Impact of climate warming on phenological asynchrony of plankton dynamics across Europe.

Climate warming alters the seasonal timing of biological events. This raises concerns that species-specific responses to warming may de-synchronize co-evolved consumer-resource phenologies, resulting in trophic mismatch and altered ecosystem dynamics. We explored the effects of warming on the synchrony of two events: the onset of the phytoplankton spring bloom and the spring/summer maximum of the grazer Daphnia. Simulation of 16 lake types over 31 years at 1907 North African and European locations under 5 climate scenarios revealed that the current median phenological delay between the two events varies greatly (20-190 days) across lake types and geographic locations. Warming moves both events forward in time and can lengthen or shorten the delay between them by up to ±60 days. Our simulations suggest large geographic and lake-specific variations in phenological synchrony, provide quantitative predictions of its dependence on physical lake properties and geographic location and highlight research needs concerning its ecological consequences.

Whole-body MRI in oncology: can a single anatomic T2 Dixon sequence replace the combination of T1 and STIR sequences to detect skeletal metastasis and myeloma?

OBJECTIVES: To compare the diagnostic accuracy of a single T2 Dixon sequence to the combination T1+STIR as anatomical sequences used for detecting tumoral bone marrow lesions in whole-body MRI (WB-MRI) examinations. METHODS: Between January 2019 and January 2020, seventy-two consecutive patients (55 men, 17 women, median age = 66 years) with solid (prostate, breast, neuroendocrine) cancers at high risk of metastasis or proven multiple myeloma (MM) prospectively underwent a WB-MRI examination including coronal T1, STIR, T2 Dixon and axial diffusion-weighted imaging sequences. Two radiologists independently assessed the combination of T1+STIR sequences and the fat+water reconstructions from the T2 Dixon sequence. The reference standard was established by consensus reading of WB-MRI and concurrent imaging available at baseline and at 6 months. Repeatability and reproducibility of MRI scores (presence and semi-quantitative count of lesions), image quality (SNR: signal-to-noise, CNR: contrast-to-noise, CRR: contrast-to-reference ratios), and diagnostic characteristics (Se: sensitivity, Sp: specificity, Acc: accuracy) were assessed per-skeletal region and per-patient. RESULTS: Repeatability and reproducibility were at least good regardless of the score, region, and protocol (0.67 ≤ AC1 ≤ 0.98). CRR was higher on T2 Dixon fat compared to T1 (p < 0.0001) and on T2 Dixon water compared to STIR (p = 0.0128). In the per-patient analysis, Acc of the T2 Dixon fat+water was higher than that of T1+STIR for the senior reader (Acc = +0.027 [+0.025; +0.029], p < 0.0001) and lower for the junior reader (Acc = -0.029 [-0.031; -0.027], p < 0.0001). CONCLUSIONS: A single T2 Dixon sequence with fat+water reconstructions offers similar reproducibility and diagnostic accuracy as the recommended combination of T1+STIR sequences and can be used for skeletal screening in oncology, allowing significant time-saving. KEY POINTS: • Replacement of the standard anatomic T1 + STIR WB-MRI protocol by a single T2 Dixon sequence drastically shortens the examination time without loss of diagnostic accuracy. • A protocol based on fat + water reconstructions from a single T2 Dixon sequence offers similar inter-reader agreement and a higher contrast-to-reference ratio for detecting lesions compared to the standard T1 + STIR protocol. • Differences in the accuracy between the two protocols are marginal (+ 3% in favor of the T2 Dixon with the senior reader; -3% against the T2 Dixon with the junior reader).

Local and continental-scale controls of the onset of spring phytoplankton blooms: Conclusions from a proxy-based model.

