Aluminum and copper conductors are compared for constructing radiologically transparent MRI surface coil detectors for use in a hybrid MRI - linear accelerator. Radiation dose to skin can cause serious reactions and skin dose is enhanced when materials are placed in the radiation beam. Therefore increases in skin dose due to surface coils must be minimized by optimized construction. A copper conductor causes a three-fold increase in skin dose compared to a similar thickness aluminum conductor. An aluminium coil (20μm thick) was used to image a phantom, yielding 93% of the SNR achieved with a copper tape coil (32μm thick).