Fluorine-19 magnetic resonance angiography of the mouse.

PURPOSE: To implement and characterize a fluorine-19 ((19)F) magnetic resonance imaging (MRI) technique and to test the hypothesis that the (19)F MRI signal in steady state after intravenous injection of a perfluoro-15-crown-5 ether (PCE) emulsion may be exploited for angiography in a pre-clinical in vivo animal study. MATERIALS AND METHODS: In vitro at 9.4T, the detection limit of the PCE emulsion at a scan time of 10 min/slice was determined, after which the T(1) and T(2) of PCE in venous blood were measured. Permission from the local animal use committee was obtained for all animal experiments. 12 µl/g of PCE emulsion was intravenously injected in 11 mice. Gradient echo (1)H and (19)F images were obtained at identical anatomical levels. Signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were determined for 33 vessels in both the (19)F and (1)H images, which was followed by vessel tracking to determine the vessel conspicuity for both modalities. RESULTS: In vitro, the detection limit was ∼400 µM, while the (19)F T(1) and T(2) were 1350±40 and 25±2 ms. The (19)F MR angiograms selectively visualized the vasculature (and the liver parenchyma over time) while precisely coregistering with the (1)H images. Due to the lower SNR of (19)F compared to (1)H (17±8 vs. 83±49, p<0.001), the (19)F CNR was also lower at 15±8 vs. 52±35 (p<0.001). Vessel tracking demonstrated a significantly higher vessel sharpness in the (19)F images (66±11 vs. 56±12, p = 0.002). CONCLUSION: (19)F magnetic resonance angiography of intravenously administered perfluorocarbon emulsions is feasible for a selective and exclusive visualization of the vasculature in vivo

Fluorine MR Imaging of Inflammation in Atherosclerotic Plaque in Vivo.

PURPOSE: To preliminarily test the hypothesis that fluorine 19 ((19)F) magnetic resonance (MR) imaging enables the noninvasive in vivo identification of plaque inflammation in a mouse model of atherosclerosis, with histologic findings as the reference standard. MATERIALS AND METHODS: The animal studies were approved by the local animal ethics committee. Perfluorocarbon (PFC) emulsions were injected intravenously in a mouse model of atherosclerosis (n = 13), after which (19)F and anatomic MR imaging were performed at the level of the thoracic aorta and its branches at 9.4 T. Four of these animals were imaged repeatedly (at 2-14 days) to determine the optimal detection time. Repeated-measures analysis of variance with a Tukey test was applied to determine if there was a significant change in (19)F signal-to-noise ratio (SNR) of the plaques and liver between the time points. Six animals were injected with a PFC emulsion that also contained a fluorophore. As a control against false-positive results, wild-type mice (n = 3) were injected with a PFC emulsion, and atherosclerotic mice were injected with a saline solution (n = 2). The animals were sacrificed after the last MR imaging examination, after which high-spatial-resolution ex vivo MR imaging and bright-field and immunofluorescent histologic examination were performed. RESULTS: (19)F MR signal was detected in vivo in plaques in the aortic arch and its branches. The SNR was found to significantly increase up to day 6 (P < .001), and the SNR of all mice at this time point was 13.4 ± 3.3. The presence of PFC and plaque in the excised vessels was then confirmed both through ex vivo (19)F MR imaging and histologic examination, while no signal was detected in the control animals. Immunofluorescent histologic findings confirmed the presence of PFC in plaque macrophages. CONCLUSION: (19)F MR imaging allows the noninvasive in vivo detection of inflammation in atherosclerotic plaques in a mouse model of atherosclerosis and opens up new avenues for both the early detection of vulnerable atherosclerosis and the elucidation of inflammation mechanisms in atherosclerosis

Characterization of perfluorocarbon relaxation times and their influence on the optimization of fluorine-19 MRI at 3 tesla.