A key phenological event in the annual cycle of many pelagic ecosystems is the onset of the spring algal bloom (OAB). Descriptions of the factors controlling the OAB in temperate to polar lakes have been limited to isolated studies of single systems and conceptual models. Here we present a validated modelling approach that, for the first time, enables a quantitative prediction of the OAB and a systematic assessment of the processes controlling its timing on a continental scale. We used a weather-driven, one-dimensional lake model to simulate the seasonal dynamics of the underwater light climate in 16 lake types characterized by the factorial combination of four lake depths with four levels of water transparency. We did so at 1962 locations across Western Europe and over 31 years (1979-2009). Assuming that phytoplankton production is light-limited in winter, we identified four patterns of OAB control across lake types and climate zones. OAB timing is controlled by (i) the timing of ice-off in ice-covered clear or shallow lakes, (ii) the onset of thermal stratification in sufficiently deep and turbid lakes and (iii) the seasonal increase in incident radiation in all other lakes, except for (iv) ice-free, shallow and clear lakes in the south, where phytoplankton is not light-limited. The model predicts that OAB timing should respond to two pervasive environmental changes, global warming and browning, in opposite ways. OAB timing should be highly sensitive to warming in lakes where it is controlled by either ice-off or the onset of stratification, but resilient to warming in lakes where it is controlled by incident radiation. Conversely, OAB timing should be most sensitive to browning where it is controlled by incident radiation, but resilient to browning where it is controlled by ice-off or the onset of stratification. Available lake data are consistent with our findings.

Repeatability and reproducibility of ADC measurements: a prospective multicenter whole-body-MRI study.

OBJECTIVES: Multicenter oncology trials increasingly include MRI examinations with apparent diffusion coefficient (ADC) quantification for lesion characterization and follow-up. However, the repeatability and reproducibility (R&R) limits above which a true change in ADC can be considered relevant are poorly defined. This study assessed these limits in a standardized whole-body (WB)-MRI protocol. METHODS: A prospective, multicenter study was performed at three centers equipped with the same 3.0-T scanners to test a WB-MRI protocol including diffusion-weighted imaging (DWI). Eight healthy volunteers per center were enrolled to undergo test and retest examinations in the same center and a third examination in another center. ADC variability was assessed in multiple organs by two readers using two-way mixed ANOVA, Bland-Altman plots, coefficient of variation (CoV), and the upper limit of the 95% CI on repeatability (RC) and reproducibility (RDC) coefficients. RESULTS: CoV of ADC was not influenced by other factors (center, reader) than the organ. Based on the upper limit of the 95% CI on RC and RDC (from both readers), a change in ADC in an individual patient must be superior to 12% (cerebrum white matter), 16% (paraspinal muscle), 22% (renal cortex), 26% (central and peripheral zones of the prostate), 29% (renal medulla), 35% (liver), 45% (spleen), 50% (posterior iliac crest), 66% (L5 vertebra), 68% (femur), and 94% (acetabulum) to be significant. CONCLUSIONS: This study proposes R&R limits above which ADC changes can be considered as a reliable quantitative endpoint to assess disease or treatment-related changes in the tissue microstructure in the setting of multicenter WB-MRI trials. KEY POINTS: • The present study showed the range of R&R of ADC in WB-MRI that may be achieved in a multicenter framework when a standardized protocol is deployed. • R&R was not influenced by the site of acquisition of DW images. • Clinically significant changes in ADC measured in a multicenter WB-MRI protocol performed with the same type of MRI scanner must be superior to 12% (cerebrum white matter), 16% (paraspinal muscle), 22% (renal cortex), 26% (central zone and peripheral zone of prostate), 29% (renal medulla), 35% (liver), 45% (spleen), 50% (posterior iliac crest), 66% (L5 vertebra), 68% (femur), and 94% (acetabulum) to be detected with a 95% confidence level.

3D Whole-Body MRI of the Musculoskeletal System.

