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Illumination
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Brightness and contrast of video
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Even illumination across the entire field of view. Contrast sufficient to see small vessels against a background of tissue.
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The video borders on being too dark or bright to distinguish vessels from tissue but the vessels are still identifiable.
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The video is oversaturated/too bright or too dark to make out analysable features. Insufficient contrast to resolve flow rate.
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Duration
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Number of frames in the video clip and how it represents the actual pathology
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Analysable video segment is ≥5 s long (>150 frames)
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Analysable video segment is 3–5 s (between 90 and 150 frames)
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Analysable video segment <3 s (90 frames)
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Focus
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Image sharpness in region of interest
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Good focus for all vessels (small and large) in the entire field of view. Plasma gaps and red blood cells are visible.
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<1/2 field of view is out of focus or edges of the vessels are slightly out of focus.
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Video is completely out of focus such that no small vessel can be seen.
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Content
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Determination of the types of vessels and/or presence of occluding artefacts in the image.
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Video is free of occlusions. Good distribution of large and small vessels. Less than 30 % of the vessels are looped upon themselves
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Video may have a few artefacts. Acceptable distribution of large and small vessels. About 30–50 % of the vessels are looped.
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Most of the field of view has occluding artefacts such as saliva or bubbles. More that 50 % vessels are looped upon themselves.
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Stability
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Frame motion that can be adequately stabilised without motion blur
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Movement is within ¼ of the field of view. No motion blur.
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Movement is within ½ field of view. No motion blur.
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Movement is greater than ½ of the field of view and/or motion blur in frame
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Pressure
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Iatrogenic mechanical pressure causing misrepresentation of flow
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Flow is constant throughout the entire movie. No obvious signs of artificially sluggish or stopped flow. Good flow in the largest vessels.
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Signs of pressure (localised sluggish flow in a specific large vessel), but flow appears to be unimpeded based on good flow in most large vessels.
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Obvious pressure artefacts associated with probe movement, and/or flow that starts and stops, reversal of flow. Poor or changing flow in larger venules.
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