A passive apparatus including a plurality of resonators increases signal-to-noise ratio of radiofrequency signals emitted by a specimen and captured by an MRI machine. The apparatus increases the magnetic field component of radiofrequency energy during signal transmission from the MRI machine to the specimen, and/or reception of signals from the specimen to the MRI machine. Moreover, the apparatus enhances specimen safety by substantially avoiding unwanted generation of an electric field, or an increase in the electric field component of the RF energy. Use of the apparatus improves the images generated by the MRI machine, and/or reduces the time necessary for the MRI machine to capture the image.