National Institutes of Health (NIH), Bethesda, Maryland, USA
18 April, 2005
The first clinical study, Zangen et al. (2005), performed at the National Institute of Health (NIH) tested the efficacy and safety aspects of the H-coil on healthy volunteers.
The H-coil was compared to a regular figure-8 coil in 6 healthy volunteers by measuring thresholds for activation of the abductor pollicis brevis (APB) representation in the motor cortex as a function of distance from each of the coils. The findings of this study indicated that the rate of decrease in the coil intensity as a function of distance is markedly slower for the H-coil.
The study confirms the theoretical calculations and phantom brain measurements indicating the ability of the H-coil to stimulate brain structures at a large distance from the coil. The comparison between the TMS coils demonstrated a significantly improved depth penetration, and a much slower rate of decay of effectiveness as a function of the distance from the coil, when using the H-coil relative to the regular figure-8 coil. As far as the safety aspects are concerned, none of the 6 subjects who participated in the study reported any significant side effects after the TMS session.
Zangen et al. (2005) did not find any change in cognitive or hearing abilities in these 6 subjects. 1 out of the 6 subjects reported a slight, transient headache. In a separate, subsequent experiment, the H-coil was used to deliver single or paired pulses at 1Hz during 20s over five different locations on the scalp in 3 additional subjects. The intensity of stimulation was 120% of motor threshold, the interval between the 20-s trains was 2 min and the total number of trains was 10 for each subject. Use of the H-coil system was found to be safe and the new coil was found to enable depth penetration of 5-6 cm, compared to 1.5-2 cm with a standard TMS coil.
The safety and the efficacy of depth penetration of the new Brainsway® Deep TMS H coil were studied. The new coil was found to enable depth penetration of 5-6 cm, compared to 1.5-2 cm with a standard TMS coil (See Figure 1).
Figure 1: Intensity needed for motor activation at different heights above the scalp