In vivo neutron activation study of the short-term kinetic behaviour of sodium and chlorine in the human hand.

The time-dependent behaviour of sodium and chlorine was studied as a spinoff from a study of aluminum in the hand of subjects suffering from Alzheimer's disease and a control group, involving 15 Alzheimer's and 16 control subjects with an age range of 63-89 years. This was achieved using the in vivo neutron activation analysis system developed at McMaster University for the non-invasive measurement of aluminum, where a subject's hand is placed in a beam of accelerator-based thermalized neutrons, which activates elements by neutron capture. Following irradiation, the subject's hand is placed in a detection system comprising 9 NaI(Tl) detectors arranged in a 4π geometry to measure activated elements. The redistribution half-lives of the activation products 24Na and 38Cl from the hand were determined after correction for the physical half-life, by means of sequential analysis of the residual activity in the hand. The kinetic behaviours of sodium and chlorine were best characterized by an exponential function corresponding to the rapidly exchangeable pool. The mean redistribution half-lives from the hand for sodium and chlorine in the control subjects were 40.5 ± 17.4 min and 24.2 ± 8.5 min, respectively. For Alzheimer's disease subjects the mean redistribution half-lives were 58.2 ± 36.1 min for sodium and 33.6 ± 16.7 min for chlorine. There was no significant difference in chlorine and sodium redistribution half-lives between the Alzheimer's disease and control group subjects. These results are promising, given that the irradiation and counting protocol were optimized for the aluminum study, rendering them suboptimal for analyzing other elements and their rate of change with time. Further improvements include optimizing the irradiation protocol, longer counting times, and measuring the activity in the un-irradiated hand in various time intervals following irradiation.

Optimization of data analysis for the in vivo neutron activation analysis of aluminum in bone.

An existing system at McMaster University has been used for the in vivo measurement of aluminum in human bone. Precise and detailed analysis approaches are necessary to determine the aluminum concentration because of the low levels of aluminum found in the bone and the challenges associated with its detection. Phantoms resembling the composition of the human hand with varying concentrations of aluminum were made for testing the system prior to the application to human studies. A spectral decomposition model and a photopeak fitting model involving the inverse-variance weighted mean and a time-dependent analysis were explored to analyze the results and determine the model with the best performance and lowest minimum detection limit. The results showed that the spectral decomposition and the photopeak fitting model with the inverse-variance weighted mean both provided better results compared to the other methods tested. The spectral decomposition method resulted in a marginally lower detection limit (5µg Al/g Ca) compared to the inverse-variance weighted mean (5.2µg Al/g Ca), rendering both equally applicable to human measurements.