Dynamic Contrast-enhanced MR Imaging of Carotid Atherosclerotic Plaque: Model Selection, Reproducibility, and Validation.

Purpose: compare four known pharmacokinetic models for their ability to describe dynamic contrast material-enhanced magnetic resonance (MR) imaging of carotid atherosclerotic plaques, to determine reproducibility, and to validate the results with histologic findings. Materials and Methods: The study was approved by the institutional medical ethics committee. Written informed consent was obtained from all patients. Forty-five patients with 30%-99% carotid stenosis underwent dynamic contrast-enhanced MR imaging. Plaque enhancement was measured at 16 time points at approximately 25-second image intervals by using a gadolinium-based contrast material. Pharmacokinetic parameters (volume transfer constant, Ktrans; extracellular extravascular volume fraction, v e; and blood plasma fraction, v p) were determined by fitting a two-compartment model to plaque and blood gadolinium concentration curves. The relative fit errors and parameter uncertainties were determined to find the most suitable model. Sixteen patients underwent imaging twice to determine reproducibility. Carotid endarterectomy specimens from 16 patients who were scheduled for surgery were collected for histologic validation. Parameter uncertainties were compared with the Wilcoxon signed rank test. Reproducibility was assessed by using the coefficient of variation. Correlation with histologic findings was evaluated with the Pearson correlation coefficient. Results: The mean relative fit uncertainty (+/- standard error) for Ktrans was 10% +/- 1 with the Patlak model, which was significantly lower than that with the Tofts (20% +/- 1), extended Tofts (33% +/- 3), and extended graphical (29% +/- 3) models (P <.001). The relative uncertainty for v p was 20% 6 2 with the Patlak model and was significantly higher with the extended Tofts (46% +/- 9) and extended graphical (35% +/- 5) models (P <.001). The reproducibility (coefficient of variation) for the Patlak model was 16% for Ktrans and 26% for v p. Significant positive correlations were found between Ktrans and the endothelial microvessel content determined on histologic slices (Pearson r = 0.72, P = .005). Conclusion: The Patlak model is most suited for describing carotid plaque enhancement. Correlation with histologic findings validated Ktrans as an indicator of plaque microvasculature, and the reproducibility of Ktrans was good. (C)RSNA, 201

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

This research was financially supported under the National Development Plan, through the Research Stimulus Fund, administered by the Department of Agriculture, Food and the Marine (Grant numbers RSF10-/RD/SC/716 and RSF11S138) and from the Department of Agriculture and Rural Development (Ref: DARD Evidence and Innovation project 13/04/06) for Northern Ireland. The first author gratefully acknowledges funding received from the Teagasc Walsh Fellowship Scheme (Ref: 2012005).peer-reviewedThe accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N2O). The IPCC default emission factor (EF) for N2O from soils is 1% of the N applied, irrespective of its form. However, N2O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N2O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N2O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N2O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81. Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN. Cumulative N2O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.Department of Agriculture and Rural Development for Northern IrelandTeagasc Walsh Fellowship ProgrammeDepartment of Agriculture, Food and the Marin

Endothelin-1 levels and conduit artery mechanical properties in end-stage renal disease

BACKGROUND: Endothelial cell (EC) dysfunction markers are increased in end-stage renal disease (ESRD). The present study focused on the relationship between EC markers, conduit artery wall mechanics and hemodynamics in ESRD. METHODS: In 29 ESRD patients and 16 controls, brachial artery diameter, distension, and wall thickness was measured and circumferential wall stress (CWS) calculated. Shear stress was determined with a shear rate-estimating system. Furthermore, von Willebrand factor antigen (vWF) and endothelin-1 (ET-1) levels were measured. RESULTS: vWF (p = 0.002) and ET-1 (p &lt; 0.001) were higher in ESRD patients and vWF was related to ET-1 (r = 0.70, p = 0.005). Peak (p = 0.001) and mean shear stress (p = 0.003) were significantly lower in ESRD patients, and ET-1 showed an inverse log linear relation with both (peak: r = -0.59, p = 0.016; mean: r = -0.64, p = 0.007). Also, ET-1 was log linearly related to CWS (r = 0.58, p = 0.014). CONCLUSION: These results indicate that, in ESRD, conduit artery shear stress is lower, which might be secondary to an increased peripheral vascular resistance caused by higher ET-1 levels

The effect of flow changes on the arterial system proximal to an arteriovenous fistula for hemodialysis

