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Friday, December 31st, 2010, 5:26 pm

Rotation of the Heart Explored

Frame of heart images

Shown here are two images derived from experiments out of which there are also videos. The set of cardiac images contains 340 images, divided into 17 groups of 20 images belonging to each. A group of 20 consecutive images represents one slice imaged throughout one cardiac cycle. This means that from the 2nd and 4th slides — images 21 and 61 respectively for example — the signal is approximately correspondent and thus can be compared. A series of experiments was performed in turn, dealing with each slice in isolation and learning how our algorithm copes with the complicated task of tracking the heart’s walls without a priori knowledge such as a model of the heart, for example (a model whose parameter values can be optimised over, for a good fit to be eventually found). We are interested in the rotation of the heart at the different vertical levels, particularly because we expect to see clockwise and counterclockwise movements throughout the cycle, depending on the slice (the heart squeezes blood by moving in different — almost opposite — directions).

The results are encouraging. Leaving aside slices that hardly contain any signal from the heart because they are at the top and bottom edges, it is quite consistently found that there is a clockwise rotation at the centre, detected by averaging the direction of the move of many salient points. In the middle slices in particular (those in which the heart gives more signal owing to greater overall area), the curves are entirely, or at least almost entirely, monotonic, which means that at each iteration the clockwise rotation continues. This can help show some otherwise-hidden information, but more datasets and rigorous testing on synthetic data for validation may be required as well.

Directions accumulator

Expansion accumulator

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