Determination of bioavailable phosphorus in water samples using bioassay methods.

The total phosphorus analyte (TP) has a long history of use in monitoring and regulatory applications relating to management of cultural eutrophication in freshwaters. It has become apparent, however, that the fraction of the TP analyte ultimately available to support algal growth varies significantly spatially (within a system), seasonally, and among systems. The algal bioassay methods described here provide an approach for determining the bioavailable fraction of the three operationally defined components of TP: soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP), and particulate phosphorus (PP) in effluents and tributaries discharging to lakes and reservoirs. Application of the technique facilitates a quantitative ranking and targeting of bioavailable phosphorus sources for management.•One congruent method to fractionate particulate and soluble phosphorus (found in aquatic samples) into bioavailable and unavailable fractions was developed based on compilation, adaptation and expansion of two methods from the late 1970s and early 1980s.•Detailed descriptions for culturing phosphorus-starved algae, sub-sampling schedules, kinetics determination, and data presentation are provided•Reproducibility is demonstrated by replication and closure of a mass balance on phosphorus.

Multidimensional growth measurements of abdominal aortic aneurysms.

BACKGROUND: Monitoring the expansion of abdominal aortic aneurysms (AAAs) is critical to avoid aneurysm rupture in surveillance programs, for instance. However, measuring the change of the maximum diameter over time can only provide limited information about AAA expansion. Specifically, regions of fast diameter growth may be missed, axial growth cannot be quantified, and shape changes of potential interest for decisions related to endovascular aneurysm repair cannot be captured. METHODS: This study used multiple centerline-based diameter measurements between the renal arteries and the aortic bifurcation to quantify AAA growth in 51 patients from computed tomography angiography (CTA) data. Criteria for inclusion were at least 1 year of patient follow-up and the availability of at least two sufficiently high-resolution CTA scans that allowed an accurate three-dimensional reconstruction. Consequently, 124 CTA scans were systematically analyzed by using A4clinics diagnostic software (VASCOPS GmbH, Graz, Austria), and aneurysm growth was monitored at 100 cross-sections perpendicular to the centerline. RESULTS: Monitoring diameter development over the entire aneurysm revealed the sites of the fastest diameter growth, quantified the axial growth, and showed the evolution of the neck morphology over time. Monitoring the development of an aneurysm's maximum diameter or its volume over time can assess the mean diameter growth (r = 0.69, r = 0.77) but not the maximum diameter growth (r = 0.43, r = 0.34). The diameter growth measured at the site of maximum expansion was ~16%/y, almost four times larger than the mean diameter expansion of 4.4%/y. The sites at which the maximum diameter growth was recorded did not coincide with the position of the maximum baseline diameter (ρ = 0 .12; P = .31). The overall aneurysm sac length increased from 84 to 89 mm during the follow-up (P < .001), which relates to the median longitudinal growth of 3.5%/y. The neck length shortened, on average, by 6.2% per year and was accompanied by a slight increase in neck angulation. CONCLUSIONS: Neither maximum diameter nor volume measurements over time are able to measure the fastest diameter growth of the aneurysm sac. Consequently, expansion-related wall weakening might be inappropriately reflected by this type of surveillance data. In contrast, localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements over the entire aneurysm sac. This information might further reinforce the quality of aneurysm surveillance programs.

Retrospective analyses of inputs of municipal wastewater effluent and coupled impacts on an urban lake.

A retrospective review and analysis are presented of the evolution of treatment, point of discharge considerations, and constituent loading from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), and the coupled water quality effects on the receiving urban lake (Onondaga Lake, New York) from the early 1970s to 2010. The analysis is based on long-term monitoring of the discharge, Onondaga Lake, and a nearby river system considered as a potential alternate to receive the effluent. The Metro discharge is extraordinarily large relative to the lake's hydrologic budget, representing approximately 25% of the total inflow, greater than for any other lake in the United States. The large loads of nitrogen and phosphorus received from the facility resulted in severe water quality effects in the lake during the early portion of record, including (1) violations of standards to protect against toxic effects of ammonia and nitrite, (2) violations of the water clarity standard for swimming safety, (3) exceedances of a limit for the summer average concentration of total phosphorus in the upper waters, and (4) lakewide violations of the oxygen standard during fall turnover. The effects of Metro were compounded by effects of discharges from soda ash/chlor-alkali and pharmaceutical manufacturing facilities. The sedimentary record of the lake indicates that even greater levels of cultural eutrophication prevailed before the monitoring commenced. Dramatic improvements in the water quality of the lake were achieved in recent years by implementing advanced treatment technologies. Exceedances of receiving water limits in the lake were eliminated, with the exception of the total phosphorus limit. A zebra mussel invasion compromised the oxygen resources and assimilative capacity of the nearby river for more than 15 years. This eliminated an option, previously supported by managers, of full diversion of the Metro effluent to the river.

