Peak Tracer Research Articles

Human parasagittal dura is a potential neuroimmune interface

Parasagittal dura (PSD) is located on both sides of the superior sagittal sinus and harbours arachnoid granulations and lymphatic vessels. Efflux of cerebrospinal fluid (CSF) to human PSD has recently been shown in vivo. Here we obtain PSD volumes from magnetic resonance images in 76 patients under evaluation for CSF disorders and correlate them to age, sex, intracranial volumes, disease category, sleep quality, and intracranial pressure. In two subgroups, we also analyze tracer dynamics and time to peak tracer level in PSD and blood. PSD volume is not explained by any single assessed variable, but tracer level in PSD is strongly associated with tracer in CSF and brain. Furthermore, peak tracer in PSD occurs far later than peak tracer in blood, implying that PSD is no major efflux route for CSF. These observations may indicate that PSD is more relevant as a neuroimmune interface than as a CSF efflux route.

Clinical application of intrathecal gadobutrol for assessment of cerebrospinal fluid tracer clearance to blood.

BACKGROUNDMethodology for estimation of cerebrospinal fluid (CSF) tracer clearance could have wide clinical application in predicting excretion of intrathecal drugs and metabolic solutes from brain metabolism and for diagnostic workup of CSF disturbances.METHODSThe MRI contrast agent gadobutrol (Gadovist) was used as a CSF tracer and injected into the lumbar CSF. Gadobutrol is contained outside blood vessels of the CNS and is eliminated along extravascular pathways, analogous to many CNS metabolites and intrathecal drugs. Tracer enrichment was verified and assessed in CSF by MRI at the level of the cisterna magna in parallel with obtaining blood samples through 48 hours.RESULTSIn a reference patient cohort (n = 29), both enrichment within CSF and blood coincided in time. Blood concentration profiles of gadobutrol through 48 hours varied between patients diagnosed with CSF leakage (n = 4), idiopathic normal pressure hydrocephalus dementia (n = 7), pineal cysts (n = 8), and idiopathic intracranial hypertension (n = 4).CONCLUSIONAssessment of CSF tracer clearance is clinically feasible and may provide a way to predict extravascular clearance of intrathecal drugs and endogenous metabolites from the CNS. The peak concentration in blood (at about 10 hours) was preceded by far peak tracer enhancement at MRI in extracranial lymphatic structures (at about 24 hours), as shown in previous studies, indicating a major role of the spinal canal in CSF clearance capacity.FUNDINGThe work was supported by the Department of Neurosurgery, Oslo University Hospital; the Norwegian Institute for Air Research; and the University of Oslo.

Tracer eluting proppants for hydraulic fracture characterization

Existing fracture characterization methods (e.g., microseismic) detect fractures created during hydraulic fracturing, but cannot determine whether the fractures are propped or not. The goal of this work is to develop a tracer-eluting proppant technique that can indicate the extent of propped fractures. A polymer coating is developed for common proppants which can release a tracer after being placed in a fracture. A small slug of coated proppants can be injected at the end or middle of the regular proppant injection during hydraulic fracturing. The released tracer can be collected during flow back and be used to better understand proppant location in fracture systems. Laboratory-scale batch tracer release experiments show that the tracer release can be triggered by an increase in temperature, salinity or pH. A proof of concept experiment was conducted in a model single fracture system. The tracer was successfully detected in the flow-back fluid and the tracer concentration was accurately estimated by a numerical tracer release model. The location of the tracer eluting proppants can be estimated from the peak tracer time in the flow-back water. This technique can be used for a wide range of proppants and tracers. Different tracers can be used in different stages.

The Human Visual Pathway Communicates Directly With the Subarachnoid Space.

