Magnetic Resonance Imaging (MRI) is of tremendous medical and economic importance. Trends in MRI are towards fasting imaging techniques such as echo-planar and hybrid imaging. Faster scanning techniques have the potential of improving the functionality of MRI (transient phenomena such as the cardiac activity and blood flow can be imaged noninvasively) and lowering the cost (each patient spends less time in an expensive machine). Preliminary results with new fast-scan hardware indicate that some subjects may be stimulated by the pulsed gradient fields; the stimulation is believed to arise from the electric field induced in the patient by the time-varying magnetic field. We propose to perform a largely experimental study of the intensities of MRI gradient fields which are required to produce peripheral nerve stimulation in human volunteers. The intensity of time-varying magnetic field (dB/dt) will be measured as a function of the pulse duration. The goal of the proposed research is to provide data that will permit establishing rational guidelines for what MRI gradient fields can be safely applied to the patient. These data will help avoid the setting of guidelines which are either too high, disturbing the tranquillity of the patient and possibly placing him or her at risk, or too low, which would needlessly limit the diagnostic advantages afforded by fast-scan techniques. There is presently very little human data on the stimulating effects of MRI gradient fields; the proposed work will provide detailed population statistics on the dB/dt strength-duration relationship. With the stimulation data that will be obtained, it will be possible for MRI system designers to devise optimal pulse sequences to maximize image resolution and speed of acquisition, while avoiding deleterious impact on the patient.
| Bourland, J D; Nyenhuis, J A; Schaefer, D J (1999) Physiologic effects of intense MR imaging gradient fields. Neuroimaging Clin N Am 9:363-77 |
