Confirming improved detection of gadolinium in bone using in vivo XRF

The feasibility of K XRF bone lead measurements in mice assessed using 3D-printed phantoms

This article describes the development of a system forin vivomeasurements of lead body burden in mice using109Cd K x-ray fluorescence (XRF). This K XRF system could facilitate early-stage studies on interventions that ameliorate or reverse organ tissue damage from lead poisoning by reducing animal numbers through a cross-sectional study approach. A novel mouse phantom was developed based on a mouse atlas and 3D-printed using PLA plastic with plaster of Paris 'bone' inserts. PLA plastic was found to be a good surrogate for soft tissue in XRF measurements and the phantoms were found to be good models of mice. As expected, lead detection limits varied with mouse size, mouse orientation, and mouse position with respect to the source and detector. The work suggests that detection limits of 10 to 20μg Pb per g bone mineral may be possible for a 2 to 3 hour XRF measurement in a single animal, an adequate limit for some pre-clinical studies. The109Cd K XRF mouse measurement system was also modeled using the Monte Carlo code MCNP. The combination of experiment and modeling found that contrary to expectation, accurate measurements of lead levels in mice required calibration using mouse-specific calibration standards due to the coherent scatter peak normalization failing when small animals are measured. MCNP modeling determined that this was because the coherent scatter signal from soft tissue, which until now has been assumed negligible, becomes significant when compared to the coherent scatter signal in bone in small animals. This may have implications for some human measurements. This work suggests that109Cd K x-ray fluorescence measurements of lead body burden are precise enough to make the system feasible for small animals if appropriately calibrated. Further work to validate the technology's measurement accuracy and performancein vivowill be required.

Association between bone trace elements and osteoporosis in older adults: a cross-sectional study

Objectives:

Metal micronutrients deficiency may be one of the risk factors for the development of osteoporosis. This study aimed to measure the trace element contents in human bone tissue to analyze the relationship between micronutrients and osteoporosis.

Design:

A cross-sectional survey was performed on data from 51 elderly patients with proximal femoral fracture.

Methods:

The concentrations of calcium, phosphorus, manganese, iron, copper, and zinc in bone tissue samples from 51 elderly patients with proximal femoral fracture were determined by energy-dispersive X-ray fluorescence (EDX). Subjects were divided into osteoporosis and non-osteoporosis groups according to their bone mineral density (BMD) T-score values. The difference in metal elements concentrations in bone tissue between the two groups was compared, and the role of metal elements in osteoporosis was discussed.

Results:

There was no statistical difference in age, sex, body mass index (BMI), serum albumin, biochemical blood indices, and bone turnover markers between the two groups. The Mann–Whitney U test was used to compare the difference in metal elements concentrations in bone tissue samples between the two groups. The results showed that manganese, copper, and zinc concentrations in the cancellous bone were significantly higher in the non-osteoporosis group than in the osteoporosis group. Multivariate logistic regression analysis indicated that high bone zinc concentration [odds ratio = 0.26, 95% confidence interval (CI) = 0.075–0.928, p = 0.038] was negatively correlated with osteoporosis.

Conclusion:

Manganese, copper, and zinc play an essential role in bone mineralization and metabolism. Among them, zinc may be most closely related to osteoporosis and play a key role in bone development and maintenance of bone mass. Therefore, we believe that the design of zinc-rich compounds or nutrients as a new complementary factor to increase the intake of zinc for the elderly could be able to prevent and intervene in the occurrence of osteoporosis in the early stage.

Detection and imaging of gadolinium accumulation in human bone tissue by micro- and submicro-XRF

Gadolinium-based contrast agents (GBCAs) are frequently used in patients undergoing magnetic resonance imaging. In GBCAs gadolinium (Gd) is present in a bound chelated form. Gadolinium is a rare-earth element, which is normally not present in human body. Though the blood elimination half-life of contrast agents is about 90 minutes, recent studies demonstrated that some tissues retain gadolinium, which might further pose a health threat due to toxic effects of free gadolinium. It is known that the bone tissue can serve as a gadolinium depot, but so far only bulk measurements were performed. Here we present a summary of experiments in which for the first time we mapped gadolinium in bone biopsy from a male patient with idiopathic osteoporosis (without indication of renal impairment), who received MRI 8 months prior to biopsy. In our studies performed by means of synchrotron radiation induced micro- and submicro-X-ray fluorescence spectroscopy (SR-XRF), gadolinium was detected in human cortical bone tissue. The distribution of gadolinium displays a specific accumulation pattern. Correlation of elemental maps obtained at ANKA synchrotron with qBEI images (quantitative backscattered electron imaging) allowed assignment of Gd structures to the histological bone structures. Follow-up beamtimes at ESRF and Diamond Light Source using submicro-SR-XRF allowed resolving thin Gd structures in cortical bone, as well as correlating them with calcium and zinc.

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.

Ex vivo quantification of lanthanum and gadolinium in post-mortem human tibiae with estimated barium and iodine concentrations using K x-ray fluorescence

OBJECTIVES

Lanthanum (La) and gadolinium (Gd) are known to deposit in bone of exposed populations, namely those who are orally administered lanthanum carbonate (LaC, La₂(CO₃)₃) or are injected with Gd-based contrast agents, respectively. In this work, bone La and Gd concentrations from the environment and diet were measured using x-ray fluorescence in ten post-mortem human tibiae. As a secondary objective, bone barium (Ba) and iodine concentrations were estimated.