With its outstanding soft tissue contrast, spatial resolution, and multiplanar capacities, magnetic resonance imaging (MRI) has become a widely used technique. Whole-body MRI (WB-MRI) has been introduced among diagnostic methods for the staging and follow-up assessment in oncologic patients, and international guidelines recommend its use. In nononcologic applications, WB-MRI is as a promising imaging tool in inflammatory diseases, such as seronegative arthritis and inflammatory myopathies. Technological advances have facilitated the introduction of three-dimensional (3D) almost isotropic sequences in MRI examinations covering the whole body. The possibility to reformat 3D images in any plane with equal or almost equal resolution offers comprehensive understanding of the anatomy, easier disease detection and characterization, and finally contributes to correct treatment planning. This article illustrates the basic principles, advantages, and limitations of the 3D approach in WB-MRI examinations and provides a short review of the literature.

Insights into tissue microstructure using a double diffusion encoding sequence on a clinical scanner: Validation and application to experimental tumor models.

PURPOSE: To present a double diffusion encoding MRI sequence on a clinical scanner to analyze micro-structure and micro-vasculature of tumors. METHODS: The sequence was tested on phantoms, asparaguses, and 2 tumors allografts in a rodent. Results were analyzed using an adapted VERDICT model to estimate microstructural parameters. The technical feasibility of the sequence on a 3T clinical system was assessed on a water phantom. The accuracy of cell size estimation was assessed on asparaguses by comparison with light microscopy. Cell size estimations were also validated when limiting relative angles of diffusion encodings to 0 and 180°. Sensitivities to restricted diffusion and incoherent flow from the vasculature were investigated in experimental tumor models. Values of microstructural parameters in viable and decaying tumor tissue were compared with those obtained from histological analysis. RESULTS: Measurements on the water phantom revealed no significant sequence artifacts and accurate apparent diffusion coefficient values within a 4% relative error. In asparaguses, quartiles and medians of pore size distributions typically deviated less than 6% from light microscopy regardless of whether the full or reduced set of relative angles was used. Signal analyses in tumors showed mixed effects of both blood flow and diffusion restriction. Microstructural parameter estimations in tumors were consistent with histology and allowed clear and histology-proven distinctions between decaying and viable tumor tissue. CONCLUSIONS: Double diffusion encoding with clinical gradients and scan times allows characterization of restricted diffusion and micro-circulation flow in tumors. Our estimated microstructural parameters are promising for further investigations in assessing microstructural evolutions in tumors.

Double Diffusion Encoding for Probing Radiation-Induced Microstructural Changes in a Tumor Model: A Proof-of-Concept Study With Comparison to the Apparent Diffusion Coefficient and Histology.

BACKGROUND: Microstructure analyses are gaining interest in cancer MRI as an alternative to the conventional apparent diffusion coefficient (ADC), of which the determinants remain unclear. PURPOSE: To assess the sensitivity of parameters calculated from a double diffusion encoding (DDE) sequence to changes in a tumor's microstructure early after radiotherapy and to compare them with ADC and histology. STUDY TYPE: Cohort study on experimental tumors. ANIMAL MODEL: Sixteen WAG/Rij rats grafted with one rhabdomyosarcoma fragment in each thigh. Thirty-one were imaged at days 1 and 4, of which 17 tumors received a 20 Gy radiation dose after the first imagery. FIELD STRENGTH/SEQUENCE: 3T. Diffusion-weighted imaging, DDE with flow compensated, and noncompensated measurements. ASSESSMENTS: 1) To compare, after irradiation, DDE-derived parameters (intracellular fraction, cell size, and cell density) to their histological counterparts (fraction of stained area, minimal Feret diameter, and nuclei count, respectively). 2) To compare percentage changes in DDE-derived parameters and ADC. 3) To evaluate the evolution of DDE-derived parameters describing perfusion. STATISTICAL TESTS: Wilcoxon rank sum test. RESULTS: 1) Intracellular fraction, cell size, and cell density were respectively lower (-24%, P < 0.001), higher (+7.5%, P < 0.001) and lower (-38%, P < 0.001) in treated tumors as compared to controls. Fraction of stained area, minimal Feret diameter, and nuclei count were respectively lower (-20%, P < 0.001), higher (+28%, P < 0.001), and lower (-34%, P < 0.001) in treated tumors. 2) The magnitude of ADC's percentage change due to irradiation (16.4%) was superior to the one of cell size (8.4%, P < 0.01) but inferior to those of intracellular fraction (35.5%, P < 0.001) and cell density (42%, P < 0.001). 3) After treatment, the magnitude of the vascular fraction's decrease was higher than the increase of flow velocity (33.3%, vs. 13.3%, P < 0.001). DATA CONCLUSION: The DDE sequence allows quantitatively monitoring the effects of radiotherapy on a tumor's microstructure, whereas ADC only reveals global changes. EVIDENCE LEVEL: 2. TECHNICAL EFFICACY: Stage 4. J. Magn. Reson. Imaging 2020;52:941-951.

