Adhesive-based liquid metal radio-frequency microcoil for magnetic resonance relaxometry measurement

This paper reports the fabrication and characterization of an adhesive-based liquid-metal microcoil for magnetic resonance relaxometry (MRR). Conventionally, microcoils are fabricated by various techniques such as electroplating, microcontact printing and focused ion beam milling. These techniques require considerable fabrication efforts and incur high cost. In this paper, we demonstrate a novel technique to fabricate three-dimensional multilayer liquid-metal microcoils together with the microfluidic network by lamination of dry adhesive sheets. One of the unique features of the adhesive-based technique is that the detachable sample chamber can be disposed after each experiment and the microcoil can be reused without cross-contamination multiple times. The integrated microcoil has a low direct-current (DC) resistance of 0.3 Ω and a relatively high inductance of 67.5 nH leading to a high quality factor of approximately 30 at 21.65 MHz. The microcoil was characterized for ∼0.5 T proton MRR measurements. The optimal pulse duration, amplitude, and frequency for the 90° pulse were 131 μs, -30 dB (1.56 W) and 21.6553 MHz, respectively. In addition, we used the liquid-metal microcoil to perform a parametric study on the transverse relaxation rate of human red blood cells at different hematocrit levels. The transverse relaxation rate increases quadratically with the hematocrit level. The results from the liquid-metal microcoil were verified by measurements with a conventional solenoid coil.