Modeling riverine pathogen fate and transport in Mexican rural communities and associated public health implications.

The discharge of untreated or poorly treated wastewater to river systems remains a major problem affecting public and environmental health, particularly in rural communities of less developed countries. One of the primary goals in setting policies for wastewater management is to reduce risks to human health associated with microbial contamination of receiving water. In this study, we apply a surface water quality model to develop an Escherichia coli based indicator that reflects the quality of surface water and the potential impact to recreational users in a large, rural river in northwest Mexico (upper Sonora River). The model assesses the relative importance of streamflow variations and the uncertainty in E. coli removal coefficient parameters for the predictions of E. coli concentrations in the river. Given the sparse information on streamflow, we use a physically-based, distributed hydrologic model to generate tributary contributions to the river. We determined the best estimate and uncertainty of E. coli removal rates to explore the impacts of parameter uncertainty on the transport of E. coli downstream from two wastewater discharge zones. Our results depict the regions in the river that are in noncompliance with fresh water pathogen norms. The impact of streamflow variability and uncertainty in the removal rates of pathogen indicators was used to derive a range of river distances in noncompliance. The comparison between two sites with different streamflow behaviors was used to illustrate the impacts of streamflow spatiotemporal variability on pathogen indicators. We derive a simple relationship that can be used to assess the relative importance of dilution (ratio of wastewater discharge to river discharge) and pathogen removal (ratio of residence time to reaction time).

Factors diminishing the effectiveness of phosphorus loading from municipal effluent: critical information for TMDL analyses.

Factors that diminish the effectiveness of phosphorus inputs from a municipal wastewater treatment facility (Metro) in contributing to phosphorus levels and its availability to support algae growth in a culturally eutrophic urban lake (Onondaga Lake, NY) were characterized and quantified. These factors included the bioavailability and settling characteristics of particulate phosphorus from this effluent, the dominant form (70%) of phosphorus in this input, and the plunging of the discharge to stratified layers in the lake. Supporting studies included: (1) chemical and morphometric characterization of the phosphorus-enriched particles of this effluent, compared to particle populations of the tributaries and lake, with an individual particle analysis technique; (2) conduct of algal bioavailability assays of the particulate phosphorus of the effluent; (3) conduct of multiple size class settling velocity measurements on effluent particles; and (4) determinations of the propensity of the discharge to plunge, and documentation of plunging through three-dimensional monitoring of a tracer adjoining the outfall. All of these diminishing effects were found to be operative for the Metro effluent in Onondaga Lake and will be integrated into a forthcoming phosphorus "total maximum daily load" analysis for the lake, through appropriate representation in a supporting mechanistic water quality model. The particulate phosphorus in the effluent was associated entirely with Fe-rich particles formed in the phosphorus treatment process. These particles did not contribute to concentrations in pelagic portions of the lake, due to local deposition associated with their large size. Moreover, this particulate phosphorus was found to be nearly entirely unavailable to support algae growth. While substantial differences are to be expected for various inputs, the effective loading concept and the approaches adopted here to assess the diminishing factors are broadly applicable.

In vitro angioplasty of atherosclerotic human femoral arteries: analysis of the geometrical changes in the individual tissues using MRI and image processing.

