Improving contrast and tracking of tags in cardiac magnetic resonance images

Cardiac tagging permits non-invasive study of myocardial motion with high a ccuracy, Unfortunately, tagging contrast is impaired at later heart phases due to longitudinal relaxation. Histogram modification is presented as a me thod for improving contrast in later, faded images of a tagging series by a ltering these images such that their intensity histograms approximate the s hape of the first, unfaded image of the series. This technique greatly impr oves the contrast and facilitates automatic detection of tags. Furthermore, a method is described for automatically tracking tag positions in short-ax is images of the left ventricle modulated with a tagging grid. The method d iffers from previously reported methods in that, in one single filtering pr ocess in the Fourier domain, both the grid crossings as well as the grid ce nters are detected, and thus increased sampling resolution is obtained. The method was validated by applying a mathematical model of left ventricular motion to tagged images of the thigh muscle. The average discrepancy betwee n theoretically predicted and automatically detected tag positions was 0.04 +/- 0.17 mm (mean +/- SD). Magn Reson Med 41:973-982, 1999. (C) 1999 Wiley -Liss, Inc.