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In JoVE (1)
Other Publications (16)
- Journal of Environmental Monitoring : JEM
- Analytical Chemistry
- Environmental Science & Technology
- Environmental Science & Technology
- The Analyst
- Environmental Science & Technology
- International Journal of Hygiene and Environmental Health
- Environmental Science & Technology
- Journal of Magnetic Resonance Imaging : JMRI
- Journal of Chromatography. A
- Magnetic Resonance Imaging
- Journal of Magnetic Resonance Imaging : JMRI
- Brain Structure & Function
- Journal of Forensic Sciences
Articles by Matthew Magnuson in JoVE
Simultaneous fMRI and Electrophysiology in the Rodent Brain
Wen-ju Pan1,2, Garth Thompson1,2, Matthew Magnuson1,2, Waqas Majeed1,2, Dieter Jaeger3, Shella Keilholz1,2
1Biomedical Engineering, Emory University, 2Biomedical Engineering, Georgia Institute of Technology, 3Biology, Emory University
We have developed a method for simultaneous functional magnetic resonance imaging and electrophysiological recording in the rodent brain, providing a platform for the investigation of the relationship between neural activity and the blood oxygenation level dependent (BOLD) MRI signal.
Other articles by Matthew Magnuson on PubMed
Microscale Extraction of Perchlorate in Drinking Water with Low Level Detection by Electrospray-mass Spectrometry
Talanta. Jun, 2000 | Pubmed ID: 18967987
Improper treatment and disposal of perchlorate can be an environmental hazard in regions where solid rocket motors are used, tested, or stored. The solubility and mobility of perchlorate lends itself to ground water contamination, and some of these sources are used for drinking water. Perchlorate in drinking water has been determined at sub-mug l(-1) levels by extraction of the ion-pair formed between the perchlorate ion and a cationic surfactant with electrospray-mass spectrometry detection. Confidence in the selective quantification of the perchlorate ion is increased through both the use of the mass based detection as well as the selectivity of the ion pair. This study investigates several extraction solvents and experimental work-up procedures in order to achieve high sample throughput. The method detection limit for perchlorate based on 3.14sigma(n-1) of seven replicate injections was 300 ng l(-1) (parts-per-trillion) for methylene chloride extraction and 270 ng l(-1) for methyl isobutyl ketone extraction. Extraction with methylene chloride produces linear calibration curves, enabling standard addition to be used to quantify perchlorate in drinking water. Perchlorate determination of a contaminated water compared favorably with results determined by ion chromatography.
Journal of Environmental Monitoring : JEM. Feb, 2002 | Pubmed ID: 11871689
Analytical chemistry is an important tier of environmental protection and has been traditionally linked to compliance and/or exposure monitoring activities for environmental contaminants. The adoption of the risk management paradigm has led to special challenges for analytical chemistry applied to environmental risk analysis. Namely, methods developed for regulated contaminants may not be appropriate and/or applicable to risk management scenarios. This paper contains examples of analytical chemistry applied to risk management challenges broken down by the analytical approach and analyte for some selected work in our laboratory. Specific techniques discussed include stable association complex electrospray mass spectrometry (cESI-MS), gas chromatography-mass spectrometry (GC-MS), split-flow thin cell (SPLITT) fractionation and matrix-assisted laser desorption time of flight mass spectrometry (MALDI-ToF-MS). Specific analytes include haloacetic acids (HAA9), perchlorate, bromate, triazine degradation products, metal-contaminated colloids and Cryptosporidium parvum oocysts.
