Sensitivity estimation in circular and square loops

Abstract

Circular and square loops are the simplest design employed as radiofrequency coils for magnetic resonance applications. Being usually much smaller than the volume coils, these loop coils have higher signal-to-noise ratio (SNR) because they receive noises only from nearby regions. However, they have a relatively poor field homogeneity and, thus, are mainly used as receive coils. In this work, author describes a coil sensitivity estimation method based on a simulator which permits the characterization of loop coils performance, in terms of magnetic field patterns and coil losses, where this last term including conductor, sample, capacitor, radiative and soldering losses. The evaluation of coil sensitivity for circular and square loops was performed at different tuning frequencies usually used in clinical scanner (21, 64, and 128 MHz) and at different distances respect to the coil plane. Simulation data were acquired for circular loop radius between 0.5 and 4 cm and for square loop side sizes between 1 and 8 cm, with the scope of evaluating the loop sizes which maximize the sensitivity in dependence of the penetration depth in the sample region and therefore to design optimized coils for maximizing SNR in MR applications.