Method for reducing local specific absorption rate in magnetic resonance imaging using radio frequency coil array dark modes

摘要

A method for reducing local specific absorption rate (“SAR”) during imaging of a subject with a magnetic resonance imaging (“MRI”) system is provided. A radio frequency (“RF”) excitation pattern is selected for an RF coil array to be used during the imaging. In this RF excitation pattern, locations in which local SAR exceeds a preselected threshold value are identified. Examples of threshold values include regulatory limits on local SAR. Using the identified local SAR hotspot locations, a cancellation electric field pattern that is defined by so-called “dark modes” of the coil array is determined. Imaging of the subject commences using the RF coil array and the MRI system, in which the RF coil array is used to simultaneously produce an RF excitation field and a cancellation electric field using the respective field patterns. This simultaneous production of the RF excitation and cancellation electric fields reduces local SAR at the hotspot locations.

主权项

1. A computer-implemented method for controlling a magnetic resonance imaging (MRI) system to reduce local specific absorption rate (SAR) when imaging a subject with the MRI system, the steps of the method comprising:
a) selecting, with a computer system, a magnetization excitation pattern for a radio frequency (RF) coil array; b) identifying, with a computer system, locations in the selected magnetization excitation pattern that are associated with local SAR values that exceed a preselected threshold value; c) determining, with a computer system, a cancellation electromagnetic field pattern that is defined by dark modes of the RF coil array using the locations identified in step b); d) controlling the MRI system, with a computer system, to direct the RF coil array to simultaneously produce an RF excitation field and a cancellation electromagnetic field using the magnetization excitation pattern selected in step a) and the cancellation electromagnetic field pattern determined in step c), respectively; e) acquiring image data with the MRI system, the image data being acquired from the subject in response to the RF excitation field and cancellation electromagnetic field produced in step d); and wherein the simultaneous production of the RF excitation field and the cancellation electromagnetic field in step d) reduces local SAR at the locations identified in step b).