In vivo assessment of nodularin-induced hepatotoxicity in the rat using magnetic resonance techniques (MRI, MRS and EPR oximetry)

Acute nodularin-induced hepatotoxicity was assessed in vivo, in rats using magnetic resonance (MR) techniques, including MR imaging (MRI), MR spectroscopy (MRS), and electron paramagnetic resonance (EPR) oximetry. Nodularin is a cyclic hepatotoxin isolated from the cyanobacterium Nodularia spumigena. Three hours following the intraperitoneal (i.p.) administration of nodularin (LD50), a region of 'damage', characterized by an increase in signal intensity, was observed proximal to the porta hepatis (PH) region in T2-weighted MR images of rat liver. Image analysis of these regions of apparent 'damage' indicated a statistically significant increase in signal intensity around the PH region following nodularin administration, in comparison with controls and regions peripheral to the PH region. An increase in signal intensity was also observed proximal to the PH region in water chemical shift selective images (CSSI) of nodularin-treated rat livers, indicating that the increased signal observed by MRI is an oedematous response to the toxin. Microscopic assessment (histology and electron microscopy) and serum liver enzyme function tests (aminotransferase (ALT) and aspartate ALT (AST)) confirmed the nodularin-induced tissue injury observed by MRI. In vivo and in vitro MRS was used to detect alterations in metabolites, such as lipids, Glu+Gln, and choline, during the hepatotoxic response (2-3 h post-exposure). Biochemical assessment of perchloric acid extracts of nodularin-treated rat livers were used to confirm the MRS results. In vivo EPR oximetry was used to monitor decreasing hepatic pO2 (approximately 2-fold from controls) 2-3 h following nodularin exposure. In vivo MR techniques (MRI, MRS and EPR oximetry) are able to highlight effects that may not have been evident in single end point studies, and are ideal methods to follow tissue injury progression in longitudinally, increasing the power of a study through repeated measures, and decreasing the number of animals to perform a similar study using histological or biochemical techniques.     

Magnetic resonance spectroscopy and measurement of tau epitopes of autopsy proven sporadic Creutzfeldt-Jakob disease in a patient with non-specific initial EEG, MRI and negative 14-3-3 immunoblot

Limited potential of electroencephalogram (EEG), magnetic resonance images (MRI) and cerebrospinal fluid (CSF) test for 14-3-3 protein in the clinical diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) resulted in developments in diagnostic premortem tehniques. Recent studies provided evidence that magnetic resonance spectroscopy (MRS) and measurement of total-tau (T-tau) and phospho-tau (P-tau) may be useful to identify patients with CJD. We combined detected metabolic changes in the brain by MRS and measured T-tau and tau-pT181 by ELISA, and tau-pT231 by Westernblot in a patient with autopsy proven sCJD. Our results show that in contrast to negative CSF 14-3-3 protein, nonspecific EEG and MRI, MRS revealed metabolic alterations in regions of the brain that has appeared normal on MRI, and tau tests has shown measurable levels of phosphorylated and non-phosphorylated isoforms in CSF. We conclude that rapidly progressive dementia with negative 14-3-3 test and non-specific initial EEG and MRI must still be considered in the differential diagnosis of the sCJD. Combination of serial functional MRI along with MRS study and measurement of tau ratio could improve the early diagnosis of sCJD. The current case is the first attempt to study results of the use of MRS and tau tests in a case of sCJD with diagnostic dilemma.     

Use of magnetic resonance to measure molecular diffusion within the brain extracellular space

Ion-selective microelectrode measurements of molecular diffusion have provided unique information about the structural characteristics of the extracellular compartment of brain tissue. Magnetic resonance (MR) techniques can also be used to perform diffusion measurements in living tissue in situ. In MR applications, the challenge to study a particular physiological compartment lies in achieving the appropriate specificity in the experimentally-observed MR signal, and many strategies have been used to provide measurements that reflect molecular diffusion within the extracellular space. This review describes how magnetic resonance and microelectrode diffusion measurements are performed, and applications using the MR technique are summarized. Comparisons of experimental results obtained from the two techniques indicate that their use in combination may further augment what is known about extracellular space structure.     

