Metabarcoding airborne pollen from subtropical and temperate eastern Australia over multiple years reveals pollen aerobiome diversity and complexity.

eDNA metabarcoding is an emergent tool to inform aerobiome complexity, but few studies have applied this technology with real-world environmental pollen monitoring samples. Here we apply eDNA metabarcoding to assess seasonal and regional differences in the composition of airborne pollen from routine samples collected across successive years. Airborne pollen concentrations over two sampling periods were determined using a continuous flow volumetric impaction air sampler in sub-tropical (Mutdapilly and Rocklea) and temperate (Macquarie Park and Richmond), sites of Australia. eDNA metabarcoding was applied to daily pollen samples collected once per week using the rbcL amplicon. Composition and redundancy analysis of the sequence read counts were examined. The dominant pollen families were mostly consistent between consecutive years but there was some heterogeneity between sites and years for month of peak pollen release. Many more families were detected by eDNA than counted by light microscopy with 211 to 399 operational taxonomic units assigned to family per site from October to May. There were 216 unique and 119 taxa shared between subtropics (27°S) and temperate (33°S) latitudes, with, for example, Poaceae, Myrtaceae and Causurinaceae being shared, and Manihot, Vigna and Aristida being in subtropical, and Ceratodon and Cerastium being in temperate sites. Certain genera were observed within the same location and season over the two years; Chloris at Rocklea in autumn of 2017-18 (0.625, p ≤ 0.004) and 2018-19 (0.55, p ≤ 0.001), and Pinus and Plantago at Macquarie Park in summer of 2017-18 (0.58, p ≤ 0.001 and 0.53, p ≤ 0.003, respectively), and 2018-19 (0.8, p ≤ 0.003 and 0.8, p ≤ 0.003, respectively). eDNA metabarcoding is a powerful tool to survey the complexity of pollen aerobiology and distinguish spatial and temporal profiles of local pollen to a far deeper level than traditional counting methods. However, further research is required to optimise the metabarcode target to enable reliable detection of pollen to genus and species level.

Feasibility of using a single MRI acquisition for fiducial marker localization and synthetic CT generation towards MRI-only prostate radiation therapy treatment planning.

Purpose.To investigate the feasibility of using a single MRI acquisition for fiducial marker identification and synthetic CT (sCT) generation towards MRI-only treatment planning for prostate external beam radiation therapy (EBRT).Methods.Seven prostate cancer patients undergoing EBRT, each with three implanted gold fiducial markers, participated in this study. In addition to the planning CT scan, all patients were scanned on a 3 T MR scanner with a 3D double-echo gradient echo (GRE) sequence. Quantitative susceptibility mapping (QSM) was performed for marker localization. QSM-derived marker positions were compared to those from CT. The bulk density assignment technique for sCT generation was adopted. The magnitude GRE images were segmented into muscle, bone, fat, and air using a combination of unsupervised intensity-based classification of soft tissue and convolutional neural networks (CNN) for bone segmentation.Results.All implanted markers were visualized and accurately identified (average error: 0.7 ± 0.5 mm). QSM generated distinctive contrast for hemorrhage, calcifications, and gold fiducial markers. The estimated susceptibility/HU values on QSM/CT for gold and calcifications were 31.5 ± 2.9 ppm/1220 ± 100 HU and 14.6 ± 0.9 ppm/440 ± 100 HU, respectively. The intensity-based soft tissue classification resulted in an average Dice score of 0.97 ± 0.02; bone segmentation using CNN resulted in an average Dice score of 0.93 ± 0.03.Conclusion.This work indicates the feasibility of simultaneous fiducial marker identification and sCT generation using a single MRI acquisition. Future works includes evaluation of the proposed method in a large cohort of patients with optimized acquisition parameters as well as dosimetric evaluations.

The ambient aerosol characterization during the prescribed bushfire season in Brisbane 2013.

