The ornamental design for a mrcoil, as shown and described.
1. MR coil
1.1 is a perspective view showing the MR coil of my design;
1.2 is a right side elevational view thereof;
1.3 is a left side elevational view thereof;
1.4 is a bottom plan view thereof;
1.5 is a top plan view thereof;
1.6 is a front elevational view thereof; and,
1.7 is a back elevational view thereof.
The portions of the MR coil shown in broken lines are included for the purpose of illustrating unclaimed portions of the MR coil and form no part of the claimed design.