L-glutamine as a T₂ exchange contrast agent

Purpose: The potential of L-glutamine as a T₂ exchange contrast agent in MRI was investigated. Methods: The T₂ relaxation rate of L-glutamine solutions prepared in various concentrations was measured at 9.4 T. A series of T₂-weighted images in a mouse cancer model was acquired with an L-glutamine solution infusion. Results: The T₂ relaxivity caused by the exchange (R_2ex) at 37°C was 0.069 s⁻¹ mM⁻¹ and 0.102 s⁻¹ mM⁻¹ for glutamine and glutamate solutions at pH = 7.2, respectively. The R_2ex of glutamine at pH = 6.1–6.7 was in the 0.097–0.1 s⁻¹ mM⁻¹ range. No significant dependence of T₁ on the concentration of glutamine was observed. The dynamic measurement of T₂-weighted images in vivo showed that the glutamine uptake was primarily observed at the localized part of the tumor. Conclusion: L-glutamine can be used as a T₂ exchange contrast agent and images of glutamine uptake in vivo can be acquired.