Evaluation of the turn variation of spiral RF surface coils for MR microscopic imaging and spectroscopy

The purpose of this study was to enhance the technical improvement so as to develop an advanced sensitive RF surface coil for investigating the sensitivities of the multi-spiral surface coils, and we eventually wanted to achieve high resolution of the microscopic MR images and MR spectra. The magnetic field inhomogeneity and the shape of a surface coil were statistically estimated by simulation of the magnetic field distribution.On the basis of the experimental results with single, three- and five-turned spiral RF surface coils in 1.5 T, we found that the three-turned coil had the highest sensitivity. The present study showed that the sensitivity of the RF surface coil was improved by increasing the number of spiral coil turns, and also the SNR of the RF surface coil was dependent upon the number of spiral coil turns. However, we found, rather strikingly, that the sensitivity of excessive turns of the coils was decreased due to the rise of the coil’s impedance. Thus, the present results demonstrated that the sensitivity was not proportional to the number of a spiral RF coil’s turns, and the number of spiral coil turns should be optimized for obtaining the highest sensitivity and SNR.