MR guidance of targeted injections into border and core of scarred myocardium in pigs

Purpose: To use (a) dysprosium-based contrast agent (sprodiamide) to confirm the site of myocardial injection and (b) T1-enhancing magnetic resonance (MR) contrast media to mark the myocardial target and T2*-enhancing contrast media to demonstrate injection sites in the margins or core of infarction on delayed contrast-enhanced images. Materials and Methods: Approval of the institutional committee on animal research was obtained. A phantom and six pigs subjected to chronic infarction (8 weeks) underwent MR-guided experiments. At inversion-recovery gradient-echo imaging, gadoterate meglumine (0.1 mmol/kg) was intravenously administered to delineate scar tissue. A catheter fitted with multiple receiver coils was used to visualize catheter navigation and injection sites. A steady-state free precession (balanced fast field-echo) sequence was used for MR fluoroscopy. A high-resolution multiphase balanced gradien-techo cine MR sequence was used after intramyocardial deposition of sprodiamide. The border and core of scarred myocardium were characterized histopathologically. The 95% confidence interval (CI) was used to demonstrate the range, extent of hyperenhanced and hypoenhanced regions after contrast media administration. Results: In the phantom and in vivo, the actively guided catheter produced a high signal intensity at the terminal portion of the shaft and tip. Scarred myocardium was recognized as a bright region on gadoterate meglumine-enhanced images. Intramyocardial injection of sprodiamide caused local and persistent signal intensity loss, and the extent was volume dependent on balanced fast field-echo and T2-weighted turbo spin-echo images. At 5 minutes after administration of 0.2, 0.4, and 0.6 mL of sprodiamide, the 95% CIs of the extents of the hypoenhanced regions were 0.08%, 0.23%; 0.27%, 0.51%; and 0.46%, 0.70%, respectively, of left ventricular (LV) surface area (P < .05, paired t test). Failure of intramyocardial injection was confirmed by a brief signal loss of LV chamber blood. Conclusion: Sprodiamide allows visualization of injection sites within enhanced infarction. A catheter with integrated receiver coils aided in effective catheter guidance and precise intramyocardial injection. (c) RSNA, 2006.