hyperpolarized-129xe-lung-mri-spectroscopy-mechanically-ventilated

Hyperpolarized <sup>129</sup>Xe Lung MRI and Spectroscopy in Mechanically Ventilated Mice

Hyperpolarized (HP) xenon-129 (129Xe) is an inhaled magnetic resonance imaging (MRI) contrast agent with unique spectral and physical properties that can ...

Cincinnati Children's Hospital Medical Center

Neonatal hydrocephalus affects about one child per 1000 births and is a major congenital brain abnormality. We previously discovered a gene mutation within the coiled-coil domain-containing 39 () gene, which causes the  () phenotype in mice due to lack of ependymal-cilia-mediated cerebrospinal fluid (CSF) flow. In this study, we used CRISPR/Cas9 to introduce the  gene mutation into rats, which are more suitable for imaging and surgical experiments. The  mutants exhibited mild ventriculomegaly at postnatal day (P)5 that progressed into severe hydrocephalus by P11 (0.001). After P11, macrophage and neutrophil invasion along with subarachnoid hemorrhage were observed in mutant brains showing reduced neurofilament density, hypomyelination and increased cell death signals compared with wild-type brains. Significantly more macrophages entered the brain parenchyma at P5 before hemorrhaging was noted and increased expression of a pro-inflammatory factor (monocyte chemoattractant protein-1) was found in the cortical neural and endothelial cells in the mutant brains at P11. Glymphatic-mediated CSF circulation was progressively impaired along the middle cerebral artery from P11 as mutants developed severe hydrocephalus (<0.001). In addition,  mutants with L1 cell adhesion molecule () gene mutation, which causes X-linked human congenital hydrocephalus, showed an accelerated early hydrocephalus phenotype (<0.05-0.01). Our findings in  mutant rats demonstrate a possible causal role of neuroinflammation in neonatal hydrocephalus development, which involves impaired cortical development and glymphatic CSF flow. Improved understanding of inflammatory responses and the glymphatic system in neonatal hydrocephalus could lead to new therapeutic strategies for this condition.This article has an associated First Person interview with the joint first authors of the paper.

Impaired neural differentiation and glymphatic CSF flow in the  rat model of neonatal hydrocephalus: genetic interaction with .

Fast apparent transverse relaxation (short T *) is a common obstacle when attempting to perform quantitative  H MRI of the lungs. While T * times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous  Xe), T * can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is especially true in preclinical studies, where high magnetic fields lead to shorter relaxation times than are typically seen in human studies. However, the T * of HP  Xe in the most common animal model of human disease (mice) has not been reported. Herein, we present a multi-echo radial flyback imaging sequence and use it to measure HP  Xe T * at 7 T under a variety of respiratory conditions. This sequence mitigates the impact of T relaxation outside the animal by using multiple gradient-refocused echoes to acquire images at a number of effective echo times for each RF excitation. After validating the sequence using a phantom containing water doped with superparamagnetic iron oxide nanoparticles, we measured the  Xe T * in vivo for 10 healthy C57Bl/6 J mice and found T * ~ 5 ms in the lung airspaces. Interestingly, T * was relatively constant over all experimental conditions, and varied significantly with sex, but not age, mass, or the O content of the inhaled gas mixture. These results are discussed in the context of T * relaxation within porous media.

Preclinical hyperpolarized  Xe MRI: ventilation and T * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using  He, it has never been validated in mice for  Xe. Here, we examine the effect of cardiac motion on diffusion imaging and validate  Xe diffusion morphometry in mice.

Validating in vivo hyperpolarized  Xe diffusion MRI and diffusion morphometry in the mouse lung.

An imaging method that allows quantitative fibrosis estimates is needed to facilitate the diagnosis of chronic liver disease. Amide proton transfer (APT) and tissue sodium concentration (TSC) estimates could meet this need.

MRI Measures of Murine Liver Fibrosis.

The creatine transporter (CrT) maintains brain creatine (Cr) levels, but the effects of its deficiency on energetics adaptation under stress remain unclear. There are also no effective treatments for CrT deficiency, the second most common cause of X-linked intellectual disabilities. Herein, we examined the consequences of CrT deficiency in brain energetics and stress-adaptation responses plus the effects of intranasal Cr supplementation. We found that CrT-deficient (CrT-/y) mice harbored dendritic spine and synaptic dysgenesis. Nurtured newborn CrT-/y mice maintained baseline brain ATP levels, with a trend toward signaling imbalance between the p-AMPK/autophagy and mTOR pathways. Starvation elevated the signaling imbalance and reduced brain ATP levels in P3 CrT-/y mice. Similarly, CrT-/y neurons and P10 CrT-/y mice showed an imbalance between autophagy and mTOR signaling pathways and greater susceptibility to cerebral hypoxia-ischemia and ischemic insults. Notably, intranasal administration of Cr after cerebral ischemia increased the brain Cr/N-acetylaspartate ratio, partially averted the signaling imbalance, and reduced infarct size more potently than intraperitoneal Cr injection. These findings suggest important functions for CrT and Cr in preserving the homeostasis of brain energetics in stress conditions. Moreover, intranasal Cr supplementation may be an effective treatment for congenital CrT deficiency and acute brain injury.

