Effect of r 1 and r 2 relaxivity of gadolinium‐based contrast agents on the T 1 ‐weighted MR signal at increasing magnetic field strengths

Most contrast agents for magnetic respnance imaging (MRI) are gadolinium‐based T 1 shortening agents. At increasing magnetic field strengths their r 1 relaxivity tends to decrease while the r 2 relaxivity increases. In parallel, at high fields the tissue T 1 times increase and may mitigate the loss in contrast enhancement in T 1 ‐weighted images owing to improved background suppression. In the present work we explored the MR signal for T 1 ‐weighted spoiled gradient echo MRI sequences by simulations at three magnetic field strengths: 3, 7 and 9.4 T. The maximal available contrast enhancement (maxCE) was evaluated in absolute terms with the purpose of assessing how much of the full, underlying magnetization can be exploited, for a wide range of compound properties ( r 1 , 2–45 m m −1  s −1 ; r 2 / r 1 , 1.2–30). Despite the theoretically predicted loss in r 1 relaxivity at high fields, the same maxCE can be obtained as at low fields if the r 2 / r 1 ratio remains unchanged, albeit at the cost of a longer sequence repetition time and 1.5–2 times higher administered doses. For a fixed maximum tissue concentration, there is an optimum field‐dependent value for the r 1 relaxivity that yields the greatest maxCE. If the upper bound for the gadolinium concentration is 2 m m , the greatest maxCE is found for compounds with a r 2 / r 1 ratio of 1.2 and an r 1 relaxivity of 20.5 m m −1  s −1 at 3 T, 18 m m −1  s −1 at 7 T and 16.5 m m −1  s −1 at 9.4 T. For compounds that do not change their r 1 relaxivity or r 2 / r 1 ratios, the necessary dose can be reduced by 10–15% owing to the improved background suppression at higher fields. Copyright © 2013 John Wiley & Sons, Ltd.