Video that Reveals the Invisible: Novel Technology for Real-Time, Non-Invasive Free Flap Monitoring
Richard S. Gaster, M.D., Ph.D.1, Aaron J. Berger, M.D., Ph.D.2, Gordon K. Lee, M.D.2.
1Harvard University, Boston, MA, USA, 2Stanford University, Stanford, CA, USA.
Our mission is to develop an effective, non-invasive method for the continuous monitoring of tissue perfusion after free flap surgeries. We sought out to re-invent the utility of the video camera by introducing mathematical algorithms capable of revealing seemingly invisible changes in video recordings, and magnifying those subtle changes into the visibly detectable range. With this tool, we propose to introduce a novel method for monitoring free flaps in patients during the immediate post-operative period.
Utilizing mathematical manipulation of video recordings, we deconstruct standard video sequences, frame-by-frame, and pixel-by-pixel, into individual data points. By comparing pixels across time, and amplifying subtle changes by up to 200-fold, we demonstrate the ability to reveal seemingly undetectable changes in both color and motion recorded in the video.
When video magnification is applied to a recording of skin, we demonstrate the ability to magnify the color change of the skin associated with capillary blood flow and identify pulsating color changes at a frequency of approximately 1.2 Hz, consistent with a heart rate of 72bpm (Figure 1). The now perceptible pulsating color changes are a direct result of each heartbeat and correlate to the pulsatile blood flow into the flap. Since the vascular blood supply of a free flap is restricted to a single artery by the nature of the procedure, one can reasonably infer that the pulsatile color change on the skin is a direct proxy for the pulsatile blood flow through the recently anastomosed artery. Therefore, if the amplitude of the color change during each pulsation is reduced or stops altogether, one can infer that the anastomosis has been compromised. Thus, we can now utilize the video camera to non-obtrusively monitor perfusion of a skin paddle in free flaps to gain insights into overall perfusion of a free flap.
In our experience, the use of video magnification holds great promise for the routine monitoring of free flaps post-operatively. This technology has the ability to relay information regarding capillary perfusion at the skin and can act as a real-time source for indirectly monitoring the blood flow through the vascular pedicle of a free flap. Such a tool has the potential to aid in potentiating rapid return of patients to the operating room in the setting of flap compromise in a continuous fashion.
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