In vivo prompt gamma neutron activation analysis of cadmium in the kidney and liver

Elemental analysis in living human subjects using biomedical devices

Today, patients undergoing dialysis are at low risk for aluminum-induced dementia. Workers are unlikely to experience cadmium-induced emphysema and the public's exposure to lead is an order of magnitude lower than in 1970. The research field of in vivo elemental analysis has played a role in these occupational and environmental health improvements by allowing the effects of people's chronic exposure to elements to be studied using non-invasive, painless, and relatively low-cost technology. From the early 1960s to the present day, researchers have developed radiation-based systems to measure the elemental content of organs at risk or storage organs. This reduces the need for (sometimes painful) biopsy and the risk of infection. Research and development has been undertaken on forty-nine in vivo measurement system designs. Twenty-nine different in vivo elemental analysis systems, measuring 22 different elements, have been successfully taken from design and testing through to human measurement. The majority of these systems employ either neutron activation analysis or x-ray fluorescence analysis as the basis of the measurement. In this review, we discuss eight of the successful systems, explaining the rationale behind their development, the methodology, the health data that has resulted from application of these tools, and provide our opinion on potential future technical developments of these systems. We close by discussing four technologies that may lead to new directions and advances in the whole field.

Gadolinium detection via in vivo prompt gamma neutron activation analysis following gadolinium-based contrast agent injection: a pilot study in 10 human participants

Gadolinium (Gd) based contrast agents are routinely used as part of many magnetic resonance imaging (MRI) procedures. The widespread use of these agents and concerns about Gd toxicity, motivated us to develop a monitoring procedure that could non-invasively measure quantitatively potential retention of toxic free Gd in tissues after use of the agent. We have been developing a method to measure Gd painlessly and non-invasively by prompt gamma neutron activation analysis. In this paper we present the results of a pilot study where we show that we can measure Gd, quantitatively in vivo, in the lower leg muscle of 10 participants. A series of three neutron leg scans were performed. The effective radiation dose for a single neutron leg scan was very low, 0.6 µSv, so multiple scans were possible. Calibration phantom and in vivo detection limits were determined to be identical: 0.58 ppm. Gd was not detectable in muscle prior to exposure to the contrast agent Gadovist(®). Gd was detected, at greater than 99% confidence, in 9 participants within 1 h of contrast administration and in 1 participant approximately 3.3 h post-contrast administration. The measured concentrations of Gd ranged from 2.0 to 17.3 ppm (6.9 to 56 uncertainties different from zero). No detectable Gd was measured in any participant in the third neutron scan (conducted 0.7 to 5.9 d post-contrast). The results of this study validate our new measurement technology. This technique could be used as a non-invasive monitoring procedure for exposure and retention of Gd from Gd-based chelates used in MRI.

Grazing-incidence neutron-induced fluorescence probes density profiles of labeled molecules at solid/liquid interfaces

We report on the use of characteristic prompt γ-fluorescence after neutron capture induced by an evanescent neutron wave to probe densities and depth profiles of labeled molecules at solid/liquid interfaces. In contrast to classical scattering techniques and X-ray fluorescence, this method of "grazing-incidence neutron-induced fluorescence" combines direct chemical specificity, provided by the label, with sensitivity to the interface, inherent to the evanescent wave. We demonstrate that the formation of a supported lipid membrane can be quantitatively monitored from the characteristic fluorescence of (157)Gd(3+) ions bound to the headgroup of chelator lipids. Moreover, we were able to localize the (157)Gd(3+) ions along the surface normal with nanometer precision. This first proof of principle with a well-defined model system suggests that the method has a great potential for biology and soft matter studies where spatial resolution and chemical sensitivity are required.

Development of methods for body composition studies

This review is focused on experimental methods for determination of the composition of the human body, its organs and tissues. It summarizes the development and current status of fat determinations from body density, total body water determinations through the dilution technique, whole and partial body potassium measurements for body cell mass estimates, in vivo neutron activation analysis for body protein measurements, dual-energy absorptiometry (DEXA), computed tomography (CT) and magnetic resonance imaging (MRI, fMRI) and spectroscopy (MRS) for body composition studies on tissue and organ levels, as well as single- and multiple-frequency bioimpedance (BIA) and anthropometry as simple easily available methods. Methods for trace element analysis in vivo are also described. Using this wide range of measurement methods, together with gradually improved body composition models, it is now possible to quantify a number of body components and follow their changes in health and disease.