APPROACH

Two calibration lines were produced for La and Gd and the minimum detection limits (MDLs) of the system were determined using a 180° irradiation-detection geometry.

MAIN RESULTS

The MDLs of the system were 0.4 µg La g^-1 bone mineral and 0.5 µg Gd g^-1 bone mineral. The mean concentrations were  -0.02  ±  0.1 µg La g^-1 bone mineral and 0.1  ±  0.2 µg Gd g^-1 bone mineral in tibiae. The average Ba and iodine concentrations estimated from the experimental La calibration line and Monte-Carlo derived sensitivity factors were determined to be 3.4  ±  0.8 µg Ba g^-1 bone mineral and  -0.5  ±  0.3 µg iodine g^-1 bone mineral. Since it was discovered that four donors previously received an iodine-based contrast agent, the mean concentrations in these donors was 27.8  ± 28.4 µg iodine g^-1 bone mineral.

SIGNIFICANCE

The XRF system has determined baseline concentrations of these four heavy metals in trace quantities from natural exposure pathways (with the exception of iodine in four donors). This indicates that the system can measure low levels in ex vivo tibiae samples and can potentially be further developed for in vivo studies involving live subjects who are directly exposed to these metals.

The biological fate of gadolinium-based MRI contrast agents: a call to action for bioinorganic chemists

Gadolinium-based contrast agents (GBCAs) are widely used with clinical magnetic resonance imaging (MRI), and 10 s of millions of doses of GBCAs are administered annually worldwide. GBCAs are hydrophilic, thermodynamically stable and kinetically inert gadolinium chelates. In clinical MRI, 5-10 millimoles of Gd ion is administered intravenously and the GBCA is rapidly eliminated intact primarily through the kidneys into the urine. It is now well-established that the Gd3+ ion, in some form(s), is partially retained in vivo. In patients with advanced kidney disease, there is an association of Gd retention with nephrogenic systemic fibrosis (NSF) disease. However Gd is also retained in the brain, bone, skin, and other tissues in patients with normal renal function, and the presence of Gd can persist months to years after the last administration of a GBCA. Regulatory agencies are restricting the use of specific GBCAs and inviting health care professionals to evaluate the risk/benefit ratio prior to using GBCAs. Despite the growing number of studies investigating this issue both in animals and humans, the biological distribution and the chemical speciation of the residual gadolinium are not fully understood. Is the GBCA retained in its intact form? Is the Gd3+ ion dissociated from its chelator, and if so, what is its chemical form? Here we discuss the current state of knowledge regarding the issue of Gd retention and describe the analytical and spectroscopic methods that can be used to investigate the Gd speciation. Many of the physical methods that could be brought to bear on this problem are in the domain of bioinorganic chemistry and we hope that this review will serve to inspire this community to take up this important problem.

Measurement of gadolinium retention: current status and review from an applied radiation physics perspective

OBJECTIVE

This article briefly reviews the main measurement techniques for the non-invasive detection of residual gadolinium (Gd) in those exposed to gadolinium-based contrast agents (GBCAs). Approach and Main results: The current status of in vivo Gd measurement is discussed and is put into the context of concerns within the radiology community. The main techniques are based on applied atomic/nuclear medicine utilizing the characteristic atomic and nuclear spectroscopic signature of Gd. The main emission energies are in the 40-200 keV region and require spectroscopic detectors with good energy resolution. The two main techniques, prompt gamma neutron activation analysis and x-ray fluorescence, provide adequate detection limits for in vivo measurement, whilst delivering a low effective radiation dose on the order of a few µSv.

SIGNIFICANCE

Gadolinium is being detected in measureable quantities in people with healthy renal function who have received FDA approved GBCAs. The applied atomic/nuclear medicine techniques discussed in this review will be useful in determining the significance of this retention, and will help on advising future administration protocols.

Standardization of 109Cd by two methods

¹⁰⁹Cd is quite a useful nuclide for the calibration of X-ray spectroscopy, gamma-ray spectroscopy or as an excitation source in X-ray fluorescence. In this work, 4π(PC)e-X coincidence counting and 4π(LS)ce counting were used to determine the activity of the ¹⁰⁹Cd solution. The two methods showed good agreement in their counting results. On the other hand, the mean value came from the results of the two methods was used to calibrate the well type ionization chambers to maintain the radioactivity measurement standard of ¹⁰⁹Cd at INER.

Coherent normalization for in vivo measurements of gadolinium in bone

OBJECTIVE

Recent evidence of gadolinium (Gd) deposition in bones of healthy individuals who have previously received Gd-based contrast agents (GBCAs) for MRI has led to a demand for in vivo measurement techniques. The technique of x-ray fluorescence provides a low risk and painless method to assess Gd deposition in bone, and has the potential to be a useful clinical tool. However, interpatient variability creates a challenge while performing in vivo measurements.

APPROACH

We explored the use of coherent normalization, which involves normalizing the Gd K x-rays to the coherent scattered γ-ray from the excitation source, for bone Gd measurements through a series of phantom-based experiments and Monte Carlo simulations.

MAIN RESULTS

We found coherent normalization is able to correct for variation in overlying tissue thickness over a wide range (0-12.2 mm). The Gd signal to coherent signal ratio is independent of tissue thickness for both experiments and Monte Carlo simulations.

SIGNIFICANCE

Coherent normalization has been demonstrated to be used in practice with normal healthy adults to improve in vivo bone Gd measurements.