Prescribed burnings are conducted in Queensland each year from August until November aiming to decrease the impact of bushfire hazards and maintain the health of vegetation. This study reports chemical characteristics of the ambient aerosol, with a focus on source apportionment of the organic aerosol (OA) fraction, during the prescribed biomass burning (BB) season in Brisbane 2013. All measurements were conducted within the International Laboratory for Air Quality and Health (ILAQH) located in Brisbane's Central Business District. Chemical composition, degree of ageing and the influence of BB emission on the air quality of central Brisbane were characterized using a compact Time of Flight Aerosol Mass Spectrometer (cToF-AMS). AMS loadings were dominated by OA (64%), followed by, sulfate (17%), ammonium (14%) and nitrates (5%). Source apportionment was applied on the AMS OA mass spectra via the multilinear engine solver (ME-2) implementation within the recently developed Source Finder (SoFi) interface. Six factors were extracted including hydrocarbon-like OA (HOA), cooking-related OA (COA), biomass burning OA (BBOA), low-volatility oxygenated OA (LV-OOA), semivolatile oxygenated OA (SV-OOA), and nitrogen-enriched OA (NOA). The aerosol fraction that was attributed to BB factor was 9%, on average over the sampling period. The high proportion of oxygenated OA (72%), typically representing aged emissions, could possess a fraction of oxygenated species transfored from BB components on their way to the sampling site.

Modeling elemental strontium in human bone based on in vivo x-ray fluorescence measurements in osteoporotic females self-supplementing with strontium citrate.

An in-house custom I-125 excited in vivo x-ray fluorescence (IVXRF) system was used to perform bone strontium (Sr) measurements in individuals suffering from osteoporosis and/or osteopenia. These individuals, who were self-administering with Sr supplements of their choice, were measured frequently, ranging from weekly to biweekly to monthly, over four years, as part of the Ryerson and McMaster Sr in Bone Research Study. Based on these data collected, data from eight subjects were used to perform kinetic modeling of Sr in human bone. Power and exponential models were used to model the data based on one and two compartmental systems. Model parameters included: mean normalized baseline bone Sr signal, half-life and bone Sr uptake. A one compartmental exponential model applied to finger and ankle bone measurements gave half-lives of (508 ± 331) d and (232 ± 183) d, respectively, but did not show statistically significant differences (p = 0.087 96). However, the values fall within literature estimates. When a two compartmental model was applied to finger bone measurements, half-lives of (300 ± 163) d and (2201 ± 1662) d were observed. Ankle bone data gave half-lives of (156 ± 117) d and (1681 ± 744) d. A two sample t-test, assuming unequal variances, showed these half-lives to be statistically different in both the finger and ankle bone measurements (p = 0.0147 and p = 0.00711, respectively). Common kinetic parameters amongst the different subjects could not be unambiguously identified due to the wide scatter of data, leading to an inconclusive kinetic model. The wide distribution of data is suggested to be physiological since technical and positioning factors were eliminated as possible causes. This outcome indicates the need for a more controlled study and further understanding of the physiological mechanism of Sr absorption.

Influence of oxygen content of the certain types of biodiesels on particulate oxidative potential.

Oxidative potential (OP) is related to the organic phase, specifically to its oxygenated organic fraction (OOA). Furthermore, the oxygen content of fuel molecules has significant influence on particulate OP. Thus, this study aimed to explore the actual dependency of the OOA and ROS to the oxygen content of the fuel. In order to reach the goal, different biodiesels blends, with various ranges of oxygen content; have been employed. The compact time of flight aerosol mass spectrometer (c-ToF AMS) enabled better identification of OOA. ROS monitored by using two assays: DTT and BPEA-nit. Despite emitting lower mass, both assays agreed that oxygen content of a biodiesel is directly correlated with its OOA, and highly related to its OP. Hence, the more oxygen included in the considered biodiesels, the higher the OP of PM emissions. This highlights the importance of taking oxygen content into account while assessing emissions from new fuel types, which is relevant from a health effects standpoint.

