Preparation of ex vivo rodent phantoms for developing, testing, and training MR imaging of the kidney and other organs

Here we describe a simple and inexpensive protocol for preparing ex vivo rodent phantoms for use in MR imaging studies. The experimental animals are perfused and fixed with formaldehyde, and then wrapped with gauze and sealed with liquid latex. This yields a phantom that preserves all organs in situ, and which avoids the need to keep fixed animals and organs in containers that have dimensions very different from living animals. This is especially important for loading in MR detectors, and specifically the RF coils, they are usually used with. The phantom can be safely stored and conveniently reused, and can provide MR scientists with a realistic phantom with which to establish protocols in preparation for preclinical in vivo studies-for renal, brain, and body imaging. The phantom also serves as an ideal teaching tool, for trainees learning how to perform preclinical MRI investigations of the kidney and other target organs, while avoiding the need for handling living animals, and reducing the total number of animals required.This protocol chapter is part of the PARENCHIMA initiative "MRI Biomarkers for CKD " (CA16103), a community-driven Action of the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers

Fluorine-19 MRI at 21.1 T: enhanced spin-lattice relaxation of perfluoro-15-crown-5-ether and sensitivity as demonstrated in ex vivo murine neuroinflammation

OBJECTIVE: Fluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of (19)F MR that can be practically achieved when moving from 9.4 to 21.1 T. MATERIALS AND METHODS: We studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B(0)), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B(0) with 2D-RARE and 2D-FLASH using (19)F volume radiofrequency resonators together. T(1) and T(2) of PFCE were measured at both B(0) strengths. RESULTS: Compared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of (19)F T(1) and T(2) relaxation on B(0) was demonstrated. High spatially resolved (19)F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T. DISCUSSION: Enhanced SNR and T(1) shortening indicate the potential benefit of in vivo (19)F MR at higher B(0) to study inflammatory processes with greater detail

Enhanced fluorine-19 MRI sensitivity using a cryogenic radiofrequency probe: technical developments and ex vivo demonstration in a mouse model of neuroinflammation

Neuroinflammation can be monitored using fluorine-19 ((19)F)-containing nanoparticles and (19)F MRI. Previously we studied neuroinflammation in experimental autoimmune encephalomyelitis (EAE) using room temperature (RT) (19)F radiofrequency (RF) coils and low spatial resolution (19)F MRI to overcome constraints in signal-to-noise ratio (SNR). This yielded an approximate localization of inflammatory lesions. Here we used a new (19)F transceive cryogenic quadrature RF probe ((19) F-CRP) that provides the SNR necessary to acquire superior spatially-resolved (19)F MRI. First we characterized the signal-transmission profile of the (19) F-CRP. The (19) F-CRP was then benchmarked against a RT (19)F/(1)H RF coil. For SNR comparison we used reference compounds including (19)F-nanoparticles and ex vivo brains from EAE mice administered with (19)F-nanoparticles. The transmit/receive profile of the (19) F-CRP diminished with increasing distance from the surface. This was counterbalanced by a substantial SNR gain compared to the RT coil. Intraparenchymal inflammation in the ex vivo EAE brains was more sharply defined when using 150 μm isotropic resolution with the (19) F-CRP, and reflected the known distribution of EAE histopathology. At this spatial resolution, most (19)F signals were undetectable using the RT coil. The (19) F-CRP is a valuable tool that will allow us to study neuroinflammation with greater detail in future in vivo studies

Fluorine ((19)F) MRI for assessing inflammatory cells in the kidney: experimental protocol

Inflammation is one underlying contributing factor in the pathology of acute and chronic kidney disorders. Phagocytes such as monocytes, neutrophils and dendritic cells are considered to play a deleterious role in the progression of kidney disease but may also contribute to organ homeostasis. The kidney is a target of life-threatening autoimmune disorders such as the antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV). Neutrophils and monocytes express ANCA antigens and play an important role in the pathogenesis of AAV. Noninvasive in vivo methods that can quantify the distribution of inflammatory cells in the kidney as well as other organs in vivo would be vital to identify the causality and significance of inflammation during disease progression. Here we describe an noninvasive technique to study renal inflammation in rodents in vivo using fluorine ((19)F) MRI. In this protocol we chose a murine ANCA-AAV model of renal inflammation and made use of nanoparticles prepared from perfluoro-5-crown-15-ether (PFCE) for renal (19)F MRI.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This experimental protocol chapter is complemented by two separate chapters describing the basic concept and data analysis

B(1) inhomogeneity correction of RARE MRI at low SNR: quantitative in vivo (19)F MRI of mouse neuroinflammation with a cryogenically-cooled transceive surface radiofrequency probe

