T1-relaxation kinetics of extracellular, intracellular and intravascular MR contrast agents in normal and acutely reperfused infarcted myocardium using echo-planar MR imaging

The objective of this study was to determine and compare if MR contrast age nts distributed into various compartments can provide estimation of fractio nal distribution volume (FDV) in normal and infarcted myocardium using inve rsion recovery echo-planar MR imaging (IR EPI). Three different types of MR agents were investigated: (a) an extra-cellular agent, GdDTPA-BMA (0.1 mmo l/kg); (b) an intravascular agent, GdDTPA-albumin (0.025 mmol/kg) and (c) a n intracellular agent, manganese chloride mmol/kg). The null point was dete rmined from a series of IR EPI images in which TI was varied from a changes in Delta R1 (Delta R1=1/T1(post)-1/T1(pre)) were, measured during the init ial 29-59 min after administration, Rats (n = 24) were subjected to 1-h cor onary artery occlusion/reperfusion. Histochemical staining confirmed the pr esence and location of infarction. GdDTPA-BMA caused increase in Delta R1 o f infarction < blood < < normal myocardium. Delta R1 ratios were 1.55 +/-0. 08 for infarction and 0.33 +/- 0.03 for normal myocardium, consistent with FDV of 0.82 +/- 0.04 and 0.18 +/- 0.01. The fractional distribution of this agent in normal myocardium approximated of FDV in normal and infarcted myo cardium in conclusion, extracellular intravascular and intracellular MR con trast agents exhibited different TI-relaxation kinetics in both normal and infarcted I myocardium. Constant Delta R1 ratio (myocardium/blood) after ad ministration of MR contrast agent is a prerequisite for estimation of FDV o f MR contrast agent in myocardium. the extracellular space of myocardium. G dDTPA-albumin caused increase in Delta R1 of < < infarction < < normal myoc ardium. Delta R1; In normal, but nut infarcted, myocardium was. constant at 0.01 +/- 0.02 and approximated fractional volume. MnCl2 caused equivalent increase in Delta R1 of normal and infarcted myocardium. Delta R1 of normal myocardium diet not change overtime, whereas Delta R1 of blood rapidly dec reased, leading to overestimation of FDV in normal and infarcted myocardium .