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MR Guidance of Targeted Injections into Border and Core of Scarred Myocardium in Pigs¹

¹ From the Departments of Radiology (M.S., A.J.M., O.W., D.R., D.S., C.B.H.) and Medicine and Cardiology (R.J.L.), University of California San Francisco, 513 Parnassus Ave, Room HSW 207 B, San Francisco, CA 94143-0628. Received June 28, 2005; revision requested August 23; revision received August 29; accepted September 22; final version accepted November 16. Address correspondence to M.S. (e-mail: maythem.saeed{at}radiology.ucsf.edu).

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 gradient-echo 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.

© RSNA, 2006

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