Analytical Chemistry. May, 2002 | Pubmed ID: 12033338
Trace Metal Leaching Behavior Studied Through the Use of Parametric Modeling of Water Borne Soil Particles Fractionated with a Split-flow Thin Cell
Environmental Science & Technology. Oct, 2002 | Pubmed ID: 12387400
Leaching of particle-bound metals affects the ability of settling ponds and other engineered structures to remove metallic pollutants, and leaching behavior is related to particle size. In this investigation, water borne soil particles were leached and fractionated with a split-flow thin cell, and the metal loadings were quantified as a function of particle size. For comparison of the metal-loading curves, different empirical modeling procedures were investigated to convert the data to a precise functional form suitable for quantitative comparison of changes in differential loading as a function of particle size. Results of this investigation are presented for a soil sample before and after leaching caused by simulated acid rain conditions. Following simulated acid rain leaching, the shape of the differential distribution curves change, and these changes reflect the particle size mediated leaching behavior. For the soil used in this demonstration, simulated acid rain leaching shifted the differential loading toward larger particle sizes, and the magnitude of the shift varied significantly among the metals. Because settling rate decreases as the square of particle size, this could potentially affect management decisions for settling ponds receiving these particles. The high precision afforded by the analysis allows the development of insight into the leaching mechanisms through comparing "partial" acid rain leaching with "total recoverable" leaching by EPA Method 3050.
Effect of UV Irradiation on Organic Matter Extracted from Treated Ohio River Water Studied Through the Use of Electrospray Mass Spectrometry
Environmental Science & Technology. Dec, 2002 | Pubmed ID: 12528657
Ohio River water was treated by settling, sand filtration, and granular activated carbon filtration. It was then irradiated by low-pressure (monochromatic) and medium-pressure (polychromatic) UV lamps to investigate the effects of UV irradiation on the extracted organic matter (EOM). When the EOM, collected by solid phase extraction cartridges, was analyzed by conventional UV spectroscopy and size exclusion chromatography (SEC), no significant changes in the EOM were revealed for various UV doses. Positive and negative electrospray ionization mass spectrometry (ESI-MS) of the EOM produced mass spectra that vary significantly with UV dose. The UV dosage conditions also appear to affect the reactivity of the EOM to subsequent chlorination. The magnitude of the spectral changes is generally greater for medium-pressure lamps than for low pressure and increases with UV exposure. Based on the observed MS peaks, the changes may be due to the presence of lignin, resulting perhaps from photooxidation and/or photo rearrangement of macromolecules in the sample. When chlorination is used for secondary disinfection, these results suggest that it may be important to consider the effects of UV irradiation on the organic matter in the water before applying UV disinfection technology to a particular source water.
The Analyst. Jan, 2003 | Pubmed ID: 12572810
Seven retail hydroponic nitrate fertilizer products, two liquid and five solid, were comparatively analyzed for the perchlorate anion (ClO4-) by ion chromatography (IC) with suppressed conductivity detection, complexation electrospray ionization mass spectrometry (cESI-MS), normal Raman spectroscopy, and infrared spectroscopy using an attenuated total reflectance crystal (ATR-FTIR) coated with a thin film of an organometallic ion-exchange compound. Three of the five solid products were found by all techniques to contain perchlorate at the level of approximately 100-350 mg kg(-1). The remaining products did not contain perchlorate above the detection level of any of the techniques. Comparative analysis using several analytical techniques that depend on different properties of perchlorate allow for a high degree of certainty in both the qualitative and quantitative determinations. This proved particularly useful for these samples, due to the complexity of the matrix. Analyses of this type, including multiple spectroscopic confirmations, may also be useful for other complicated matrixes (e.g., biological samples) or in forensic/regulatory frameworks where data are likely to be challenged. While the source of perchlorate in these hydroponic products is not known, the perchlorate-to-nitrate concentration ratio (w/w) in the aqueous extracts is generally consistent with the historical weight percent of water soluble components in caliche, a nitrate-bearing ore found predominantly in Chile. This ore, which is the only well-established natural source of perchlorate, is mined and used, albeit minimally, as a nitrogen source in some fertilizer products.
Environmental Science & Technology. Apr, 2005 | Pubmed ID: 15871218
International Journal of Hygiene and Environmental Health. 2005 | Pubmed ID: 16078642
Some strains of Penicillium chrysogenum produce a proteinaceous hemolysin, chrysolysinTM, when incubated on sheep's blood agar at 37 degrees C but not at 23 degrees C. However, 92% (11/12) of the indoor air isolates produced hemolysis but only 43% (3/7) of the non-indoor air isolates did so. Chrysolysin is an aggregating protein composed of approximately 2kDa monomers, contains one cysteine amino acid, and has an isoelectric point of 4.85. Treatment of murine macrophage cell line RAW 264.7 with purified chrysolysin caused statistically significant (T-test, p < 0.05) increased production of macrophage inflammatory protein-2 (MIP-2) in a dose dependent manner after 6 h treatment. This suggests that chrysolysin might act to promote the host's inflammatory response after P. chrysogenum exposures.
