[Mechanisms of delayed myocardial enhancement and value of MR and CT contrast materials in the evaluation of myocardial viability]. / Mécanismes du rehaussement tardif myocardique et apport des produits de contraste en IRM et scanner dans le diagnostic de viabilité myocardique.

The purpose of this article is to present a brief theoretical review of the models characterizing delayed myocardial enhancement applicable to both MR and CT imaging, review the different characteristics of commercially available gadolinium-based and iodinated contrast materials, and summarize the literature on the potential value of dedicated MR imaging contrast currently in development for the diagnosis of myocardial viability. The intensity of myocardial enhancement following infarction is related to two factors: expansion of the interstitial volume (15+/-2% in normal myocardium and 80+/-3% within necrosis) secondary to cell necrosis and perfusion abnormalities due to the absence of revascularization or lesions to the microcirculation. A kinetic model of contrast material properties within myocardium could be constructed from Kety's equation with regards to enhancement within the different myocardial tissues (viable myocardium, necrotic myocardium, fibrosis, no-reflow zones, stunned or hibernating myocardium). This model can be applied to both CT and MR since clinically available contrast agents are extracellular, inert and kinetically comparable. The development of dedicated contrast agents for viability and necrosis or molecular contrast agents open new horizons for preclinical research.