In Vivo NMR Studies of Neurodegenerative Diseases in Transgenic and Rodent Models

In vivo magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) provide unique quality to attain neurochemical, physiological, anatomical, and functional information noninvasively. These techniques have been increasingly applied to biomedical research and clinical usage in diagnosis and prognosis of diseases. The ability of MRS to detect early yet subtle changes of neurochemicals in vivo permits the use of this technology for the study of cerebral metabolism in physiological and pathological conditions. Recent advances in MR technology have further extended its use to assess the etiology and progression of neurodegeneration. This review focuses on the current technical advances and the applications of MRS and MRI in the study of neurodegenerative disease animal models including amyotrophic lateral sclerosis, Alzheimer's, Huntington's, and Parkinson's diseases. Enhanced MR measurable neurochemical parameters in vivo are described in regard to their importance in neurodegenerative disorders and their investigation into the metabolic alterations accompanying the pathogenesis of neurodegeneration.     

Magnetic resonance imaging and magnetic resonance spectroscopy in a patient with amyotrophic lateral sclerosis and frontotemporal dementia

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) have been investigated in a single neurodegenerative disease manifesting as either amyotrophic lateral sclerosis (ALS) or frontotemporal dementia (FTD) alone, but have not been examined in combined disorders such as ALS with FTD (ALS-FTD). To our knowledge, this study is the first attempt to demonstrate relationship between MRI abnormalities and MR spectroscopic metabolite changes of the motor cortex, frontal white matter and corticospinal tract in a patient with the diagnosis of ALS with probable upper motor neuron signs (ALS-PUMNS) and FTD. Patient presented underwent MRI of the brain and MRS. The ratio of N-acetylaspartate (NAA) to creatine (Cr), choline to Cr, myo-inositol (ml) to Cr and glutamate-glutamine (Glx) to Cr were derived from peak area measurement. Spectra from the right motor cortex, frontal white matter and corticospinal tract were obtained. MR images were evaluated for sulcus centralis enlargement, corticospinal tract hyperintensity and frontal lobes atrophy. Spectra showed reduced NAA/Cr and Glx/Cr ratio, yet the ratio of Cho/Cr exhibited significant elevation. MR images revealed sulcus centralis enlargement, high signal intensity of corticospinal tract and atrophy of both frontal lobes. Proton spectroscopic metabolic changes in a current patient fully correlate with previously reported MRS metabolic changes in ALS alone. Surprisingly, normal ml (glial marker) values have been found in almost all measured voxels of interest except in the frontal white matter. These findings differ from the previous findings in ALS or FTD alone. In conclusion, these findings support the concept that ALS, FTD and ALS-FTD may represent different manifestations of a single pathological continuum.     

Magnetic Resonance Imaging Part II—Clinical Applications

Magnetic resonance (MR) imaging is the most promising new technology to appear in the clinical imaging arena since the advent of x-ray transmission computed tomography in the early 1970s. Five independent tissue characteristics (spin density, spin-lattice and spin-spin relaxation times, flow and spectral shift information) are accessible to MR imaging, and their relative influence in the magnetic resonance image can be varied by appropriate selection of pulse sequences and pulse times. All major organ systems appear to be amenable to MR imaging, and some are revealed with superior definition compared with their appearance in images obtained by alternate imaging technologies. Of particular interest is the superior contrast resolution in MR images of the brain and spinal cord, and the absence of bone- and motion-induced artifacts in images of the abdomen and pelvis. Applications of MR imaging to the heart and great vessels are just developing, as are new types of contrast agents for use in MR imaging. In vivo chemical spectroscopic measurements by magnetic resonance are heralded by some investigators as the most significant contribution that magnetic resonance will make ultimately to clinical diagnosis.At present, the number of MR imaging units is extremely low, and clinical studies are proceeding at a slow rate. Nevertheless, it is possible to provide a preliminary evaluation of the usefulness of MR imaging in a variety of clinical applications. This article is such an evaluation, tempered by the acknowledgement that much additional work remains to be done.     

Hyperpolarized MRI,functional MRI,MR spectroscopy and CEST to provide metabolic information in vivo

Access to metabolic information in vivo using magnetic resonance (MR) technologies has generally been the niche of MR spectroscopy (MRS) and spectroscopic imaging (MRSI). Metabolic fluxes can be studied using the infusion of substrates labeled with magnetic isotopes, with the use of hyperpolarization especially powerful. Unfortunately, these promising methods are not yet accepted clinically, where fast, simple, and reliable measurement and diagnosis are key. Recent advances in functional MRI and chemical exchange saturation transfer (CEST) MRI allow the use of water imaging to study oxygen metabolism and tissue metabolite levels. These, together with the use of novel data analysis approaches such as machine learning for all of these metabolic MR approaches, are increasing the likelihood of their clinical translation.     

