Figure 24

Relative SI levels in Phase Sensitive IR sequence. By restoring signal polarity (Figure23), normal myocardial signal remains markedly lower than scar, even if the null point is underestimated by 40 ms. Note that negative signal intensities correspond to tissues who’s longitudinal magnetization has not recovered past M_z = 0 at time TI. For image display purposes, tissues with zero magnetisation values are mapped onto the middle of the image pixel intensity range. Tissues with a positive magnetisation are then displayed with image pixel intensities increasing from this middle value, while tissues with a negative magnetisation are displayed with images pixel intensities decreasing from this middle value. ‘Nulling’ the normal myocardium can then be achieved retrospectively by adjusting the window and level on the viewing console and there is no longer an ambiguity between tissues with positive and negative magnetisation values.