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.

Microscan 101

The hardware used in this study allows us to capture video from an area much smaller than a pin head. This video, which is captured under the patient’s tongue, clearly shows the structure and dynamic flow of the microvasculature. Further analysis of the videos collected during this study will help quantify how microcirculation is effected by different disease states.

But capturing a clear video can still be a little tricky. The Microscan Manual has some helpful hints so we’ll start by extracting some of the more important ones.

Brace Yourself
There are two different methods for holding the probe described in our manual. While you’re training, try both and see which one feels more natural. It can help to steady the probe by bracing yourself with your non dominant elbow against the bed as seen in the photo above. Keeping the patient comfortable also helps. If their mouth is open too wide it may reduce the image quality.

Pressure
It can be hard to avoid creating pressure artifacts. Applying too much will occlude flow, too little and you might not be able to focus. Check out an example of what a pressure artifact looks like here. The more you practice the easier it will become to judge the right amount of pressure.

Plastic Caps
Always remember to keep the lens of the device covered with a plastic cap. It helps to designate one cap to use for storing the probe. Also, make sure the cap is fully secured before beginning your scan. A red light will stay on until the cap is secured. It will be impossible to get a focused image if this is not secured.

Keep it Charging
When you are not using the device remember to keep the battery pack and the laptop plugged in so they keep a charge. And while everything is tethered to the wall, why not back up your scans on an external drive?

Check out the full manual posted here using Scribd

Sepsis Study Overview

Investigating microcirculatory dysfunction in ER and ICU sepsis patients using new Microscan imaging technology

PI: Nathan Shapiro, MD, MPH

Background: It is believed that many of the pathophysiologic effects of sepsis are caused by alterations in the microvascular circulation to tissues, independent of arterial blood pressure changes. An imaging technique using Orthogonal Polarization Spectral (OPS) technology was initially developed to visualize these microcirculatory changes, but it required large, high powered light sources that are inconvenient for use in the ICU and ED settings. This led to the development of a portable device called Microscan, which uses a small probe and low-powered, high-intensity bright light emitting diodes (LEDs) to directly illuminate and magnify tissue and provide real-time video of microcirculatory flow. Identification of microcirculatory dysfunction may allow for earlier detection in patients at risk for systemic inflammatory syndromes, sepsis, and septic shock, enabling clinicians to implement earlier antibiotic treatment and goal directed therapy. It may also be useful as a risk stratification tool.

Summary: This is a prospective, cohort study that will analyze the microcirculation of the sublingual mucosa in ED and ICU patients with suspected infection and compare them to healthy controls. The primary outcome measure will be a calculated microcirculatory flow index, which involves scoring the flow in each Microscan video clip as follows: no flow (0 points), intermittent flow (1 point), sluggish flow (2 points), or continuous flow (3 points). Secondary outcome measures will be ICU admission, organ failure, length of stay, SOFA (organ dysfunction/failure) score, and APACHE-II (disease severity) score.