Evaluation of Gd-DTPA-labeled dextran as an intravascular MR contrast agent: imaging characteristics in normal rat tissues

Dextran covalently linked to moieties of gadolinium diethylenetriamine pentaacetic acid (DTPA), for use as a macromolecular, intravascular blood pool marker for contrast material-enhanced magnetic resonance (MR) imaging was characterized by means of physicochemical and relaxivity measurements and MR imaging in healthy rats. Dextran labeled with 15 Gd-DTPA moities (molecular weight of approximately 75,000 d) had a T1 relaxivity at 0.25 T and 37 degrees C of 157.1 mmol-1.sec-1 per molecule and 10.5 mmol-1.sec-1 per gadolinium atom, more than twice that of unbound Gd-DTPA. Osmolality was 300-350 mOsm/kg at a gadolinium concentration of 0.01 mmol/L. Tissue enhancement was essentially linearly related to injected dose in the gadolinium dose range of 0.01-0.05 mmol/kg of body weight. Approximate typical enhancement values over baseline for normal tissues at 10 minutes after a gadolinium dose of 0.05 mmol/kg were as follows: cardiac muscle, adrenal gland, and liver, 40%-50%; lungs, 160%-200%; renal cortex, 130%; renal medulla, 240%; spleen, 75%; muscle, 15%; and brain, 5%-10%. Projection-subtraction images showed that dextran-(Gd-DTPA)15 remained intravascular for at least 1 hour after injection. The prolonged and easily appreciated levels of tissue enhancement with dextran-(Gd-DTPA)15, at a gadolinium dose less than that routinely used in Gd-DTPA, indicate further evaluation of this macromolecular marker.