The effect of the skull of low-birthweight neonates on applied potential tomography imaging of centralised resistivity changes.

An investigation is presented into the likely effects of the neonatal skull on impedance images produced by applied potential tomography (APT) by imaging impedance changes inside the skull of a human infant of occipito-frontal circumference 30 cm. Measurements have been made with the skull immersed in a tank of saline and electrodes fixed to the perimeter of the tank. Sensitivity measurements have been assessed for imaging a small target close to the centre of the skull as compared with images produced without the skull. The results obtained compare favourably with measurements on a more realistic model of the neonatal head constructed by filling the skull with agar jelly to leave only a thin exterior coating of jelly to simulate the scalp. These experiments suggest that in the central region of the head of a neonate, measured changes by the APT technique are about 44% of that expected from a homogeneous phantom, but that this might vary from 32% to 55% at different points in the image in a very complex manner.