The H-coil is the magnetic coil used in Deep TMS. Unlike the flat figure-eight coil used in conventional rTMS, which concentrates its field in a small area about two to three centimeters below the scalp, the H-coil is a complex arrangement of wire loops housed inside a padded helmet. Its geometry spreads the magnetic field so that it reaches deeper into the brain while decreasing less sharply with distance. That design lets it stimulate deeper and wider regions of the prefrontal cortex and related circuits involved in mood, motivation and compulsive behavior.
There are several H-coil versions, each shaped for a different target. The H1 coil is used for major depressive disorder and anxious depression, the H7 coil for obsessive-compulsive disorder, and the H4 coil for smoking cessation. Your psychiatrist chooses the coil based on the condition being treated, and the helmet is fitted and calibrated to your head before the first session. Calibration involves finding your motor threshold, the lowest pulse intensity that produces a small twitch in your hand, so that treatment intensity can be set as a percentage of that number. The H-coil itself does not touch your brain. It delivers brief pulses through the scalp and skull, and the sensation most people describe is tapping or knocking rather than pain. Stedfast Psychiatry uses the BrainsWay H-coil system at Palm Beach Gardens.