Correlation between structure and resistivity variations of the live human skull.

A study on correlation between structure and resistivity variations was performed for live adult human skull. The resistivities of 388 skull samples, excised from 48 skull flaps of patients undergoing surgery, were measured at body temperature (36.5 degrees C) using the well-known four-electrode method in the frequency range of 1-4 MHz. According to different structures of the skull samples, all the 388 samples were classified into six categories and measured their resistivities: standard trilayer skull (7943 +/- 1752 ohm x cm, 58 samples), quasi-trilayer skull (14,471 +/- 3061 ohm x cm, 110 samples), standard compact skull (26,546 +/- 5374 ohm x cm, 62 samples), quasi-compact skull (19,824 +/- 3232 ohm x cm, 53 samples), dentate suture skull (5782 +/- 1778 ohm x cm, 41 samples), and squamous suture skull (12747 +/- 4120 ohm x cm, 64 samples). The results showed that the skull resistivities were not homogenous and were significantly influenced by local structural variations. The presence of sutures appeared to decrease the overall resistivity of particular regions largely and dentate suture decreased the resistivity more than squamous suture. The absence of diploe appeared to increase skull resistivity. The percentage on thickness of diploe would be the primary factor in determining the resistivity of the skull sample without suture. From resistivity spectra results, an inverse relationship between skull resistivity and signal frequency was found.