Acceptance of 7T MRI for Human Imaging

Purpose: Prerequisites for transferring ultra-high-field MRI (>3T) into clinical diagnostic workup are sufficient patient acceptance and a low rate of side effects. Publications on subjective examination experiences are thus far missing. We present the results of short-term effects and procedure acceptance at our 7T research site.

Material and Methods: The local ethics committee authorized the 7T examinations as part of fundamental research on high-field MR. All subjects were informed that the 7T exam would not yield any individual diagnostic information. One hundred subjects (22 volunteers, 78 patients) undergoing a 7T examination judged sources of discomfort (e.g. examination duration, room temperature) and physiological sensations (e.g. vertigo, light flashes) on a 10-point scale. The effects were differentiated between movement and stationary positioning in the field as well as position on the table (head-first, feet-first). For comparison, an identical questionnaire was completed in 43 of these 100 subjects after undergoing a 1.5T examination.

Results: Vertigo was the most disturbing physiological sensation at 7T (Fig.1a); 5/100 rated it as very unpleasant (grade 8–10; none at 1.5T), which was relativized by the fact that the lengthy exam duration (mean 73min) was regarded as even more disturbing (Fig.1b).: Although the number of side effects increases at 7T compared to 1.5T, 7T was well tolerated in the majority of subjects.

Conclusion: Vertigo can perhaps be avoided by further reducing table movement speed. The 'willingness' to accept disturbing factors will almost certainly increase once patients can derive a diagnostic benefit from the examination.

Fig.1. (a) Mean grading of various sensations while the scanner table was moving (striped bars) and while stationary during MR measurements (solid bars) for 7T (n=100) and 1.5T (=43). Note the relatively high grading for vertigo (statistically significantly different) while moving in the 7T field. During the stationary scanning phase, both groups show relatively few side effects. (b) Comparison of various causes for discomfort between 7T (n=100) and 1.5T (n=43). Average grades lie below 3 ('very well tolerable') except for exam duration at 7T. *=p<0.05 for unpaired test; *=p<0.05 for paired test