Automatic quadratic calibration for correction of pixel classification boundaries to an accuracy of 2.5 millimeters: an application in cardiac imaging

Left ventricle (LV) boundaries estimated using automated pixel-based classifiers fall short in the apical zone and are not close the ground truth boundaries as delineated by the cardiologists. These errors are not random. They have a systematic positional and orientational bias, the boundary being under-estimated in the apex zone. They have a mean apex error of about 10.5 mm. The main reasons for bias errors are the poor contrast in the apex zone, nonhomogeneous mixing of the dye with the blood inside the left ventricle and interference of the diaphragm with inferior wall. Suri et al. (1996, 1997) showed, in earlier work, techniques to remove these bias errors using calibration schemes utilizing convex information of the left ventricle that consists of the aortic valve and the apex. This convex information was linear in nature. This paper presents an improved method of two calibration schemes using the quadratic nature of convex information. They are the quadratic identical coefficient and the quadratic independent coefficient methods. Using linear calibration, the independent coefficient method yields an error of 3.47 mm without utilizing apex, while quadratic calibration with convex information has a mean error of 2.49 mm. The goal set by the cardiologists is 2.5 mm