SEQUENTIAL DYNAMIC SUSCEPTIBILITY CONTRAST MR EXPERIMENTS IN HUMAN BRAIN - RESIDUAL CONTRAST AGENT EFFECT, STEADY-STATE, AND HEMODYNAMIC PERTURBATION

The stability and reproducibility of the dynamic susceptibility contra st (DSC) MRI method for sequential relative cerebral blood volume (rel CBV) measurements was evaluated to validate the method for use in quan titative studies of cerebral hemodynamics in humans. A spin echo echo planar imaging protocol was used in conjunction with multiple bolus in jections of the susceptibility contrast agent gadoteridol (GD). The ef fects of variation in interbolus interval (10 min to 4 h). the number of injections (two to four), and the effect of the cerebral vasodilati ng agent acetazolamide (ACZ) were evaluated in 44 experiments performe d with 22 normal subjects. Two fundamental observations were made. Fir st, with multiple injections of GD, the change in MR signal over time was not consistent from first to subsequent boluses. A second bolus ad ministered 10 min to 2 h after an initial bolus resulted in signal cha nge of greater amplitude and duration, resulting in artifactually elev ated estimates of relCBV, consistent with a residual effect of GD. Sec ond, a relative steady state could be reached with serial injections o f GD, such that the profile of subsequent boluses closely paralleled t hose of previous ones, This facilitates the reliable measurement of re lCBV during activation, as demonstrated by use of ACZ.