A system to obtain radiotracer uptake data simultaneously with NMR spectra in a high field magnet

Radiotracer techniques and nuclear magnetic resonance (NMR) spectroscopy are two complementary methods that are widely used to investigate cardiac metabolism. We have now developed a novel gamma photon detector system that will operate within a wide-bore, 9.4 T magnet. With this detector in position, it is possible to acquire radiotracer uptake data while simultaneously collecting NMR spectra. The advantages of this new system are firstly, that it enables correlations between radiotracer and NMR data to be made on individual rat hearts, and secondly that it allows the number of experiments required to obtain results of statistical significance to be greatly decreased. The extension of our system, to one in which positron emission tomography (PET) and magnetic resonance imaging (MRI) data are acquired simultaneously, clearly has enormous clinical potential. The detector consists of a NaI(Tl) scintillation crystal coupled to a magnetic field-insensitive photomultiplier tube by a 72.5 cm long, acrylic light pipe. This detector configuration satisfies the two, conflicting requirements of the crystal being near the sample, and thus in a high magnetic field, and the PMT being in a low magnetic field and thus far from the sample. The performance of the detector is not significantly altered by either the magnetic field or the collection of NMR data and, conversely, the performance of the NMR system is not affected by the presence of the detector. As expected, the light pipe causes a decrease in the amount of scintillation light reaching the photomultiplier tube; however, this does not constitute a significant problem for the sensitivity of the complete detector system. In this paper we present the technical specifications of our new system together with what we believe are the first examples of simultaneously acquired NMR spectra and 18F-fluorodeoxyglucose (18FDG) uptake data, obtained from isolated, perfused rat hearts.