Most MR exams are performed at magnetic fields of 1.5 T or lower. Recently, magnetic fields up to 4.1 T has become available for human studies. Naturally, safety of such fields have been a concern despite mounting evidence from a large number of studies which indicate that provided the subjects are not moved rapidly in or near the high field, none or minimal effects are perceived by the subjects. However, often anecdotal experiences of unpleasant encounters at high fields or infrequent but non-negligible negative responses from volunteers continue to raise concerns. It is possible that some of these negative experiences are the result of """"""""suggestions"""""""" and anticipation because the subjects are informed of possible risks and adverse sensation in the consent form they must read prior to an exam. In order to evaluate this possibility, we have conducted sham studies at zero magnetic field during a period when the magnetic field of the 4-Tesla imager/spectrometer was ramped down. Subjects who had never enrolled in a 4 T study previously were asked to participate in one of our ongoing functional imaging protocols. These subjects were recruited from the same list generated as a result of advertising in the university community to seek volunteers for our normal studies. Subjects were asked to go through the paradigm performing a motor learning task or a visually guided complex motor task as in the normal studies. Subjects had to reed and sign the consent form, and were instructed on the paradigm prior to going into the magnet, as normally done. During the study, prerecorded noises generated by imaging sequences were broadcast into the magnet bore by means of speakers placed in the RF cabin near the magnet bore. Subjects were asked to fill out our normal exit form upon completion of the study. * The exit form asks the volunteers to answer yes, no, or uncertain (Unc) to whether they have experienced any one of eight possible sensations listed in the exit form. In addition, they are asked to report any other unusual experiences. The results of this study are tabulated below and compared with results obtained on 134 volunteers participating in our studies at 4 Tesla during the previous year: Five of the 11 subjects examined at zero field also answered yes to the question """"""""Did you experience any other unusual sensations while in the magnet?"""""""" and listed the following sensations: i) """"""""After I got up, I walked into the room and the floor started moving up and down."""""""" ii) """"""""My heel (right foot) got very irritated-I'm not really sure why, perhaps just from the pressure of laying flat."""""""" iii) """"""""Very minor headache"""""""". iv) """"""""Tingling in hands, 20 cm from hand after 3 imaging, 10 minutes"""""""". v) """"""""I had an upset stomach before starting and felt queasy at first"""""""". Of the 134 people studies at 4 Tesla, ~30% also provided an answer to the same question and listed experiences that are qualitatively similar in context to the ones reported at zero field. These results suggest that significant number of adverse effects reported by volunteers experiencing high magnetic fields are not causally related to the magnetic field. Rather, they may be due to anticipation following """"""""suggestion"""""""" as a result of reading the consent forms which documents all potential adverse affects based on previous experiences of other subjects. Based on the limited sample of zero field studies, the only experience that was significantly absent at zero field was metallic taste.
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