Method and system for magnetic resonance imaging

Abstract

Parallel transmit Magnetic Resonance MR scanner used to image a conductive object such as an interventional device like a guidewire within a subject. This is achieved by determining which Radio Frequency RF transmission modes produced by the parallel RF transmission elements couple with the conductive object and then transmitting at significantly reduced power so as to prevent excessive heating of the conductive object to an extent that would damage the surrounding tissue of the subject, for example, the coupling RF transmission modes may be generated at less than 30%, preferably around 10% of the normal power levels that would conventionally be used for MR imaging. However, even at these low power levels sufficient electric currents are induced in the conductive device to cause detectable MR signals; the location of the conductive object within the subject can thus be visualised. By fast alternate, or simultaneous, iterative application of low-power coupling mode and normal-power non-coupling modes, both the subject and the conductive object can be imaged. During the calibration step of determining which RF transmission modes couples with the conductive object, instead of physically measuring the current induced in the conductive object using sensors, imaging the conductive object using additional very short series of flip angle RF pulses (vLFA) gives a good approximation of the coupling matrix.