Researchers interested in measuring perfusion and hyperpolarisation of ultra-long T1 15N compounds.Hyperpolarisation and imaging of isotopically labelled compounds is an active research field, focusing mainly on the NMR-active, stable 13C isotope. Main limitation of the technology is still T1 relaxation, which in case of [1-13C]pyruvate is approximately one minute in vitro and 20s in vivo at B0=3T. While this is relatively long as compared to normal MR T1 times, it is short as compared to radioactive decay in case of PET imaging (eg half-life of 18F=110min). The physiological processes must therefore be rapid to be detectable with hyperpolarised 13C compounds. 15N labelled compounds can exhibit extremely long T1 relaxation times, such as 4-5 minutes in case of α-trideuteromethyl[15N]glutamine (in vitro) [1]. Goal of this work was to establish an MRI experimental setup including hard- and software for 15N and measure perfusion in healthy rats with this 15N glutamine compound.The resonance frequency of 15N is -12.95 MHz at 3T, roughly 40% of 13C and 10% of 1H. All experiments were performed on a 3T HDx scanner (GE Healthcare), using a commercially purchased 15N TR switch (Rapid Biomedical) and a custom-built butter-fly transmit-receive coil. 15N images were encoded using a single-shot spiral trajectory (nominal matrix size 32×32, FOV=8cm) in a slice through the rat kidneys (slice thickness = 2cm; flip angle=10°). Image acquisition started at the beginning of the injection, with 16 images being acquired with TR=1s and the rest with TR=5s. Gradients were nulled every 16th excitation to acquire a slice-selective spectrum for control purposes. The data was reconstructed using NUFFT [2], after a 15-Hz Gaussian apodisation. α-Trideuteromethyl[15N]glutamine (15N-Gln) (Fig. 1) was synthesised according to [1] and polarised using a mixture of 3M 15N-Gln, 28mM OX063 radical (GE Healthcare) and 2.5mM Dotarem (Guerbet) dissolved in ethylene glycol and D2O (Sigma Aldrich). A small amount of [1-13C]pyruvate was added to monitor the build-up of polarisation. After polarising for 1-3 hours in a HyperSense DNP polariser (OxfordInstruments), the sample was dissolved rapidly in a D2O solution to a concentration of ~100mM 15N-Gln.The excretion of 15N-Gln was evaluated by mass spectrometry of tissue, blood and urine samples. Four healthy male Lewis rats (Charles River) were anaesthetised with 1-3% Isoflurane gas inhalation and injected with 1ml of hyperpolarised 15N-Gln or ~150mM [13C,15N2]urea solution in a separate injection to compare it to 13C perfusion measurements. The setup for 15N-Gln experiments is shown in Fig. 2. All animal experiments were approved governmentally by the Tierschutzbehörde (Regierung von Oberbayern).α-Trideuteromethyl[15N]glutamine yields clear, localised images of the rat kidneys (Fig. 3). It is possible to detect signal much longer with 15N-Gln as compared to 13C urea (Figs. 4 and 5). T1 of 15N-Gln in vivo is with 146s approximately eight times as long as that of 13C urea. 15N-Gln shows a strong localisation in the kidneys with little background signal as compared to urea. The rapid excretion of 15N-Gln within the time scale of the hyperpolarised experiment was confirmed by the mass spectrometry.The investigated 15N-Gln compound exhibits an extraordinarily long T1 relaxation both in vitro [1] and in vivo. Cellular uptake and enzymatic conversion are limited, hence its main application is as a perfusion agent. Due to its long T1, it is a promising candidate to observe renal function and filtration, happening in the order of a few minutes. The advantage of 15N-Gln over gadolinium chelates is its smaller size and direct, positive contrast.