Advances in MRI-Based Detection of Cerebrovascular Changes after Experimental Traumatic Brain Injury

Traumatic brain injury is a heterogeneous and multifaceted neurological disorder that involves diverse pathophysiological pathways and mechanisms. Thorough characterization and monitoring of the brain’s status after neurotrauma is therefore highly complicated. Magnetic resonance imaging (MRI) provides a versatile tool for in vivo spatiotemporal assessment of various aspects of central nervous system injury, such as edema formation, perfusion disturbances and structural tissue damage. Moreover, recent advances in MRI methods that make use of contrast agents have opened up additional opportunities for measurement of events at the level of the cerebrovasculature, such as blood–brain barrier permeability, leukocyte infiltration, cell adhesion molecule upregulation and vascular remodeling. It is becoming increasingly clear that these cerebrovascular alterations play a significant role in the progression of post-traumatic brain injury as well as in the process of post-traumatic brain repair. Application of advanced multiparametric MRI strategies in experimental, preclinical studies may significantly aid in the elucidation of pathomechanisms, monitoring of treatment effects, and identification of predictive markers after traumatic brain injury

Characterisation of tumour vasculature in mouse brain by USPIO contrast-enhanced MRI

To enhance the success rate of antiangiogenic therapies in the clinic, it is crucial to identify parameters for tumour angiogenesis that can predict response to these therapies. In brain tumours, one such parameter is vascular leakage, which is a response to tumour-derived vascular endothelial growth factor-A and can be measured by Gadolinium-DTPA (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). However, as vascular permeability and angiogenesis are not strictly coupled, tumour blood volume may be another potentially important parameter. In this study, contrast-enhanced MR imaging was performed in three orthotopic mouse models for human brain tumours (angiogenic melanoma metastases and E34 and U87 human glioma xenografts) using both Gd-DTPA to detect vascular leakage and ultrasmall iron oxide particles (USPIO) to measure blood volume. Pixel-by-pixel maps of the enhancement in the transverse relaxation rates (ΔR2 and ΔR2*) after injection of USPIO provided an index proportional to the blood volume of the microvasculature and macrovasculature, respectively, for each tumour. The melanoma metastases were characterised by a blood volume and vessel leakage higher than both glioma xenografts. The U87 glioblastoma xenografts displayed higher permeability and blood volume in the rim than in the core. The E34 glioma xenografts were characterised by a relatively high blood volume, accompanied by only a moderate blood–brain barrier disruption. Delineation of the tumour was best assessed on post-USPIO gradient-echo images. These findings suggest that contrast-enhanced MR imaging using USPIOs and, in particular, ΔR2 and ΔR2* quantitation, provides important additional information about tumour vasculature

Activatable Nanoprobes for Intracellular Drug Delivery

An activatable nanoprobe is provided having a core component and an active agent associated with the core component via a bond configured to be cleaved upon exposure to an endogenous compound

Clinically Translatable Cell Tracking and Quantification by MRI in Cartilage Repair Using Superparamagnetic Iron Oxides

Background: Articular cartilage has very limited intrinsic regenerative capacity, making cell-based therapy a tempting approach for cartilage repair. Cell tracking can be a major step towards unraveling and improving the repair process of these therapies. We studied superparamagnetic iron oxides (SPIO) for labeling human bone marrow-derived mesenchymal stem cells (hBMSCs) regarding effectivity, cell viability, long term metabolic cell activity, chondrogenic differentiation and hBMSC secretion profile. We additionally examined the capacity of synovial cells to endocytose SPIO from dead, labeled cells, together with the use of magnetic resonance imaging (MRI) for intra-articular visualization and quantification of SPIO labeled cells. Methodology/Prinicipal Findings: Efficacy and various safety aspects of SPIO cell labeling were determined using appropriate assays. Synovial SPIO re-uptake was investigated in vitro by co-labeling cells with SPIO and green fluorescent protein (GFP). MRI experiments were performed on a clinical 3.0T MRI scanner. Two cell-based cartilage repair techniques were mimicked for evaluating MRI traceability of labeled cells: intra-articular cell injection and cell implantation in cartilage defects. Cells were applied ex vivo or in vitro in an intra-articular environment and immediately scanned. SPIO labeling was effective and did not impair any of the studied safety aspects, including hBMSC secretion profile. SPIO from dead, labeled cells could be taken up by synovial cells. Both injected and implanted SPIO-labeled cells could accurately be visualized by MRI in a clinically relevant sized joint model using clinically applied cell doses. Finally, we quantified the amount of labeled cells seeded in cartilage defects using MR-based relaxometry. Conclusions: SPIO labeling appears to be safe without influencing cell behavior. SPIO labeled cells can be visualized in an intra-articular environment and quantified when seeded in cartilage defects.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Development and Optimization of 19F-MRI for Tracking Cellular Therapeutics