Feasibility of measuring arsenic and selenium in human skin using in vivo x-ray fluorescence (XRF)--a comparison of methods.

In recent years, in vivo measurement systems of arsenic in skin by K-shell x-ray fluorescence (XRF) have been developed, including one which was applied in a pilot study of human subjects. Improved tube-based approaches suggest the method can be further exploited for in vivo studies. Recently, it has been suggested that selenium deficiency is correlated with arsenic toxicity. A non-invasive measurement of both elements could therefore be of potential interest. The main aim of this current study was to evaluate and compare the performance of an upgraded portable XRF system and an advanced version of the benchtop XRF system for both selenium and arsenic. This evaluation was performed in terms of arsenic and selenium Kα detection limits for a 4W gold anode Olympus InnovX Delta portable analyzer (40 kVp) in polyester resin skin-mimicking phantoms. Unlike the polychromatic source earlier reported in the literature, the benchtop tube-based technique involves monochromatic excitation (25 W silver anode, manufactured by x-ray optics, XOS) and a higher throughput detector type. Use of a single exciting energy allows for a lower in vivo dose delivered and superior signal-noise ratio. For the portable XRF method, arsenic and selenium minimum detection limits (MDLs) of 0.59 ± 0.03 ppm and 0.75 ± 0.02 ppm respectively were found for 1 min measurement times. The MDLs for arsenic and selenium using the benchtop system were found to be 0.35 ± 0.01 ppm and 0.670 ± 0.004 ppm respectively for 30 min measurement times. In terms of a figure of merit (FOM), allowing for dose as well as MDL, the benchtop system was found to be superior for arsenic and the two systems were equivalent, within error, for selenium. We shall discuss the performance and possible improvements of each system, their ease of use and potential for field application.

Non Tumor Perfusion Changes Following Stereotactic Radiosurgery to Brain Metastases.

Purpose: To evaluate early perfusion changes in normal tissue following stereotactic radiosurgery (SRS). Methods: Nineteen patients harboring twenty-two brain metastases treated with SRS were imaged with dynamic susceptibility magnetic resonance imaging (DSC MRI) at baseline, 1 week and 1 month post SRS. Relative cerebral blood volume and flow (rCBV and rCBF) ratios were evaluated outside of tumor within a combined region of interest (ROI) and separately within gray matter (GM) and white matter (WM) ROIs. Three-dimensional dose distribution from each SRS plan was divided into six regions: (1) <2 Gy; (2) 2-5 Gy; (3) 5-10 Gy; (4) 10-12 Gy; (5) 12-16 Gy; and (6) >16 Gy. rCBV and rCBF ratio differences between baseline, 1 week and 1 month were compared. Best linear fit plots quantified normal tissue dose-dependency. Results: Significant rCBV ratio increases were present between baseline and 1 month for all ROIs and dose ranges except for WM ROI receiving <2 Gy. rCBV ratio for all ROIs was maximally increased from baseline to 1 month with the greatest changes occurring within the 5-10 Gy dose range (53.1%). rCBF ratio was maximally increased from baseline to 1 month for all ROIs within the 5-10 Gy dose range (33.9-45.0%). Both rCBV and rCBF ratios were most elevated within GM ROIs. A weak, positive but not significant association between dose, rCBV and rCBF ratio was demonstrated. Progressive rCBV and rCBF ratio increased with dose up to 10 Gy at 1 month. Conclusion: Normal tissue response following SRS can be characterized by dose, tissue, and time specific increases in rCBV and rCBF ratio.

Monitoring bone strontium levels of an osteoporotic subject due to self-administration of strontium citrate with a novel diagnostic tool, in vivo XRF: a case study.

