Plusieurs études menées chez le petit animal ont montré que l'IRM réhaussé avec les nanoparticules d'oxyde de fer (USPIO) permettait de détecter la neuroinflammation. Cependant, à notre connaissance, aucune équipe n'avait à ce jour étudié le potentiel de cette approche pour le suivi d'un traitement anti-inflammatoire. Dans ce contexte, nous avons démontré la faisabilité de cette approche pour monitorer les effets de la minocycline suite à une ischémie cérébrale chez la souris. L'IRM est une technique très sensible pour la détection du fer, mais la localisation précise des USPIO tout comme leur quantification est difficile. Nous avons donc proposé de compléter l'approche IRM par une technique inédite à notre connaissance dans le domaine de l'imagerie cérébrale des USPIO : la tomographie par rayonnement Synchrotron. Nous présentons ici les tous premiers résultats montrant la faisabilité de l'approche, ainsi qu'une étude comparée de la sensibilité, des deux techniques pour la détection des USPIO dans le cerveau. Dans la première partioe de notre travail , nous apportons nos résultats concernant la biotransformation des USPIOs dans la rate de la souris dans les 40 premiers jours suivant leur injection intraveineuse obtenus en microscopie électronique par transmission (MET). / Several studies on small animals have shown that MRI enhanced with nanoparticles of iron oxide (USPIO) is able to detect the neuroinflammation. However, to our knowledge, no team had yet investigated the potential of this approach for monitoring an anti-inflammatory treatment. In this context, we have demonstrated the feasibility of this approach to monitor the effects of minocycline after cerebral ischemia in mice. MRI is a very sensitive technique for the detection of iron, but the precise location of USPIO as well as their quantification is difficult. We therefore propsed to complete the MRI approach by a new technique to our knowledge in the field of USPIO imaging in the brain : Synchrotron radiation tomography. We here present the first results showing the feasibility of this approach and a comparative study of the sensitivity of two techniques used for the detection of USPIO in the brain. In the last part of our work, we report our results on the biotransformation of USPIOs in the spleen of the mouse during the first 40 days after intravenous injection obtained by transmission electron microscopy (TEM).

Le travail présenté dans ce mémoire avait pour but d’étudier le potentiel de nouvelles sondes fluorescentes pour la mise au point d’agents d’imagerie optique et d’imagerie Cherenkov inédits. Le premier chapitre porte sur la synthèse de subphtalocyanines et phtalocyanines fluorescentes possédant des fonctions chimiques qui confèrent à la molécule des propriétés adaptées à une application en imagerie médicale. Les composés obtenus ont été étudiés pour déterminer s’ils possèdent les propriétés requises pour l’application visée, en considération du cahier des charges propre aux fluorophores. Dans un deuxième temps, certaines sondes fonctionnelles préparées ont été utilisées pour créer des agents d’imagerie inédits. Dans le cas des subphtalocyanines, la biovectorisation a été explorée par association directe de la sonde avec un peptide, ou indirecte grace à un liposome encapsulant la sonde. Dans le cas des phtalocyanines, les sondes fonctionnelles ont été engagées dans la préparation de nanohybrides constitués de nanoparticules d’oxyde de fer ou de nanotubes d’oxyde de titane, afin d’obtenir des agents bimodaux ou théranostiques. Le troisième chapitre présente l’étude du phénomène de transfert d’énergie (CRET) entre des radioéléments émetteurs Cherenkov et des fluorophores organiques a été étudié. La détermination des paramètres de transfert optimaux a ensuite guidé la mise au point d’une sonde CRET composée d’un fragment fluorescéine lié covalentement à un complexe d’yttrium-90. Pour finir, la possibilité d’émettre dans la fenêtre du proche infrarouge a été explorée par multi-transfert de type CRETFRET. / The goal of this work was to prepare and study new fluorescent probes, which could give rise to novel optical or Cherenkov imaging agents. The first section of this work describes the synthesis of fluorescent subphthalocyanines and phthalocyanines probes, which possess relevant chemicals groups suitable for optical imaging applications. The optical and physico-chemical properties of the new probes were carefully examined to ensure they comply with the specification of the fluorophores for the desired application. The second part focused on the subsequent development of a few selected probes into real imaging agents. The biovectorisation of subphtalocyanines was achieved upon conjugation of a peptide either with the probe or with a liposome that encapsulate the probe. Phthalocyanine-based functional probes were engaged in the synthesis of nanohybrides made of iron oxide nanoparticles or titania nanotubes, to afford bimodal or theranostic agents. In a final part, the energy transfer phenomenon (CRET) between Cherenkov emitting radionuclides and organic fluorophores was studied. The optimal transfer parameters were considered to prepare a CRET probe made of a fluorescein moiety covalently attached to an Yttrium-90 complex. Finally, the ability to emit in the near infrared window was explored by multi-CRET-FRET transfer.

