A coil apparatus and methods for magnetic resonance imaging involving a wire winding, the wire winding having at least one of: a hollow cross-section wire and a solid cross-section wire, the solid cross-section wire having at least one of: a solid small cross-section wire and a solid large cross-section wire, the solid large cross-section wire having a thickness greater than that of the solid small cross-section wire, and the solid small cross-section wire disposed in one of adjacent and proximate at least one of the hollow cross-section wire and the solid large cross-section wire, whereby at least one of current density, winding density, and heat extraction are increasable.