Quantitative Structure--property Relationships for Enhancing Predictions of Synthetic Organic Chemical Removal from Drinking Water by Granular Activated Carbon
Environmental Science & Technology. Oct, 2005 | Pubmed ID: 16245848
Granular activated carbon is a frequently explored technology for removing synthetic organic contaminants from drinking water sources. The success of this technology relies on a number of factors based not only on the adsorptive properties of the contaminant but also on properties of the water itself, notably the presence of substances in the water which compete for adsorption sites. Because it is impractical to perform field-scale evaluations for all possible contaminants, the pore surface diffusion model (PSDM) has been developed and used to predict activated carbon column performance using single-solute isotherm data as inputs. Many assumptions are built into this model to account for kinetics of adsorption and competition for adsorption sites. This work further evaluates and expands this model, through the use of quantitative structure-property relationships (QSPRs) to predict the effect of natural organic matter fouling on activated carbon adsorption of specific contaminants. The QSPRs developed are based on a combination of calculated topographical indices and quantum chemical parameters. The QSPRs were evaluated in terms of their statistical predictive ability,the physical significance of the descriptors, and by comparison with field data. The QSPR-enhanced PSDM was judged to give results better than what could previously be obtained.
Journal of Magnetic Resonance Imaging : JMRI. Aug, 2009 | Pubmed ID: 19629982
To examine spatiotemporal dynamics of low frequency fluctuations in rat cortex.
Journal of Chromatography. A. Jan, 2010 | Pubmed ID: 20022012
Although the herbicide atrazine has been reported to not react measurably with free chlorine during drinking water treatment, this work demonstrates that at contact times consistent with drinking water distribution system residence times, a transformation of atrazine can be observed. Some transformation products detected through the use of high performance liquid chromatography-electrospray mass spectrometry are consistent with the formation of N-chloro atrazine. The effects of applied chlorine, pH, and reaction time on the transformation reaction were studied to help understand the practical implications of the transformation on the accurate determination of atrazine in drinking waters. The errors in the determination of atrazine are a function of the type of dechlorinating agent applied during sample preparation and the analytical instrumentation utilized. When a reductive dechlorinating agent, such as sodium sulfite or ascorbic acid is used, the quantification of the atrazine can be inaccurate, ranging from 2-fold at pH 7.5 to 30-fold at pH 6.0. The results suggest HPLC/UV and ammonium chloride quenching may be best for accurate quantification. Hence, the results also appear to have implications for both compliance monitoring and health effects studies that utilize gas chromatography analysis with sodium sulfite or ascorbic acid as the quenching agent.
Comparison of Alpha-chloralose, Medetomidine and Isoflurane Anesthesia for Functional Connectivity Mapping in the Rat
Magnetic Resonance Imaging. Sep, 2010 | Pubmed ID: 20456892
Functional connectivity measures based upon low-frequency blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) signal fluctuations have become a widely used tool for investigating spontaneous brain activity in humans. Still unknown, however, is the precise relationship between neural activity, the hemodynamic response and fluctuations in the MRI signal. Recent work from several groups had shown that correlated low-frequency fluctuations in the BOLD signal can be detected in the anesthetized rat - a first step toward elucidating this relationship. Building on this preliminary work, through this study, we demonstrate that functional connectivity observed in the rat depends strongly on the type of anesthesia used. Power spectra of spontaneous fluctuations and the cross-correlation-based connectivity maps from rats anesthetized with alpha-chloralose, medetomidine or isoflurane are presented using a high-temporal-resolution imaging sequence that ensures minimal contamination from physiological noise. The results show less localized correlation in rats anesthetized with isoflurane as compared with rats anesthetized with alpha-chloralose or medetomidine. These experiments highlight the utility of using different types of anesthesia to explore the fundamental physiological relationships of the BOLD signal and suggest that the mechanisms contributing to functional connectivity involve a complicated relationship between changes in neural activity, neurovascular coupling and vascular reactivity.