Ce travail de thèse s'inscrit dans le cadre d'une collaboration avec le groupe Guerbet. Il visait à caractériser la lésion qui fait suite à un accident vasculaire cérébral (AVC) ischémique en imagerie par résonance magnétique (IRM) grâce à des agents de contraste novateurs. Guerbet et leurs collaborateurs ont développés des USPIO ciblés (ultrasmall superparamagnetic iron oxide), particules de fer couplées à des peptides reconnaissant spécifiquement un biomarqueur. Dans un modèle d’ischémie cérébrale avec reperfusion réalisé chez la souris, nous avons recherché la capacité de ces agents à caractériser la lésion d’une part en terme de type de mort cellulaire par le ciblage de la phosphatidylsérine (PS), marqueur cellulaire externalisé au cours de l’apoptose, et d’autre part en terme de déficit vasculaire par le ciblage de VCAM-1, molécule d’adhésion impliquée dans le processus inflammatoire. En ce qui concerne l’apoptose, nous avons tout d’abord montré par immunohistochimie l’expression de caspase-3 active, marqueur apoptotique, dès 6 heures et jusqu’à 72 heures après l’ischémie. Cependant, en IRM, l’utilisation d’USPIO ciblant la PS (le P03234 et le P03675) n’a pas permis la détection du phénomène apoptotique. Actuellement d’autres agents de contraste de ce type sont en cours de développement chez Guerbet. En ce qui concerne l’inflammation vasculaire, l’étude de l’expression de VCAM-1 par immunohistochimie a montré l’apparition d’un marquage dès 6 heures après l’ischémie avec un maximum à 24 heures. L’utilisation d’un USPIO-VCAM-1 (le P03011) a permis de mettre en évidence sur les images IRM des zones d’hypointensités dans la lésion, ce qui correspond à la présence de particules de fer. L'analyse histologique de ces cerveaux a montré une colocalisation de l’USPIO avec sa cible VCAM-1, ce qui établit la preuve de concept. Ces travaux ont permis mettre en évidence la capacité d’USPIO développés par Guerbet à cibler des marqueurs biologiques, notamment VCAM-1, à la suite d’une ischémie cérébrale. Ceci suggère que ce type d’agent de contraste pourrait être un bon outil clinique pour la caractérisation de la lésion ischémique chez les patients victimes d’AVC. / This work is a collaboration with Guerbet group. It aimed to characterize the lesion that follows an ischemic stroke with magnetic resonance imaging (MRI) by innovative contrast agents. Guerbet developped targeted USPIO (ultrasmall superparamagnetic iron oxide), which are iron particles coupled to peptides which specifically bind a biomarker. In a mouse model of cerebral ischemia-reperfusion, we studied the capacity of these agents to characterize the lesion on the one hand in terms of cellular death by targeting phosphatidylserin (PS), a cellular marker externalized during apoptosis, and on the other hand in terms of vascular deficit by targeting VCAM-1, an adhesion molecule implied in the inflammatory process. Concerning apoptosis, we showed by immunohistochemistry the expression of active caspase-3, an apoptotic marker, between 6 and 72 hours after ischemia. Nevertheless on MRI, the use of USPIO targeting PS (both P03234 and P03675) did not allow us to detect the apoptotic phenomenon. Currently, other PS-targeted contrast agents are developed by Guerbet. Concerning vascular inflammation, the study of VCAM-1 by immunohistochemistry showed an up-regulated expression 6 hours after ischaemia which reached a maximum at 24 hours. VCAM-1-USPIO (P03011) induced a decrease of the MRI signal appearing as hypointense foci in the lesion, which correspond to iron particles. The histological analysis of these brains showed a colocalisation of the USPIO with its target VCAM-1, which establishes the proof of concept. This work showed the capacity of USPIO developed by Guerbet to target biological markers, particularly VCAM-1, following cerebral ischemia. This suggests that this kind of contrast agent could be a good clinical tool to characterize the ischemic lesion in patients suffering from stroke.