Explore in vivo whether there is direct communication between the cerebrospinal fluid (CSF) and extravascular compartment of human visual pathway structures. A prospective and observational study included 10 subjects who underwent intrathecal gadolinium-enhanced magnetic resonance imaging (MRI) for suspected CSF circulation disorder, but with a negative result and with no known ophthalmic diseases. After precontrast T1-weighted MRI, 0.5 mL of gadobutrol (Gadovist, 1.0 mmol/mL) was injected intrathecally. Gadobutrol distributes in the extravascular space, and served as a CSF tracer. Consecutive MRI scans were obtained throughout 24 to 48 hours. To assess gadobutrol contrast enrichment, regions of interest (ROIs) were placed at multiple locations along the visual pathway, from the primary visual cortex to the eye's vitreous body. CSF tracer dependent T1 signal was measured in each ROI. A linear mixed-model was used for statistical analyses. CSF tracer enrichment was found within the optic nerve, optic chiasm, optic tract, and primary visual cortex (P < 0.001). Peak tracer enrichment in the visual pathway generally occurred after 24 hours and was preceded by peak enhancement in the prechiasmatic cistern after 4 to 6 hours. The results indicate direct communication between CSF of subarachnoid space and the extravascular space of the human visual pathway. Extravascular entry of the CSF tracer is a prerequisite for a glymphatic system, the present findings may suggest its presence. The existence of a glymphatic system in the human visual pathway could bring novel perspectives on the pathophysiology and treatment of ophthalmic diseases.

Effects of crude oil on water and tracer movement in the unsaturated and saturated zones

A tracer test was conducted to aid in the investigation of water movement and solute transport at a crude-oil spill site near Bemidji, Minnesota. Time of travel was measured using breakthrough curves for rhodamine WT and bromide tracers moving from the soil surface through oil-contaminated and oil-free unsaturated zones to the saturated zone. Results indicate that the rates of tracer movement were similar in the oil-free unsaturated and saturated zones compared to the oily zones. These results are somewhat surprising given the oil contamination in the unsaturated and saturated zones. Rhodamine tracer breakthrough in the unsaturated and saturated zones in general was delayed in comparison to bromide tracer breakthrough. Peak tracer concentrations for the lysimeters and wells in the oily zone were much greater than at the corresponding depths in the oil-free zone. Water and tracer movement in the oily zone was complicated by soil hydrophobicity and decreased oil saturations toward the periphery of the oil. Preferential flow resulted in reduced tracer interaction with the soil, adsorption, and dispersion and faster tracer movement in the oily zone than expected. Tracers were freely transported through the oily zone to the water table. Recharge calculations support the idea that the oil does not substantially affect recharge in the oily zone. This is an important result indicating that previous model-based assumptions of decreased recharge beneath the oil were incorrect. Results have important implications for modeling the fate and transport of dissolved contaminants at hydrocarbon spill sites.

68Ga-PSMA PET/CT Imaging Predicting Intraprostatic Tumor Extent, Extracapsular Extension and Seminal Vesicle Invasion Prior to Radical Prostatectomy in Patients with Prostate Cancer.

68Ga-labeled prostate-specific membrane antigen (PSMA) ligand positron emission tomography/computed tomography (PET/CT) has shown promising results in patients with biochemical recurrence after primary therapy for prostate cancer. In this study, we evaluated the usefulness of PSMA I&T (imaging and therapy) PET/CT prior to radical prostatectomy. The study population consisted of 21 patients with prostate cancer who underwent 68Ga-PSMA I&T PET/CT before either open or laparoscopic radical prostatectomy. Intraprostatic tumor extent, extracapsular extension (ECE) and seminal vesicle invasion (SVI) were assessed on the PET/CT scans. Tracer uptake was quantified in terms of standardized uptake values (SUVs). Imaging findings were correlated with final whole-gland histopathology. Of the 21 patients, two had T stage 2b disease, nine stage 2c, six stage 3a and four stage 3b. The median Gleason score was 7. The SUVmean of the primary tumors was 9.5 ± 8.8. SUVmean was higher in tumors with ECE than in organ-confined tumors (13.8 ± 11.0 vs. 5.6 ± 3.2, p = 0.029). Peak tracer uptake was significantly positively correlated with Gleason score (rs = 0.49, p = 0.025). Sensitivity, specificity, positive predictive value and negative predictive value were, respectively, 94.7%, 75.0%, 97.3% and 60.0% for tumor infiltration of an individual prostate lobe, 75.0%, 100.0%, 100.0% and 97.4% for SVI, and 90.0%, 90.9%, 90.0% and 90.9% for ECE, using an angulated contour of the prostate as the criterion. Tumor volume derived from 68Ga-PSMA I&T PET/CT was significantly correlated with preoperative prostate-specific antigen value (rp = 0.75, p < 0.001) and tumor volume on histopathology (rp = 0.45, p = 0.039). 68Ga-PSMA I&T PET/CT prior to radical prostatectomy can contribute to presurgical local staging of prostate cancer. In this pilot study, 68Ga-PSMA I&T PET/CT showed promising results for prediction of lobe infiltration, ECE and SVI.

