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FOCUS ISSUE: CARDIAC IMAGING: CLINICAL RESEARCH

Discrimination of Myocardial Acute and Chronic (Scar) Infarctions on Delayed Contrast Enhanced Magnetic Resonance Imaging With Intravascular Magnetic Resonance Contrast Media

Maythem Saeed, DVM, PhD^_*,_*, Oliver Weber, PhD^_*, Randall Lee, MD, PhD, Loi Do, BS^_*, Alastair Martin, PhD^_*, David Saloner, PhD^_*, Philip Ursell, MD, Philippe Robert, PhD, Claire Corot, PhD and Charles B. Higgins, MD, FACC^_*

^_* Radiology
Medicine/Cardiology
Pathology, University of California San Francisco, San Francisco, California
Guerbet-Group, Paris, France

Manuscript received November 9, 2005; revised manuscript received January 26, 2006, accepted March 1, 2006.

^_* Reprint requests and correspondence: Dr. Maythem Saeed, Department of Radiology, University of California San Francisco, 513 Parnassus Avenue, HSW 207B, San Francisco, California 94134-0628. (Email: Maythem.Saeed{at}radiology.UCSF.edu).

OBJECTIVES: The purpose of this study was to examine the potential of intravascular gadolinium (Gd)-chelates in discriminating acute from chronic myocardial infarctions (MIs).

BACKGROUND: A potential limitation of delayed contrast enhanced magnetic resonance imaging with standard extracellular Gd-chelates is its inability to distinguish acute from chronic MIs.

METHODS: Eight pigs with MIs were studied at 3 days and 8 weeks. Inversion recovery gradient echo (IR-GRE), T₁-turbo spin echo (TSE), and T₂-TSE images were acquired before and after administration of intravascular and extracellular Gd-chelates. Triphenyltetrazolium chloride (TTC) was used to delineate infarctions at postmortem. Masson's trichrome and Biotinylated Bandeiria simplicifolia Isolectin B4 stains were used to characterize scarred myocardium. Analysis of variance was used to compare signal intensity (SI) ratios and determine differences in infarct extent.

RESULTS: The intravascular agent produced differential enhancement of acute infarctions at 3 days (SI ratio 5.8 ± 1.3) but not at 8 weeks (1.6 ± 0.4, p < 0.01). The extracellular agent provided differential enhancement of both acute (SI ratio 7.7 ± 1.4) and chronic (7.5 ± 0.9) infarctions. The extents of enhanced regions in acute infarctions were not different after intravascular (16.0 ± 1.3%) or extracellular (17.1 ± 1.7%) agents; at 8 weeks the extent of extracellular enhanced and TTC regions were smaller (13.2 ± 1.4% and 12.0 ± 1.5%, respectively). Masson's trichrome stain demonstrated dense scar tissue, signaling the complete healing of infarction. The vascular stain showed that scar tissue contained fewer microvessels oriented in a haphazard array.

CONCLUSIONS: The combination of intravascular and extracellular Gd-chelates discriminates acute from chronic infarctions on delayed images. This double contrast agent approach can be used to determine the age and extent of infarctions.

Abbreviations and Acronyms   AMI = acute myocardial infarction   D = Dalton   Gd = gadolinium   IR-GRE = inversion recovery gradient echo   LV = left ventricle/ventricular   MI = myocardial infarction   MRI = magnetic resonance imaging   SI = signal intensity   TE = echo time   TR = repetition time   TSE = turbo spin echo   TTC = triphenyltetrazolium chloride

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