Transplacental Toxicity of Zinc Oxide Nanoparticles: Maternal-Fetal DNA Damage and Organ Accumulation.

Accurate identification of specific cranial points is essential for both research and therapeutic applications of non-invasive brain stimulation (NIBS). Among these, the left dorsolateral prefrontal cortex (DLPFC) is of particular relevance, given its role in motor planning, executive control, and mood regulation. The DLPFC is estimated to span an area of 10–20 cm depending on the definition applied, which complicates the selection of an optimal stimulation site. This challenge is especially critical in repetitive transcranial magnetic stimulation (rTMS) for major depressive disorder (MDD), where treatment response rates remain limited, with only 40–50% of patients with treatment-resistant depression achieving significant improvement. Insufficient precision in localizing stimulation targets has been proposed as one of the main contributors to this variability, underscoring the clinical importance of accurate and reliable methods for identifying stimulation sites. The accuracy of cortical target localization is therefore likely to play a decisive role in both the efficacy of rTMS and the advancement of NIBS research. Contributing factors to variability include coil positioning (inclination, orientation, and coil-to-scalp distance), individual differences in cranial and cortical anatomy, and the lack of standardized stimulation protocols. The International 10–20 system provides a standardized framework for electrode and coil placement, aligning scalp points with underlying cortical regions. Within this framework, F3 serves as the anatomical guide for DLPFC targetin. However, locating F3 using the full 10–20 procedure is time-consuming, prone to operator error, and impractical in routine clinical environments. To streamline this process, heuristic methods like Beam-F3 and the 5.5 cm rule were developed, relying on cranial landmarks to approximate the F3 position. Alternative methods for DLPFC localization have been proposed as locating a midpoint of a line drawn between AF3 and F3; using F5 coil positioning as a preferred stimulation site when MRI co-registration is unavailable; or using updated scalp heuristic methodology. Among these, Beam-F3 has become the most widely used approach because of its simplicity and current endorsement in consensus guidelines. Its original design emphasized simplicity and efficiency. The so-called Adjusted Beam-F3 is a minor modification of this procedure, in which a constant offset (+ 0.35 cm) is added to one of the distances, with the aim of better aligning with neuronavigation methods. However, different studies have demonstrated systematic localization deviations that correlate with cranial morphology, suggesting the geometric assumptions underlying Beam-F3 do not hold universally. The Scalp Geometry-based Parameter (SGP) method has recently been proposed as an alternative approach for localizing the DLPFC. Unlike Beam-F3 method, which relies on straightforward scalp distance measurements, SGP operates within a different coordinate framework based on MNI space and averaged F3 positions. While this strategy can improve accuracy in some contexts, it reduces clinical applicability because it is less intuitive for clinicians and departs from the simple distance-based procedures used in Beam-F3 method. A recent study comparing Beam-F3 and SGP reported higher accuracy for the latter. However, that analysis was conducted using head models with limited variability in head circumference and cranial shape, thereby not fully capturing real-world anatomical diversity.