateral Sclerosis Severity Scale (ALSSS). The data was analysed using SPSS-PC. In total 153 people participated (response rate 92%), and as expected with this patient group the study recruited more men (57%) than women. Sixty per cent of the sample was severely disabled as measured on the ALSSS. Health services did not meet the needs of respondents in 19% of the cases and social services failed to do so according to 24% of respondents. Eighty per cent of patients with MND had an identified carer. Nearly four out of 10 of these carers had their sleep disturbed regularly, and nearly a quarter of them would have liked to have more help. In addition, differences were found in service provision between the East and West of Scotland, and consequently differences in respondent's perceptions about the extent to which needs were met. As found in similar studies, the formal health and social care sectors in conjunction with voluntary organisations are only partially managing the trajectory of patients with a rare progressive degenerative disease.