g. intravenously injected hyperpolarized 13C-pyruvate conversion to lactate. In contrast GSK-3 inhibitor review to conventional (thermally polarized) MR, the hyperpolarized signal is transitory due to T1 relaxation. This means that the dDNP experiment must be conducted as rapidly as possible, within a few multiples of the T1 relaxation time, before the signal decay becomes too significant. The hyperpolarized signals are acquired rapidly to provide spectroscopic information
on the conversion of the injected substrate to its metabolites within the tissue of interest and has been applied to the imaging of tumors [2] and their response to drug treatment [3]. Further development of the methodology has allowed the temporal signal plots obtained from tissue to be fitted to compartmental models to estimate kinetic rate constants [4]. We have shown previously that a reproducible injection/withdrawal system can be used to provide a consistent arterial input function for compartmental modelling and extraction of physiological parameters [5]. A rapid and reproducible injection regime is also highly desirable for comparative hyperpolarization studies, where a precisely delivered dose to each subject is of prime importance. A previously developed automated injection system [6] provided reproducible injection volumes, rates and timing for animal studies [5]. However, because of its syringe-based
design, it was limited in the range of volumes it could deliver: 0.6–2.4 ml – a volume Venetoclax manufacturer range typically used for the injection of rats. Also, the injection was delayed by a few seconds because of the syringe PDK4 filling stage required by this system. As the hyperpolarized signal lifetime is governed by
T1 relaxation, reducing the delay between dissolution and injection can improve the magnitude of the signal, particularly for short T1 molecules. Moreover, extending the working range of the injectable volume would allow the application of the injection system to a wider range of species. Other design features for the injection system should ensure homogeneous composition of the final hyperpolarized substrate, coupled with flow control to minimize the dead volume of the injection received by the animal, monitoring of pH and ease of use. Here we show an improved MR compatible automated injector system that fulfils these requirements. The injector consists of a peristaltic pump directly driven through a flexible drive shaft by a stepper motor. A high torque bipolar stepper motor (57BYG621, Wantai Motor, Changzhou, China) was mounted on to a housing fixed to the magnet room filter plate outside the 5 G line of the magnet, see Fig. 1. The non-magnetic flexible drive shaft was constructed of a 4 mm phosphor-bronze shaft, 2.5 m in length (SS White Technologies Ltd., Milton Keynes, UK), inserted into a 6 mm O.D. nylon tube. The drive shaft was interfaced with a plastic peristaltic pump (150 series, Williamson Pumps Ltd.