A previously developed in vivo X-ray fluorescence (IVXRF) I-125 based system was used to measure bone strontium levels non-invasively in an osteoporotic female volunteer. The volunteer was recruited in December 2008, as part of the Ryerson and McMaster University Strontium in Bone Research Study and measured at twice weekly, weekly and monthly intervals. Thirty minute measurements were taken at the finger and ankle bone sites, representing primarily cortical and trabecular bone, respectively and the strontium K-alpha X-ray peak at 14.16 keV was used in the analysis. Since the volunteer had no prior history of strontium based medications or supplementation, baseline natural strontium levels were obtained followed by a 24h measurement of first intake of strontium citrate supplements (680 mg Sr/day). While the baseline levels of 0.38 ± 0.05 and 0.39 ± 0.10 for the finger and ankle, respectively, were on par with those previously reported in Caucasians among twenty-two healthy non-supplementing strontium individuals by our group, an increase began to be seen after 24 hrs of 0.62 ± 0.14 and 0.45 ± 0.12 for the finger and ankle, respectively. By 120 h, the increase was statistically significant at 0.68 ± 0.07 and 0.93 ± 0.05, respectively. Further increases occurred within an interval of 90-180 days, with the most recent, after 800 days, at the finger and ankle being 7 and 15 times higher than the initial baseline reading. The intriguing results show bone strontium incorporation and retention follow a pattern, suggesting strontium levels, at least in the ankle, do not plateau within two to three years and will continue to increase over time, as an individual takes strontium supplements. The ability of this IVXRF system to monitor and measure bone strontium levels over time provides a useful diagnostic tool to help gain insight into strontium bone kinetics.

Aluminium and strontium in calcium supplements and antacids: a concern to haemodialysis patients?

Trace elements, most notably aluminium and strontium, have been noted for their role in the development of secondary bone disorders in haemodialysis patients. Due to the large dosages of calcium required for the maintenance of dialysis patients, this study investigated whether the source of calcium chosen for supplementation, including the form of administration (i.e. chewable forms or capsules), has an influence on the total amount of strontium and aluminium ingested daily. A convenience sample of various calcium supplement tablets and antacids was acquired, and strontium and aluminium quantification was performed by wavelength-dispersive X-ray fluorescence spectrometry. The use of readily available oyster shell-based calcium was found potentially to increase the total amount of ingested strontium substantially with concentrations reaching (2.26 +/- 0.05) (mg Sr).(g Ca)(-1), while the use of antacids or chewable supplements was found to contain concentrations reaching as high as (1.2 +/- 0.3) (mg Al).(g Ca)(-1) in the supplements analysed within this work. It is recommended that the choice of calcium supplement prescribed to individuals undergoing haemodialysis be closely regulated and noted as a possible factor in the prevalence of bone disorders reported in these patients.

Evaluation of imaging technologies to correct for photon attenuation in the overlying tissue for in vivo bone strontium measurements.

The interpretation of measurements of bone strontium in vivo using energy dispersive x-ray fluorescence spectroscopy is presently hindered by overlying skin and soft-tissue absorption of the strontium x-rays. The use of imaging technologies to measure the overlying soft-tissue thickness at the index finger measuring site might allow correction of the strontium reading to estimate its concentration in bone. An examination of magnetic resonance (MR), computed tomography (CT) and high-frequency ultrasound (US) imaging technologies revealed that 55 MHz US had the smallest range of measurement uncertainty at 3.2% followed by 1 Tesla MR, 25 MHz US, 8 MHz US and CT at 4.3, 5.4, 6.6 and 7.1% uncertainty, respectively. Of these, only CT imaging appeared to underestimate total thickness (p < 0.05). Furthermore, an inter-study comparison on the accuracy of US measurements of the overlying tissue thickness at finger and ankle in nine subjects was investigated. The 8 MHz US system used in prior in vivo experiments was found to perform satisfactorily in a repeat study of ankle measurements, but indicated that finger thickness measurements may have been misread in previous studies by up to 17.7% (p < 0.025). Repeat ankle measurements were not significantly different from initial measurements at 2.2% difference.

