Rapid relaxation times measurements by MRI: an in vivo application to contrast agent modeling for muscle fiber types characterization

This paper is a description of a simulation method to evaluate the contrast in NMR imaging and its aim is to help to optimize the use of contrast medi a in clinical imaging. Indeed, there is a need to define objective criteria in order to choose among several contrast media the ones that are the most effective and to define their optimal conditions of use, such as: the dose to be injected, the required time after injection to obtain the best enhan cement and the optimal imaging sequence parameter values. The method is bas ed on NMR signal simulation in the presence of contrast media and requires the fast measurement of the T-1 and T-2 relaxation times to obtain the dyna mic relaxometry variation of tissues after contrast injection. In this work , the fast imaging techniques that are to be described enable the measureme nt of T-1 and T-2 with a 30sec temporal resolution on 128*256 matrix images . The accuracy of the method was assessed in rabbit muscles after the injec tion of two gadolinium chelates (Gd-DTPA and Gd-DOTA) with the aim of impro ving the in vivo characterization of fast-twitch and slow-twitch muscle fib er types. The simulation results were in close agreement with contrast imag e analysis and showed, for relevant clinical doses, a small efficacy for bo th chelates, The interest of the proposed simulation method Lies in the fac t that it enables to objectively compare the efficacy of different contrast agents, to forecast the efficacy of a given contrast reagent and to define the optimal dose and the optimal imaging sequence parameters that give the best contrast. This simulation method obviates numerous prior experiments to evaluate the benefit expected from different contrast media. The method, which has been evaluated here for muscle investigations is applicable to a ny tissue analysis and can help to guide the best condition of use of contr ast agents in MR imaging. (C) 2001 Elsevier Science Inc. All rights reserve d.