Abstract Non-alcoholic steatohepatitis (NASH) is characterized from its early stages by a profound remodeling of the liver microenvironment, encompassing changes in the composition and activities of multiple cell types and associated gene expression patterns. Hyperpolarized (HP) 13C MRI provides a unique view of the metabolic microenvironment, with potential relevance for early diagnosis of liver disease. Previous studies have detected changes in HP 13C pyruvate to lactate conversion, catalyzed by lactate dehydrogenase (LDH), with experimental liver injury. HP $$\propto $$ ∝ -ketobutyrate ( $$\propto $$ ∝ KB) is a close molecular analog of pyruvate with modified specificity for LDH isoforms, specifically attenuated activity with their LDHA-expressed subunits that dominate liver parenchyma. Building on recent results with pyruvate, we investigated HP $$\propto $$ ∝ KB in methionine-choline deficient (MCD) diet as a model of early-stage NASH. Similarity of results between this new agent and pyruvate (~ 50% drop in cytoplasmic reducing capacity), interpreted together with gene expression data from the model, suggests that changes are mediated through broad effects on intermediary metabolism. Plausible mechanisms are depletion of the lactate pool by upregulation of gluconeogenesis (GNG) and pentose phosphate pathway (PPP) flux, and a possible shift toward increased lactate oxidation. These changes may reflect high levels of oxidative stress and/or shifting macrophage populations in NASH.

Diffusion-weighted images of the human liver are prone to artifacts from bulk motions, poor SNR, non-uniformity of magnetic field gradients, and non-optimal choice of diffusion weightings. These factors markedly affect diffusion tensor imaging (DTI) metrics such as mean diffusivity (MD) and fractional anisotropy (FA). This work presents a simple preprocessing pipeline for enhanced magnetic field gradient non-uniformity calibration and analysis of the systematic bias removal attained in each correction step. Liver DTI scans were conducted in two isotropic phantoms and one healthy volunteer. Diffusion tensor was calculated for the original data and after denoising, B1 correction, rigid body registration, and magnetic field gradient non-uniformity correction applying the B-matrix spatial distribution (BSD) method and then, compared with the standard approach (sDTI). MD and FA were determined in three segments of the right lobe from DTI using four different combinations of b-values from the set 0, 400, and 800 s/mm2. Results showed that the proposed preprocessing and BSD methods have a significant impact on MD and FA values in off- and iso-centered isotropic phantoms. The applied corrections applied to the human liver resulted in a 11% change in MD and a - 64% change in FA. By manipulating the b-values used in the diffusion tensor calculation, DTI metrics that reflect only morphology or additional information about liver tissue physiology can be obtained. Accurate quantification of the human liver by diffusion requires appropriate preprocessing and carefully chosen b-value. Noise, B1 inhomogeneity, mis-registration, and non-uniform magnetic field gradients significantly change distributions of DTI metrics in isotropic phantoms and the human liver. Basic preprocessing and the B-matrix spatial distribution (BSD) method perform differently for off-center and isocenter locations. In the human liver, they removed systematic bias of FA and MD by up to -63% and 11%, respectively. Visible variability of FA and MD among b-value sets indicates the possibility of DTI sensitization to different liver compartments.

Abstract The successful translation of gene therapy for clinical application will require the assessment of transgene activity as a measure of the biological function of a therapeutic transgene. Although current imaging permits the noninvasive detection of transgene expression, the critical need for quantitative imaging of the action of the expressed transgene has not been met. In vivo magnetic resonance spectroscopic imaging (MRSI) was applied to quantitatively delineate both the concentration and activity of a cytosine deaminase–uracil phosphoribosyltransferase (CD-UPRT) fusion enzyme expressed from a transgene. MRSI enabled the generation of anatomically accurate maps of the intratumoral heterogeneity in fusion enzyme activity. We observed an excellent association between the CD-UPRT concentration and activity and the percentage of CD-UPRT+ cells. Moreover, the regional levels of UPRT activity, as measured by imaging, correlated well with the biological affect of the enzyme. This study presents a translational imaging paradigm for precise, in vivo measurements of transgene activity with potential applications in both preclinical and clinical settings. [Cancer Res 2008;68(8):2878–84]