Existing atherosclerotic plaque imaging techniques such as intravascular ultrasound, multidetector computed tomography, optical coherence tomography, and high-resolution magnetic resonance imaging (hrMRI) require computerized methods to separate and analyze the plaque morphology. In this work, we perform in vitro balloon angioplasty experiments with 10 human femoral arteries using hrMRI and image processing. The vessel segments contain low-grade to high-grade lesions with very different plaque compositions. The experiments are designed to mimic the in vivo situation. We use a semi-automatic image processing tool to extract the three-dimensional (3D) geometries of the tissue components at four characteristic stages of the angioplasty procedure. The obtained geometries are then used to determine geometrical and mechanical indices in order to characterize, classify, and analyze the atherosclerotic plaques by their specific geometrical changes. During inflation, three vessels ruptured via helical crack propagation. The adventitia, media, and intima did not preserve their area/volume during inflation; the area changes of the lipid pool during inflation were significant. The characterization of changes in individual 3D tissue geometries, together with tissue-specific mechanical properties, may serve as a basis for refined finite element (FE) modeling, which is key to better understand stress evolution in various atherosclerotic plaque configurations.

Micromechanical characterization of intra-luminal thrombus tissue from abdominal aortic aneurysms.

The reliable assessment of Abdominal Aortic Aneurysm rupture risk is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. Intra-luminal thrombus (ILT) has multiple biomechanical and biochemical impacts on the underlying aneurysm wall and thrombus failure might be linked to aneurysm rupture. Histological slices from 7 ILTs were analyzed using a sequence of automatic image processing and feature analyzing steps. Derived microstructural data was used to define Representative Volume Elements (RVE), which in turn allowed the estimation of microscopic material properties using the non-linear Finite Element Method. ILT tissue exhibited complex microstructural arrangement with larger pores in the abluminal layer than in the luminal layer. The microstructure was isotropic in the abluminal layer, whereas pores started to orient along the circumferential direction towards the luminal site. ILT's macroscopic (reversible) deformability was supported by large pores in the microstructure and the inhomogeneous structure explains in part the radially changing macroscopic constitutive properties of ILT. Its microscopic properties decreased just slightly from the luminal to the abluminal layer. The present study provided novel microstructural and micromechanical data of ILT tissue, which is critically important to further explore the role of the ILT in aneurysm rupture. Data provided in this study allow an integration of structural information from medical imaging for example, to estimate ILT's macroscopic mechanical properties.

Hemodynamics of the normal aorta compared to fusiform and saccular abdominal aortic aneurysms with emphasis on a potential thrombus formation mechanism.

Abdominal Aortic Aneurysms (AAAs), i.e., focal enlargements of the aorta in the abdomen are frequently observed in the elderly population and their rupture is highly mortal. An intra-luminal thrombus is found in nearly all aneurysms of clinically relevant size and multiply affects the underlying wall. However, from a biomechanical perspective thrombus development and its relation to aneurysm rupture is still not clearly understood. In order to explore the impact of blood flow on thrombus development, normal aortas (n = 4), fusiform AAAs (n = 3), and saccular AAAs (n = 2) were compared on the basis of unsteady Computational Fluid Dynamics simulations. To this end patient-specific luminal geometries were segmented from Computerized Tomography Angiography data and five full heart cycles using physiologically realistic boundary conditions were analyzed. Simulations were carried out with computational grids of about half a million finite volume elements and the Carreau-Yasuda model captured the non-Newtonian behavior of blood. In contrast to the normal aorta the flow in aneurysm was highly disturbed and, particularly right after the neck, flow separation involving regions of high streaming velocities and high shear stresses were observed. Naturally, at the expanded sites of the aneurysm average flow velocity and wall shear stress were much lower compared to normal aortas. These findings suggest platelets activation right after the neck, i.e., within zones of pronounced recirculation, and platelet adhesion, i.e., thrombus formation, downstream. This mechanism is supported by recirculation zones promoting the advection of activated platelets to the wall.

A methodology to analyze changes in lipid core and calcification onto fibrous cap vulnerability: the human atherosclerotic carotid bifurcation as an illustratory example.

