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Thresholding has been extensively used to separate myocardium from two-dimensional echocardiograms. We present a critical review of the existing threshold-based methods, and propose a new interactive method that uses the known average wall thickness at the indicated region to determine a reference global threshold. The thickness of the wall as seen in the thresholded image is important for quantization of cardiac parameters such as ventricular volume, ejection fraction, etc. In echocardiograms, owing to the characteristics of the imaging environment, the cardiac wall thickness depends on the threshold. Many existing methods concentrate on extracting continuous wall regions. In our scheme we select a threshold that yields walls of proper thickness, and then we attempt to obtain a continuous region. In our scheme, a user picks two points on a clearly visible section of the wall where the thickness is known. We compute a threshold by analyzing the regional histogram at that wall section so that average thickness of the regional thresholded pattern is equal to the known wall thickness. This gives a reference threshold that is varied locally by regional three-dimensional morphology to obtain local thresholds. The thresholding scheme suppresses noise and generates smooth boundaries.
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