Expired Drugs in the Remote Environment.

INTRODUCTION: The British Antarctic Survey Medical Unit works in a very remote area of the world, with several Antarctic bases receiving only a single annual resupply of consumable goods. Pharmaceuticals supplied in this manner will often be approaching or past the end of their nominal shelf life before the following year's resupply. Drugs are transported from the UK via ship; the hold is not temperature controlled, and the ship crosses through the tropics (air temperature 25-30°C for approximately 3 wk). The drugs then must be transported from the ship to the base, often in temperatures substantially below freezing. This study assessed the stability of 5 expired drugs (atropine, nifedipine, flucloxacillin, naproxen, and bendroflumethiazide) returned from Antarctic bases. METHODS: Drugs were opportunistically obtained and tested using stability-indicating assays. RESULTS: All tested drugs were stable. CONCLUSIONS: The results suggest that the studied drugs may be stable beyond expiry, even when not maintained in strictly temperature-controlled conditions.

A comparative study of the sensitivity of diffusion-related parameters obtained from diffusion tensor imaging, diffusional kurtosis imaging, q-space analysis and bi-exponential modelling in the early disease course (24 h) of hyperacute (6 h) ischemic stroke patients.

OBJECTIVES: To compare the sensitivity and early temporal changes of diffusion parameters obtained from diffusion tensor imaging (DTI), diffusional kurtosis imaging (DKI), q-space analysis (QSA) and bi-exponential modelling in hyperacute stroke patients. MATERIALS AND METHODS: A single investigational acquisition allowing the four diffusion analyses was performed on seven hyperacute stroke patients with a 3T system. The percentage change between ipsi- and contralateral regions were compared at admission and 24 h later. Two out of the seven patients were imaged every 6 h during this period. RESULTS: Kurtoses from both DKI and QSA were the most sensitive of the tested diffusion parameters in the few hours following ischemia. An early increase-maximum-decrease pattern of evolution was highlighted during the 24-h period for all parameters proportional to diffusion coefficients. A similar pattern was observed for both kurtoses in only one of two patients. CONCLUSION: Our comparison was performed using identical diffusion encoding timings and on patients in the same stage of their condition. Although preliminary, our findings confirm those of previous studies that showed enhanced sensitivity of kurtosis. A fine time mapping of diffusion metrics in hyperacute stroke patients was presented which advocates for further investigations on larger animal or human cohorts.

Whole-body 3D T1-weighted MR imaging in patients with prostate cancer: feasibility and evaluation in screening for metastatic disease.