Early-Time Analysis of Tracers for Use in Enhanced-Oil-Recovery Flood Optimization

Summary Tracer testing is a powerful tool for reservoir surveillance. Conducting and analyzing an interwell tracer test (IWTT) before starting an enhanced-oil-recovery (EOR) flood provides specific information required to balance the pattern's swept pore volume (PV) and to optimize chemical or solvent use. Tracer testing also plays an important role in EOR by establishing a baseline for estimating incremental volume swept and recovery factor. A key limitation to tracer testing is the time required to obtain a complete interpretation of the test results. Conventional interpretation methods require observing exponential decline in the tracer concentration from all producers; depending on the pattern size and processing rate, this can take many months or years. Meanwhile, the EOR flood is delayed, thereby eroding its value and reducing the remaining oil target. We have developed a method for analyzing tracer data from relatively early times that is based, in part, on a new way to extrapolate the tracer data, providing timely information to optimize flood performance. The extrapolation can be performed soon after the peak tracer concentration is observed in the well with the slowest response. We illustrate the extrapolation procedure with a synthetic, yet realistic, data set showing that the new methods result in a good approximation at much earlier times. We then compare ‘early time analysis’ swept PVs with the (correct) swept PVs using the complete tracer data set. We also discuss how early-time approximations can thus provide the opportunity to optimize chemical-flood performance and to enable field startup of EOR floods in a timely fashion.

Streamline-Based History Matching for Multicomponent Compositional Systems

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174750, “Streamline-Based History Matching of Arrival Times and Bottomhole-Pressure Data for Multicomponent Compositional Systems,” by Shusei Tanaka, Dongjae Kam, Akhil Datta-Gupta, and Michael J. King, Texas A&amp;M University, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. Streamline-based history-matching techniques have provided significant capabilities in integrating field-scale water-cut and tracer data into high-resolution geologic models. However, application of the streamline-based approach for simultaneous integration of water cut and bottomhole pressure (BHP) has been rather limited. In this paper, the authors introduce a novel semianalytic approach to compute the sensitivity of the BHP data with respect to gridblock properties. Introduction The streamline-based method has many advantages in terms of computational efficiency and applicability. The main advantage of the streamline-based method is that it is able to calculate parameter sensitivity with a single streamline simulation or post-processing of the grid-based finite-difference simulation results. The calculated sensitivity is comparable with the sensitivities computed from numerical perturbation or with adjoint-based sensitivities. It is possible to calculate the parameter sensitivity from a commercial finite-difference simulator by use of streamlines traced using the flux field. This allows accounting for detailed physics by means of finite-difference simulation while taking advantage of the power of the streamlines for sensitivity computations. Streamline and Parameter Sensitivity Streamline-based history matching starts with the tracing of streamlines from a given set of static and dynamic conditions. This process is outlined in detail in the complete paper. Amplitude, Travel-Time, and Generalized Travel-Time Inversion (GTTI) Methods The approach to minimizing the objective function through all the observed points and simulation results is defined as amplitude inversion. The travel-time inversion, instead, attempts to match single reference times such as water-breakthrough point or peak tracer response. The amplitude matching is general in terms of reduction of the objective function, because while the travel-time inversion reduces the objective function at only a single point, the amplitude matching can cover all the data points. However, the travel-time-based approach is often used because amplitude inversion is a highly nonlinear problem and presents difficulties in computational cost and in reducing the objective function when there is a large amount of wells and data points.

