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A Bit of History
Published in Luisa Ciobanu, Microscopic Magnetic Resonance Imaging, 2017
Magnetic resonance microscopy has been initially defined as magnetic resonance imaging with spatial resolutions on the order of one hundred microns (Glover, 2002; Johnson, 1986) . At such resolutions MRM allows the investigation of small animals, mice in particular with adequate anatomical detail. In this category performing in vivo longitudinal studies represents one of the main advantages of MRM compared to other imaging techniques. A review of the main MRM applications to live animal imaging is available in Ref. (Badea, 2013). The focus of this book is on magnetic resonance microscopy studies with resolutions between several microns and several tens of microns (which we refer to as high‐resolution MRM). Such studies aim at visualizing single cells or small groups of cells and are typically performed on ex vivo or in vitro tissue samples. Recent technological advances made possible the visualization of mammalian neurons,⋅ such investigations are, howeverJ very time consuming, preventing dynamic investigations. Systems containing large neurons are definitely advantageous for high‐resolution MRM studies. Among these, the marine mollusk Aplysia has the largest somatic cells in the animal kingdom. In vertebrates, only eggs can be larger In the first part of this chapter Section 7.1, we introduce the Aplysia as model system for high‐resolution MRM studies, as it will be used by the majority of the applications described in the remainder of the book. In the second part we present a brief history of single cell MR microscopy and a survey of recent advances.
Routine and Special Techniques in Toxicologic Pathology
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Daniel J. Patrick, Matthew L. Renninger, Peter C. Mann
MRI uses nuclear magnetic resonance, and the signal is primarily derived from the hydrogen nuclei (protons) of water molecules. The technique uses a powerful magnetic field to align the magnetization of atoms in the organism and a pulse of radiofrequency to alter the alignment of this magnetization. The scanner then detects the magnetic field to produce an image of the scanned area. Unlike radiography or CT, no ionizing radiation is used. Intravenous contrast agents are used to enhance signal and help delineate vessels or tumors (Pathak et al. 2010). MRI is most useful for imaging soft tissues, especially those with little density contrast such as the liver or brain and is most frequently used to provide anatomic images and delineate lesions such as tumors or areas of necrosis. Magnetic resonance microscopy is MRI with resolutions of better than 100 μm3. Advantages of this technique include high resolution (roughly 10–100 μm with no limit of depth) and high soft-tissue contrast; disadvantages include limited molecular applications and long scanning times (Ying and Monticello 2006). In vivo MRI allows for longitudinal evaluations (repeated evaluations of the same animal over a period), and ex vivo MRI of fixed tissues allows for evaluation of multiple planes through the intact tissue, providing a thorough examination while allowing for subsequent histology and microscopic evaluation (Tempel-Brami 2015). Functional information can be gathered in a related technique known as MRS, which provides information on particular endogenous biochemicals (metabolites) since a specific pattern of metabolites can be associated with certain diseases and tumors or on the concentration and distribution of magnetic nuclear isotope–labeled drugs in tissues (Willmann et al. 2008).
Non-destructive approaches for assessing biofouling of household reverse osmosis membranes
Published in Biofouling, 2018
Stephen D. Markwardt, Nirmala Ronnie, Anne K. Camper
Noting the limitations of the above methods, there is a need for non-destructive approaches to determine the type and extent of membrane biofouling so that action can be taken to prevent irreversible damage. Several approaches to this have been investigated, including feed water assays, including assimilable organic carbon (Vrouwenvelder and van der Kooij 2001; Vrouwenvelder et al. 2011b) and biofilm formation rate (Vrouwenvelder and van der Kooij 2001; Vrouwenvelder et al. 2011a, 2011b); the use of membrane fouling simulators (Vrouwenvelder et al. 2011a, 2011b), measuring specific oxygen consumption rate to equate oxygen consumption to biomass (Kappelhof et al. 2003; Farhat et al. 2015), counting bacterial cells in retentate water using flow cytometry (Dixon et al. 2012), applying a fluorescence spectrum-based assessment to analyze for organism-produced extracellular polymeric substances (EPS) in the retentate (Hwang et al. 2012), using electrical impedance spectroscopy where shifts in potential across the membrane surface are measured (Kavanagh et al. 2009; Sim et al. 2013), employing surface-enhanced Raman spectroscopy in a simulator (Kögler et al. 2016), the use of optical coherence tomography for imaging feed spacer fouling (West et al. 2016) and imaging membrane surfaces with nuclear magnetic resonance microscopy to detect biofouling (Graf von der Schulenburg et al. 2008; Pintelon et al. 2010; Vrouwenvelder et al. 2011a; van Loosdrecht et al., 2012; Fridjonsson et al. 2015). These methods show promise, but most are suited for large RO plants with laboratories that contain sophisticated instruments. The industry still needs economic, easily validated methods suitable for both large and small systems so that RO membrane design and operation can be advanced. This is critical for household units that treat questionable water sources for potable use, since fouling and subsequent loss of membrane integrity may contribute to pathogen breakthrough, especially viruses (Mia et al. 2004; Antony et al. 2012).