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Figure 5. Curves showing changes in signal intensity on T2* weighted gradient echo images at different concentrations of standard paramagnetic contrast material. Note that the use of a low flip angle (bottom graph) results in almost no sensitivity to contrast media so that this strategy can be used in areas of marked contrast leakage. However, note that overall signal is far lower than is obtained with higher flip angles. At higher flip angles there is a significant contrast effect resulting in elevation of signal intensity as contrast concentration rises. However, this rise reaches a plateau after which the response to contrast concentration remains linear and eventually drops. This acts as the basis for a second strategy to remove the effect of contrast leakage by pre-enhancing tissues with a preliminary dose of contrast in order to reach a plateau phase. If this is achieved then the second injection of contrast will not be affected by further contrast leakage.