Augmentation of groundwater monitoring networks using information theory and ensemble modeling with pedotransfer functions

Summary Improving understanding of chemical transport in the subsurface commonly employs evolving groundwater monitoring networks. The objective of this work was to apply the information theory to propose an objective algorithm for augmenting a subsurface monitoring network (SMN) with the purpose of discrimination of conceptually different subsurface flow and transport models. This method determines new monitoring locations where the Kullback–Leibler total information gain is maximized. The latter is computed based on estimates of the uncertainty in modeling results and uncertainty in observations. The method was applied to discriminate models in (1) a synthetic case of groundwater contamination from a point source; (2) the tracer experiment conducted at the USDA-ARS OPE3 research site where a pulse of KCL solution was applied with irrigation water and CL − concentrations were subsequently monitored. Models were compared that included or ignored the effect of subsurface soil lenses on chemical transport. Pedotransfer functions were used to develop the ensemble of models for estimating the uncertainty in modeling results obtained with the numerical 3D flow and transport model. Peak tracer breakthrough concentrations were used to define the information gains. The determination of the new locations to augment existing ones was conducted on a 2-D grid. The information gain peaked in small area, and additional observation locations were very well spatially defined. Well-calibrated models provided a single optimal location, whereas, if models were not calibrated well, the Bayesian estimates of the new observation location depended on the activation sequence assumed for existing locations. The information gain maximization can suggest data collection locations to reduce uncertainties in the conceptual models of subsurface flow and transport.

Application of field portable X-ray fluorescence to the analysis of desert varnish samples in areas affected by coal-fired power plants

Environmental context Rock surfaces are often covered with a dark coating called desert varnish that can capture and retain air pollutants. A field portable X-ray fluorescence spectrometer was used for direct non-destructive analysis of varnished rocks in the fallout zones of two coal-fired power plants. At one power plant where tracer studies had been carried out, the highest concentration of elements including Cr, As, Pb and Zn in the rock varnish samples, coincides with the peak tracer concentration locations. AbstractDesert varnish samples were collected near two coal-fired power plants to determine if the varnish contained a record of recent air pollution. Samples were collected: (1) in the fallout patterns of the shuttered Mohave Power Plant (MPP), located in Laughlin, NV; and (2) near the operating Reid-Gardner Power Plant (RGPP), just east of Las Vegas, NV. Small pieces of varnished rocks were analysed by field portable X-ray fluorescence spectroscopy (FPXRF). Results were obtained for 15 elements: Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, Mo, Hg and Pb. The FPXRF data indicate that the elements commonly found in fly ash from coal-fired power plants (e.g. Cr, Zn, As and Pb) had significantly higher concentrations in the rock coatings in relation to the unvarnished substrate rock. For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the desert varnish coincided with the peak tracer concentration locations. Thus, these elements in desert varnish hold promise for identifying those geographical regions affected by nearby power plants. However, additional samples are required to demonstrate unequivocally that the power plants are indeed the sources of these elements. Overall, it is apparent that desert varnish can be utilised as a passive environmental monitor to investigate recent air pollution (past 20–30 years) and that FPXRF can be used as a surveying tool to obtain multi-element data from a large number of samples.

Fluorescent dye imaging of the volume sampled by single well forced-gradient tracer tests evaluated in a laboratory-scale aquifer physical model

This study presents a new method to visualise forced-gradient tracer tests in 2-D using a laboratory-scale aquifer physical model. Experiments were designed to investigate the volume of aquifer sampled in vertical dipole flow tracer tests (DFTT) and push–pull tests (PPT), using a miniature monitoring well and straddle packer arrangement equipped with solute injection and recovery chambers. These tests have previously been used to estimate bulk aquifer hydraulic and transport properties for the evaluation of natural attenuation and other remediation approaches. Experiments were performed in a silica glass bead-filled box, using a fluorescent tracer (fluorescein) to deduce conservative solute transport paths. Digital images of fluorescein transport were captured under ultraviolet light and processed to analyse tracer plume geometry and obtain point-concentration breakthrough histories. Inorganic anion mixtures were also used to obtain conventional tracer breakthrough histories. Concentration data from the conservative tracer breakthrough curves was compared with the digital images and a well characterised numerical model. The results show that the peak tracer breakthrough response in dipole flow tracer tests samples a zone of aquifer close to the well screen, while the sampling volume of push–pull tests is limited by the length of the straddle packers used. The effective sampling volume of these single well forced-gradient tests in isotropic conditions can be estimated with simple equations. The experimental approach offers the opportunity to evaluate under controlled conditions the theoretical basis, design and performance of DFTTs and PPTs in porous media in relation to measured flow and transport properties. 2 2 DFTT = Dipole Flow Tracer Test, PPT = Push Pull Tracer Test.

