"Early array coils came in the form of switchable arrays, with 3 coil segments being positioned and switchable across the cervical, thoracic and lumbar spinal segments. Modern array coils (e.g. phased arrays) combine a larger number of smaller coils into separate receiver chains. Phased array coils overlap and have low input impedance preamplifiers to control coupling between neighbouring coils. This has a synergistic effect resulting in a significantly greater signal-to-noise ratio than for a single coil."