Kannie Wai Yan Chan^1,2, Xiaolei Song^1,2, Guanshu Liu^1,3, Dian Arifin^1,2, Heechul Kim^1,2, Chulani Galpoththawela^1,2, Ming Yang⁴, Justin Hanes^4,5, Assaf Gilad^1,2, Piotr Walczak^1,2, Jeff W. M. Bulte^1,2, and Michael T McMahon^1,3
1Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Baltimore, MD, United States, ³F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, ⁴Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States,⁵Department of Oncology and The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Semi-permeable microcapsules have been used previously to immunoprotect and visualize therapeutic cells after transplantation. We have constructed pH-sensitive microcapsules which generate CEST contrast dependent on the local physicochemical microenvironment. These capsules can be tracked and also used as a unique way to monitor cell viability through MRI. In this study, we have tested whether or not our new CEST microcapsules could monitor the viability of hepatocytes expressing luciferase both in vitro and in vivo. We observed a decrease in CEST contrast with decreasing hepatocyte viability upon administration of STS in vitro and also after subcutaneous transplantation into mice, as validated with bioluminescent imaging.

Liu Qi Chen¹, Vipul R Sheth², Christine A Howison³, Phillip H Kuo⁴, and Mark D Pagel^5
1Chemistry and Biochemistry, University of Arizona, Tucson, AZ, United States, ²Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States,³Arizona Research Laboratories, University of Arizona, Tucson, AZ, United States, ⁴Radiology, Medicine, Biomedical Engineering, University of Arizona, Tucson, AZ, United States, ⁵Biomedical Engineering and Chemistry & Biochemistry, University of Arizona, Tucson, AZ, United States

Ultravist®, a contrast agent that is clinically approved for X-ray/CT imaging, can also serve as a DIAmagnetic CEST (DIACEST) MRI contrast agent. A ratio of the two CEST effects from Ultravist® can be used to measure pH over a range of 6.2-7.4 pH units with a precision of 0.070 pH units. This ratiometric approach obviates the need to know the agent's concentration or sample's T_1sat relaxation time when measuring pH. We have used this DIACEST agent and a CEST-FISP MRI method to measure the extracellular pH (pHe) within a subcutaneous tumor and muscle of a mouse model of PANC-1 pancreatic cancer.

Yajie Liang^1,2, Amnon Bar-Shir^1,2, Xiaolei Song^1,2, Assaf A Gilad^1,2, Jeff W.M Bulte^1,2, and Piotr Walczak^1,2
1Division of MR Research, Russell H. Morgan Dept. of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, ²Cellular Imaging Section, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, United States

Chemical Exchange Saturation Transfer (CEST) MRI was used to monitor hydrogel scaffold that is now widely applied in encapsulation of stem cells for transplantation studies. By correlating bioluminescent imaging and histological results, we demonstrated that changes in CEST signals in vivo over time could allow monitoring molecular gel composition and potentially provide new insights on mechanism underlying cell migration in scaffold after transplantation. Along with the increasing use of biomaterials encapsulating stem cells in regenerative medicine, CEST MRI could be a valuable tool in investigation of dynamic changes in scaffold materials in the context of cell transplantation in vivo.

Carolyn W.-H. WU¹, Olga Vasalatiy², Leslie G Ungerleider³, and Gary Griffiths^2
1NeuroSpin / CEA, Gif Sur Yvette, Île-de-France, France, ²IPDC /NHLBI / NIH, Rockville, MD, United States, ³LBC /NIMH /NIH, Bethesda, MD, United States

Understanding neuron functions including axonal transport and metabolic clearance rats are important to study why the diseased brains are malfunctional. Our recent developed MRI visible contrast agent GdDOTA-CTB allows longitudinally monitoring monosynaptically anatomically connected brain circutary. In this study we further test its application to study axonal transport and neuronal turnover in the olfactory system. This study will open the new possibility to study the olfactory related malfunctions in various neurodegeneration diseases.

Jamu K. Alford¹, Christian T. Farrar¹, Yan Yang¹, William Bradfield Handler², Blaine A. Chronik², Timothy J Scholl³, Gunjan Madan⁴, and Peter Caravan^1
1Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Physics and Astronomy, The University of Western Ontario, London, ON, Canada, ³Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada, ⁴Siemens Medical Solutions Inc., Malvern, PA, United States

We present the first example of direct protein imaging in a living animal. Delta relaxation enhanced MR (dreMR) is a method that exploits the strong magnetic field dependence of slow-tumbling gadolinium-based contrast agents. A 1.5T, clinical MRI was outfitted with an actively shielded electromagnet to dynamically control the magnetic field in the imaging region. A nude mouse implanted with LS174T tumors was imaged within the electromagnetic insert using the albumin-bindin agent MS-325. Using the insert, the B0 field was varied from 1.4T to 1.6T to produce images of albumin distribution throughout the mouse.

