Transcranial

Transcranial, from Latin trans- “across” and cranium “skull,” is an umbrella term for processes, imaging, or modulation that interact with the brain through the skull. It contrasts with intracranial methods that involve penetration or implantation within the brain. In medicine and neuroscience, transcranial techniques aim to affect brain activity noninvasively or to visualize cerebral structures without opening the skull.

Common transcranial modalities include transcranial magnetic stimulation (TMS), in which rapidly changing magnetic fields induce electric currents in cortical neurons; transcranial direct current stimulation (tDCS), which applies low-intensity electrical currents across scalp electrodes to modulate cortical excitability; and transcranial Doppler ultrasound (TCD), which uses ultrasound to measure blood flow velocities in major cerebral arteries. Transcranial color-coded duplex sonography (TCCD) combines Doppler with real-time imaging to visualize vessels and blood flow.

Transcranial methods are used in clinical and research settings. TMS is employed for mapping brain function and as a noninvasive treatment for certain conditions such as treatment-resistant depression; tDCS is explored for cognitive enhancement and rehabilitation, with mixed evidence. TCD and TCCD are diagnostic tools for assessing cerebral hemodynamics, detecting vasospasm after subarachnoid hemorrhage, monitoring intracranial atherosclerosis, and evaluating stroke risk.

Limitations include variability in skull thickness and anatomy, limited depth of stimulation, and the need for safety monitoring. Transcranial approaches are part of a broader spectrum of noninvasive brain interventions and are distinct from intracranial procedures or implanted devices.