MR Arthrography: A proposal for solution optimization with lidocaine. An in vitro experience

Purpose. Pain on capsule distension in painful joints may affect feasibility of the MR Arthrography. We tried to overcome this limitation by adding a local anesthetic (lidocaine) to the paramagnetic contrast agent solution. We aimed at: a) investigating which contrast agent dilution provides the best signal-to-noise ratio in the SE T1 sequences; b) evaluating the effects of lidocaine on the signal intensity and on the viscosity of the solutions; assessing the viscosity of solutions containing iodinated contrast agent. Materials and methods. The paramagnetic contrast agent was diluted with saline and lidocaine at various concentrations. Signal intensity was measured with a 1.5 Tesla superconductive MR unit with a dedicated head coil; we used T1-weighted spin-echo sequence. The viscosity coefficient of the solutions was analyzed and compared with that of solutions containing iodinated contrast agents (but not lidocaine). Results. Signal intensity is also unaffected by variations in the concentration of lidocaine, which does not interfere with the biphasic behavior of Gadolinium. Viscosity is scarcely affected by changes in lidocaine concentration when the paramagnetic contrast agent concentration is not changed. Conclusions. The optimal signal-to-noise ratio in T1-weighted sequences is provided by 0.4%, contrast agent dilution but contrast agent-saline solutions, with(out) lidocaine, cannot be considered steady and signal intensity values change over time. The addition of lidocaine does not significantly influence the signal-to-noise ratio and the viscosity of the solutions. The low viscosity of the paramagnetic contrast agent appears to favor quicker spread of the solution, even in tiny defects; thanks to its anesthetic effect, lidocaine could facilitates execution of the examination in painful joints without affecting the diagnostic result.