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Degradation, Metabolism and Relaxation Properties of Iron Oxide Particles for Magnetic Resonance Imaging

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Degradation, Metabolism and Relaxation Properties of Iron Oxide Particles for Magnetic Resonance Imaging Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1362 Degradation, Metabolism and Relaxation Properties of Iron Oxide Particles for Magnetic Resonance Imaging BY KAREN BRILEY SAEBO ACTA UNIVERSITATIS UPSALIENSIS UPPSALA 2004 Uppsala University Department of Oncology, Radiology and Clinical Immunology Section of Radiology Akademiska sjukhuset SE-751 85 Uppsala, Sweden Dissertation in Radiology to be publicly examined in Gröwallsalen, Akademiska sjukhuset, Uppsala, Th ursday, June 3, 2004, at 13:15, for the degree of Doctor of Philosophy (Faculty of Medicine). Th e examination will be conducted in English. Abstract Briley Saebo, K. Degradation, Metabolism and Relaxation Properties of Iron Oxide Particles for Mag- netic Resonance Imaging. Acta Universitatis Upsaliensis. Comprehensive summaries of Uppsala Disser- tations from the Faculty of Medicine 1362. 92 pp. Uppsala. ISBN 91-554-5998-6. Whereas the eff ect of size and coating material on the pharmacokinetics and biodistribution of iron oxide based contrast agents are well documented, the eff ect of these parameters on liver metabolism has never been investigated. Th e primary purpose of this work was to evaluate the eff ect of iron oxide particle size and coating on the rate of liver clearance and particle degradation using a rat model. Th e magnetic and relaxation properties of fi ve diff erent iron oxide contrast agents were determined prior to the onset of the animal studies. Th e R2* values and the T1-enhancing effi cacy of the agents were also evaluated in blood using phantom models. Th e results of these studies indicated that the effi - cacy of these agents was matrix and frequency dependent. Correlations between the R2* values and the magnetic properties of the agents were established and a new parameter, Msat/r1, was created to enable better estimations of contrast agent T1-enhancing effi cacy in blood. Th e bio-distribution of one of the agents was also evaluated to assess the importance of sub-cellular particle distribution, using an isolated rat liver cell model. Phantom models were also used to verify that materials with magnetic properties similar to the particle breakdown products (ferritin/hemo- siderin) may induce signal reduction when compartmentalized in a liver cell suspension. Th e results revealed that the cellular distribution of the agent did not infl uence the rate of particle degradation. Th is fi nding confl icted with current theory. Additionally, the study indicated that the compartmen- talization of magnetic materials similar to ferritin may induce signifi cant signal loss. Methods enabling the accurate determination of contrast agent concentration in the liver were devel- oped and validated using one of the agents. From these measurements the liver half-life of the agent was estimated and compared to the rate of liver clearance, as determined from the evolution of the eff ective transverse relaxation rate (R2*) in rat liver. Th e results indicate that the liver R2* enhance- ment persisted at time points when the concentration of contrast agent present in the liver was below method detection limits. Th e prolonged R2* enhancement was believed to be a result of the compart- mentalisation of the particle breakdown products within the liver cells. Finally, the liver clearance and degradation rates of the fi ve diff erent iron oxide particles in rat liver were evaluated. Th e results revealed that for materials with similar iron oxide cores and particle sizes, the rate of liver clearance was aff ected by the coating material present. Materials with similar coating, but diff erent sizes, exhibited similar rates of liver clearance. In conclusion, the results of this work strongly suggest that coating material of the iron oxide par- ticles may contribute signifi cantly to the rate of iron oxide particle clearance and degradation in rat liver cells. Key words: Magnetic Resonance Imaging; contrasts agents, iron oxide particles, metabolism, relaxa- tion mechanisms. Karen Briley Saebo, Department of Oncology, Radiology and Clinical Immunology, Akademiska sjukhuset, Uppsala University, SE-751 85 Uppsala, Sweden © Karen Briley Saebo 2004 ISSN 0282-7476 ISBN 91-554-5998-6 urn:nbn:se:uu:diva-4311 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4311) ˜ To my loving husband Jan Eystein. To love someone deeply gives you strength. Being loved by someone deeply gives you courage. ˜ ORIGINAL PAPERS I. Characterisation of Th e Relaxation and Magnetic Properties of Five Diff erent Iron Oxide Particles: Evaluation of T1-enhancing Effi cacy. Karen Briley-Saebo, Yves Gossuin, Alan Roch, Håkan Ahlström, Robert N Muller and Atle Bjornerud Submitted MRM II. Hepatic Cellular Distribution and Degradation of Iron Oxide Nanoparticles Fol- lowing Single Intravenous Injection in Rats: Implications For Magnetic Resonance Imaging. Karen Briley-Saebo, Atle Bjornerud, Derek Grant, Håkan Ahlström, Trond Berg and Grete Mork Kindberg In press Cell Tissue Res. 2004 III. Long-Term Imaging Eff ects in Rat Liver Following a Single Injection of an Iron Oxide Nanoparticle Based MR Contrast Agent. Karen Briley-Saebo, Svein Olaf Hustvedt, Anita Haldorsen and Atle Bjornerud Accepted JMRI 2004 IV. Temporal Changes in Liver R2* Values of Various Superparamagnetic Iron Oxide Contrast Agents: Importance of Hydrated Particle Size and Coating Material on Th e Rate of Liver Clearance. Karen C. Briley-Saebo, Lars O. Johansson, Svein Olaf Hustvedt, Anita Haldorsen, Atle Bjornerud and Håkan Ahlström Submitted Invest Radiol 5 CONTENTS Abstract ......................................................................................................3 Original papers ............................................................................................5 1. Abbreviations ........................................................................................8 2. Introduction ....................................................................................... 11 Summary ................................................................................................................11 2.1 Basics of MRI ........................................................................................... 12 2.1.1 Historical Overview ..................................................................................12 2.1.2 Classical Physics of MRI ............................................................................13 2.1.3 Magnetic Properties of Molecules .............................................................17 2.1.4 Contrast Agents and Measurement of Relaxation Times .......................... 24 2.1.5 Relaxation of water protons by iron oxide particles: Relaxation theory ......35 2.2 Iron metabolism .......................................................................................46 2.2.1 Transferrin ................................................................................................48 2.2.2 Ferritin ......................................................................................................51 2.2.3 Th e Liver and Cells of the RES ..................................................................53 3. Study Aims ......................................................................................... 57 3.1 Main Aims ................................................................................................57 3.2 Specifi c Aims .............................................................................................57 3.3 Purpose of individual studies .....................................................................57 3.3.1 Study I .......................................................................................................57 3.3.2 Study II ....................................................................................................58 3.3.3 Study III ...................................................................................................58 3.3.4 Study IV ...................................................................................................58 6 4. Methods .............................................................................................. 59 4.1 Test systems ...............................................................................................59 4.2 Ex vivo Models (All studies) .......................................................................59 4.3 Animal Models (Studies II, III and IV) .....................................................61 4.4 Contrast Agents ........................................................................................62 4.5 MR Imaging (All studies) ......................................................................... 63 4.6 Determination of R2* values (All studies) ................................................ 64 4.7 Relaxation Analysis ...................................................................................64 4.8 Magnetisation and core size (Study I) ....................................................... 66 4.9 Particle size (Studies I and IV) ..................................................................66 4.10 Total Iron determination (All studies) ...................................................... 66 4.11 Phantom preparation (Studies I and II) .................................................... 66 5. Results and Discussions ...................................................................... 67 5.1 Study I .......................................................................................................67 5.2 Study II ....................................................................................................72
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