Les nanoparticules d’oxyde de fer de structure spinelle ouvrent de nombreuses voies dans le domaine biomédical. Parmi les applications possibles, les propriétés superparamagnétiques des cristallites d'une dizaine de nanomètres permettent de les utiliser pour le diagnostic médical, notamment en Imagerie par Résonance Magnétique (IRM).Ce travail a consisté à élaborer des suspensions colloïdales de nanoparticules de magnétite ou de maghémite (nommées USPIO pour Ultrasmall SuperParamagnetic Iron Oxide) compatibles avec les conditions physiologiques (pH = 7,4 et [NaCl] = 0,15 M).Par co-précipitation classique, des USPIO, de taille de cristallites de 8 nm, de surface spécifique de 110 m².g-1 et agrégés en assemblages d’environ 20 nm ont été obtenus. Pour stabiliser ces nano-objets, deux voies ont été explorées. Des agents électrostatiques (acide citrique et DMSA) ont modifié la charge nette de surface des oxydes de fer. La stabilisation stérique a également été explorée par greffage de méthoxy-PEG couplés à des fonctions silanes (mPEG-Si). Par combinaison de mPEG2000-Si et de DMSA, des suspensions stables ont également été obtenues. De plus, les fonctions thiols apportées par le DMSA et présentes à la surface des agrégats se trouvent protégées de leur oxydation naturelle par l'encombrement stérique des chaînes de polymère (la formation de ponts disulfures est évitée). La post-fonctionnalisation de ces nanoparticules via ces fonctions thiols est alors possible plusieurs semaines après leur synthèse. Ce concept a été validé par post-greffage d’un fluorophore (0,48 RITC/nm²) pour la détection in vitro en microscopie à fluorescence.En parallèle de cette étude en « batch », des nanoparticules d’oxyde de fer ont été synthétisées en continu à l’aide d’un procédé hydrothermal pouvant s’étendre au domaine eau supercritique. En voie hydrothermale classique, des USPIO stabilisés par des ions citrates ont été obtenus en continu. Grâce aux propriétés physicochimiques de l’eau supercritique, la co-précipitation de magnétite a été possible sans l’utilisation de base.La cytotoxicité et l’internalisation cellulaire de ces USPIO ont été évaluées sur trois modèles cellulaires (macrophages RAW, hépatocytes HepG2 et cardiomyocytes) et les efficacités comme agents de contraste en IRM de ces nanoparticles ont été mesurées sur gel et sur modèle murin et comparées à un agent de contraste commercial à base d’oxyde de fer. Les nanohybrides étudiés n’ont pas présenté de cytotoxicité et ont développé des pouvoirs contrastants comparables à l’agent commercial. La biodistribution hépatique des nanoparticules couplées au mPEG-Si a été retardée de plus de 3 heures ouvrant la voie à des détections spécifiques. / Spinel structured iron oxide nanoparticles open the way of biomedical applications of nanomaterials.Superparamagnetic properties of ten nanometer size crystallites permit to use them in diagnosis such as Magnetic Resonance Imaging (MRI).The aim of this work was to synthesize colloidal suspension of magnetite or maghemite (called USPIO for Ultrasmall SuperParamagnetic Iron Oxide) stable in physiological conditions (pH = 7.4 and [NaCl] = 0.15M).By classical co-precipitation method, UPSIO were synthesized with a mean crystallite size of 8 nm, with a specific surface area of 110 m².g-1 and an aggregate size of 20 nm. To stabilize these nano-objects, two ways were investigated. Electrostatic agents (like citric acid and DMSA) modified iron oxide surface charge. Steric stabilization was also studied by grafting methoxy-PEG coupled with a silane function (mPEG-Si).and the combination mPEG - DMSA also resulted in stable suspensions. Moreover thiols functions coming from DMSA and present on the surface of the nanoparticles were prevented from oxidation thanks to steric protection of polymer chains. Thanks to this method post-functionalization of USPIO was possible several weeks after synthesis. This concept was validated with the post-grafting of a dye (0.48 RITC per nm²) used for in vitro detection in fluorescent microscopy.Nanoparticles were also synthesized in a continuous way with a hydrothermal process which could work from soft chemistry to supercritical water. In classical hydrothermal conditions, USPIO stabilized with citrates were obtained in a continuous way. Thanks to the physico-chemical properties of supercritical water, co-precipitation of magnetite without base adding was possible.Cytotoxicity and cellular internalization assays were done with our USPIO in three cellular models (macrophages RAW, hepatocytes HePG2 and cardiomyocytes). Moreover the efficiency as MRI contrast agents were measured in gels tubes and on mice models and compared to an iron oxide commercial product. Late hepatic biodistribution (more than three hours) was proven with pegylated nanoparticles, which opens the way of specific detections.

