Video Quality: What is good enough?

Capturing videos of sufficient quality for quantitative analysis can be challenging. For the current study, videos of sublingual microcirculation are captured at a number of sites and analyzed off-line by researchers at Beth Israel Deaconess Medical Center. A variety of measurements are collected from these videos, ranging from vessel densities to semi-quantitative flow measurements of individual vessels. Before this analysis can occur, videos are clipped to shorter lengths (less than 20s) to make them more manageable. Multiple clips will be collected from a single patient at a given time-point. To help subjectively choose the best clips to analyze we’ve implementing the quality-scoring metric briefly described below. A more detailed description will be published at a later date.

After the videos are received, shorter clips are made to isolate some of the better quality video. In many cases, longer video clips will have sudden movements, changes in focus or pressure, or artifacts such as saliva obstructing the view of the vessels. From these shorter clips, a quality-scoring metric is implemented to rate six areas independently: intensity, duration, focus, content, stability, and pressure.

Illumination is based on the overall image intensity. When an image is over-illuminated or under illuminated it will appear too bright or dark, respectively.

Duration is a function of the length of the video clip. Videos are clipped from larger segments to help reduce the influence of other degrading factors. A certain video length is required to visually inspect the flow velocities.

Focus is a measure of image sharpness, which is apparent along the edges and within the small vessels (<20um).

To see how Illumination, Duration, and Focus metrics are scored see the video posted here.

Content looks at image artifacts and vessel structure, which would be debilitating to the analysis. In sublingual SDF images, artifacts can include small bubbles and cloudy or bloody saliva, which can all block the view of vessels.

Stability of the image is a measure of the overall image movement. Without practice it can be difficult to capture a stable image, because in most cases, the technician is holding a microscope free-hand under a moving patient’s tongue.

To see how Content, and Stability metrics are scored see the video posted here.

Pressure is an artifact caused by pressing too hard with the probe tip causing the blood flow to slow or stop. While contact is needed to focus the image, too much pressure will collapse larger vessels resulting a falsely sluggish or stopped flow.

To see how Pressure is scored see the video posted here.