In MR imaging, the time-varying magnetic field associated with gradients induces electric fields in the human body and may stimulate nerves and even the heart. The time rate of change in gradient magnetic fields on echo planar imaging (EPI) needs to exceed 20 mT/ms. EPI has recently become more widely used in the clinical field, and the protection of patient safety during MR scans has become an issue. However, dB/dt as an index of the time-varying magnetic field is not displayed on the operating monitor. Therefore, dB/dt of various scan techniques was measured using a search coil and storage oscilloscope, according to the IEC standard method. The results demonstrated that dB/dt of EPI, spin-echo, and field-echo techniques are much the same. Thus, the possibility of a risk to health resulting from EPI scanning is the same as that for other scanning techniques that use a high-performance MRI system. Therefore, even with spin-echo scanning, it is necessary to consider biological change in patients.