<p>Knowledge of the relationship between <i>in vivo</i> contrast agent concentration and magnetic resonance (MR) signal response is an important requirement in contrast enhanced MR imaging in general and in MR based perfusion imaging in particular. This relationship is a complex function of the properties of the contrast agent as well as the structure of the target tissue. The aim of the present work was to quantify the effects of the iron oxide nanoparticle based intravascular contrast agent, NC100150 Injection, on proton relaxation rates in different tissue systems <i>in vivo</i> in a pig model and <i>ex vivo</i> in phantoms containing whole blood. Methods that enabled accurate relaxation rate measurements in these organs were developed, and validated. From these measurements, trans-compartmental water exchange rates and blood volume could be estimated and the MR signal response could be predicted as a function of contrast agent concentration under relevant imaging conditions. </p><p>Using a 1.5 Tesla clinical MR system, the longitudinal (R₁=1/T₁) proton relaxation rates in blood, renal cortex, paraspinal muscle and myocardium were measured <i>in vivo</i> as a function of plasma concentration (C_p) of NC100150 Injection. The transverse (R₂^* = 1/T₂^*) relaxation rates were measured <i>in vivo</i> in blood, renal cortex and muscle as a function of C_p and <i>ex vivo</i> in blood as a function of C_p and blood oxygenation tension. The proton nuclear MR (NMR) linewidth and lineshape were analysed as a function of C_p and blood oxygen tension <i>ex vivo</i> at 7.05 T. </p><p>In muscle and renal cortex, there was a linear correlation between R₂^* and C_p whereas R₂^* increased as a quadratic function of C_pin blood. The NMR linewidth increased linearly with C_p in fully oxygenated blood whereas in deoxygenated blood the linewidth initially decreased with increasing Cp, reaching a minimum and then increasing again with further increase in C_p. R₁ increased linearly with C_p in blood and from the slope of R₁ vs. C_p the T₁-relaxivity (r₁) of NC100150 Injection in blood at 1.5 T was estimated to be (mean ± SD) 13.9 ± 0.9 s^-1mM^-1. In tissue, the maximum increase in R₁ was limited by the rate of water exchange between the intravascular and interstitial tissue compartments. Using a two-compartment exchange-limited relaxation model, the permeability surface area (PS) product was estimated to be 61.9 ± 2.9 mL/min/g in renal cortex and 10.1 ± 1.5 mL/min/g in muscle and the total myocardial water exchange rate, <i>k</i><i>t</i>, was 13.5 ± 6.4 s^-1. The estimated blood volumes obtained from the same model were 19.1 ± 1.4 mL/100 g, 2.4 ± 1.4 mL/100 g and 11.2 ± 2.1 mL/100 g, respectively in renal cortex, muscle and myocardium.</p><p>Current T₂^* based first-pass MR perfusion methods assume a linear correlation between R₂^* and C_p both in blood and tissue and our results therefore suggest that quantitative perfusion values can not easily be obtained with existing tracer kinetic models. The correlation between MR signal response and C_p is further complicated in the kidney by a significant first-pass increase in R₁ which may lead to an underestimation of C_p. In T₁-based perfusion methods, low concentrations of NC100150 Injection must be used in order to maintain a linear dose-response relationship between R₁ and C_p. The effect of blood oxygenation on the NMR linewidth in the presence of NC100150 Injection enabled accurate estimation of magnetic susceptibility of deoxyhemoglobin and the effect can potentially be used to determine blood oxygenation status.</p><p>In conclusion, NC100150 Injection is well suited as a T₂^* perfusion agent due to the large magnetisation and intravascular biodistribution of this agent. T₁-based perfusion imaging with this agent is limited by water exchange effects and large T₂^* effects at higher contrast agent concentrations. Quantitative perfusion assessment is unlikely to be feasible with any of these approaches due to the non-linear dose response.</p>