Quantitative magnetic resonance spectroscopy reveals a potential relationship between radiation-induced changes in rat brain metabolites and cognitive impairment

To test the efficacy of magnetic resonance spectroscopy (MRS) in identifying radiation-induced brain injury, adult male Fischer 344 rats received fractionated whole-brain irradiation (40 or 45 Gy given in 5-Gy fractions twice a week for 4 or 4.5 weeks, respectively); control rats received sham irradiation. Twelve and 52 weeks after whole-brain irradiation, rats were subjected to high-resolution MRI and proton MRS. No apparent lesions or changes in T(1)- or T(2)-weighted images were noted at either time. This is in agreement with no gross changes being found in histological sections from rats 50 weeks postirradiation. Analysis of the MR spectra obtained 12 weeks after fractionated whole-brain irradiation also failed to show any significant differences (P > 0.1) in the concentration of brain metabolites between the whole-brain-irradiated and sham-irradiated rats. In contrast, analysis of the MR spectra obtained 52 weeks postirradiation revealed significant differences between the irradiated and sham-irradiated rats in the concentrations of several brain metabolites, including increases in the NAA/tCr (P < 0.005) and Glx/tCr (P < 0.001) ratios and a decrease in the mI/tCr ratio (P < 0.01). Although the cognitive function of these rats measured by the object recognition test was not significantly different (P > 0.1) between the irradiated and sham-irradiated rats at 14 weeks postirradiation, it was significantly different (P < 0.02) at 54 weeks postirradiation. These findings suggest that MRS may be a sensitive, noninvasive tool to detect changes in radiation-induced brain metabolites that may be associated with the radiation-induced cognitive impairments observed after prolonged fractionated whole-brain irradiation.     

Magnetic relaxation switches capable of sensing molecular interactions

Highly sensitive, efficient, and high-throughput biosensors are required for genomic and proteomic data acquisition in complex biological samples and potentially for in vivo applications. To facilitate these studies, we have developed biocompatible magnetic nanosensors that act as magnetic relaxation switches (MRS) to detect molecular interactions in the reversible self-assembly of disperse magnetic particles into stable nanoassemblies. Using four different types of molecular interactions (DNA-DNA, protein-protein, protein-small molecule, and enzyme reactions) as model systems, we show that the MRS technology can be used to detect these interactions with high efficiency and sensitivity using magnetic relaxation measurements including magnetic resonance imaging (MRI). Furthermore, the magnetic changes are detectable in turbid media and in whole-cell lysates without protein purification. The developed magnetic nanosensors can be used in a variety of biological applications such as in homogeneous assays, as reagents in miniaturized microfluidic systems, as affinity ligands for rapid and high-throughput magnetic readouts of arrays, as probes for magnetic force microscopy, and potentially for in vivo imaging.     

MRI of intact plants

Nuclear magnetic resonance imaging (MRI) is a non-destructive and non-invasive technique that can be used to acquire two- or even three-dimensional images of intact plants. The information within the images can be manipulated and used to study the dynamics of plant water relations and water transport in the stem, e.g., as a function of environmental (stress) conditions. Non-spatially resolved portable NMR is becoming available to study leaf water content and distribution of water in different (sub-cellular) compartments. These parameters directly relate to stomatal water conductance, CO₂ uptake, and photosynthesis. MRI applied on plants is not a straight forward extension of the methods discussed for (bio)medical MRI. This educational review explains the basic physical principles of plant MRI, with a focus on the spatial resolution, factors that determine the spatial resolution, and its unique information for applications in plant water relations that directly relate to plant photosynthetic activity.     

Automated analysis of low-field brain MRI in cerebral malaria

A central challenge of medical imaging studies is to extract biomarkers that characterize disease pathology or outcomes. Modern automated approaches have found tremendous success in high-resolution, high-quality magnetic resonance images. These methods, however, may not translate to low-resolution images acquired on magnetic resonance imaging (MRI) scanners with lower magnetic field strength. In low-resource settings where low-field scanners are more common and there is a shortage of radiologists to manually interpret MRI scans, it is critical to develop automated methods that can augment or replace manual interpretation, while accommodating reduced image quality. We present a fully automated framework for translating radiological diagnostic criteria into image-based biomarkers, inspired by a project in which children with cerebral malaria (CM) were imaged using low-field 0.35 Tesla MRI. We integrate multiatlas label fusion, which leverages high-resolution images from another sample as prior spatial information, with parametric Gaussian hidden Markov models based on image intensities, to create a robust method for determining ventricular cerebrospinal fluid volume. We also propose normalized image intensity and texture measurements to determine the loss of gray-to-white matter tissue differentiation and sulcal effacement. These integrated biomarkers have excellent classification performance for determining severe brain swelling due to CM.     

