SUPERPARAMAGNETIC IRON-OXIDE PARTICLES AND POSITIVE ENHANCEMENT FOR MYOCARDIAL PERFUSION STUDIES ASSESSED BY SUBSECOND T-1-WEIGHTED MRI

Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T-2 MR contrast agents, reducing signal intensity (SI) on T-2-weig hted MR images (negative enhancement). This study reports the original use of SPIOs as T-1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial pe rfusion defect. Using a strongly T-1-weighted subsecond MR sequence wi th SPIOs intravenous (IV) bolus injection, MR imaging of myocardial va scularization after reperfusion was performed, on a dog model of coron ary occlusion followed by reperfusion. Immediately after the intraveno us bolus injection of 20 mu mol/kg of SPIOs, a positive signal intensi ty enhancement was observed respectively, in the right and left ventri cular cavity and in the nonischemic left myocardium. Moreover, compare d to normal myocardium, the remaining ischemic myocardial region (ante rior wall of the left ventricle) appeared as a lower and delayed SI en hancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocard ium (anterior wall) (110 +/- 23% vs. 74 +/- 22%, Mann-Whitney test alp ha < 1%, n(1) = 6, n(2) - n(1) = 0, U > 2). In conclusion, the T-1 eff ect of SPIOs at low dose, during their first intravascular distributio n, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the ''no-reflow phenomenon.''