PURPOSE: To develop and assess the diagnostic performance of a three-dimensional (3D) whole-body T1-weighted magnetic resonance (MR) imaging pulse sequence at 3.0 T for bone and node staging in patients with prostate cancer. MATERIALS AND METHODS This prospective study was approved by the institutional ethics committee; informed consent was obtained from all patients. Thirty patients with prostate cancer at high risk for metastases underwent whole-body 3D T1-weighted imaging in addition to the routine MR imaging protocol for node and/or bone metastasis screening, which included coronal two-dimensional (2D) whole-body T1-weighted MR imaging, sagittal proton-density fat-saturated (PDFS) imaging of the spine, and whole-body diffusion-weighted MR imaging. Two observers read the 2D and 3D images separately in a blinded manner for bone and node screening. Images were read in random order. The consensus review of MR images and the findings at prospective clinical and MR imaging follow-up at 6 months were used as the standard of reference. The interobserver agreement and diagnostic performance of each sequence were assessed on per-patient and per-lesion bases. RESULTS: The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were significantly higher with whole-body 3D T1-weighted imaging than with whole-body 2D T1-weighted imaging regardless of the reference region (bone or fat) and lesion location (bone or node) (P < .003 for all). For node metastasis, diagnostic performance (area under the receiver operating characteristic curve) was higher for whole-body 3D T1-weighted imaging (per-patient analysis; observer 1: P < .001 for 2D T1-weighted imaging vs 3D T1-weighted imaging, P = .006 for 2D T1-weighted imaging + PDFS imaging vs 3D T1-weighted imaging; observer 2: P = .006 for 2D T1-weighted imaging vs 3D T1-weighted imaging, P = .006 for 2D T1-weighted imaging + PDFS imaging vs 3D T1-weighted imaging), as was sensitivity (per-lesion analysis; observer 1: P < .001 for 2D T1-weighted imaging vs 3D T1-weighted imaging, P < .001 for 2D T1-weighted imaging + PDFS imaging vs 3D T1-weighted imaging; observer 2: P < .001 for 2D T1-weighted imaging vs 3D T1-weighted imaging, P < .001 for 2D T1-weighted imaging + PDFS imaging vs 3D T1-weighted imaging). CONCLUSION: Whole-body MR imaging is feasible with a 3D T1-weighted sequence and provides better SNR and CNR compared with 2D sequences, with a diagnostic performance that is as good or better for the detection of bone metastases and better for the detection of lymph node metastases.

Trophic mismatch requires seasonal heterogeneity of warming.

Climate warming has been shown to advance the phenology of species. Asynchronous changes in phenology between interacting species may disrupt feeding interactions (phenological mismatch), which could have tremendous consequences for ecosystem functioning. Long-term field observations have suggested asynchronous shifts in phenology with warming, whereas experimental studies have not been conclusive. Using proxy-based modeling of three trophic levels (algae, herbivores, and fish), we .show that asynchronous changes in phenology only occur if warming is seasonally heterogeneous, but not if warming is constant throughout the year. If warming is seasonally heterogeneous, the degree and even direction of asynchrony depends on the specific seasonality of the warming. Conclusions about phenological mismatches in food web interactions may therefore produce controversial results if the analyses do not distinguish between seasonally constant and seasonal specific warming. Furthermore, our results suggest that predicting asynchrony between interacting species requires reliable warming predictions that resolve sub-seasonal time scales.

Importance of the autumn overturn and anoxic conditions in the hypolimnion for the annual methane emissions from a temperate lake.

Changes in the budget of dissolved methane measured in a small temperate lake over 1 year indicate that anoxic conditions in the hypolimnion and the autumn overturn period represent key factors for the overall annual methane emissions from lakes. During periods of stable stratification, large amounts of methane accumulate in anoxic deep waters. Approximately 46% of the stored methane was emitted during the autumn overturn, contributing ∼80% of the annual diffusive methane emissions to the atmosphere. After the overturn period, the entire water column was oxic, and only 1% of the original quantity of methane remained in the water column. Current estimates of global methane emissions assume that all of the stored methane is released, whereas several studies of individual lakes have suggested that a major fraction of the stored methane is oxidized during overturns. Our results provide evidence that not all of the stored methane is released to the atmosphere during the overturn period. However, the fraction of stored methane emitted to the atmosphere during overturn may be substantially larger and the fraction of stored methane oxidized may be smaller than in the previous studies suggesting high oxidation losses of methane. The development or change in the vertical extent and duration of the anoxic hypolimnion, which can represent the main source of annual methane emissions from small lakes, may be an important aspect to consider for impact assessments of climate warming on the methane emissions from lakes.