Knowledge of the relationship between in vivo contrast agent concentration and magnetic resonance (MR) signal response is an important requirement in contrast enhanced MR imaging in general and in MR based perfusion imaging in particular. This relationship is a complex function of the properties of the contrast agent as well as the structure of the target tissue. The aim of the present work was to quantify the effects of the iron oxide nanoparticle based intravascular contrast agent, NC100150 Injection, on proton relaxation rates in different tissue systems in vivo in a pig model and ex vivo in phantoms containing whole blood. Methods that enabled accurate relaxation rate measurements in these organs were developed, and validated. From these measurements, trans-compartmental water exchange rates and blood volume could be estimated and the MR signal response could be predicted as a function of contrast agent concentration under relevant imaging conditions. Using a 1.5 Tesla clinical MR system, the longitudinal (R1=1/T1) proton relaxation rates in blood, renal cortex, paraspinal muscle and myocardium were measured in vivo as a function of plasma concentration (Cp) of NC100150 Injection. The transverse (R2* = 1/T2*) relaxation rates were measured in vivo in blood, renal cortex and muscle as a function of Cp and ex vivo in blood as a function of Cp and blood oxygenation tension. The proton nuclear MR (NMR) linewidth and lineshape were analysed as a function of Cp and blood oxygen tension ex vivo at 7.05 T. In muscle and renal cortex, there was a linear correlation between R2* and Cp whereas R2* increased as a quadratic function of Cp in blood. The NMR linewidth increased linearly with Cp in fully oxygenated blood whereas in deoxygenated blood the linewidth initially decreased with increasing Cp, reaching a minimum and then increasing again with further increase in Cp. R1 increased linearly with Cp in blood and from the slope of R1 vs. Cp the T1-relaxivity (r1) of NC100150 Injection in blood at 1.5 T was estimated to be (mean ± SD) 13.9 ± 0.9 s-1mM-1. In tissue, the maximum increase in R1 was limited by the rate of water exchange between the intravascular and interstitial tissue compartments. Using a two-compartment exchange-limited relaxation model, the permeability surface area (PS) product was estimated to be 61.9 ± 2.9 mL/min/g in renal cortex and 10.1 ± 1.5 mL/min/g in muscle and the total myocardial water exchange rate, kt, was 13.5 ± 6.4 s-1. The estimated blood volumes obtained from the same model were 19.1 ± 1.4 mL/100 g, 2.4 ± 1.4 mL/100 g and 11.2 ± 2.1 mL/100 g, respectively in renal cortex, muscle and myocardium. Current T2* based first-pass MR perfusion methods assume a linear correlation between R2* and Cp both in blood and tissue and our results therefore suggest that quantitative perfusion values can not easily be obtained with existing tracer kinetic models. The correlation between MR signal response and Cp is further complicated in the kidney by a significant first-pass increase in R1 which may lead to an underestimation of Cp. In T1-based perfusion methods, low concentrations of NC100150 Injection must be used in order to maintain a linear dose-response relationship between R1 and Cp. The effect of blood oxygenation on the NMR linewidth in the presence of NC100150 Injection enabled accurate estimation of magnetic susceptibility of deoxyhemoglobin and the effect can potentially be used to determine blood oxygenation status. In conclusion, NC100150 Injection is well suited as a T2* perfusion agent due to the large magnetisation and intravascular biodistribution of this agent. T1-based perfusion imaging with this agent is limited by water exchange effects and large T2* effects at higher contrast agent concentrations. Quantitative perfusion assessment is unlikely to be feasible with any of these approaches due to the non-linear dose response.

