Choice of metal ion and formulation concentration for first-pass brain perfusion studies with magnetic resonance imaging at 1.5 tesla.

RATIONALE AND OBJECTIVES

Gadolinium (Gd) and dysprosium (Dy) analogues, chelated with HP-DO3A, were compared at both 0.5- and 1.0-mol/L concentrations for efficacy in first-pass brain studies on magnetic resonance (MR) imaging at 1.5 tesla (T).

METHODS

Ten healthy cats were examined with a dose of 0.3 mmol/kg, using two concentrations of each agent (0.5 mol/L and 1.0 mol/L, 20 examinations). Gadolinium-HP-DO3A (gadoteridol or ProHance) or Dy-HP-DO3A was injected at 9 mL/second, with acquisition of 64 sequential steady-state free precession (SSFP) images at a rate of one each 0.6 second.

RESULTS

The change in white matter signal intensity, at the peak of the first pass of the contrast agent bolus in the brain, was -231 +/- 68 for the 0.5-mol/L formulation of Gd-HP-DO3A, compared with -267 +/- 57 for the 1.0-mol/L formulation. Using the 0.5-mol/L formulation of Dy-HP-DO3A, the change at peak was -318 +/- 42, a result statistically improved compared with both the 0.5-mol/L (P < 0.02) and 1.0-mol/L (P < 0.04) Gd-HP-DO3A formulations. A further improvement was observed with the 1.0-mol/L Dy-HP-DO3A formulation, with the change being -368 +/- 33.

CONCLUSIONS

First-pass brain MR studies at 1.5 T are improved by use of higher concentration Gd chelate formulations (1.0 versus 0.5 mol/L) and by substitution of the Dy ion for the Gd ion in the chelate. Injection of higher-concentration formulations results in higher initial arterial metal ion concentration. Incomplete blood mixing on transit during first pass causes the higher initial concentration, which then results in a greater susceptibility effect on imaging. The superiority of the Dy formulation compared with the Gd formulation is anticipated because of the higher magnetic moment of Dy. The curves for tissue signal intensity versus time during first pass return artifactually to near baseline after Gd chelate injection (when SSFP imaging techniques are used), a differentiating feature from results with the Dy chelate. This difference can be explained by a substantial T1 effect of the Gd chelate, despite acquisition of images that are predominantly susceptibility weighted.