Impact of ecosystem metabolism on CO2 emissions: Insights from high-resolution time series of pH measured in situ.

Lakes and reservoirs are important sources/sinks of atmospheric CO2. Primary production and respiration transforming inorganic to organic carbon and vice versa alter CO2 concentrations in the surface waters and thus affect CO2 emissions. Here we investigate the link between net-production (NEP) and CO2 concentrations and emissions at high temporal resolution over more than two months in a German pump storage reservoir. Continuous in-situ pH measurements in combination with few alkalinity measurements provided concentrations of CO2 and dissolved inorganic carbon (DIC) at high temporal resolution over more than 75 days. Time series of metabolic rates of carbon were determined with an open-water diel pH technique, which utilizes the diel changes in DIC obtained from the observed diel changes in pH and data on alkalinity. During the measuring period, average NEP was positive and CO2 concentrations were typically substantially under-saturated. On average, the reservoir acted as a sink for CO2, whereby CO2 uptake was 39% larger in the evening than in the morning. Only few consecutive days with negative NEP were sufficient to turn the reservoir temporally into a source of CO2. Therefore, the average CO2 uptake determined from continuous data can be 80% larger to 30% smaller than estimates of average uptake based on bi-weekly data. Daily mean NEP explained only 9% and 4% of the variance of daily mean DIC and CO2. Note that NEP is proportional to the time derivative of DIC and therefore not expected to correlate well with DIC in general. Because CO2 changes nonlinearly with DIC, NEP explains less variance of CO2 than of DIC. Numerical experiments confirmed the arguments above and revealed that at positive average NEP the total CO2 uptake over several weeks is not well predicted by average NEP but depends on the detailed temporal pattern of NEP. However, if average NEP is negative, average NEP may be a good predictor of total CO2 emissions. Similar conclusions apply for high and low alkalinity waters, but uptake rates and temporal variability of CO2 emissions are smaller in high than in low alkalinity waters. Assessment of the link between NEP and CO2 emissions requires differentiation between lakes with different alkalinity and, because of the non-linear relationship between NEP and CO2, strongly benefits from data with high temporal resolution especially during time-periods with positive net-production.

Early (72-hour) detection of radiotherapy-induced changes in an experimental tumor model using diffusion-weighted imaging, diffusion tensor imaging, and Q-space imaging parameters: a comparative study.

PURPOSE: To assess and compare the potential of various diffusion-related magnetic resonance imaging (MRI) parameters to detect early radiotherapy (RT)-induced changes in tumors. MATERIALS AND METHODS: Nineteen tumors in a rat model were imaged on a clinical 3T system before and 72 hours after a single RT session. Diffusion imaging was performed using an echo planar sequence containing 16 b-factors and six gradient directions. This allowed us to perform a tensor analysis of mono- and biexponential decays and a q-space analysis. Parametric maps (both trace and fractional anisotropy) were reconstructed for: 2-point apparent diffusion coefficient (ADC), 16-point ADC, biexponential amplitudes and ADCs, and height, width, and kurtosis of the probability density function (PDF). A texture analysis yielded quantities such as average and contrast. The sensitivity of diffusion-related parameters was quantified in terms of the mean relative difference (when comparing pre- and post-RT status). RESULTS: Traces and anisotropies display differences in response to RT. Average traces are most sensitive for ADCs and kurtosis. Average anisotropies are all very sensitive except the slow biexponential component. The best contrast (traces) was found for the ADCs and the width of the PDF. CONCLUSION: ADC performed well, but high b-values analysis added extra sensitive parameters for monitoring early RT-induced changes.

Role of phytoplankton cell size on the competition for nutrients and light in incompletely mixed systems.