Creatine transporter deficiency impairs stress adaptation and brain energetics homeostasis.

Two recently developed novel rodent models have been reported to ablate microglia, either by genetically targeting microglia (via Cx3cr1-creER: iDTR + Dtx) or through pharmacologically targeting the CSF1R receptor with its inhibitor (PLX5622). Both models have been widely used in recent years to define essential functions of microglia and have led to high impact studies that have moved the field forward.

Diphtheria toxin induced but not CSF1R inhibitor mediated microglia ablation model leads to the loss of CSF/ventricular spaces in vivo that is independent of cytokine upregulation.

The brain's neuroreparative capacity after injuries such as ischemic stroke is contained in the brain's neurogenic niches, primarily the subventricular zone (SVZ), which lies in close contact with the cerebrospinal fluid (CSF) produced by the choroid plexus (ChP). Despite the wide range of their proposed functions, the ChP/CSF remain among the most understudied compartments of the central nervous system (CNS). Here we report a mouse genetic tool (the ROSA26iDTR mouse line) for non-invasive, specific, and temporally controllable ablation of CSF-producing ChP epithelial cells to assess the roles of the ChP and CSF in brain homeostasis and injury. Using this model, we demonstrate that ChP ablation causes rapid and permanent CSF volume loss accompanied by disruption of ependymal cilia bundles. Surprisingly, ChP ablation did not result in overt neurological deficits at one-month post-ablation. However, we observed a pronounced decrease in the pool of SVZ neuroblasts following ChP ablation, which occurs due to their enhanced migration into the olfactory bulb. In the MCAo model of ischemic stroke, neuroblast migration into the lesion site was also reduced in the CSF-depleted mice. Thus, our study establishes an important and novel role of ChP/CSF in regulating the regenerative capacity of the adult brain under normal conditions and after ischemic stroke.

The choroid plexus maintains ventricle volume and adult subventricular zone neuroblast pool, which facilitates post-stroke neurogenesis.

The quantification of cardiac motion using cardiac magnetic resonance imaging (CMR) has shown promise as an early-stage marker for cardiovascular diseases. Despite the growing popularity of CMR-based myocardial strain calculations, measures of complete spatiotemporal strains (i.e., three-dimensional strains over the cardiac cycle) remain elusive. Complete spatiotemporal strain calculations are primarily hampered by poor spatial resolution, with the rapid motion of the cardiac wall also challenging the reproducibility of such strains. We hypothesize that a super-resolution reconstruction (SRR) framework that leverages combined image acquisitions at multiple orientations will enhance the reproducibility of complete spatiotemporal strain estimation. Two sets of CMR acquisitions were obtained for five wild-type mice, combining short-axis scans with radial and orthogonal long-axis scans. Super-resolution reconstruction, integrated with tissue classification, was performed to generate full four-dimensional (4D) images. The resulting enhanced and full 4D images enabled complete quantification of the motion in terms of 4D myocardial strains. Additionally, the effects of SRR in improving accurate strain measurements were evaluated using an in-silico heart phantom. The SRR framework revealed near isotropic spatial resolution, high structural similarity, and minimal loss of contrast, which led to overall improvements in strain accuracy. In essence, a comprehensive methodology was generated to quantify complete and reproducible myocardial deformation, aiding in the much-needed standardization of complete spatiotemporal strain calculations.

Elizabeth M. Fugate

Imaging Research Center,
Department of Radiology,
Imaging Research Center, Department of Radiology

Cincinnati Children's Hospital Medical Center

Hyperpolarized ¹²⁹Xe Lung MRI and Spectroscopy in Mechanically Ventilated Mice

Elizabeth M. Fugate

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Imaging Research Center,Department of Radiology,Imaging Research Center, Department of Radiology

Cincinnati Children's Hospital Medical Center

Hyperpolarized 129Xe Lung MRI and Spectroscopy in Mechanically Ventilated Mice

Imaging Research Center,
Department of Radiology,
Imaging Research Center, Department of Radiology

Hyperpolarized ¹²⁹Xe Lung MRI and Spectroscopy in Mechanically Ventilated Mice