Empirical validation of statistical parametric mapping for group imaging of fast neural activity using electrical impedance tomography.

Electrical impedance tomography (EIT) allows for the reconstruction of internal conductivity from surface measurements. A change in conductivity occurs as ion channels open during neural activity, making EIT a potential tool for functional brain imaging. EIT images can have >10 000 voxels, which means statistical analysis of such images presents a substantial multiple testing problem. One way to optimally correct for these issues and still maintain the flexibility of complicated experimental designs is to use random field theory. This parametric method estimates the distribution of peaks one would expect by chance in a smooth random field of a given size. Random field theory has been used in several other neuroimaging techniques but never validated for EIT images of fast neural activity, such validation can be achieved using non-parametric techniques. Both parametric and non-parametric techniques were used to analyze a set of 22 images collected from 8 rats. Significant group activations were detected using both techniques (corrected p < 0.05). Both parametric and non-parametric analyses yielded similar results, although the latter was less conservative. These results demonstrate the first statistical analysis of such an image set and indicate that such an analysis is an approach for EIT images of neural activity.

Comparison of frequency difference reconstruction algorithms for the detection of acute stroke using EIT in a realistic head-shaped tank.

Imaging of acute stroke might be possible using multi-frequency electrical impedance tomography (MFEIT) but requires absolute or frequency difference imaging. Simple linear frequency difference reconstruction has been shown to be ineffective in imaging with a frequency-dependant background conductivity; this has been overcome with a weighted frequency difference approach with correction for the background but this has only been validated for a cylindrical and hemispherical tank. The feasibility of MFEIT for imaging of acute stroke in a realistic head geometry was examined by imaging a potato perturbation against a saline background and a carrot-saline frequency-dependant background conductivity, in a head-shaped tank with the UCLH Mk2.5 MFEIT system. Reconstruction was performed with time difference (TD), frequency difference (FD), FD adjacent (FDA), weighted FD (WFD) and weighted FDA (WFDA) linear algorithms. The perturbation in reconstructed images corresponded to the true position to <9.5% of image diameter with an image SNR of >5.4 for all algorithms in saline but only for TD, WFDA and WFD in the carrot-saline background. No reliable imaging was possible with FD and FDA. This indicates that the WFD approach is also effective for a realistic head geometry and supports its use for human imaging in the future.

Prevalence and first-line treatment of diarrhoeal symptoms in the community.

By systematically sampling patient registers in two socio-economically contrasting Scottish urban general practices, 440 households were selected and contracted by a research health visitor who interviewed a household member in 425 of them (response rate = 97%). Information was obtained on the point and period prevalence of diarrhoeal symptoms in all household members (n = 1,335), and on the knowledge, attitudes and behaviour of the respondents. While the point prevalence was low (under 1% of the household members), around 12% were reported to have experienced symptoms in the three-month period prior to the interview, and these were associated with a small but far from negligible loss of time from school or work. There were no significant seasonal differences in prevalence rates, nor were there significant differences between the two practices. Knowledge about appropriate treatment was high, but there was some confusion about the administration of liquids (especially milk) other than water, and a high level of ignorance about the existence and purpose of oral rehydration solutions. These findings have implications for public education about the initial management of acute diarrhoeal symptoms.