We investigate the effects of algal cell size on the competition for nutrients and light in an incompletely mixed water column, employing a spatially explicit variable internal stores approach and previously published allometric scaling relationships for modeling phytoplankton growth. We analyze the interplay between the size-dependent vertical assimilation and uptake profiles and the role of environmental settings such as mixing intensity, nutrient loading and background turbidity for the outcome of competition. Our results suggest that a potentially beneficial factor for resource competition in spatially heterogeneous systems is a low ratio of subsistence nutrient quota to the maximal quota, q(min)/q(max), which is a decreasing function of cell size according to allometric relationships. Environmental parameters such as mixing intensity and nutrient availability are shown to modulate the relevance of the q(min)/q(max) ratio for the competitive outcome and thereby have non-monotonic impacts on the algal size selection. The outcome of competition further depends on the temporal and spatial variability of mixing. In particular, the presence of a metalimnion with low diffusivity and periodic perturbation of the depth of the metalimnion strongly influences the relative success of differently sized algae. This suggests that the anticipated reduction in wind induced mixing events due to climate warming will have context-dependent consequences for algal size selection.

MRI of iron-oxide labelled transplanted hepatocytes in mice: effect of treatment with cyclophosphamide.

PURPOSE: To assess if 1.5T MRI can be used to study the transport to the liver, the intrahepatic distribution and engraftment of iron-oxide labelled hepatocytes in cyclophosphamide-treated and untreated mice. MATERIALS AND METHODS: Hepatocytes were isolated from C57bl/6 mice and were labelled with 1.63 microm iron-oxide particles. Seventeen mice were pretreated with cyclophosphamide to disrupt the sinusoidal endothelium and 15 were left untreated. Seven days after splenic injection of the labelled hepatocytes, T2*-weighted gradient-echo images at 1.5T were acquired. The hepatic transport, distribution and engraftment of the labelled hepatocytes were assessed with signal intensity (SI) and T2* measurements, electron paramagnetic resonance (EPR), texture analysis and histology. RESULTS: Lower hepatic SI (P = 0.005), lower T2* (P = 0.033) and larger number of particles at histology (P = 0.006) suggested increased transport to the liver of labelled hepatocytes in cyclophosphamide-treated mice versus untreated mice. At histology, most particles were located in Kupffer cells. Particles distribution was heterogeneous. No difference between both groups was observed at texture analysis. CONCLUSION: MRI is useful to assess the transport to the liver and intrahepatic distribution of transplanted labelled hepatocytes. The preferential location of iron-oxide particles within Kupffer cells after seven days limits the value of MRI for assessing hepatocyte engraftment.

Vigorous exchange between the Indian and Atlantic oceans at the end of the past five glacial periods.

The magnitude of heat and salt transfer between the Indian and Atlantic oceans through 'Agulhas leakage' is considered important for balancing the global thermohaline circulation. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water formation. Here we show that modern Agulhas waters, which migrate into the south Atlantic Ocean in the form of an Agulhas ring, contain a characteristic assemblage of planktic foraminifera. We use this assemblage as a modern analogue to investigate the Agulhas leakage history over the past 550,000 years from a sediment record in the Cape basin. Our reconstruction indicates that Indian-Atlantic water exchange was highly variable: enhanced during present and past interglacials and largely reduced during glacial intervals. Coherent variability of Agulhas leakage with northern summer insolation suggests a teleconnection to the monsoon system. The onset of increased Agulhas leakage during late glacial conditions took place when glacial ice volume was maximal, suggesting a crucial role for Agulhas leakage in glacial terminations, timing of interhemispheric climate change and the resulting resumption of the Atlantic meridional overturning circulation.

Magnetic resonance elastography for the noninvasive staging of liver fibrosis.