Noninvasive measurement of aluminium in human bone: preliminary human study and improved system performance.

Aluminium has been measured in the hands of 18 referent subjects and six aluminium welders using the technique of in vivo neutron activation analysis. The minimal detection limit (MDL) in the human subjects was 28.0 microgAl/gCa, whereas it was 19.5 microgAl/gCa in calibration standards. On average the aluminium exposed subjects had higher levels of aluminium in their hands than did the referent subjects. However, this difference only just achieved significance at the 5% level and should be treated with caution, since the study had not been deliberately designed to assess this difference. Following the preliminary human study, improvements were made to the measurement system with respect to the gamma-ray detector array and to the timing sequence of irradiation-transfer-counting. These improvements were tested on the calibration standards, lowering the MDL from 19.5 microgAl/gCa to 8.32 microgAl/gCa. A similar improvement in human measurements would result in an in vivo MDL of 12.0 microgAl/gCa.

Opportunities to improve the in vivo measurement of manganese in human hands.

Manganese (Mn) is an element which is both essential for regulating neurological and skeletal functions in the human body and also toxic when humans are exposed to excessive levels. Its excessive inhalation as a result of exposure through industrial and environmental emissions can cause neurological damage, which may manifest as memory deficit, loss of motor control and reduction in the refinement of certain body motions. A number of clinical studies demonstrate that biological monitoring of Mn exposure using body fluids, particularly blood, plasma/serum and urine is of very limited use and reflect only the most recent exposure and rapidly return to within normal ranges. In this context, a non-invasive neutron activation technique has been developed at the McMaster University accelerator laboratory that could provide an alternative to measure manganese stored in the bones of exposed subjects. In a first pilot study we conducted recently on non-exposed human subjects to measure the ratio of Mn to Ca in hand bones, it was determined that the technique needed further development to improve the precision of the measurements. It could be achieved by improving the minimum detection limit (MDL) of the system from 2.1 microg Mn/g Ca to the reference value of 0.6 microg g(-1) Ca (range: 0.16-0.78 microg Mn/g Ca) for the non-exposed population. However, the developed procedure might still be a suitable means of screening patients and people exposed to excessive amounts of Mn, who could develop many-fold increased levels of Mn in bones as demonstrated through various animal studies. To improve the MDL of the technique to the expected levels of Mn in a reference population, the present study investigates further optimization of irradiation conditions, which includes the optimal selection of proton beam energy, beam current and irradiation time and the effect of upgrading the 4pi detection system. The maximum local dose equivalent that could be given to the hand as a result of irradiation was constrained to be less than 150 mSv as opposed to the previously imposed dose equivalent limit of 20 mSv. A maximum beam current, which could be delivered on the lithium target to produce neutrons, was restricted to 500 microA. The length of irradiation intervals larger than 10 min, was considered inconvenient and impractical to implement with Mn measurements in humans. To fulfil the requirements for developing a protocol for in vivo bone Mn measurements, a revised estimate of the dose equivalent has been presented here. Beam energy of 1.98 MeV was determined to be optimal to complete the irradiation procedure within 10 min using 500 microA beam current. The local dose equivalent given to hand was estimated as 118 mSv, which is lower by a factor of 1.5 compared to that of 2.00 MeV. The optimized beam parameters are expected to improve the currently obtained detection limit of 2.1 microg Mn/g Ca to 0.6 microg Mn/g Ca. Using this dose equivalent delivered to the central location of the hand, the average dose equivalent to the hand of 74 mSv and an effective dose of approximately 70 microSv will be accompanying the non-invasive, in vivo measurements of bone Mn, which is little over the chest radiograph examination dose.

In vivo measurement of bone aluminum in population living in southern Ontario, Canada.

