Noninvasive Imaging of Early Venous Thrombosis by ¹⁹ F Magnetic Resonance Imaging With Targeted Perfluorocarbon Nanoemulsions

Abstract

Background— Noninvasive detection of deep venous thrombi and subsequent pulmonary thromboembolism is a serious medical challenge, since both incidences are difficult to identify by conventional ultrasound techniques. Methods and Results— Here, we report a novel technique for the sensitive and specific identification of developing thrombi using background-free 19 F magnetic resonance imaging, together with α2-antiplasmin peptide (α2 AP )–targeted perfluorocarbon nanoemulsions (PFCs) as contrast agent, which is cross-linked to fibrin by active factor XIII. Ligand functionality was ensured by mild coupling conditions using the sterol-based postinsertion technique. Developing thrombi with a diameter <0.8 mm could be visualized unequivocally in the murine inferior vena cava as hot spots in vivo by simultaneous acquisition of anatomic matching 1 H and 19 F magnetic resonance images at 9.4 T with both excellent signal-to-noise and contrast-to-noise ratios (71±22 and 17±5, respectively). Furthermore, α2 AP -PFCs could be successfully applied for the diagnosis of experimentally induced pulmonary thromboembolism. In line with the reported half-life of factor XIIIa, application of α2 AP -PFCs >60 minutes after thrombus induction no longer resulted in detectable 19 F magnetic resonance imaging signals. Corresponding results were obtained in ex vivo generated human clots. Thus, α2 AP -PFCs can visualize freshly developed thrombi that might still be susceptible to pharmacological intervention. Conclusions— Our results demonstrate that 1 H/ 19 F magnetic resonance imaging, together with α2 AP -PFCs, is a sensitive, noninvasive technique for the diagnosis of acute deep venous thrombi and pulmonary thromboemboli. Furthermore, ligand coupling by the sterol-based postinsertion technique represents a unique platform for the specific targeting of PFCs for in vivo 19 F magnetic resonance imaging.

An unmet clinical need: The history of thrombus imaging

“…105 The results corroborated the thrombus 1 H imaging earlier in dogs in 1998 102 and later in vitro and then in vivo during 2000 to 2001 106,107 with 4.7T and clinical 1.5T scanners, respectively. As previously mentioned, the first of many reports involving the Epix paramagnetic peptides agent reached the scientific literature in 2004, representing the first modern MR thrombus imaging program to reach Phase II clinical studies.…”

High field magnetic resonance imaging of rodents in cardiovascular research

“…19 F MRI combined with injection of perfluorocarbon (PFC) allows study of inflammatory processes in the context of cardiac ischemia [50], myocarditis (Fig. 6) [70,153], atherosclerotic [152] or thromboembolic processes [142]. PFCs are inert, nontoxic carbohydrates with fluorine that are phagocytized by circulating cells.…”

Quantification of vascular damage in acute kidney injury with fluorine magnetic resonance imaging and spectroscopy

“…28,44 These studies indicate the potential of thrombin targeted NP to serve as theranostic agents that both inhibit and image developing thrombi with the use of specific 19 F MRI signatures. Although we have reported previously that thrombin-targeted nanoparticles are useful for improving kidney function after AKI when administered prior to ischemic events, here we report that thrombin-targeted NP do not enhance recovery of kidney function when administered after ischemic injury due to the rapidity of onset of the nonreperfusion condition.…”