Supplementary Figure 4 from Imaging Transgene Activity In vivo

Supplementary Figure 4 from Imaging Transgene Activity In vivo

Supplementary Figure Legends 1-4 from Imaging Transgene Activity In vivo

Supplementary Figure 2 from Imaging Transgene Activity In vivo

Supplementary Figure 3 from Imaging Transgene Activity In vivo

Supplementary Figure 1 from Imaging Transgene Activity In vivo

Supplementary Figure 1 from Imaging Transgene Activity In vivo

Purpose To assess changes in intracellular diffusion as a mechanism for the reduction in water ADC that accompanies brain injury. Using NAA as a marker of neuronal cytoplasmic diffusion, NAA diffusion was measured before and after global ischemia (immediately postmortem) in the female Sprague–Dawley rat. Methods Diffusion‐weighted PRESS spectra, with diffusion encoding in a single direction, were acquired from large voxels of rat brain gray matter in vivo and postischemia employing either pairs of pulsed half‐sine–shaped gradients (in vivo and postischemia, b max = 19 ms/μm 2 ) or sinusoidal oscillating gradients (in vivo only) with frequencies of 99.2–250 Hz. A 2D randomly oriented cylinder (neurite) model gave estimates of longitudinal and transverse diffusivities ( D L and D T , respectively). In this model, D L represents the “free” diffusivity of NAA, whereas D T reflects highly restricted diffusion. Using oscillating gradients, the frequency dependence of D T [ D T (ω)] gave estimates of the cylinder (axon/dendrite) radius. Results A 10% decrease in D L,NAA followed global ischemia, dropping from 0.391 ± 0.012 μm 2 /ms to 0.350 ± 0.009 μm 2 /ms. Modeling D T,NAA (ω) provided an estimate of the neurite radius of 1.0 ± 0.6 μm. Conclusion Whereas the increase in apparent intraneuronal viscosity suggested by changes in D L,NAA may contribute to the overall reduction in water ADC associated with brain injury, it is not sufficient to be the sole explanation. Estimates of neurite radius based on D T (ω) were consistent with literature values.

Neuroimaging plays an important role in assessing axonal pathology after traumatic spinal cord injury. However, coexisting inflammation confounds imaging assessment of the severity of axonal injury. Herein, we applied diffusion basis spectrum imaging (DBSI) to quantitatively differentiate and quantify underlying pathologies in traumatic spinal cord injury at 3 days post-injury. Results reveal that DBSI was capable of detecting and differentiating axonal injury, demyelination, and inflammation-associated edema and cell infiltration in contusion-injured spinal cords. DBSI was able to detect and quantify axonal loss in the presence of white matter tract swelling. The DBSI-defined apparent axonal volume correlated with the corresponding histological markers. DBSI-derived pathological metrics could serve as neuroimaging biomarkers to differentiate and quantify coexisting white matter pathologies in spinal cord injury, providing potential surrogate outcome measures to assess spinal cord injury progression and response to therapies.

Pressures in the intracranial, intraocular and intravascular spaces are clinically useful for the diagnosis and management of traumatic brain injury, glaucoma and hypertension, respectively. Conventional devices for measuring these pressures require surgical extraction after a relevant operational time frame. Bioresorbable sensors, by contrast, eliminate this requirement, thereby minimizing the risk of infection, decreasing the costs of care and reducing distress and pain for the patient. However, the operational lifetimes of bioresorbable pressure sensors available at present fall short of many clinical needs. Here, we present materials, device structures and fabrication procedures for bioresorbable pressure sensors with lifetimes exceeding those of previous reports by at least tenfold. We demonstrate measurement accuracies that compare favourably to those of the most sophisticated clinical standards for non-resorbable devices by monitoring intracranial pressures in rats for 25 days. Assessments of the biodistribution of the constituent materials, complete blood counts, blood chemistry and magnetic resonance imaging compatibility confirm the biodegradability and clinical utility of the device. Our findings establish routes for the design and fabrication of bioresorbable pressure monitors that meet requirements for clinical use.

Repetitive electrical activity produces microstructural alteration in myelinated axons, which may afford the opportunity to non-invasively monitor function of myelinated fibers in peripheral nervous system (PNS)/CNS pathways. Microstructural changes were assessed via two different magnetic-resonance-based approaches: diffusion fMRI and dynamic T-2 spectroscopy in the ex vivo perfused bullfrog sciatic nerves. Using this robust, classical model as a platform for testing, we demonstrate that noninvasive diffusion fMRI, based on standard diffusion tensor imaging (DTI), can clearly localize the sites of axonal conduction blockage as might be encountered in neurotrauma or other lesion types. It is also shown that the diffusion fMRI response is graded in proportion to the total number of electrical impulses carried through a given locus. Dynamic T-2 spectroscopy of the perfused frog nerves point to an electrical-activity-induced redistribution of tissue water and myelin structural changes. Diffusion basis spectrum imaging (DBSI) reveals a reversible shift of tissue water into a restricted isotropic diffusion signal component. Submyelinic vacuoles are observed in electron-microscopy images of tissue fixed during electrical stimulation. A slowing of the compound action potential conduction velocity accompanies repetitive electrical activity. Correlations between electrophysiology and MRI parameters during and immediately after stimulation are presented. Potential mechanisms and interpretations of these results are discussed.

