FREQUENCY-DEPENDENCE OF MR RELAXATION-TIMES .1. PARAMAGNETIC-IONS

T1 and T2 of paramagnetic ions in free and chelated form were measured over the range of clinical magnetic resonance imaging field strengths (0.02-1.5 T). T1 values agreed with published data; however, to our k nowledge, the field dependence of T2 has not been systematically studi ed before. Mn2+, Cr3+, and Fe3+ all showed T2 reduction at high field strengths, although reduction due to Fe3+ was minimal. This is believe d to be due to ''contact'' interactions, which have been previously no ted for manganese. No such T2 reduction was seen in the chelates, exce pt that dysprosium chelate (but not free ion) showed an anomalous decr ease in T2 at high field strengths, which may possibly be explained by a dephasing effect caused by the large magnetic moment of Dy3+.