rTMS, the end of cap marking ?

Are there any observable differences between the cap method and the use of a neuronavigator?

Currently, there are two ways of positioning the rTMS coil.

The first method involves using measurements to mark the cap positioned on the patient's head.

The second uses a neuronavigator to determine the patient's target based on their MRI scan.

Do the methods used change anything in terms of positioning, treatment, etc?

To answer, Professor Mark S. George and his team carried out a study* involving more than 11,000 measurements. The measurements obtained were based on the participation of the 6 rTMS technicians in the team.

The results of this publication* highlight 3 differences :

1. As the sessions progressed, with the cap marking method, there was a dispersion in the distance from the target which varied from 6.6 mm to 12.4 mm. They obtained an average off target of 10.6 mm compared with 0.3 mm with the neuronavigator (see image 1).

2. There was also a variation in the angle and tangency of the coil, with average values of 7.79° and 5.99° respectively for the cap method, compared with 0.34° and 0.22° for the neuronavigator (see images 2 and 3).

3. Another difference revealed by the study* is the dispersion of the dose. It would appear that from one session to another and from one patient to another, the stimulation dose received by the target is different. The experiment was carried out with stimulation at 120% of motor threshold. With the cap method, the electric field (E-Field) received was in average 110.7% but varied from 58.3% to 127.4%. With the neuronavigator, the average obtained was 119.9%, with a range of 115% to 123.3% (see image 4).

* Caulfield KA, Fleischmann HH, Cox CE, Wolf JP, George MS, McTeague LM. Neuronavigation maximizes accuracy and precision in TMS positioning: Evidence from 11,230 distance, angle, and electric field modeling measurements. Brain Stimul. 2022 Sep-Oct;15(5):1192-1205. doi: 10.1016/j.brs.2022.08.013. Epub 2022 Aug 27. PMID: 36031059; PMCID: PMC10026380.