Brain functional studies with standard BOLD (Blood Oxygen Level Dependent) fMRI rely upon coupling of hemodynamic response to functional activation, but are essentially limited to grey matter. On the other hand, a number of neurological disorders originate with white-matter pathology, and white matter accounts for approximately half of the volume of the human brain. Thus, a technique for non-invasive assessment of white-matter functionality would be a valuable tool for basic neuroscience and clinical diagnostic purposes. This has motivated our work in developing white-matter diffusion fMRI. By way of introduction, this talk begins with an overview of our previous work, which demonstrated the utility of diffusion fMRI to assess function and dysfunction in healthy and diseased mouse optic nerves in vivo [1, 2]. However, the majority of this presentation will focus on mechanistic studies involving perfused ex vivo frog sciatic nerves. Because of its exceptionally robust nature, the ex vivo frog sciatic nerve has been the subject of numerous electrophysiology and MRI studies over the years. We report on diffusion fMRI signal changes resulting from repetitive in-magnet electrical stimulation in this model test system. We have developed and implemented an inexpensive perfusion system allowing for good long-term in-magnet stability and simultaneous MRI/electrophysiology studies in perfused nerves. Decreased diffusivity of tissue water and reduced compound action potential conduction velocities accompany prolonged periods of repetitive electrical stimulation. The electrophysiology and diffusion fMRI results are both consistent with hypothesized microstructural alterations of the PNS myelinated fibers. Recent T2 spectral analyses also shed light on this interesting biophysical phenomenon. Finally, perfused nerves were fixed inmagnet in attempts to “lock in” microstructural alterations for electron microscopy imaging. References. [1]. WM Spees, TH Lin, SK Song, NeuroImage 65: 209-215 (2013). [2]. TH Lin, WM Spees, CW Chiang, K Trinkaus, AH Cross, SK Song, Neurobiology of Disease 67: 1-8 (2014). Figure 1. Imaging Conduction Blockage. A perfused frog sciatic nerve tied off at the center with silk sutures underwent electrical stimulation applied at the top of the nerve (60 min  100 Hz). The before vs. after changes in radial diffusivity are depicted in the ADC color maps. Left: six axial slices at different positions along the nerve’s length. Changes in  from DTI analysis. Right: ADC shown for a single longitudinal cut through the nerve. For the longitudinal slice, a single diffusion direction (perpendicular to the axonal fibers was used to estimate ADC.

Optic neuritis is a frequent and early symptom of multiple sclerosis (MS). Conventional magnetic resonance (MR) techniques provide means to assess multiple MS-related pathologies, including axonal injury, demyelination, and inflammation. A method to directly and non-invasively probe white-matter function could further elucidate the interplay of underlying pathologies and functional impairments. Previously, we demonstrated a significant 27% activation-associated decrease in the apparent diffusion coefficient of water perpendicular to the axonal fibers (ADC⊥) in normal C57BL/6 mouse optic nerve with visual stimulation using diffusion fMRI. Here we apply this approach to explore the relationship between visual acuity, optic nerve pathology, and diffusion fMRI in the experimental autoimmune encephalomyelitis (EAE) mouse model of optic neuritis. Visual stimulation produced a significant 25% (vs. baseline) ADC⊥ decrease in sham EAE optic nerves, while only a 7% (vs. baseline) ADC⊥ decrease was seen in EAE mice with acute optic neuritis. The reduced activation-associated ADC⊥ response correlated with post-MRI immunohistochemistry determined pathologies (including inflammation, demyelination, and axonal injury). The negative correlation between activation-associated ADC⊥ response and visual acuity was also found when pooling EAE-affected and sham groups under our experimental criteria. Results suggest that reduction in diffusion fMRI directly reflects impaired axonal-activation in EAE mice with optic neuritis. Diffusion fMRI holds promise for directly gauging in vivo white-matter dysfunction or therapeutic responses in MS patients.

Manganese‐enhanced MRI (MEMRI) with topical loading of MnCl 2 provides optic nerve enhancement comparable to that seen by intravitreal injection. However, the impact of this novel and non‐invasive Mn 2+ loading method on visual function requires further assessments. The objective of this study is to determine the optimal topical Mn 2+ loading dosage for MEMRI and to assess visual function after MnCl 2 loading. Intravitreal administration was performed to compare the two approaches of MnCl 2 loading. Twenty‐four hours after topical loading of 0, 0.5, 0.75, and 1 M MnCl 2 , T 1 ‐weighted, T2‐weighted, diffusion tensor imaging and visual acuity (VA) assessments were performed to determine the best topical loading dosage for MEMRI measurements and to assess the integrity of retinas and optic nerves. Mice were perfusion fixed immediately after in vivo experiments for hematoxylin and eosin and immunohistochemistry staining. Topical loading of 1 M MnCl 2 damaged the retinal photoreceptor layer with no detectable damage to retina ganglion cell layers or prechiasmatic optic nerves. For the topical loading, 0.75 M MnCl 2 was required to see sufficient enhancement of the optic nerve. At this concentration the visual function was significantly affected, followed by a slow recovery. Intravitreal injection (0.25 μL of 0.2 M MnCl 2 ) slightly affected VA, with full recovery a day later. To conclude, intravitreal MnCl 2 injection provides more reproducible results with less adverse side‐effects than topical loading. Copyright © 2014 John Wiley & Sons, Ltd.