Multimodality Molecular Imaging of Cardiac Cell Transplantation: Part II. In Vivo Imaging of Bone Marrow Stromal Cells in Swine with PET/CT and MR Imaging.

Purpose To quantitatively determine the limit of detection of marrow stromal cells (MSC) after cardiac cell therapy (CCT) in swine by using clinical positron emission tomography (PET) reporter gene imaging and magnetic resonance (MR) imaging with cell prelabeling. Materials and Methods Animal studies were approved by the institutional administrative panel on laboratory animal care. Seven swine received 23 intracardiac cell injections that contained control MSC and cell mixtures of MSC expressing a multimodality triple fusion (TF) reporter gene (MSC-TF) and bearing superparamagnetic iron oxide nanoparticles (NP) (MSC-TF-NP) or NP alone. Clinical MR imaging and PET reporter gene molecular imaging were performed after intravenous injection of the radiotracer fluorine 18-radiolabeled 9-[4-fluoro-3-(hydroxyl methyl) butyl] guanine ((18)F-FHBG). Linear regression analysis of both MR imaging and PET data and nonlinear regression analysis of PET data were performed, accounting for multiple injections per animal. Results MR imaging showed a positive correlation between MSC-TF-NP cell number and dephasing (dark) signal (R(2) = 0.72, P = .0001) and a lower detection limit of at least approximately 1.5 × 10(7) cells. PET reporter gene imaging demonstrated a significant positive correlation between MSC-TF and target-to-background ratio with the linear model (R(2) = 0.88, P = .0001, root mean square error = 0.523) and the nonlinear model (R(2) = 0.99, P = .0001, root mean square error = 0.273) and a lower detection limit of 2.5 × 10(8) cells. Conclusion The authors quantitatively determined the limit of detection of MSC after CCT in swine by using clinical PET reporter gene imaging and clinical MR imaging with cell prelabeling. (©) RSNA, 2016 Online supplemental material is available for this article.

Multimodality Molecular Imaging of Cardiac Cell Transplantation: Part I. Reporter Gene Design, Characterization, and Optical in Vivo Imaging of Bone Marrow Stromal Cells after Myocardial Infarction.

Purpose To use multimodality reporter-gene imaging to assess the serial survival of marrow stromal cells (MSC) after therapy for myocardial infarction (MI) and to determine if the requisite preclinical imaging end point was met prior to a follow-up large-animal MSC imaging study. Materials and Methods Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care. Mice (n = 19) that had experienced MI were injected with bone marrow-derived MSC that expressed a multimodality triple fusion (TF) reporter gene. The TF reporter gene (fluc2-egfp-sr39ttk) consisted of a human promoter, ubiquitin, driving firefly luciferase 2 (fluc2), enhanced green fluorescent protein (egfp), and the sr39tk positron emission tomography reporter gene. Serial bioluminescence imaging of MSC-TF and ex vivo luciferase assays were performed. Correlations were analyzed with the Pearson product-moment correlation, and serial imaging results were analyzed with a mixed-effects regression model. Results Analysis of the MSC-TF after cardiac cell therapy showed significantly lower signal on days 8 and 14 than on day 2 (P = .011 and P = .001, respectively). MSC-TF with MI demonstrated significantly higher signal than MSC-TF without MI at days 4, 8, and 14 (P = .016). Ex vivo luciferase activity assay confirmed the presence of MSC-TF on days 8 and 14 after MI. Conclusion Multimodality reporter-gene imaging was successfully used to assess serial MSC survival after therapy for MI, and it was determined that the requisite preclinical imaging end point, 14 days of MSC survival, was met prior to a follow-up large-animal MSC study. (©) RSNA, 2016 Online supplemental material is available for this article.

PFO and paradoxical embolism producing events other than stroke.

BACKGROUND: A patent foramen ovale (PFO) is a risk factor for cerebral events such as cryptogenic stroke, transient ischemic attacks, and migraine headaches. Far less commonly, PFO is associated with non-cerebral, paradoxical systemic embolic events such as myocardial infarction (MI), renal infarct, and limb ischemia. This report details the incidence of systemic paradoxical emboli at our institution. METHODS: 416 patients were referred for evaluation of PFO related conditions from 2001 to 2009. Clinical history and medical records of the patients were reviewed for incidence of cryptogenic stroke, transient ischemic attack (TIA), migraine headache, arterial desaturation, and noncerebral systemic embolism. RESULTS: As the primary presenting symptom, 219 patients had a diagnosis of cryptogenic stroke, 38 patients had migraine headaches, and 80 patients had transient neurologic deficits consistent with a TIA or complex headache. Twelve patients (2.9% of the total population) presented with a presumptive diagnosis of systemic embolism. Eight of these patients had acute MI diagnosed by elevated cardiac biomarkers, electrocardiogram changes, and/or imaging evidence of a left ventricular wall motion abnormality, without evidence of obstructive coronary disease on angiography. Four patients had evidence of peripheral embolism to a systemic artery, including the popliteal artery, ophthalmic artery, and brachial artery. PFO closure was performed in 197 patients (47.4% of the total population), including eight patients in the systemic embolism group. All closure procedures were successful. CONCLUSION: Although most paradoxical emboli travel to the brain, noncerebral paradoxical embolism is also associated with PFO. In addition to embolism of thrombus, there may be paradoxical passage of vasoactive chemicals that induce intense coronary spasm and myocardial infarction. Diagnosis is often challenging, given the lack of definitive criteria and the need to exclude other potential etiologies.