Functional Connectivity in Blood Oxygenation Level-dependent and Cerebral Blood Volume-weighted Resting State Functional Magnetic Resonance Imaging in the Rat Brain
Journal of Magnetic Resonance Imaging : JMRI. Sep, 2010 | Pubmed ID: 20815055
To directly compare functional connectivity and spatiotemporal dynamics acquired with blood oxygenation level-dependent (BOLD) and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) in anesthetized rats.
Brain Structure & Function. Aug, 2010 | Pubmed ID: 20853181
Correlated low frequency fluctuations in the blood oxygenation level dependent signal have been widely observed in highly connected brain regions and are considered to be indicative of coordinated activity within those regions. A typical functional connectivity MRI study consists of hundreds of time points acquired from thousands of image voxels, and thus exploratory data analysis is a significant challenge. This paper investigates the utilization of analytical methods based upon graph theory that can potentially provide a data-driven approach to examining the relationships between and within groups of voxels. Three algorithms, based on reachable groups, path-length analysis, and hierarchical clustering, are described and evaluated in the relatively simple context of the rodent brain. Analysis indicates that (based on the cross-correlation coefficient) cortical voxels are the most strongly connected network nodes. These voxels exhibit stronger clustering than would be expected in a randomly connected graph, and the amount of clustering is dependent on the cross-correlation threshold chosen. The analysis algorithms identify core groups in somatosensory areas and indicate that left and right somatosensory regions are more strongly connected to each other than to midline cortical areas. The results show that algorithms based on graph theory are well-suited for the data-driven analysis of functional connectivity studies.
Guidelines for the Identification of Unknown Samples for Laboratories Performing Forensic Analyses for Chemical Terrorism*
Journal of Forensic Sciences. Dec, 2011 | Pubmed ID: 22211294
Since the early 1990s, the FBI Laboratory has sponsored Scientific Working Groups to improve discipline practices and build consensus among the forensic community. The Scientific Working Group on the Forensic Analysis of Chemical, Biological, Radiological and Nuclear Terrorism developed guidance, contained in this document, on issues forensic laboratories encounter when accepting and analyzing unknown samples associated with chemical terrorism, including laboratory capabilities and analytical testing plans. In the context of forensic analysis of chemical terrorism, this guidance defines an unknown sample and addresses what constitutes definitive and tentative identification. Laboratory safety, reporting issues, and postreporting considerations are also discussed. Utilization of these guidelines, as part of planning for forensic analysis related to a chemical terrorism incident, may help avoid unfortunate consequences not only to the public but also to the laboratory personnel.
NeuroImage. Jan, 2011 | Pubmed ID: 20728554
Most studies involving spontaneous fluctuations in the BOLD signal extract connectivity patterns that show relationships between brain areas that are maintained over the length of the scanning session. In this study, however, we examine the spatiotemporal dynamics of the BOLD fluctuations to identify common patterns of propagation within a scan. A novel pattern finding algorithm was developed for detecting repeated spatiotemporal patterns in BOLD fMRI data. The algorithm was applied to high temporal resolution T2*-weighted multislice images obtained from rats and humans in the absence of any task or stimulation. In rats, the primary pattern consisted of waves of high signal intensity, propagating in a lateral to medial direction across the cortex, replicating our previous findings (Majeed et al., 2009a). These waves were observed primarily in sensorimotor cortex, but also extended to visual and parietal association areas. A secondary pattern, confined to subcortical regions consisted of an initial increase and subsequent decrease in signal intensity in the caudate-putamen. In humans, the most common spatiotemporal pattern consisted of an alteration between activation of areas comprising the "default-mode" (e.g., posterior cingulate and anterior medial prefrontal cortices) and the "task-positive" (e.g., superior parietal and premotor cortices) networks. Signal propagation from focal starting points was also observed. The pattern finding algorithm was shown to be reasonably insensitive to the variation in user-defined parameters, and the results were consistent within and between subjects. This novel approach for probing the spontaneous network activity of the brain has implications for the interpretation of conventional functional connectivity studies, and may increase the amount of information that can be obtained from neuroimaging data.