A dedicated automated injection system for dynamic contrast-enhanced MRI experiments in mice.

Purpose: To develop a reproducible small-animal dynamic contrast-enhanced (DCE) MRI set-up for mice through which volumes <100 μL can be accurately and safely injected and to test this set-up by means of DCE measurements in resting muscle and tumor tissue.

Materials And Methods: The contrast agent (CA) injection system comprised 2 MR-compatible syringe pumps placed 50 cm from the 7T magnet bore where the fringe field is approximately 40 mT. Microbore tubing and T-connector, close to the injection site, minimized dead volume (<10 μL). For DCE-MRI measurements in 8 CB-17 SCID mice with 1500-2500 mm(3) large orthotopic neuroblastoma, a bolus of 10-fold-diluted Gd-DTPA CA solution (0.1 mmol/kg) was delivered (5 μL/s), followed by a 50-μL saline flush. Retro-orbital injections were given instead of tail vein injections, because the peripheral vasculature was reduced because of large tumor burden.

Results: The CA injection was successful in 19 of 24 experiments. Optical assessment showed minimal dispersion of ink-colored CA bolus. Mean (± SD) pharmacokinetic parameters retrieved from DCE-MRI examinations in resting muscle (K(trans) = 0.038 ± 0.025 min(-1), k(ep) = 0.66 ± 0.48 min(-1), v(e) = 0.060 ± 0.014, v(p) = 0.033 ± 0.021) and tumor (K(trans) = 0.082 ± 0.071 min(-1), k(ep) = 0.82 ± 0.80 min(-1), v(e) = 0.121 ± 0.075, v(p) = 0.093 ± 0.051) agreed with those reported previously.

Conclusion: We successfully designed and implemented a DCE-MRI set-up system with short injection lines and low dead volume. The system can be used at any field strength with the syringe pumps placed at a sufficiently low fringe field (<40 mT).