To characterize and optimize javax.xml.bind.JAXBElement@7524a985 F MRI for different perfluorocarbons (PFCs) at 3T and quantify the loss of acquisition efficiency as a function of different temperature and cellular conditions. The T javax.xml.bind.JAXBElement@1ef4ca84 and T javax.xml.bind.JAXBElement@295b7e6f relaxation times of the commonly used PFCs perfluoropolyether (PFPE), perfluoro-15-crown-5-ether (PFCE), and perfluorooctyl bromide (PFOB) were measured in phantoms and in several different conditions (cell types, presence of fixation agent, and temperatures). These relaxation times were used to optimize pulse sequences through numerical simulations. The acquisition efficiency in each cellular condition was then determined as the ratio of the signal after optimization with the reference relaxation times and after optimization with its proper relaxation times. Finally, PFC detection limits were determined. The loss of acquisition efficiency due to parameter settings optimized for the wrong temperature and cellular condition was limited to 13%. The detection limits of all PFCs were lower at 24 °C than at 37 °C and varied from 11.8 ± 3.0 mM for PFCE at 24 °C to 379.9 ± 51.8 mM for PFOB at 37 °C. Optimizing javax.xml.bind.JAXBElement@30187e57 F pulse sequences with a known phantom only leads to moderate loss in acquisition efficiency in cellular conditions that might be encountered in in vivo and in vitro experiments. Magn Reson Med 77:2263-2271, 2017. © 2016 International Society for Magnetic Resonance in Medicine

Cardiovascular Molecular Imaging With Fluorine-19 MRI: The Road to the Clinic.

Fluorine-19 ( <sup>19</sup> F) magnetic resonance imaging is a unique quantitative molecular imaging modality that makes use of an injectable fluorine-containing tracer that generates the only visible <sup>19</sup> F signal in the body. This hot spot imaging technique has recently been used to characterize a wide array of cardiovascular diseases and seen a broad range of technical improvements. Concurrently, its potential to be translated to the clinical setting is being explored. This review provides an overview of this emerging field and demonstrates its diagnostic potential, which shows promise for clinical translation. We will describe <sup>19</sup> F magnetic resonance imaging hardware, pulse sequences, and tracers, followed by an overview of cardiovascular applications. Finally, the challenges on the road to clinical translation are discussed

In vivo clearance of 19F MRI imaging nanocarriers is strongly influenced by nanoparticle ultrastructure

Perfluorocarbons hold great promise both as imaging agents, particularly for (19)F MRI, and in therapy, such as oxygen delivery. (19)F MRI is unique in its ability to unambiguously track and quantify a tracer while maintaining anatomic context, and without the use of ionizing radiation. This is particularly well-suited for inflammation imaging and quantitative cell tracking. However, perfluorocarbons, which are best suited for imaging - like perfluoro-15-crown-5 ether (PFCE) - tend to have extremely long biological retention. Here, we showed that the use of a multi-core PLGA nanoparticle entrapping PFCE allows for a 15-fold reduction of half-life in vivo compared to what is reported in literature. This unexpected rapid decrease in (19)F signal was observed in liver, spleen and within the infarcted region after myocardial infarction and was confirmed by whole body NMR spectroscopy. We demonstrate that the fast clearance is due to disassembly of the ~200 nm nanoparticle into ~30 nm domains that remain soluble and are cleared quickly. We show here that the nanoparticle ultrastructure has a direct impact on in vivo clearance of its cargo i.e. allowing fast release of PFCE, and therefore also bringing the possibility of multifunctional nanoparticle-based imaging to translational imaging, therapy and diagnostics

In vivo mapping of deep tissue pO2 in a murine model of peripheral artery disease by noninvasive ^19F MR relaxometry

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RV POSEIDON Cruise Report POS473 LORELEI II: LOphelia REef Lander Expedition and Investigation II, Tromsø – Bergen – Esbjerg, 15.08. – 31.08. – 04.09.2014