Diethylenetriaminepentaacetic acid-gadolinium (DTPA-Gd)-conjugated polysuccinimide derivatives as magnetic resonance imaging contrast agents

Biocompatible polysuccinimide (PSI) derivatives conjugated with diethylenetriaminepentaacetic acid gadolinium (DTPA-Gd) were prepared as magnetic resonance imaging (MRI) contrast agents. In this study, we synthesized PSI derivatives incorporating methoxy-poly(ethylene glycol) (mPEG) as hydrophilic ligand, hexadecylamine as hydrophobic ligand, and DTPA-Gd as contrast agent. PSI was synthesized by the polycondensation polymerization of aspartic acid. All the synthesized materials were characterized by proton nuclear magnetic resonance (1H NMR). Critical micellization concentrations were determined using fluorescent probes (pyrene). Micelle size and shape were measured by electro-photometer light scattering (ELS) and atomic force microscopy (AFM). The formed micelle size ranged from 100 to 300 nm. The T1-weighted MR images of the phantom prepared with PSI-mPEG-C16-(DTPA-Gd) were obtained in a 3.0 T clinical MR imager, and the conjugates showed a great potential as MRI contrast agents.     

Applications of nuclear magnetic resonance in parasitology

The basis of the nuclear magnetic resonance (NMR) phenomenon is described in a classical framework with emphasis on magnetic nuclei of 1/2 spin, including 1H, 13C, and 31P. Biological applications of NMR spectroscopy and magnetic resonance imaging (MRI) are outlined briefly. NMR spectroscopic studies on parasitic protozoa, cestodes, nematodes, trematodes, and hymenopterous insect parasites are reviewed. NMR and MRI investigations on the pathophysiology of the host are also discussed, and the potential future of NMR applications in parasitology outlined.     

Identification of cholesteryl esters in human carotid atherosclerosis by ex vivo image-guided proton MRS

Vulnerable atherosclerotic plaques may be identified by their large lipid component, particularly liquid cholesteryl ester (CE), covered by a fibrous cap. We hypothesized that image-guided 1H proton magnetic resonance spectroscopy (MRS) would identify mobile CE in discrete, preselected regions of atherosclerotic plaque. Human carotid endarterectomy specimens (n = 10) were imaged ex vivo by magnetic resonance imaging (MRI) at high field (11.7 T) utilizing standard T1- and T2-weighted spin echo protocols. MRS spectra were acquired from 1 mm3 voxels, localized to plaque regions that we judged by MRI to be lipid rich or lipid poor. The spectra revealed methyl and methylene resonances of fatty acyl chains with relative intensities and linewidths characteristic of pure CE, by comparison with lipid standards. Regions judged to be lipid rich by MRI showed much more intense CE resonances than did lipid-poor regions. The integrated intensities of lipid peaks were 5.5 +/- 2.0% (lipid-rich regions) versus 0.9 +/- 0.6% (lipid-poor regions) of the unsuppressed water peak (P < 0.0001). Lipid distribution by histology, MRS, and MRI showed strong correlation. Image-guided proton MRS accurately identified CE in selected regions of atherosclerotic plaque as small as 1 mm3 in an ex vivo setting. This procedure may permit the noninvasive detection and quantification of CE in atherosclerotic plaque in vivo.     

Hyperpolarized Xenon for NMR and MRI Applications

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 T generate only a small detectable net-magnetization of the sample at room temperature ¹. Hence, most NMR and MRI applications rely on the detection of molecules at relative high concentration (e.g., water for imaging of biological tissue) or require excessive acquisition times. This limits our ability to exploit the very useful molecular specificity of NMR signals for many biochemical and medical applications. However, novel approaches have emerged in the past few years: Manipulation of the detected spin species prior to detection inside the NMR/MRI magnet can dramatically increase the magnetization and therefore allows detection of molecules at much lower concentration ².Here, we present a method for polarization of a xenon gas mixture (2-5% Xe, 10% N₂, He balance) in a compact setup with a ca. 16000-fold signal enhancement. Modern line-narrowed diode lasers allow efficient polarization ⁷ and immediate use of gas mixture even if the noble gas is not separated from the other components. The SEOP apparatus is explained and determination of the achieved spin polarization is demonstrated for performance control of the method.The hyperpolarized gas can be used for void space imaging, including gas flow imaging or diffusion studies at the interfaces with other materials ^8,9. Moreover, the Xe NMR signal is extremely sensitive to its molecular environment ⁶. This enables the option to use it as an NMR/MRI contrast agent when dissolved in aqueous solution with functionalized molecular hosts that temporarily trap the gas ^10,11. Direct detection and high-sensitivity indirect detection of such constructs is demonstrated in both spectroscopic and imaging mode.     