BACKGROUND & AIMS: The purpose of our study was to prospectively compare the success rate and diagnostic accuracy of magnetic resonance elastography, ultrasound elastography, and aspartate aminotransferase to platelets ratio index (APRI) measurements for the noninvasive staging of fibrosis in patients with chronic liver disease. METHODS: We performed a prospective blind comparison of magnetic resonance elastography, ultrasound elastography, and APRI in a consecutive series of patients who underwent liver biopsy for chronic liver disease in a university-based hospital. Histopathologic staging of liver fibrosis according to the METAVIR scoring system served as the reference. RESULTS: A total of 141 patients were assessed. The technical success rate of magnetic resonance elastography was higher than that of ultrasound elastography (133/141 [94%] vs 118/141 [84%]; P = .016). Magnetic and ultrasound elastography, APRI measurements, and histopathologic analysis of liver biopsy specimens were technically successful in 96 patients. The areas under the receiver operating characteristic curves of magnetic resonance elasticity (0.994 for F >or= 2; 0.985 for F >or= 3; 0.998 for F = 4) were larger (P < .05) than those of ultrasound elasticity, APRI, and the combination of ultrasound elasticity and APRI (0.837, 0.709, and 0.849 for F >or= 2; 0.906, 0.816, and 0.936 for F >or= 3; 0.930, 0.820, and 0.944 for F = 4, respectively). CONCLUSIONS: Magnetic resonance elastography has a higher technical success rate than ultrasound elastography and a better diagnostic accuracy than ultrasound elastography and APRI for staging liver fibrosis.

On the calculation of lake metabolic rates: Diel O2 and 18/16O technique.

Metabolic transformations have a major impact on the development of primary producers in aquatic systems and thus affect the dynamics of the entire aquatic food web. Furthermore, metabolic transformations contribute to the carbon budget and thereby influence CO2 emissions from aquatic systems. Several techniques have been developed that aim at an easy assessment of metabolic rates over long time periods or in many systems. The 18/16O technique, which utilizes the isotopic fractionation between 18O and 16O isotopes due to metabolic transformations, is receiving increasing popularity in studies comparing the metabolism in many different lakes and served as basis for the conclusions that production increases with increasing atmospheric CO2 and that surprisingly little terrestrial carbon is recycled in lakes of the arid circumpolar landscape. However, we demonstrate here that the steady state assumptions underlying the 18/16O technique cause large uncertainties in the estimated metabolic rates. This conclusion is based on a sensitivity analysis using a numerical model of dissolved oxygen, DO, and of dissolved 18O, 18ODO, but is also confirmed by published metabolic rates estimated from the 18/16O and the diel O2 techniques. Metabolic rates obtained from the 18/16O technique appear unsuited for correlation analyses between lakes but may provide reasonable estimates in systems with low and long-term stable production. In addition we illustrate that the combination of few 18O measurements with the diel O2 technique and an inverse fitting procedure can improve estimates of metabolic rates and in particular of respiration rates.

Sediment fluxes rather than oxic methanogenesis explain diffusive CH4 emissions from lakes and reservoirs.

Methane emissions from lakes and reservoirs are a major natural source in the global budget of atmospheric CH4. A large fraction of these emissions are due to diffusive transport of CH4 from surface waters to the atmosphere. It was suggested recently that CH4 production in the oxic surface waters is required to compensate for diffusive CH4 emissions from lakes. In contrast, we demonstrate here that typical diffusive CH4-fluxes from sediments in shallow water zones, Fsed,S, suffice to explain CH4 emissions to the atmosphere. Our analysis is based on the combination of an exceptional data set on surface concentrations of CH4 with a mass balance model of CH4 that is focused on the surface mixed layer and considers CH4-fluxes from sediments, lateral transport, gas exchange with the atmosphere, and includes temperature dependencies of sediment fluxes and gas exchange. Fsed,S not only explains observed surface CH4 concentrations but also concentration differences between shallow and open water zones, and the seasonal variability of emissions and lateral concentration distributions. Hence, our results support the hypothesis that diffusive fluxes from shallow sediments and not oxic methanogenesis are the main source of the CH4 in the surface waters and the CH4 emitted from lakes and reservoirs.