Elemental Analysis of Desert Varnish Samples in the Vicinity of Coal-Fired Power Plants and the Nevada Test Site Using Laser Ablation ICPMS

Desert varnish is a thin manganese-iron rich dark coating that forms on rocks most often in arid climates. This coating may be up to a few hundred microns in thickness and is thought to grow by approximately one micron per thousand years. Recent research has shown that many elements are incorporated into this coating, and, in spite of its slow growth, it may serve as a passive environmental monitor for recent and historical air pollution. To test this hypothesis, small pieces of varnished rock were probed directly by laser ablation inductively coupled plasma mass spectrometry (LA- ICPMS). Results were obtained for 11 elements (13 isotopes: 9 Be, 107 Ag, 111 Cd, 118 Sn, 121 Sb, 138 Ba, 184 W, 205 Tl, 206 Pb, 207 Pb, 208 Pb, 232 Th, and 238 U) by magnetic sector ICPMS and for 23 elements (25 isotopes: same as before plus 51 V, 52 Cr, 59 Co, 60 Ni, 65 Cu, 66 Zn, 88 Sr, 98 Mo, 115 In, 133 Cs, 197 Au, and 209 Bi) by quadrupole ICPMS. Varnished rock samples were collected mainly in the fallout patterns of two coal-fired power plants and downwind from the Nevada Test Site (NTS). The LA-ICPMS data indicate that many of the elements commonly found in fly ash from coal-fired power plants (e.g., Cr, Co, Ni, Cu, Zn, Cd, Sn, Sb, Tl and Pb) were highly enriched in the rock coatings in relation to the upper continental crust (UCC). For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the rock varnish coincide with the peak tracer concentration locations. Thus, these elements in rock varnish hold promise for identifying those geographical regions impacted by nearby power plants. Overall, the results indicate that rock varnish can be used as a passive environmental monitor of relatively recent events, and that the trace element fingerprints held in rock varnish may also hold much potential in forensic air pollution studies.

Imaging Vascular Endothelial Growth Factor (VEGF) Receptors in Turpentine-Induced Sterile Thigh Abscesses with Radiolabeled Single-Chain VEGF

Angiogenesis plays a central role in the pathogenesis of chronic inflammatory disorders. Vascular endothelial growth factor (VEGF) and its receptors are the most important regulators of angiogenesis. We wished to determine whether labeled forms of single-chain VEGF (scVEGF) could be used to image VEGF receptors in a well-characterized model of sterile soft-tissue inflammation induced by intramuscular injection of turpentine. Anesthetized adult male Swiss-Webster mice received a 20-microL intramuscular injection of turpentine into the right thigh. At 4, 7, or 10 d later, groups of 3-5 mice were injected via the tail vein with 50 microg of either scVEGF that had been site specifically labeled with Cy5.5 (scVEGF/Cy) or inactivated scVEGF/Cy (inVEGF/Cy) and then examined by fluorescence imaging. At 3, 4, 6, 7, 9, 10, or 12 d, additional groups of 3-5 mice were injected via the tail vein with 74-111 MBq of (99m)Tc-scVEGF (or (99m)Tc-inVEGF) and then examined by SPECT imaging. On days 3 through 10, both forms of scVEGF (scVEGF/Cy and (99m)Tc-scVEGF) showed significantly higher uptake (P < 0.05) in the right (abscessed) thigh than in the contralateral thigh (and higher uptake than the inactivated tracer). Peak uptake occurred on day 7 (3.67 +/- 1.79 [ratio of uptake in abscessed thigh to uptake in normal thigh, mean +/- SD] and 0.72 +/- 0.01 for scVEGF/Cy and inVEGF/Cy, respectively, and 3.49 +/- 1.22 and 1.04 +/- 0.41 for (99m)Tc-scVEGF and (99m)Tc-inVEGF, respectively) and slowly decreased thereafter. Autoradiography revealed peak tracer uptake in the thick irregular angiogenic rim of the abscess cavity on day 9 (5.83 x 10(-7) +/- 9.22 x 10(-8) and 5.85 x 10(-8) +/- 5.95 x 10(-8) percentage injected dose per pixel for (99m)Tc-scVEGF and (99m)Tc-inVEGF, respectively); in comparison, a thin circumscribed rim of uptake was seen with (99m)Tc-inVEGF. Immunostaining revealed that VEGFR-2 (VEGF receptor) colocalized with CD31 (endothelial cell marker) at all time points in the abscess rim, whereas F4/80 (macrophage) immunostaining reached a maximum at day 7 and decreased by day 10. The uptake of scVEGF in turpentine-induced abscesses was specific and directly related to VEGFR-2 expression in the neovasculature of the angiogenic rim. Peak tracer uptake coincided with maximum macrophage infiltration, suggesting that scVEGF imaging may be useful for the detection, localization, and monitoring of chronic inflammation in bone, joints, or soft tissues.