PURPOSE: Low SNR in fluorine-19 (19F) MRI benefits from cryogenically-cooled transceive surface RF probes (CRPs), but strong B(1) inhomogeneities hinder quantification. Rapid acquisition with refocused echoes (RARE) is an SNR-efficient method for MRI of neuroinflammation with perfluorinated compounds but lacks an analytical signal intensity equation to retrospectively correct B(1) inhomogeneity. Here, a workflow was proposed and validated to correct and quantify (19)F-MR signals from the inflamed mouse brain using a (19)F-CRP. METHODS: In vivo (19)F-MR images were acquired in a neuroinflammation mouse model with a quadrature (19)F-CRP using an imaging setup including 3D-printed components to acquire co-localized anatomical and (19)F images. Model-based corrections were validated on a uniform (19)F phantom and in the neuroinflammatory model. Corrected (19)F-MR images were benchmarked against reference images and overlaid on in vivo (1)H-MR images. Computed concentration uncertainty maps using Monte Carlo simulations served as a measure of performance of the B(1) corrections. RESULTS: Our study reports on the first quantitative in vivo (19)F-MR images of an inflamed mouse brain using a (19)F-CRP, including in vivo T(1) calculations for (19)F-nanoparticles during pathology and B(1) corrections for (19)F-signal quantification. Model-based corrections markedly improved (19)F-signal quantification from errors > 50% to < 10% in a uniform phantom (p < 0.001). Concentration uncertainty maps ex vivo and in vivo yielded uncertainties that were generally < 25%. Monte Carlo simulations prescribed SNR ≥ 10.1 to reduce uncertainties < 10%, and SNR ≥ 4.25 to achieve uncertainties < 25%. CONCLUSION: Our model-based correction method facilitated (19)F signal quantification in the inflamed mouse brain when using the SNR-boosting (19)F-CRP technology, paving the way for future low-SNR (19)F-MRI applications in vivo

In vivo detection of teriflunomide-derived fluorine signal during neuroinflammation using fluorine MR spectroscopy

BACKGROUND: Magnetic resonance imaging (MRI) is indispensable for diagnosing neurological conditions such as multiple sclerosis (MS). MRI also supports decisions regarding the choice of disease-modifying drugs (DMDs). Determining in vivo tissue concentrations of DMDs has the potential to become an essential clinical tool for therapeutic drug monitoring (TDM). The aim here was to examine the feasibility of fluorine-19 ((19)F) MR methods to detect the fluorinated DMD teriflunomide (TF) during normal and pathological conditions. METHODS: We used (19)F MR spectroscopy to detect TF in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis (MS) in vivo. Prior to the in vivo investigations we characterized the MR properties of TF in vitro. We studied the impact of pH and protein binding as well as MR contrast agents. RESULTS: We could detect TF in vivo and could follow the (19)F MR signal over different time points of disease. We quantified TF concentrations in different tissues using HPLC/MS and showed a significant correlation between ex vivo TF levels in serum and the ex vivo (19)F MR signal. CONCLUSION: This study demonstrates the feasibility of (19)F MR methods to detect TF during neuroinflammation in vivo. It also highlights the need for further technological developments in this field. The ultimate goal is to add (19)F MR protocols to conventional (1)H MRI protocols in clinical practice to guide therapy decisions

Higher spin quaternion waves in the Klein-Gordon theory

Electromagnetic interactions are discussed in the context of the Klein-Gordon fermion equation. The Mott scattering amplitude is derived in leading order perturbation theory and the result of the Dirac theory is reproduced except for an overall factor of sixteen. The discrepancy is not resolved as the study points into another direction. The vertex structures involved in the scattering calculations indicate the relevance of a modified Klein-Gordon equation, which takes into account the number of polarization states of the considered quantum field. In this equation the d'Alembertian is acting on quaternion-like plane waves, which can be generalized to representations of arbitrary spin. The method provides the same relation between mass and spin that has been found previously by Majorana, Gelfand, and Yaglom in infinite spin theories

Continuous diffusion spectrum computation for diffusion-weighted magnetic resonance imaging of the kidney tubule system

BACKGROUND: The use of rigid multi-exponential models (with a priori predefined numbers of components) is common practice for diffusion-weighted MRI (DWI) analysis of the kidney. This approach may not accurately reflect renal microstructure, as the data are forced to conform to the a priori assumptions of simplified models. This work examines the feasibility of less constrained, data-driven non-negative least squares (NNLS) continuum modelling for DWI of the kidney tubule system in simulations that include emulations of pathophysiological conditions. METHODS: Non-linear least squares (LS) fitting was used as reference for the simulations. For performance assessment, a threshold of 5% or 10% for the mean absolute percentage error (MAPE) of NNLS and LS results was used. As ground truth, a tri-exponential model using defined volume fractions and diffusion coefficients for each renal compartment (tubule system: D(tubules), f(tubules); renal tissue: D(tissue), f(tissue); renal blood: D(blood), f(blood);) was applied. The impact of: (I) signal-to-noise ratio (SNR) =40–1,000, (II) number of b-values (n=10–50), (III) diffusion weighting (b-range(small)=0-800 up to b-range(large)=0-2,180 s/mm(2)), and (IV) fixation of the diffusion coefficients D(tissue) and D(blood) was examined. NNLS was evaluated for baseline and pathophysiological conditions, namely increased tubular volume fraction (ITV) and renal fibrosis (10%: grade I, mild) and 30% (grade II, moderate). RESULTS: NNLS showed the same high degree of reliability as the non-linear LS. MAPE of the tubular volume fraction (f(tubules)) decreased with increasing SNR. Increasing the number of b-values was beneficial for f(tubules) precision. Using the b-range(large) led to a decrease in MAPE(ftubules) compared to b-range(small). The use of a medium b-value range of b=0-1,380 s/mm(2) improved f(tubules) precision, and further bmax increases beyond this range yielded diminishing improvements. Fixing D(blood) and D(tissue) significantly reduced MAPE(ftubules) and provided near perfect distinction between baseline and ITV conditions. Without constraining the number of renal compartments in advance, NNLS was able to detect the (fourth) fibrotic compartment, to differentiate it from the other three diffusion components, and to distinguish between 10% vs. 30% fibrosis. CONCLUSIONS: This work demonstrates the feasibility of NNLS modelling for DWI of the kidney tubule system and shows its potential for examining diffusion compartments associated with renal pathophysiology including ITV fraction and different degrees of fibrosis

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe