Over recent years hyperpolarization by dissolution dynamic nuclear polarization has become an established
technique for studying metabolism in vivo in animal models. Temporal signal plots obtained from
the injected metabolite and daughter products, e.g. pyruvate and lactate, can be fitted to compartmental
models to estimate kinetic rate constants. Modeling and physiological parameter estimation can be made
more robust by consistent and reproducible injections through automation. An injection system previously
developed by us was limited in the injectable volume to between 0.6 and 2.4 ml and injection
was delayed due to a required syringe filling step. An improved MR-compatible injector system has been
developed that measures the pH of injected substrate, uses flow control to reduce dead volume within the
injection cannula and can be operated over a larger volume range. The delay time to injection has been
minimized by removing the syringe filling step by use of a peristaltic pump. For 100 ll to 10.000 ml, the
volume range typically used for mice to rabbits, the average delivered volume was 97.8% of the demand
volume. The standard deviation of delivered volumes was 7 ll for 100 ll and 20 ll for 10.000 ml demand
volumes (mean S.D. was 9 ul in this range). In three repeat injections through a fixed 0.96 mm O.D. tube
the coefficient of variation for the area under the curve was 2%. For in vivo injections of hyperpolarized
pyruvate in tumor-bearing rats, signal was first detected in the input femoral vein cannula at 3–4 s
post-injection trigger signal and at 9–12 s in tumor tissue. The pH of the injected pyruvate was
7.1 ± 0.3 (mean ± S.D., n = 10). For small injection volumes, e.g. less than 100 ll, the internal diameter
of the tubing contained within the peristaltic pump could be reduced to improve accuracy. Larger injection
volumes are limited only by the size of the receiving vessel connected to the pump.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)