An in situ mesocosm method for quantifying nitrogen cycling rates in oligotrophic wetlands using 15N tracer techniques

Short term nitrogen uptake dynamics in the marshes of the southern Everglades, USA, were determined through implementation of a field mesocosm and isotopic enrichment method. The approach was tested using six mesocosms, three enriched with a 300‰ 15N tracer, Ca(NO3)2 (± 98% 15N) and three unenriched mesocosms. This 15N tracer technique allowed the determination of nitrogen fluxes between key ecosystem components. The in situ mesocosm experiment was conducted in a freshwater marl prairie marsh habitat for a period of 21 days. Macrophytes (Cladium jamaicense), periphyton, soil, and consumers (Gambusia holbrooki) were sampled at prescribed intervals to determine the optimal sampling periods necessary to capture peak 15N tracer uptake. Over the course of the study period, 15N tracer was detected in all ecosystem components sampled except for soils. Periphyton exhibited the most rapid initial 15N tracer uptake, with an increase of 3.86‰ to 7.79‰ (± 1.70) only 5 minutes after tracer addition. Periphyton 15N signatures continued to increase to 16.49‰ (± 6.45) and 108.15‰ (± 49.40) after 10 minutes and 6 hours, respectively. Increased 15N signatures were also noted in the macrophyte and consumer components, with peak tracer uptake values occurring in aboveground macrophyte tissue at t = 9 day (26.62‰ (± 5.00)), the belowground macrophyte tissue at t = 15 day (22.01‰ (± 5.83)), and in consumers at t = 15 day (297.09‰ (± 127.36)). Tracer uptake by the soil component was minimal with no significant amount of tracer being detected in any of the three soil layers sampled (0–1, 1–5, and 5–10 cm). This testing of the in situ mesocosm and 15N isotopic enrichment approach provides a foundation for further experimentation with the method at this and other wetland study sites.

Biodistribution and Radiation Dosimetry of the Synthetic Nonmetabolized Amino Acid Analogue Anti-18F-FACBC in Humans

The synthetic leucine amino acid analog anti-1-amino-3-(18)F-fluorocyclobutane-1-carboxylic acid (anti-(18)F-FACBC) is a recently developed ligand that permits the evaluation of the L-amino acid transport system. This study evaluated the whole-body radiation burden of anti-(18)F-FACBC in humans. Serial whole-body PET/CT scans of 6 healthy volunteers (3 male and 3 female) were acquired for 2 h after a bolus injection of anti-(18)F-FACBC (366 +/- 51 MBq). Organ-specific time-activity curves were extracted from the reconstructed data and integrated to evaluate the individual organ residence times. A uniform activity distribution was assumed in the body organs with urine collection after the study. Estimates of radiation burden to the human body were calculated on the basis of the recommendations of the MIRD committee. The updated dynamic bladder model was used to calculate dose to the bladder wall. All volunteers showed initially high uptake in the pancreas and liver, followed by rapid clearance. Skeletal muscle and bone marrow showed lower and prolonged uptake, with clearance dominated by the tracer half-life. The liver was the critical organ, with a mean absorbed dose of 52.2 microGy/MBq. The estimated effective dose was 14.1 microSv/MBq, representing less than 20% of the dose limit recommended by the Radioactive Drug Research Committee for a 370-MBq injection. Bladder excretion was low and initially observed 6 min after injection, well after peak tracer uptake in the body organs. The PET whole-body dosimetry estimates indicate that an approximately 370-MBq injection of anti-(18)F-FACBC yields good imaging and acceptable dosimetry. The nonmetabolized nature of this tracer is favorable for extraction of relevant physiologic parameters from kinetic models.

