The effect of transmission bandwidth on the quality of ophthalmological still and video images.
We have examined the minimum realtime transmission speed for video-angiography with the Rodenstock scanning laser ophthalmoscope (SLO) with respect to spatial and contrast resolution. An SLO fluorescein video-angiography sequence was recorded using high-quality media and relayed to a remote site at transmission speeds ranging from T3 (4.5 Mbit/s) to 0.125 T (197 kbit/s). Images were compared with each other subjectively by an ophthalmologist and objectively with image processing software. When compared qualitatively there was little difference between the T3 and T1 images. The T1 images scored well on clarity and contrast, while 0.5 T was satisfactory but inferior to T1. Transmission speeds below 0.5 T were inadequate. The digital analysis showed a slight difference between T3 and T1. We calculated that there was up to a 92% loss of resolution at 0.25 T and up to a 98% loss at 0.125 T. Based on our quantitative and qualitative analysis, a T3 line provided the highest bandwidth and best resolution, as expected. However, 0.5 T gave satisfactory results for realtime consultations and appears to be the minimum speed required for ophthalmic purposes, producing few motion artefacts and good resolution.
Cuzzani
O
O
Gimbel Eye Centre, Calgary, Alberta, Canada. ocuzzani@gimbel.com
Bromwich
M
M
Penno
E
E
Gimbel
H
H
D002387:Cataract Extraction / Q000295:instrumentation; D006801:Humans; D009887:Ophthalmoscopy / Q000592:standards*; D017216:Telemedicine / Q000592:standards*; D013686:Telemetry / Q000379:methods* / Q000592:standards