The harmful biological effect of excessive aluminum (Al) load in humans has been well documented in the literature. Al stored in bone, for instance due to dialysis treatment or occupational exposure, can interfere with normal bone remodeling leading to osteodystrophy, osteoarthritis, or osteomalacia. On the other hand, the relationship between chronic Al exposure and the risk of Alzheimer's disease remains controversial. In this work, the feasibility of in vivo neutron activation analysis (IVNAA) for measuring Al levels in the human hand bone, using the thermal neutron capture reaction 27Al(n, gamma)28 Al, is reported. This noninvasive diagnostic technique employs a high beam current Tandetron accelerator based neutron source, an irradiation/shielding cavity, a 47pi NaI(Tl) detector system, and a new set of hand bone phantoms. The photon spectra of the irradiated phantom closely resemble those collected from the hands of nonexposed healthy subjects. A protocol was developed using the newly developed hand phantoms, which resulted in a minimum detectable limit (MDL) of 0.29 mg Al in the human hand. Using the ratio of Al to Ca as an index of Al levels per unit bone mass, the MDL was determined as 19.5 +/- 1.5 microg Al/g Ca, which is within the range of the measured levels of 20-27 microg Al/g Ca [ICRP Report of the Task Group on Reference Man, Publication 23 (Pergamon, Oxford, 1975)] found in other in vivo and in vitro studies. Following the feasibility studies conducted with phantoms, the diagnostic technique was used to measure Al levels in the hand bones of 20 healthy human subjects. The mean hand bone Al concentration was determined as 27.1 +/- 16.1 (+/-1 SD) microg Al/g Ca. The average standard error (1sigma) in the Al/Ca is 14.0 microg Al/g Ca, which corresponds to an average relative error of 50% in the measured levels of Al/Ca. These results were achieved with a dose equivalent of 17.6 mSv to a hand and an effective dose of 14.4 microSv. This effective dose is approximately half of that received in a chest radiograph examination. It is recommended to investigate the use of the bone Al IVNAA diagnostic technique for in vivo measurements of patients with documented overload of Al in bone.

Quantification of manganese in human hand bones: a feasibility study.

Manganese is both an essential element to human health and also toxic when humans are exposed to excessive levels, particularly by means of inhalation. Biological monitoring of manganese exposure is problematic. It is subject to homeostasis; levels in blood (or serum/plasma) reflect only the most recent exposure and rapidly return to within normal ranges, even when there has been a temporary excursion in response to exposure. In this context, we have been developing a non-invasive technique for measurement of manganese stored in bone, using in vivo neutron activation analysis. Following preliminary feasibility studies, the technique has been enhanced by two significant infrastructure advances. A specially designed irradiation facility serves to maximize the activation of manganese with respect to the dose of ionizing radiation. Secondly, an array of eight NaI(Tl) crystals provides a detection system with very close to 4 pi geometry. This feasibility study, using neutron activation analysis to measure manganese in the bones of the hand, takes two features into account. Firstly, there is considerable magnesium present in the bone and this produces a spectral interference with the manganese. The 26 Mg(n,gamma)27 Mg reaction produces gamma -rays of 0.843 MeV from the decay of 27 Mg, which interfere with the 0.847 MeV gamma -rays from the decay of 56 Mn,produced by the 55 Mn(n,gamma)56 Mn reaction. Secondly, this work provides estimates of the levels of manganese to be expected in referent subjects. A revised estimate has been made from the most recent literature to explore the potential of the technique as a suitable means of screening patients and people exposed to excessive amounts of Mn who could develop many-fold increased levels of Mn in bones as demonstrated through various animal studies. This report presents the enhancements to the neutron activation system, by which manganese can be measured, which resulted in a detection limit in the hand of human subjects of 1.6 microg/g Ca. It also provides a revised estimate of expected referent levels of manganese in bone, now estimated to be 0.63 microg/g Ca and highlights the extent to which technical improvements will be required to further extend the application of the technique for in vivo measurements in non-exposed human subjects.