Dextran-coated ultra-small, superparamagnetic, iron oxide particles (USPIO) have been proposed as magnetic resonance (MR) lymph node contrast agents. This thesis analyzed the topographic distributions of the pelvic and inguinal lymph nodes and quantified their spatial relations with the adjacent vascular system. We hypothesized that USPIO would facilitate identification of normal lymph nodes in a manner superior to that afforded by computed tomography or unenhanced MR, but using current clinically available scanners would be unlikely to identify microscopic nodal metastases. We have constructed a high quality nodal atlas describing probability distributions for lymph node number, size and position. Using this model, we then defined a generic three-dimensional nodal clinical target volume and a means of accurate delineation of this volume in a three-dimensional representation. This is the most quantitative assessment of the pelvic and inguinal lymphatics to date and will help to improve the successful targeting of lymph nodes for radiotherapy.

Dextran-coated ultra-small, superparamagnetic, iron oxide particles (USPIO) have been proposed as magnetic resonance (MR) lymph node contrast agents. This thesis analyzed the topographic distributions of the pelvic and inguinal lymph nodes and quantified their spatial relations with the adjacent vascular system. We hypothesized that USPIO would facilitate identification of normal lymph nodes in a manner superior to that afforded by computed tomography or unenhanced MR, but using current clinically available scanners would be unlikely to identify microscopic nodal metastases. We have constructed a high quality nodal atlas describing probability distributions for lymph node number, size and position. Using this model, we then defined a generic three-dimensional nodal clinical target volume and a means of accurate delineation of this volume in a three-dimensional representation. This is the most quantitative assessment of the pelvic and inguinal lymphatics to date and will help to improve the successful targeting of lymph nodes for radiotherapy.

Background Although abdominal aortic aneurysm (AAA) growth is non-linear, serial measurements of aneurysm diameter are the mainstay of aneurysm surveillance and contribute to decisions on timing of intervention. Aneurysm biology plays a key part in disease evolution but is not currently routinely assessed in clinical practice. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography-Computed Tomography (PET-CT) provide insight into disease processes on a cellular or molecular level, and represent exciting new imaging biomarkers of disease activity. Macrophage-mediated inflammation may be assessed using ultrasmall superparamagnetic particles of iron oxide (USPIO) MRI and the PET radiotracer 18FSodium Fluoride (18F-NaF) identifies microcalcification which is a response to underlying necrotic inflammation. The central aim of this thesis was to investigate these imaging modalities in patients with AAA. Methods and Results USPIO MRI: MULTI-CENTRE STUDY In a prospective multi-centre observational cohort study, 342 patients (85.4% male, mean age 73.1±7.2 years, mean AAA diameter 49.6±7.7mm) with asymptomatic AAA ≥4 cm anteroposterior diameter underwent MRI before and 24-36 hours after intravenous administration of USPIO. Colour maps (depicting the change in T2* caused by USPIO) were used to classify aneurysms on the basis of the presence of USPIO uptake in the aneurysm wall, representing mural inflammation. Intra- and inter-observer agreement were found to be very good, with proportional agreement of 0.91 (kappa 0.82) and 0.83 (kappa 0.66), respectively. At 1 year, there was 29.3% discordant classification of aneurysms on repeated USPIO MRI and at 2 years, discordance was 65%, suggesting that inflammation evolves over time. In the observational study, after a mean of 1005±280 days of follow up, there were 126 (36.8%) aneurysm repairs and 17 (5.0%) ruptures. Participants with USPIO enhancement (42.7%) had increased aneurysm expansion rates (3·1±2·5 versus 2·5±2·4 mm/year; difference 0·6 [95% confidence intervals (CI), 0·02 to 1·2] mm/year, p=0·0424) and had higher rates of aneurysm rupture or repair (69/146=47·3% versus 68/191=35·6%; difference 11·7%, 95% CI 1·1 to 22·2%, p=0·0308). USPIO MRI was therefore shown to predict AAA expansion and the composite of rupture or repair, however this was not independent of aneurysm diameter (c-statistic, 0·7924 to 0·7926; unconditional net reclassification -13·5%, 95% confidence intervals -36·4% to 9·3%). 