Background : In addition to the structural information afforded by 1 H MRI, the use of X-nuclei, such as sodium-23 ( 23 Na) or phosphorus-31 ( 31 P), offers important complementary information concerning physiological and biochemical parameters. By then combining this technique with PET, which provides valuable insight into a wide range of metabolic and molecular processes by using of a variety of radioactive tracers, the scope of medical imaging and diagnostics can be significantly increased. While the use of multimodal imaging is undoubtedly advantageous, identifying the optimal combination of these parameters to diagnose a specific dysfunction is very important and is advanced by the use of sophisticated imaging techniques in specific animal models.Methods : In this pilot study, rats with intracerebral 9L gliosarcomas were used to explore a combination of sequential multinuclear MRI using a sophisticated switchable coil set in a small animal 9.4 T MRI scanner and, subsequently, a small animal PET with the tumour tracer O-(2-[ 18 F]-fluoroethyl)-L-tyrosine ( 18 F-FET). This enabled in vivo multinuclear MR-PET experiments to be conducted without compromising the performance of either multinuclear MR or PET.Results : High-quality in vivo images and spectra including high-resolution 1 H imaging, 23 Na-weighted imaging, detection of 31 P metabolites and 18 F-FET uptake were obtained, allowing the characterisation of tumour tissues in comparison to a normal brain. These parameters have been shown to be useful in the identification of the genetic profile of gliomas, particularly concerning the mutation of the isocitrate hydrogenase gene, which is highly relevant for treatment strategy.Conclusions : The combination of multinuclear MR and PET in, for example, brain tumour models with specific genetic mutations will enable the physiological background of signal alterations to be explored and the identification of the optimal combination of imaging parameters for the non-invasive characterisation of the molecular profile of tumours.