Floating axis does not reduce motion artifacts in a model of left ventricular wall motion in dogs

Methods of measuring regional wall motion of the left ventricle superimpose end-diastolic and end-systolic images. Differences in dimensions between images are assumed to be due to contraction, but they are also due to motion artifacts. To determine whether the errors caused by motion artifacts are reduced when measured with floating-axis referencing, and whether the measurement method affects these errors, we simulated end-systolic angiograms of a pure contraction (control) and contractions affected by motion artifacts and then measured differences in wall motion between angiograms with hemichord, radial, and trapezoid methods, using floating-axis and fixed-axis referencing. We chose these three methods because they form the basis for other methods, e.g., the center line method. For the simulations, we applied deformation patterns of the left ventricle, computed from the motion of tantalum markers implanted in the endocardiums of six dogs, to end-diastolic angiograms. This marker method measured the myocardial wall motion directly, independent of the angiogram. We found that differences caused by motion artifacts were not significantly reduced when measured with floating-axis referencing in our model. Normalized differences measured by radial and trapezoid methods were not significantly different, but they were significantly smaller than those measured by the hemichord method. We conclude that the axis referencing system has no significant effect on errors caused by motion artifacts in regional wall motion in our model. The measurement method, however, does affect these errors, with the radial and trapezoid methods being superior to the hemichord method.