Lingzhi Hu¹, Junjie Chen¹, Shelton D Caruthers¹, Gregory M Lanza¹, and Samuel A Wickline^1
1Washington University in St. Louis, St. Louis, MO, United States

In the field of molecular imaging with nanoparticle contrast agents, it would be advantageous to know not only that a particle binds to its target but also that it is internalized and subsequently processed and sorted to the subcellular compartment.Here we develop an analytical description and experimental validation of 19F longitudinal T1 relaxation as an indicator for assessing the integrity of paramagnetic PFC NP. When Gd is stripped from the nanoparticle surface, a “relaxation switch” occurs revealing the transition from intact bound particle to processed constituents.

Mohammed Salman Shazeeb^1,2, Christopher Howard Sotak^1,3, and Alexei Bogdanov, Jr.^3,4
1Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA, United States, ²Graduate School of Biomedical Sciences, University of Massachusetts Medical School, Worcester, MA, United States, ³Radiology, University of Massachusetts Medical School, Worcester, MA, United States, ⁴Cell biology, University of Massachusetts Medical School, Worcester, MA, United States

Specific targeted EGF receptor imaging in Gli36 tumor xenografts implanted in the rat brain was achieved using anti-EGFR monoclonal antibody conjugates (mACs) that facilitate local binding of a paramagnetic molecular substrate diTyr-DTPA(Gd) at the EGFR/EGFRvIII-overexpressing sites. Following anti-EGFR mAC administration, diTyr-DTPA(Gd) was retained for a significantly longer period of time as compared to the administration of the contrast agent without mAC or with anti-EpCAM mAC pre-treatment. Retention of diTyr-DTPA(Gd) following anti-EGFR mAC administration is consistent with enzyme-mediated coupling of the paramagnetic agent to EGFR/EGFRvIII-overexpressing cells in the tumor allowing effective MRI visualization of conjugate co-localization at the targeted site.

Veronica Clavijo Jordan¹, and Kevin M Bennett^1
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, United States

The enhancement of R1 due to paramagnetic ions can be modulated by controlling the sequestration and exchange of water protons around the ion. Here we report a new synthesis technique to enhance R1 by strategic placement of manganese (II) ions on the surface hydrophilic channels of apoferritin, causing a strong increase in R1. The results indicate that these manganese ions, when clustered in such channels on a highly filled apoferritin cavity (magnetoferritin), can create a per-ion R1 of 330mM-1s-1.

Deepak K Kadayakkara^1,2, and Eric T Ahrens^1,2
1Carnegie Mellon University, Pittsburgh, PA, United States, ²Pittsburgh NMR Center for Biomedical Research, Pittsburgh, PA, United States

In this study, we characterize inflammatory burden in a mouse model of inflammatory bowel disease (IBD) by in situ macrophage labeling using perfluorocarbon emulsion. Using fluorine-19 MRI, changes in bowel inflammation and macrophage activity in response to treatments are monitored non-invasively in vivo. In vivo MRI results are validated by ex vivo MRI of the excised colon samples, confocal microscopy, histology score and qRT PCR analysis of macrophages. Our results demonstrate that fluorine-19 MRI is an effective method to quantitatively measure macrophage activity in vivo and assess treatment response in IBD.

Tessa Geelen¹, Sin Yuin Yeo¹, Leonie E Paulis¹, Bram F Coolen¹, Klaas Nicolay¹, and Gustav J Strijkers^1
1Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands

After a myocardial infarction, macrophages infiltrate the damaged tissue to remove dead cells and promote left ventricular remodeling. The aim of this study was to characterize the presence of these macrophages with MRI. Phosphatidylserine (PS) was incorporated in paramagnetic liposomes to promote uptake by macrophages. In vitro, liposomes containing 6 mol% PS showed the highest uptake by murine macrophages. These liposomes were applied after mouse cardiac ischemia/reperfusion injury and visualized with T₁-weighted MRI and confocal microscopy. PS-liposomes were specifically associated with macrophages in the infarcted myocardium 2.5 hours after injection. After 24 hours of circulation, passive accumulation was predominant.