Photographs of the three main components of the high-permittivity material (HPM) helmet array. For imaging, the ceramic HPM helmet (left) was placed within the 30-loop receive (Rx) array (middle), which in turn was placed within the 8-dipole transmit (Tx) array. For the array without HPM, a 3D-printed air-filled shell matching the geometry of the HPM helmet was placed within the 30-loop Rx array of identical geometry, but with different capacitor values, which in turn was placed in the same 8-dipole Tx array shown here