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M J Cree

Publications and source records attributed to M J Cree.

5 recordsLinked to original sources
PubMed1999

The preprocessing of retinal images for the detection of fluorescein leakage.

Images of the human retina are routinely used in clinical practice for the diagnosis and management of eye disease. Increased permeability of retinal blood vessels, which is a clinically significant feature, can be visualized with a process known as fluorescein angiography as leakage of fluorescence dye into the surrounding tissues. Analyses of such images can be quantified but significant degradation of images due to uneven illumination or occluded optical pathways is often incurred during image capture. We describe a procedure to restore fluorescein angiographic retinal images so that quantitative computation can be reliably performed. Analysis of the image acquisition system reveals that captured images are composed of two functions, one describing the true underlying image and the other the degradation incurred. These two functions are independent of one another and it is possible to estimate the degradation from an isolated captured image and restore it appropriately. Any leakage of fluorescein dye is then detected by analysing the restored angiographic sequence over time and finding areas of the image that do not have the usual decrease in fluorescence intensity.

Eye Diseases↗
PubMed1998

A comparison of computer based classification methods applied to the detection of microaneurysms in ophthalmic fluorescein angiograms.

We compared the performance of three computer based classification methods when applied to the problem of detecting microaneurysms on digitised angiographic images of the retina. An automated image processing system segmented 'candidate' objects (microaneurysms or spurious objects), and produced a list of features on each candidate for use by the classifiers. We compared an empirically derived rule based system with two automated methods, linear discriminant analysis and a learning vector quantiser artificial neural network, to classify the objects as microaneurysms or otherwise. ROC analysis shows that the rule based system gave a higher performance than the other methods (p = 0.92) although a much greater development time is required.

Aneurysm↗
PubMed1998

In vivo cell tracking by scanning laser ophthalmoscopy: quantification of leukocyte kinetics.

PURPOSE: To image peripheral blood leukocyte traffic in the normal retinal and choroidal vasculature and to quantify the differences in the circulation dynamics between normal and concanavalin A (ConA)-activated leukocytes. METHODS: Normal or ConA-activated splenocytes were fluorescently labeled in vitro with 6-carboxyfluorescein diacetate (CFDA) and reinfused in vivo where they were tracked in the retinal and choroidal circulations of syngeneic rats by means of a scanning laser ophthalmoscope (SLO). Simultaneous digital and video images were captured for as long as 30 minutes, and the initial 15 seconds of image sequences and leukocyte dynamics were analyzed from digitized images by recording the velocity of trafficking cells and the number of stationary cells that accumulated with time, using a customized software package. RESULTS: Mean velocity (+/-SD) was 29.8 +/- 15.3 mm/sec in the retinal arteries, 14.7 +/- 7.2 mm/sec in the retinal veins, and 3.0 +/- 3.6 mm/sec in the retinal capillaries. Mean velocity in the choroidal vessels was 6.1 +/- 6.0 mm/sec. No significant difference in leukocyte velocity was found between activated and normal leukocytes in any of the vessel systems. However, activated leukocytes were observed to accumulate more within the choroidal vasculature (P < 0.001) and the retinal capillaries (P < 0.001) than in control animals, but not in larger retinal vessels. CONCLUSIONS: A technique to measure the kinetics of circulating leukocytes in vivo has been developed. Although leukocyte activation itself is insufficient to cause slowing of leukocyte velocity, the data indicate that leukocyte adherence to endothelium can be induced in the absence of local or systemic activating stimuli.

Animals↗
PubMed1997

A fully automated comparative microaneurysm digital detection system.

A fully automated digital image processing system, which provides an objective and repeatable way to quantify microaneurysms in digitised fluorescein angiograms, has been developed. The automated computer processing includes registration of same-eye retinal images for serial studies, cutting of regions-of-interest centred on the fovea, the detection of microaneurysms and the comparison of serial images for microaneurysm turnover. The microaneurysm detector was trained against a database of 68 images of patients with diabetes containing 394 true microaneurysms, as identified by an ophthalmologist. The microaneurysm detector achieved 82% sensitivity with 2.0 false-positives per image. An independent test set, comprising 20 images containing 297 true microaneurysms, was used to compare the microaneurysm detector with clinicians. The microaneurysm detector achieved a sensitivity of 82% for 5.7 false-positives per image, whereas the clinician receiver-operator-characteristic (ROC) curve gives 3.2 false-positives per image at a sensitivity of 82%. It is concluded that the computer system can reliably detect microaneurysms. The advantages of the computer system include objectivity, repeatability, speed and full automation.

Aneurysm↗