Arterial remodeling in response to flow changes is controlled by the endothelium, sensing wall shear stress (SS) changes. The present study focuses on the remodeling capacities of the brachial (BA) and radial artery (RA) of 16 renal failure patients after arteriovenous fistula creation. Pre- and postoperatively at predetermined time-points, diameter, wall thickness and peak and mean SS were assessed. After arteriovenous fistula creation, acute increases in BA SS (p = 0.018) and lumen diameter (p = 0.028) were observed. The diameter further increased in the next year (p = 0.023), whereas BA SS remained unchanged. RA SS and diameter increased acutely (p = 0.005) and remained unaltered after 1 y. RA wall thickness tended to decrease acutely (p = 0.059) and increased steadily during 1 y (p = 0.008). BA and RA diameter acutely increased after an acute SS rise and remained augmented after 1 y. Also, the RA vessel wall thickness enlarged, indicating structural remodeling. After 1 y, however, these changes did not result in SS restoration. (E-mail: )

In Situ Preservation of Kidneys From Donors After Cardiac Death: Results and Complications

OBJECTIVES:: To describe the results and complications of in situ preservation (ISP) of kidneys from donors after cardiac death (DCD). BACKGROUND:: DCD donors are increasingly being used to expand the pool of donor kidneys. ISP reduces warm ischemic injury which is associated with DCD donation. METHODS:: Insertion of a double-balloon triple-lumen catheter allows selective perfusion of the abdominal aorta to preserve the kidneys in situ. From January 2001 until August 2005, 133 ISP procedures were initiated in our procurement area. RESULTS:: Fifty-six (42%) ISP procedures led to transplantation; in the remaining 77 cases (58%), the donation procedure was abandoned or both kidneys were discarded because of ISP complications (n = 31), poor graft quality (n = 23), no consent for donation (n = 13), medical contraindications (n = 8), or unknown cause (n = 2). Increasing donor age (odds ratio (OR) 1.06 per year, P < 0.001) and uncontrolled DCD donation (OR 5.4, P < 0.001) were independently correlated with ISP complications. After transplantation, prolonged double-balloon triple-lumen catheter insertion time was an independent predictor of graft failure (OR 2.0, P = 0.05). Selected controlled DCD donors were managed by rapid laparotomy and direct aortic cannulation; graft survival of these kidneys was superior to kidneys from controlled DCD donors managed by ISP. CONCLUSIONS:: A minority of initiated ISP procedures led to transplantation, resulting in a high workload compared with donation after brain death. The association between increasing catheter insertion time and inferior graft outcome emphasizes the need for fast and effective surgery. Therefore, rapid laparotomy with direct aortic cannulation is preferred over ISP in controlled DCD donation. Despite these limitations, we have expanded our donor pool 3- to 4-fold by procuring DCD kidneys that were preserved in situ

Assessment of human atherosclerotic carotid plaque components with multisequence MR imaging: initial experience

PURPOSE: To prospectively determine, by using a stepwise logistic regression model, the optimal magnetic resonance (MR) weighting (ie, pulse sequence) combinations for plaque assessment and corresponding cutoff values of relative signal intensities (rSIs). MATERIALS AND METHODS: Institutional review board approval and patient consent were obtained. Eleven patients (seven men, four women; mean age ± standard deviation, 68 years ± 4) with symptomatic carotid disease and stenosis of more than 70% were investigated at MR imaging before carotid endarterectomy. The MR images were matched with histologic features of the endarterectomy specimens (reference standard). The rSIs (compared with that of muscle tissue) from regions of interest were assessed qualitatively and semiquantitatively. For all major components (calcification, lipid core, intraplaque hemorrhage, and fibrous tissue), optimal cutoff points for the rSIs were determined for five MR weightings by means of receiver operating characteristic curves. The best predicting combinations of these five dichotomized MR weightings were selected by means of stepwise logistic regression analysis. The potential sensitivity and specificity of MR imaging for vulnerable plaque with hemorrhage and/or lipid core were determined. RESULTS: The same optimal MR weighting combinations for identifying the four plaque components were found with qualitative and semiquantitative analysis. Sensitivity and specificity for vulnerable plaque were 93% (95% confidence interval: 77%, 99%) and 96% (95% confidence interval: 86%, 100%), respectively, for the qualitative analysis and 76% (95% confidence interval: 56%, 90%) and 100% (95% confidence interval: 93%, 100%) for the semiquantitative analysis. CONCLUSION: This study demonstrates the potential of a systematic approach of atherosclerotic plaque assessment with multisequence MR imaging by using the information provided from five different MR weightings in a stepwise logistic regression model. © RSNA, 2005