Quantitative salivary gland scintigraphy can distinguish patients with primary Sjøgren’s syndrome during the evaluation of sicca symptoms

Abnormal findings on salivary gland scintigraphy (SGS) are part of the classification criteria for Sjøgren's syndrome (SS), but SGS is operator dependent and poorly standardised. We studied the use of quantitative data on the uptake, concentration and excretion of the four major salivary glands in the evaluation of sicca patients. During an initial clinical evaluation for sicca symptoms (mean duration, 51 months), 24 subjects were classified as either SS (n = 8) or isolated sicca (IS; n = 16). SGS was then performed after i.v. injection of 200 MBq pertecnetat. Digitalised quantitative data on time-to-peak uptake (Tmax), peak tracer distribution (C%) and stimulated excretion (E%) were calculated from time-activity curves and compared between groups and controls (n = 8) and correlated to clinical data. Statistical analysis was performed with non-parametric tests. SS patients had longer Tmax in both parotic glands (18.1 min; p < 0.01)) and both submandibular glands (mean 13.7 min, p < 0.05); whereas Tmax in IS patients was similar as in controls in both parotic (10.4 min; p > 0.2) and submandibular glands (9.4 min; p > 0.4). C% was significantly lower in the parotic glands of both the SS and the IS group compared to the controls (p < 0.01). E% was significantly reduced in SS patients (16.3% for parotic and 17.4% for submandibular glands; p < 0.01); whereas in the IS patients, excretion (32, 2% for parotic and 26, 9% for submandibular glands) was similar from all glands as in the control groups (35, 2% for parotic and 27, 8% for submandibular glands). No correlation was found between these SGS results and age, focus score, erythrocyte sedimentation rate, serum creatinin or immunoglobulin levels. No IS patient progressed to full-blown pSS during the 4 years of follow-up. Quantitative SGS data are useful and objective tools to distinguish patients with SS.

Relating transient storage to channel complexity in streams of varying land use in Jackson Hole, Wyoming

Transient storage processes are important to biogeochemical cycling in many streams and depend greatly upon stream fluvial structure. Fluvial geomorphic structure establishes patterns of surface water and subsurface head distributions, often driving hyporheic exchange through steps, riffles, and meanders, and controls the potential for in‐channel dead zone storage in side pools, eddies, etc. We performed stream tracer experiments and geomorphological assessments (topographic thalweg surveys, channel dimension measurement, and sediment size analyses) in six streams in Jackson Hole, Wyoming, two agricultural streams, two urban streams, and two reference streams surrounded by native vegetation, to relate stream water transient storage to channel complexity. We propose that the inclusion of agricultural and urban streams increases the range of channel complexity and transient storage response over an assessment of numerous reaches within a single land use type. Stream tracer experiments were performed in each of the six reaches with slugs of Rhodamine WT (RWT). Downstream RWT breakthrough curves (BTCs) were simulated with a one‐dimensional solute transport model, STAMMT‐L, capable of simulating several transient storage residence time distribution types. As an indication of transient storage, relative BTC residence times were compared to timescale of advection, tadv (taken to be the time of peak tracer concentration). Reference streams were geomorphically complex, agricultural streams were intermediate, and urban streams were least complex. Urban streams had the shortest total relative residence times (&lt;5tadv) and short mean storage residence times (0.34 hour, n = 2), and reference streams consistently had the longest total relative residence times (13–20tadv) and the longest mean storage residence times (1.82 hours, n = 2). These results indicate that increased geomorphic complexity increases the potential for transient storage, likely both in the channel and in the subsurface, as demonstrated in reaches in a range of land use settings.