Introduction: This thesis aims to advance magnetic resonance imaging (MRI) for imaging cellular therapeutics. Traditional, proton-based, MRI provides detailed anatomical images, particularly of soft tissue. However, in order to obtain information at a cellular level specialized imaging agents are required to detect the cells of interest. Perfluorocarbons containing non-radioactive fluorine-19 (19F) are both biologically safe and MR sensitive. Methods: Pre-clinical 19F-MRI was implemented on a Varian 9.4T MRI scanner, using a dual 19F/1H-tuned birdcage volume coil. Mesenchymal stromal cells (MSC) were pre-labeled with a commercial, FDA approved 19F-perfluorocarbon emulsion, then implanted intramuscularly into the mouse hindlimb. To track the inflammation resulting from transplantation, a dual-agent cellular MRI technique was developed. This technique utilizes 19F to track MSC and superparamagnetic iron oxide nanoparticles (SPIO) to image macrophages, through the presence of signal quenching. A clinical imaging protocol was developed to translate 19F-MRI on a 3T GE MR750 scanner with a dual 19F/1H-tuned surface coil. Peripheral blood mononuclear cells (PBMC) were labeled with a FDA-approved 19F-agent and injected into a ham shank phantom for protocol optimization. Results: The balanced steady-state free precession pulse sequence was chosen for all studies due to the high signal-to-noise per unit time. Image acquisition was optimized for 19F detection sensitivity, accuracy of quantification, and compatibility with isoflurane. In vivo quantification of MSC on the day of implantation was in strong agreement with the expected number of cells. The change in 19F-signal was quantified over time and compared between two murine transplantation models. When iron oxide was administered i.v., the migration of immune cells could be tracked to the injection site. The presence of SPIO decreased both the 1H and 19F signal, indicating that transplant rejection was occurring. On a clinical system, as few as 4x106 PBMC could be imaged following both surface and subcutaneous injection. The minimum number of detectable cells was strongly influenced by intracellular 19F uptake. Conclusions: 19F-MRI is a promising tool for imaging cellular therapeutics. By pre-labeling cells of interest, they can be localized and the change in signal can be quantified over time. The technique shows promise for both pre-clinical and clinical applications

Cellular Imaging in Regenerative Medicine, Cancer and Osteoarthritis

In this thesis we showed different methods to label cells for cellular imaging to determine their role in diagnosis and therapy of various diseases

Acute effects of ferumoxytol on regulation of renal hemodynamics and oxygenation

The superparamagnetic iron oxide nanoparticle ferumoxytol is increasingly used as intravascular contrast agent in magnetic resonance imaging (MRI). This study details the impact of ferumoxytol on regulation of renal hemodynamics and oxygenation. In 10 anesthetized rats, a single intravenous injection of isotonic saline (used as volume control) was followed by three consecutive injections of ferumoxytol to achieve cumulative doses of 6, 10, and 41 mg Fe/kg body mass. Arterial blood pressure, renal blood flow, renal cortical and medullary perfusion and oxygen tension were continuously measured. Regulation of renal hemodynamics and oxygenation was characterized by dedicated interventions: brief periods of suprarenal aortic occlusion, hypoxia, and hyperoxia. None of the three doses of ferumoxytol resulted in significant changes in any of the measured parameters as compared to saline. Ferumoxytol did not significantly alter regulation of renal hemodynamics and oxygenation as studied by aortic occlusion and hypoxia. The only significant effect of ferumoxytol at the highest dose was a blunting of the hyperoxia-induced increase in arterial pressure. Taken together, ferumoxytol has only marginal effects on the regulation of renal hemodynamics and oxygenation. This makes ferumoxytol a prime candidate as contrast agent for renal MRI including the assessment of renal blood volume fraction