Step-down infusions of Gd–DTPA yield greater contrast-enhanced magnetic resonance images of BBB damage in acute stroke than bolus injections

A rat model of transient suture occlusion of one middle cerebral artery (MCA) was used to create a unilateral reperfused cerebral ischemic infarct with blood–brain barrier (BBB) opening. Opening of the BBB was visualized and quantitated by magnetic resonance (MR) contrast enhancement with a Look-Locker T1-weighted sequence either following an intravenous bolus injection (n=7) or during a step-down infusion (n=7) of gadolinium–diethylenetriaminepentaacetic acid (Gd–DTPA). Blood levels of Gd–DTPA after either input were monitored via changes in sagittal sinus relaxation rate. Blood-to-brain influx constants (Ki) were calculated by Patlak plots. On the basis of the MRI parameters and lesion size, the ischemic injury was determined to be similar in the two groups. The bolus injection input produced a sharp rise in blood levels of Gd–DTPA that declined quickly, whereas the step-down infusion led to a sharp rise that was maintained relatively constant for the period of imaging. Visual contrast enhancement and signal-to-noise (S/N) ratios were better with the step-down method (S/N=1.8) than with bolus injection (S/N=1.3). The Ki values were not significantly different between the two groups (P>.05) and were around 0.005 ml/(g min). The major reason for the better imaging of BBB opening by the step-down infusion was the higher amounts of Gd–DTPA in plasma and tissue during most of the experimental period. These results suggest that step-down MR contrast agent (MRCA) administration schedule may be more advantageous for detection and delineation of acute BBB injury than the usually used bolus injections.