Magstim FAQ 8

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8. What coils are used for which applications?

Please refer to the following table for coil selection:

Circular Coils for Cortical and Peripheral Stimulation

Double Coils for Focal Stimulation

Small 50mm Coil
Applications include:

  • Facial nerve
  • Superficial peripheral nerves

The 50mm coils are focal and effective for nerves 5-15mm deep.

Double Small 25mm Coil
Applications include:

  • Facial nerve
  • Median nerve
  • Ulnar nerve
  • Somatosensory evoked potentials
  • F-Wave and reflexes

The double small coil has been designed for enhanced positional accuracy in peripheral stimulation.

Medium 70mm Coil
Applications include:

  • Peripheral nerves
  • Motor cortex

The 70mm Coil is designed for Paediatric and Infant use.

Double 70mm Coil
Applications include:

  • Excitation of spinal roots
  • Motor cortex
  • Peripheral nerves

The Double 70mm Coil is capable of accurate stimulation of cortical areas and spinal nerve roots.

High Power 90mm Coil
Applications include:

  • Motor cortex
  • Cervical nerve roots
  • Lumbosacral nerve roots
  • Phrenic nerve roots

The High Power 90mm Coil can be used for central motor conduction studies. The design of the coil allows 140 stimuli at the maximum power level.

Double Cone Coil
Applications include:

  • Central motor disorders
  • Spinal Injuries
  • O.R. monitoring
  • Urology

The Double Cone Coil elicits responses from relaxed muscles of the lower pelvic floor and lower limbs.

The High Power 90mm coil is primarily designed to easily stimulate the motor cortex to obtain responses from muscles in the arms and hands. When the centre of the coil is positioned over the vertex the mean diameter of the windings sit over the motor strip of both hemispheres. In the case of all circular coils, stimulation takes place under the winding and not the coil centre.  When recording from muscles in the lower limbs, move the stimulating coil forward from the vertex and contra lateral to the target muscle by approximately 2 inches each way, such that the mean diameter of the coil winding lies over the central fissure.

Other coils may be more localised in their area of stimulation. The Double Cone coil, for instance, predominantly stimulates over the central fissure and enables good responses to be obtained from the lower pelvic floor and lower limbs at lower power levels than from a circular coil.  Smaller coils are more focal in their area of stimulation but generally have less depth of penetration than larger coils and therefore need higher discharge currents. For reproducible results from cortical stimulation, the most effective site of stimulation should established and marked upon a lightweight, close fitting cap. For peripheral sites, the stimulation site can be marked with a suitable pen.