As a result of the raising CO2-emissions and the resultant ocean acidification (decreasing pH and carbonate ion concentration), the impact on marine organism that build their skeletons and protective shells with calcium carbonate (e.g., mollusks, sea urchins, coccolithophorids, and stony corals) becomes more and more detrimental. In the last few years, many experiments with tropical reef building corals have shown, that a lowering of the carbonate ion concentration significantly reduces calcification rates and therefore growth (e.g., Gattuso et al. 1999; Langdon et al. 2000, 2003; Marubini et al. 2001, 2002). In the middle of this century, many tropical coral reefs may well erode faster than they can rebuild. Cold-water corals are living in an environment (high geographical latitude, cold and deep waters) already close to a critical carbonate ion concentration below calcium carbonate dissolves. Actual projections indicate that about 70% of the currently known Lophelia reef structures will be in serious danger until the end of the century (Guinotte et al. 2006). Therefore L. pertusa was cultured at GEOMAR to determine its long-term response to ocean acidification. Our work has revealed that – unexpectedly and controversially to the majority of warm-water corals – this species is potentially able to cope with elevated concentrations of CO2. Whereas short-term (1 week) high CO2 exposure resulted in a decline of calcification by 26-29 % for a pH decrease of 0.1 units and net dissolution of calcium carbonate, L. pertusa was capable to acclimate to acidified conditions in long-term (6 months) incubations, leading to slightly enhanced rates of calcification (Form & Riebesell, 2012). But all these studies were carried out in the laboratory under controlled conditions without considering natural variability and ecosystem interactions with the associated fauna. Moreover, only very little is known about the nutrition (food sources and quantity) of cold-water corals in their natural habitat. In a multifactorial laboratory study during BIOACID phase II we could show that food availability is one of the key drivers that promote the capability of these organisms to withstand environmental pressures such as alterations in the carbonate chemistry and temperature (Büscher, Form & Riebesell, in prep.). To take into account the influences of natural fluctuations and interactions (e.g. bioerosion), we aim to merge in-situ results from the two research cruises POS455 and POS473 with laboratory experimental studies for a comprehensive understanding of likely ecosystem responses under past, present and future environmental conditions

Phenotyping placental oxygenation in Lgals1 deficient mice using (19)F MRI

Placental hypoperfusion and hypoxia are key drivers in complications during fetal development such as fetal growth restriction and preeclampsia. In order to study the mechanisms of disease in mouse models, the development of quantitative biomarkers of placental hypoxia is a prerequisite. The goal of this exploratory study was to establish a technique to noninvasively characterize placental partial pressure of oxygen (PO(2)) in vivo in the Lgals1 (lectin, galactoside-binding, soluble, 1) deficient mouse model of preeclampsia using fluorine magnetic resonance imaging. We hypothesized a decrease in placental oxygenation in knockout mice. Wildtype and knockout animals received fluorescently labeled perfluoro-5-crown-15-ether nanoemulsion i.v. on day E14-15 during pregnancy. Placental PO(2) was assessed via calibrated (19)F MRI saturation recovery T(1) mapping. A gas challenge with varying levels of oxygen in breathing air (30%, 60% and 100% O(2)) was used to validate that changes in oxygenation can be detected in freely breathing, anesthetized animals. At the end of the experiment, fluorophore-coupled lectin was injected i.v. to label the vasculature for histology. Differences in PO(2) between breathing conditions and genotype were statistically analyzed with linear mixed-effects modeling. As expected, a significant increase in PO(2) with increasing oxygen in breathing air was found. PO(2) in Lgals1 knockout animals was decreased but this effect was only present at 30% oxygen in breathing air, not at 60% and 100%. Histological examinations showed crossing of the perfluorocarbon nanoemulsion to the fetal blood pool but the dominating contribution of (19)F MR signal is estimated at > 70% from maternal plasma based on volume fraction measurements of previous studies. These results show for the first time that (19)F MRI can characterize oxygenation in mouse models of placental malfunction