A preliminary study for non-invasive quantification of manganese in human hand bones.

Manganese (Mn) is a nutrient essential for regulating neurological and skeletal functions in the human body, but it is also toxic when humans are excessively exposed to Mn. Blood (or serum/plasma) and other body fluids reflect only the most recent exposure and rapidly return to within normal ranges, even when there has been a temporary excursion in response to exposure. In this context, we have been developing a non-invasive measurement of Mn stored in bone, using in vivo neutron activation analysis. Following feasibility studies, a first pilot study, using neutron activation analysis to measure Mn in the bones of the hand of ten healthy male human subjects, was conducted with the approval of the concerned research ethics boards. The participants of this study had no known history of exposure to Mn. Two volunteers were excluded from this study due to technical problems with their measurements. The inverse variance weighted mean value of Mn/Ca for the participants of this study is 0.12+/-0.68 microg Mn/g Ca which is comparable within uncertainties with the estimated range of 0.16-0.78 microg Mn/g Ca and mean value of 0.63+/-0.30 microg Mn/g Ca derived from cadaver data. It is recommended to investigate the use of the diagnostic technique for in vivo measurements of workers exposed occupationally to excessive amounts of Mn who could develop many-fold increased levels of Mn in bones as demonstrated through various animal studies. The technique needs further development to improve the precision of in vivo measurements in the non-exposed population.

Coherent normalization of finger strontium XRF measurements: feasibility and limitations.

A non-invasive in vivo x-ray fluorescence (XRF) method of measuring bone strontium concentrations has previously been reported as a potential diagnostic tool able to detect strontium concentration in the finger and ankle bones. The feasibility of coherent normalization for (125)I-source-based finger bone strontium x-ray fluorescence (XRF) measurements is assessed here by theoretical considerations and Monte Carlo simulations. Normalization would have several advantages, among which are the correction for the signal attenuation by the overlying soft tissue, and intersubject variability in the bone size and shape. The coherent normalization of bone strontium XRF measurements presents several challenges dictated by the behaviour of the coherent cross section and mass attenuation coefficient at the energies involved. It was found that the coherent normalization alone with either 22.1 keV or 35.5 keV photons was not successful in correcting for the overlying soft tissue attenuation. However, it was found that the coherent peak at 35.5 keV was able to correct effectively for variability in the finger bone size between people. Thus, it is suggested that, if the overlying soft tissue thickness can be obtained by means of an independent measurement, the 35.5 keV peak can be used to correct for the bone size, with an overall accuracy of the normalization process of better than 10%.

In vivo assessment of magnesium status in human body using accelerator-based neutron activation measurement of hands: a pilot study.

Magnesium (Mg) is an element essential for many enzymatic reactions in the human body. Various human and animal studies suggest that changes in Mg status are linked to diseases such as cardiac arrhythmia, coronary heart disease, hypertension, premenstrual syndrome, and diabetes mellitus. Thus, knowledge of Mg levels in the human body is needed. A direct measurement of human blood serum, which contains only 0.3% of the total body Mg, is generally used to infer information about the status of Mg in the body. However, in many clinical situations, Mg stored in large levels, for example in bones, muscles, and soft tissues, needs to be monitored either to evaluate the efficacy of a treatment or to study the progression of diseases associated with the deficiency of total body Mg. This work presents a feasibility study of a noninvasive, in vivo neutron activation analysis (IVNAA) technique using the 26Mg (n, gamma) 27Mg reaction to measure Mg levels in human hands. The technique employs the McMaster University high beam current Tandetron accelerator hand irradiation facility and an array of eight NaI (T1) detectors arranged in a 4 pi geometry for delayed counting of the 0.844 and 1.014 MeV gamma rays emitted when 27Mg decays in the irradiated hand. Mg determination in humans using IVNAA of hands has been demonstrated to be feasible, with effective doses as low as one-quarter of those delivered in chest x rays. The overall experimental uncertainty in the measurements is estimated to be approximately 5% (1 sigma). The results are found to be in the range of the in vitro measurements reported for other cortical bones collected from different sites of the human skeleton, which confirms that this technique mainly provides a measure of the amount of Mg in hand bones. The average concentration of Mg determined in human hands is 10.96 +/- 1.25 (+/- 1 SD) mg Mg/g Ca. The coefficient of variation (11%) observed in this study is comparable with or lower than several studies using in vitro measurements reported in the literature and therefore allows for a quantitative intersubject comparison, even if to a limited extent. The features of the developed technique such as its simplicity, rapidity, accuracy, robustness, noninvasive nature, and very effective use of radiation doses, present the technique as a viable diagnostic tool available for trial in a clinical environment.

