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A new method is introduced to detect magnetic field modulation arising from brain activation-induced BOLD effects. This approach uses a two-dimensional high-bandwidth, high-resolution conventional gradient-echo steady-state imaging sequence known as TrueFISP. The ability to visualize changes in oxygen saturation comes from the fact that the method is sensitive to the local field. As is well known, as the oxygen saturation changes so does the local field associated with the venous blood. We demonstrate that it is possible to visualize not only venous blood with this approach on a macroscopic level for major veins, but also to measure conventional oscillatory like signal changes during activated and resting states. Unfortunately, the method has two major drawbacks. First, a long TR is needed to maximize signal changes and, second, the field must be very well shimmed or numerous experiments need to be run to find the activation, as the signal response is sensitive to the starting frequency in the resting state. Nevertheless, these images can be compared directly with anatomical images collected with the same method without the need for distortion correction.
Scheffler et al. (Thu,) studied this question.