Effect of bedrock permeability on subsurface stormflow and the water balance of a trenched hillslope at the Panola Mountain Research Watershed, Georgia, USA

AbstractThe effect of bedrock permeability on subsurface stormflow initiation and the hillslope water balance is poorly understood. Previous hillslope hydrological studies at the Panola Mountain Research Watershed (PMRW), Georgia, USA, have assumed that the bedrock underlying the trenched hillslope is effectively impermeable. This paper presents a series of sprinkling experiments where we test the bedrock impermeability hypothesis at the PMRW. Specifically, we quantify the bedrock permeability effects on hillslope subsurface stormflow generation and the hillslope water balance at the PMRW. Five sprinkling experiments were performed by applying 882–1676 mm of rainfall over a ∼5·5 m × 12 m area on the lower hillslope during ∼8 days. In addition to water input and output captured at the trench, we measured transpiration in 14 trees on the slope to close the water balance. Of the 193 mm day−1 applied during the later part of the sprinkling experiments when soil moisture changes were small, &lt;14 mm day−1 was collected at the trench and &lt;4 mm day−1 was transpired by the trees, with residual bedrock leakage of &gt;175 mm day−1 (91%). Bedrock moisture was measured at three locations downslope of the water collection system in the trench. Bedrock moisture responded quickly to precipitation in early spring. Peak tracer breakthrough in response to natural precipitation in the bedrock downslope from the trench was delayed only 2 days relative to peak tracer arrival in subsurface stormflow at the trench. Leakage to bedrock influences subsurface stormflow at the storm time‐scale and also the water balance of the hillslope. This has important implications for the age and geochemistry of the water and thus how one models this hillslope and watershed. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Comparison of tracer techniques for monitoring sewer losses

Two different experimental techniques employing conservative tracers to determine exfiltration losses in a sewer system are reported. Both techniques compare the in-sewer responses measured along designated indicator and reference sections to assess the level of exfiltration although with different degrees of reliability. The experimental and interpretation errors associated with a pulse dosing technique, in which Rhodamine WT is used as the single tracer, are described. The estimation of exfiltration requires the comparison of indicator and reference peaks which need to be well resolved and reproducible in order to provide realistic results. A more consistent technique involves the continuous dosing of two different tracers with the objective of producing simultaneous downstream peak tracer concentrations. Any errors due to flow variations are eliminated and the longer measurement period allows both peak and background concentrations to be more accurately determined. Rhodamine WT, Li and Br were used in different combinations over the approximately 20 min duration of each continuous dosing experiment and were found to demonstrate conservative behaviours with measured recoveries of 97.6-100.6%, 97.3-101.4% and 108.4-109.2%, respectively. The analytical problems associated with the determination of the different tracers in sewage are described and are shown to be responsible for the reduced accuracy of the results associated with the use of Br. The preferred combination of tracers is Rhodamine WT as the indicator and Li as the reference and these are shown to be capable of estimating sewer losses to an accuracy of +/-1.0% using the continuous dosing approach.

Mechanism of cerebral edema in children with diabetic ketoacidosis

Objectives Cerebral edema during diabetic ketoacidosis (DKA) has been attributed to osmotic cellular swelling during treatment. We evaluated cerebral water distribution and cerebral perfusion during DKA treatment in children. Study design We imaged 14 children during DKA treatment and after recovery, using both diffusion and perfusion weighted magnetic resonance imaging (MRI). We assessed the apparent diffusion coefficients (ADCs) and measures reflecting cerebral perfusion. Results The ADC was significantly elevated during DKA treatment (indicating increased water diffusion) in all regions except the occipital gray matter. Mean reductions in the ADC from initial to postrecovery MRI were: basal ganglia 4.7 ± 2.5 × 10 −5 mm 2/s ( P = .002), thalamus 3.7 ± 2.8 × 10 −5 mm 2/s, ( P = .002), periaqueductal gray matter 4.3 ± 5.1 × 10 −5 mm 2/s ( P = .03), and frontal white matter 2.0 ± 3.1 × 10 −5 mm 2/s ( P = .03). In contrast, the ADC in the occipital gray matter increased significantly from the initial to postrecovery MRI (mean increase 3.9 ± 3.9 × 10 −5 mm 2/s, P = .004). Perfusion MRI during DKA treatment revealed significantly shorter mean transit times (MTTs) and higher peak tracer concentrations, possibly indicating increased cerebral blood flow (CBF). Conclusions Elevated ADC values during DKA treatment suggests a vasogenic process as the predominant mechanism of edema formation rather than osmotic cellular swelling.