 The next development was by David Cohen, who used a magnetically shielded room to reduce the background, and a smaller coil with better electronics; the heart signals were now less noisy, allowing a magnetic map to be made, verifying the magnetic properties and source of the signal.However, the use of an inherently noisy coil detector discouraged widespread interest in the MCG.The turning point came with the development of the sensitive detector called the SQUID (superconducting quantum interference device) by James Zimmerman.