Manganese-enhanced MRI of mouse heart during changes in inotropy.

Recently the dual properties of manganese ion (Mn(2+)) as an MRI contrast agent and a calcium analogue to enter excitable cells has been used to mark specific cells in brain and as a potential intracellular cardiac contrast agent. Here the hypothesis that in vivo manganese-enhanced MRI (MEMRI) can detect changes in inotropy in the mouse heart has been tested. T(1)-weighted images were acquired every minute during an experimental time course of 75 min. Varying doses of Mn(2+) (3.3-14.0 nmoles/min/g BW) were infused during control and altered inotropy with dobutamine (positive inotropy due to increased calcium influx) and the calcium channel blocker diltiazem (negative inotropy). Infusion of MnCl(2) led to a significant increase in signal enhancement in mouse heart that saturated above 3.3 +/- 0.1 nmoles/min/g BW Mn(2+) infusion. At the highest Mn(2+) dose infused there was a 41-47% increase in signal intensity with no alteration in cardiac function as measured by MRI-determined ejection fractions. Dobutamine increased both the steady-state level of enhancement and the rate of MRI signal enhancement. Diltiazem decreased both the steady-state level of enhancement and the rate of MRI signal enhancement. These results are consistent with the model that Mn(2+)-induced enhancement of cardiac signal is indicative of the rate of calcium influx into the heart. Thus, the simultaneous measurement of global function and calcium influx using MEMRI may provide a useful method of evaluating in vivo responses to inotropic therapy.

In vivo neuronal tract tracing using manganese-enhanced magnetic resonance imaging.

Development of efficient imaging techniques to trace neuronal connections would be very useful. Manganese ion (Mn2+) is an excellent T1 contrast agent for magnetic resonance imaging (MRI). Four reports utilizing radioactive Mn2+ in fish and rat brain indicate that Mn2+ may be useful for tracing neuronal connections. Therefore, the purpose of this work was to determine if Mn2+ can be used as an in vivo MRI neuronal tract tracer. The results indicate that topical administration of MnCI2 solution to the naris of mice as well as to the retinal ganglion cells via intravitreal injection leads to enhancement of contrast along the respective pathways. Therefore, application of Mn2+ to neurons allows the use of MRI to visualize neuronal connections.