FUNCTIONAL MRI STUDIES OF WORD-STEM COMPLETION - RELIABILITY ACROSS LABORATORIES AND COMPARISON TO BLOOD-FLOW IMAGING WITH PET

Functional magnetic resonance imaging (fMRI) based on blood oxygen lev el-dependent (BOLD) contrast has become an increasingly popular techni que for mapping the brain. The relationship between BOLD-fMRI imaging and imaging of blood flow activation with positron emission tomography (PET) remains unclear. Moreover, BOLD imaging strategies and analysis procedures vary widely across laboratories. To examine the relationsh ip between these different methods, we compared brain activation maps of a word-stem completion task obtained both using PET and using fMRI across two separate institutions (Washington University and Massachuse tts General Hospital) with different acquisitions (gradient-refocused echo and asymmetric spin echo) and different analysis techniques. Over all, activation maps were highly similar across both fMRI methods and PET. A set of activated brain areas, in consistent locations in Talair ach atlas space, were identified across all three studies, including v isual striate and extrastriate, left prefrontal, supplementary motor a rea (SMA), and right cerebellar areas. Decreases in activation were al so consistently observed in medial parietal, posterior insular, and me dial inferior frontal areas. Some differences were noted that may be r elated to the silent performance of the task with fMRI. The largely co nsistent results suggest that comparisons can be made appropriately ac ross imaging modalities and laboratory methods. A further implication of the consistencies, which extended to both increases and decreases i n signal, is that the underlying brain physiology leading to BOLD cont rast may be more similar to blood flow than originally appreciated Hum . Brain Mapping 6:203-215, 1998. (C) 1998 Wiley-Liss, Inc.