A lipid core that occupies a high proportion of the plaque volume in addition to a thin fibrous cap is a predominant indicator of plaque vulnerability. Nowadays, noninvasive imaging modalities can identify such structural components, however, morphological criteria alone cannot reliably identify high-risk plaques. Information, such as stresses in the lesion's components, seems to be essential. This work presents a methodology able to analyze the effect of changes in the lipid core and calcification on the wall stresses, in particular, on the fibrous cap vulnerability. Using high-resolution magnetic resonance imaging and histology of an ex vivo human atherosclerotic carotid bifurcation, a patient-specific three-dimensional geometric model, consisting of four tissue components, is generated. The adopted constitutive model accounts for the nonlinear and anisotropic tissue behavior incorporating the collagen fiber orientation by means of a novel and robust algorithm. The material parameters are identified from experimental data. A novel stress-based computational cap vulnerability index is proposed to assess quantitatively the rupture-risk of fibrous caps. Nonlinear finite element analyses identify that the highest stress regions are located at the vicinity of the shoulders of the fibrous cap and in the stiff calcified tissue. A parametric analysis reveals a positive correlation between the increase in lipid core portion and the mechanical stress in the fibrous cap and, hence, the risk for cap rupture. The highest values of the vulnerability index, which correlate to more vulnerable caps, are obtained for morphologies for which the lipid cores were severe; heavily loaded fibrous caps were thus detected. The proposed multidisciplinary methodology is able to investigate quantitatively the mechanical behavior of atherosclerotic plaques in patient-specific stenoses. The introduced vulnerability index may serve as a more quantitative tool for diagnosis, treatment and prevention.

Dissection properties of the human aortic media: an experimental study.

Aortic dissection occurs frequently and is clinically challenging; the underlying mechanics remain unclear. The present study investigates the dissection properties of the media of 15 human abdominal aortas (AAs) by means of direct tension tests (n=8) and peeling tests (n=12). The direct tension test demonstrates the strength of the media in the radial direction, while the peeling test allows a steady-state investigation of the dissection propagation. To explore the development of irreversible microscopic changes during medial dissection, histological images (n=8) from four AAs at different peeling stages are prepared and analyzed. Direct tension tests of coin-shaped medial specimens result in a radial failure stress of 140.1+/-15.9 kPa (mean+/-SD, n=8). Peeling tests of rectangular-shaped medial strips along the circumferential and axial directions provide peeling force/width ratios of 22.9+/-2.9 mN/mm (n=5) and 34.8+/-15.5 mN/mm (n=7); the related dissection energies per reference area are 5.1+/-0.6 mJ/cm(2) and 7.6+/-2.7 mJ/cm(2), respectively. Although student's t-tests indicate that force/width values of both experimental tests are not significantly different (alpha=0.05, p=0.125), the strikingly higher resisting force/width obtained for the axial peeling tests is perhaps indicative of anisotropic dissection properties of the human aortic media. Peeling in the axial direction of the aorta generates a remarkably "rougher" dissection surface with respect to the surface generated by peeling in the circumferential direction. Histological analysis of the stressed specimens reveals that tissue damage spreads over approximately six to seven elastic laminae, which is about 15-18% of the thickness of the abdominal aortic media, which forms a pronounced cohesive zone at the dissection front.

Layer-specific 3D residual deformations of human aortas with non-atherosclerotic intimal thickening.

Data relating to residual deformations in human arteries are scarce. In this paper we investigate three-dimensional residual deformations for intact strips and for their separate layers from human aortas in their passive state. From 11 abdominal aortas with identified anamnesis, 16 pairs of rings and axial strips were harvested, and the rings cut open. After 16 h images of the resulting geometries were recorded, and the strips were separated into their three layers; after another 6 h images were again recorded. Image processing and analysis was then used to quantify residual stretches and curvatures. For each specimen histological analysis established that the intima, media and adventitia were clearly separated, and the separation was atraumatic. Axial in situ stretches were determined to be 1.196+/-0.084. On separation, the strips from the adventitia and media shortened (between 4.03 and 8.76% on average), while the intimal strips elongated on average by 3.84% (circumferential) and 4.28% (axial) relative to the associated intact strips. After separation, the adventitia from the ring sprang open by about 180 degrees on average, becoming flat, the intima opened only slightly, but the media sprang open by more than 180 degrees (as did the intact strip). The adventitia and intima from the axial strips remained flat, while the media (and the intact strip) bent away from the vessel axis. This study has shown that residual deformations are three dimensional and cannot be described by a single parameter such as 'the' opening angle. Their quantification and modeling therefore require consideration of both stretching and bending, which are highly layer-specific and axially dependent.

