Imaging brain abscesses with diffusion-weighted and other sequences.

possible pervasiveness of the effects. Although a gross respiratory change such as a 30-second breath-hold would be unlikely to occur during a conventional fMR imaging experiment, more subtle respiratory changes could accompany some activation paradigms, particularly those with ‘‘surprise’’ components. This could result in MR signal changes secondary to the unanticipated respiratory (or cardiac) responses. Statistical analysis might classify erroneously respiratory responses as noise, false localization of a cognitive task, or a true but secondary phenomenon. The latter possibility reemphasizes the complexity, as well as the richness, of these new functional imaging techniques. R. NICK BRYAN Senior Editor, AJNR