'By optimizing the relationship between signal and noise in a magnetic resonance imaging (mri) and mri system'

摘要

The invention relates to a system comprising an array of two or more receiving antennas (11, 12, 13) for receiving RF signals, each receiving antenna being connected, via a matching network (19, 20, 21), to a low-noise amplifier (22, 23, 24) presenting an input impedance to the matching network (19, 20, 21), each chain consisting of a receiving antenna (11, 12, 13), a matching network (19, 20, 21) and a low-noise amplifier (22, 23, 24) constituting a part of a receiving channel of the system, the matching networks (19, 20, 21) transforming optimum impedances of the low-noise amplifiers (22, 23, 24), the optimum impedances providing optimum noise performance of the low-noise amplifiers (22, 23, 24), wherein each receiving channel comprises at least one switchable impedance (28, 29, 30) at the input of each low-noise amplifier (22, 23, 24) for switching the input impedance as presented to each matching network (19, 20, 21) to a value being the complex conjugate of the optimum impedance of the respective low-noise amplifier (22, 23, 24). The system is arranged to perform an optimization procedure comprising the following steps: a) switching the input impedance as presented to the matching network (19, 20, 21) in each receiving channel to the complex conjugate of the optimum impedance of the respective low-noise amplifier (22, 23, 24); b) receiving RF signals via the receiving antennas (11, 12, 13); c) forming a weighted sum of the signal power of the received RF signals; d) modifying the matching networks (19, 20, 21) of all receiving channels so as to find an optimum matching condition by maximizing the weighted power sum; c) switching the input impedance in each receiving channel back to a value for regular operation of the system.