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

Dynamic radioisotope uptake data and NMR spectra can both be used in the investigation of cardiac metabolism with an isolated perfused rat heart model. The authors have developed a gamma ray detector that will operate within a wide bore 9.4 Tesla magnet. With this detector, radioisotope and NMR spectroscopy measurements can be made simultaneously. This allows correlations between radiotracer and NMR data to be made on individual rat hearts, and the number of experiments required to obtain statistically significant results can be greatly reduced. The detector consists of a NaI(Tl) scintillation crystal positioned dose to the sample at the centre of the magnet. The crystal is coupled to a magnetic field-insensitive photomultiplier tube by a 72.5 cm long acrylic light pipe. This combination satisfies the requirement of operation in a high magnetic field and operation near the sample, which is maintained at a temperature of 37°C. The performance of the scintillator/photomultiplier combination is not significantly changed by the magnetic field or by the operation of the NMR system. The light pipe causes a factor of 4 reduction in the amount of scintillation light reaching the photomultiplier tube. The performance of the NMR system is not affected by the presence of the detector. The system is now aiding the investigation of cardiac metabolism using the isolated perfused rat heart model, and some examples of its use are presented