3-D reconstruction of tissue components for atherosclerotic human arteries using ex vivo high-resolution MRI.

Automatic computer-based methods are well suited for the image analysis of the different components in atherosclerotic plaques. Although several groups work on such analysis some of the methods used are oversimplified and require improvements when used within a computational framework for predicting meaningful stress and strain distributions in the heterogeneous arterial wall under various loading conditions. Based on high-resolution magnetic resonance imaging of excised atherosclerotic human arteries and a series of two-dimensional (2-D) contours we present a segmentation tool that permits a three-dimensional (3-D) reconstruction of the most important tissue components of atherosclerotic arteries. The underlying principle of the proposed approach is a model-based snake algorithm for identifying 2-D contours, which uses information about the plaque composition and geometric data of the tissue layers. Validation of the computer-generated tissue boundaries is performed with 100 MR images, which are compared with the results of a manual segmentation performed by four experts. Based on the Hausdorff distance and the average distance for computer-to-expert differences and the interexpert differences for the outer boundary of the adventitia, the adventitia-media, media-intima, intima-lumen and calcification boundaries are less than 1 pixel (0.234 mm). The percentage statistic shows similar results to the modified Williams index in terms of accuracy. Except for the identification of lipid-rich regions the proposed algorithm is automatic. The nonuniform rational B-spline-based computer-generated 3-D models of the individual tissue components provide a basis for clinical and computational analysis.

An automatic nonrigid registration for stained histological sections.

Automatic computer-based analyses of histological sections which are differently stained require that they are related to each other. Most registration methods are only able to perform rigid-body motion and are sensitive to noise and artifacts. Histological images, however, are accompanied by several artifacts and different contrasts, which require a nonrigid registration. In this paper, we present a hierarchical nonrigid registration algorithm able to align images, which contain minor image artifacts. The algorithm requires no a priori knowledge of the true image. The hierarchical design of the algorithm enhances robustness and accuracy, and saves computational costs. The proposed algorithm is decomposed into a fast, coarse, rigid registration step and a slower, but finer, nonrigid step. For the coarse registration, we use image pyramids, while for the second step, we combine a point-based registration with an elastic thin-plate spline interpolation. Accuracy tests, performed for 20 histological images obtained from human arteries, have shown that the error measure is acceptable, and that the image noise does not cause a problem. The associated convergence rate of the mean pixel displacement error during the rigid and nonrigid registrations is satisfying. The algorithm can be applied to various multicontrast elastic registration problems in medical imaging and may be extended to three dimensions.

Diffusion tensor imaging using single-shot SENSE-EPI.

SENSitivity Encoding (SENSE) greatly enhances the quality of diffusion-weighted echo-planar imaging (EPI) by reducing blurring and off-resonance artifacts. Such improvement would also be desirable for diffusion tensor imaging (DTI), but measures derived from the diffusion tensor can be extremely sensitive to any kind of image distortion. Whether DTI is feasible in combination with SENSE has not yet been explored, and is the focus of this study. Using a SENSE-reduction factor of 2, DTI scans in eight healthy volunteers were carried out with regular- and high-resolution acquisition matrices. To further improve the stability of the SENSE reconstruction, a new coil-sensitivity estimation technique based on variational calculus and the principles of matrix regularization was applied. With SENSE, maps of the trace of the diffusion tensor and of fractional anisotropy (FA) had improved spatial resolution and less geometric distortion. Overall, the geometric distortions were substantially removed and a significant resolution enhancement was achieved with almost the same scan time as regular EPI. DTI was even possible without the use of quadrature body coil (QBC) reference scans. Geometry-factor-related noise enhancement was only discernible in maps generated with higher-resolution matrices. Error boundaries for residual fluctuations in SENSE reconstructions are discussed. Our results suggest that SENSE can be combined with DTI and may present an important adjunct for future neuroimaging applications of this technique.