Magnetic resonance coil for (31) P spectroscopy of skin over curved body surfaces

Background/aims: Increasing signal-to-noise ratio for skin spectroscopy means increasing area, but increased area usually means resorting to Fourier window techniques to prevent overwhelming muscle contamination. The aim of this work was to develop a simple coil that would allow large areas of skin to be sampled while limiting muscle contamination simply by the coil's geometry. Methods: The coil design was arrived at by using simulations that were calibrated by phantom tests with prototype units. It was then fabricated by using an etched circuitboard technique and tested on three volunteers for comparison with predicted performance. Results: The new coil acquires magnetic resonance signals from a 140 cm2 contoured layer of surface tissue with sufficient selectivity that 81% of the signal comes from tissue less than 1.9 mm deep. For skin and fat thicknesses of 1.1 and 3.1 mm, respectively, tending toward a worst case in-vivo situation, muscle contamination is only 3.3%. With the new coil, in 1 h, it was possible to directly acquire 31P skin spectra comparable to those formerly obtained in 4 h in two separate acquistions that then had to be subtracted to obtain the desired skin spectra. Conclusion: Increasing the area of skin sampled while maintaining selectivity to limit muscle contamination, relying simply on coil geometry, is practical using a parallel configuration of long narrow strip coils.