18F-NaF PET-CT: SINGLE-CENTRE STUDY A sub-group of 76 patients also underwent 18F-NaF PET-CT, which was evaluated using the maximum tissue-to-background ratio (TBRmax) in the most diseased segment (MDS), a technique that showed very good intra- (ICC 0.70-0.89) and inter-observer (ICC 0.637-0.856) agreement. Aneurysm tracer uptake was compared firstly in a case-control study, with 20 patients matched to 20 control patients for age, sex and smoking status. 18F-NaF uptake was higher in aneurysm when compared to control aorta (log2TBRmax 1.712±0.560 vs. 1.314±0.489; difference 0.398 (95% CI 0.057, 0.739), p=0.023), or to non-aneurysmal aorta in patients with AAA (log2TBRmax 1.647±0.537 vs. 1.332±0.497; difference 0.314 (95% CI 0.0685, 0.560), p=0.004). An ex vivo study was performed on aneurysm and control tissue, which demonstrated that 18F-NaF uptake on microPET-CT was higher in the aneurysm hotspots and higher in aneurysm tissue compared to control tissue. Histological analysis suggested that 18F-NaF was highest in areas of focal calcification and necrosis. In an observational cohort study, aneurysms were stratified by tertiles of TBRmax in the MDS and followed up for 510±196 days, with 6 monthly serial ultrasound measurements of diameter. Those in the highest tertile of tracer uptake expanded more than 2.5 times more rapidly than those in the lowest tertile (3.10 [3.58] mm/year vs. 1.24 [2.41] mm/year, p=0.008) and were also more likely to experience repair or rupture (15.3% vs. 5.6%, log-rank p=0.043). In multivariable analyses, 18F-NaF uptake on PET-CT emerged as an independent predictor of AAA expansion (p=0.042) and rupture or repair (HR 2.49, 95% CI1.07, 5.78; p=0.034), even when adjusted for age, sex, body mass index, systolic blood pressure, current smoking and, crucially, aneurysm diameter. Conclusion These are the largest USPIO MRI and PET-CT studies in AAA disease to date and the first to investigate 18F-NaF. Both USPIO MRI and 18F-NaF PET-CT are able to predict AAA expansion and the composite of rupture and repair, with 18F-NaF PETCT emerging as the first imaging biomarker that independently predicts expansion and AAA events, even after adjustment for aneurysm diameter. This represents an exciting new predictor of disease progression that adds incremental value to standard clinical assessments. Feasibility and randomised clinical trials are now required to assess the potential of this technique to change the management and outcome of patients with AAA.

Several studies on small animals have shown that MRI enhanced with nanoparticles of iron oxide (USPIO) is able to detect the neuroinflammation. However, to our knowledge, no team had yet investigated the potential of this approach for monitoring an anti-inflammatory treatment. In this context, we have demonstrated the feasibility of this approach to monitor the effects of minocycline after cerebral ischemia in mice. MRI is a very sensitive technique for the detection of iron, but the precise location of USPIO as well as their quantification is difficult. We therefore propsed to complete the MRI approach by a new technique to our knowledge in the field of USPIO imaging in the brain : Synchrotron radiation tomography. We here present the first results showing the feasibility of this approach and a comparative study of the sensitivity of two techniques used for the detection of USPIO in the brain. In the last part of our work, we report our results on the biotransformation of USPIOs in the spleen of the mouse during the first 40 days after intravenous injection obtained by transmission electron microscopy (TEM).