MRI denoising using nonlocal neutrosophic set approach of Wiener filtering

In this paper, a new filtering method is presented to remove the Rician noise from magnetic resonance images (MRI) acquired using single coil MRI acquisition system. This filter is based on nonlocal neutrosophic set (NLNS) approach of Wiener filtering. A neutrosophic set (NS), a part of neutrosophy theory, studies the origin, nature, and scope of neutralities, as well as their interactions with different ideational spectra. Now, we apply the neutrosophic set into image domain and define some concepts and operators for image denoising. First, the nonlocal mean is applied to the noisy MRI. The resultant image is transformed into NS domain, described using three membership sets: true (T), indeterminacy (I) and false (F). The entropy of the neutrosophic set is defined and employed to measure the indeterminacy. The ω-Wiener filtering operation is used on T and F to decrease the set indeterminacy and to remove the noise. The experiments have been conducted on simulated MR images from Brainweb database and clinical MR images. The results show that the NLNS Wiener filter produces better denoising results in terms of qualitative and quantitative measures compared with other denoising methods, such as classical Wiener filter, the anisotropic diffusion filter, the total variation minimization and the nonlocal means filter. The visual and the diagnostic quality of the denoised image are well preserved.     

High-field (9.4 T)1H magnetic resonance microscopy of mouse brain

The FLASH and STEAM pulse sequences were used to perform the microimaging and localized spectroscopy of brain of living and dead mice, respectively. The phase-shift presaturation approach was used to suppress water NMR signal. The experimental results show that the differences in localized spectra and MR images of brain between live and dead mice can be observed by means of magnetic resonance microscopy.     

High-field (9.4 T) 1H magnetic resonance microscopy of mouse brain

The FLASH and STEAM pulse sequences were used to perform the microimaging and localized spectroscopy of brain of living and dead mice, respectively. The phase-shift presaturation approach was used to sup-press water NMR signal. The experimental results show that the differences in localized spectra and MR images of brain between live and dead mice can be observed by means of magnetic resonance microscopy.     

In vivo phenotyping of the ob/ob mouse by magnetic resonance imaging and 1H-magnetic resonance spectroscopy

Objective: We studied ob/ob and wild‐type (WT) mice to characterize the adipose tissues depots and other visceral organs and to establish an experimental paradigm for in vivo phenotyping. Research Methods and Procedures: An in vivo evaluation was conducted using magnetic resonance imaging and ¹H‐magnetic resonance spectroscopy (¹H‐MRS). We used T1‐weighted images and three‐dimensional spin echo T1‐weighted images for the morphological analysis and ¹H‐MRS spectra on all body mass, as well as ¹H‐MRS spectra focalized on specific lipid depots [triglyceride (TG) depots] for a molecular analysis. Results: In ob/ob mice, three‐dimensional evaluation of the trunk revealed that ～64% of the volume consists of white adipose tissue, which is 72% subcutaneous and 28% visceral. In vivo ¹H‐MRS showed that 20.00 ± 6.92% in the WT group and 58.67 ± 6.65% in the ob/ob group of the total proton content is composed of TG protons. In in vivo‐localized spectra of ob/ob mice, we found a polyunsaturation degree of 0.5247 in subcutaneous depots. In the liver, we observed that 48.7% of the proton signal is due to water, whereas in the WT group, the water signal amounted to 82.8% of the total proton signal. With the sequences used, the TG amount was not detectable in the brain or kidneys. Discussion: The present study shows that several parameters can be obtained by in vivo examination of ob/ob mice by magnetic resonance imaging and ¹H‐MRS and that the accumulated white adipose tissue displays low polyunsaturation degree and low hydrolipidic ratio. Relevant anatomical alterations observed in urinary and digestive apparatuses should be considered when ob/ob mice are used in experimental paradigms.