In vivo study of an x-ray fluorescence system to detect bone strontium non-invasively.

An x-ray fluorescence (XRF) system using 125I as the source was developed to measure strontium in bone in vivo. As part of an in vivo pilot study, 22 people were measured at two bone sites, namely the index finger and the tibial ankle joint. Ultrasound measurements were used to obtain the soft tissue thickness at each site, which was necessary to correct the signal for tissue attenuation. For all 22 people, the strontium peak was clearly distinguishable from the background, proving that the system is able to measure Sr in vivo in people having normal bone Sr levels. Monte Carlo simulations were carried out to test the feasibility and the limitations of using the coherently scattered peak at 35.5 keV as a means to normalize the signal to correct for the bone size and shape. These showed that the accuracy of the normalized Sr signal when comparing different people is about 12%. An interesting result arising from the study is that, in the measured population, significantly higher measurements of bone Sr concentration were observed in continental Asian people, suggesting the possibility of a dietary or race dependence of the bone Sr concentration or a different bone biology between races.

Dosimetric characterization of the irradiation cavity for accelerator-based in vivo neutron activation analysis.

A neutron irradiation cavity for in vivo activation analysis has been characterized to estimate its dosimetric specifications. The cavity is defined to confine irradiation to the hand and modifies the neutron spectrum produced by a low energy accelerator neutron source to optimize activation per dose. Neutron and gamma-ray dose rates were measured with the microdosimetric technique using a tissue-equivalent proportional counter at the hand irradiation site and inside the hand access hole. For the outside of the cavity, a spherical neutron dose equivalent meter and a Farmer dosemeter were employed instead due to the low intensity of the radiation field. The maximum dose equivalent rate at the outside of the cavity was 2.94 microSv/100 microA min, which is lower by a factor of 1/2260 than the dose rate at the hand irradiation position. The local dose contributions from a hand, an arm and the rest of a body to the effective dose rate were estimated to be 1.73, 0.782 and 2.94 microSv/100 microA min, respectively. For the standard irradiation protocol of the in vivo hand activation, 300 microA min, an effective dose of 16.3 microSv would be delivered.

In vivo measurement of bone aluminium: recent developments.

A biomarker of aluminium accumulation in the human body can play a valuable role in determining health effects of chronic aluminium exposure, complementing other human and environmental monitoring data. In vivo neutron activation provides such a non-invasive biomarker. To date, the best in vivo neutron activation system used thermalised neutrons from a nuclear reactor at Brookhaven National Laboratory, which suffered only slightly from interference from other elements, primarily phosphorus, and from the disadvantage of restricted accessibility. At McMaster, we use a nuclear reaction on an accelerator to select neutron energy, which eliminates the interferences. Spectral decomposition analysis improved sensitivity. A new 4pi detection system also enhanced sensitivity. Together these improvements yield a minimum detection limit of 0.24 mgAl in a hand, slightly better than at Brookhaven and equivalent to "normal" levels. Further improvements should result from a new irradiation cavity and from using a higher proton current on the accelerator to shorten irradiation times. The system is now ready for pilot human studies.