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Video-Based Pulse Measurement System Could Help Diagnose Cardiac Disease

MIT researchers have developed an algorithm that measures the heart rates of people pictured in regular digital video by analyzing imperceptibly small head movements that accompany the rush of blood caused by the heart's contractions. Their algorithm has given pulse measurements consistently within a few beats per minute of those produced by electrocardiograms (EKGs). It has also provided useful estimates of the time intervals between beats, a measurement that can be used to identify patients at risk for cardiac events. This system could be useful for monitoring newborns or the elderly, whose sensitive skin could be damaged by frequent attachment and removal of EKG leads. The technique could also measure cardiac output, or the volume of blood pumped by the heart, which is used in the diagnosis of several types of heart disease.

Topics:
Diagnostics Imaging Measuring Instruments Medical Test & Measurement Video

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    Transcript

    00:00:00 in this video we demonstrate that it's possible to analyze cardiac pulse from regular videos by extracting the imperceptible motions of the head caused by blood flow recent work has enabled the extraction of pulse from videos based on color changes in the skin due to blood circulation if you've seen someone blush you know that pumping blood to the face can produce a color

    00:00:20 change in contrast our approach leverages a perhaps more surprising effect the inflow of blood doesn't just change the Skin's color it also causes the head to move this movement is too small to be visible with the naked eye but we can use video amplification to reveal it believe it or not we all move like bobbleheads with different motions at

    00:00:42 our heart rate but at a much smaller amplitude than this now you might wonder what causes the head to move like this at each cardiac cycle the heart's left ventricle contracts and ejects blood at high speed to the aorta during the cycle roughly 12 gr of blood flow to the Head from the aorta by the cded artery on either side of the neck it is this influx of blood that generates a force

    00:01:04 on the head due to Newton's third law the force of the blood on the head equals the force of the head acting on the blood causing a reactionary cyclical head movement to demonstrate this process we created a toy model using a transparent mannequin head with rubber tubes stand for simplified arteries instead of pumping blood we will pump compressed air provided by this air tank

    00:01:26 and I can release the air using this valve now watch what happens as I open and close close the valve once a second similar to a normal heart rate ready here this motion is fairly similar to the Amplified motion of real heads that we've seen before we exploit this effect to develop a technique that can analyze pulse and regular videos of a person's head our method takes an input video of

    00:01:48 a stationary person and returns a one-dimensional signal corresponding to the Head motions from this signal we can extract an average pulse rate as well as beat locations for deeper clinical analysis we Begin by locating the face using a face detector and selecting feature points within the area the feature points are tracked from frame to frame of the video using the Lucas Kady

    00:02:10 tracking algorithm we use the vertical or Y component of each of the feature point trajectories for our analysis next we temporarily filter the signals to a pass band encompassing a normal pulse range while excluding extraneous Motions like respiration we decompose the multi-dimensional motion of the head described by the trajectories into sub

    00:02:30 motions using principal component analysis or PCA PCA Returns the main directions along which the head moves we project the motion of the head onto each component and choose the signal with the clearest dominant frequency we use the dominant frequency to obtain an average pulse rate finally we perform Peak detection on the chosen signal to obtain beat locations for further analysis such

    00:02:52 as heart rate variability we tested our method on different people varying in skin tone and gender and were're able to get nearly exact pulse rates compared to an ECG device in addition our method produced similar beat length distributions to the ECG an exciting result that shows that we can capture more subtle information about the heart

    00:03:11 than just an average rate finally our method is robust to different views of the head we obtained a pulse from a sleeping newborn from the back of a subject's head and even when a person is wearing a mask