T2 quantitation of articular cartilage at 1.5 T

Purpose: To evaluate sources of error when using a multiecho sequence for quantitative T2 mapping of, articular cartilage at 1.5 T. Materials and Methods: Phantom measurements were used to assess the contribution of stimulated echoes to inaccuracy of T2 measurements in cartilage using a multiecho sequence. Five volunteer studies compared in vivo single-echo spin echo results to multiecho, single-slice and multiecho, multislice acquisitions for assessment of both the, stimulated echo and magnetization transfer contrast (MTC) contributions to T2 measurement inaccuracy. Results: Phantom experiments demonstrated that substantial inaccuracy (10%-13% longer T2 values) is introduced from stimulated echoes with a multiecho sequence with slice-selective refocusing pulses. The in vivo volunteer studies also demonstrated increases in measured T2 by up to 48% with a multiecho, sequence. Use of the multiecho sequence in the multislice mode resulted in T2 values closer to the single-echo standards for the volunteer studies. However, this apparent increased accuracy should be regarded as circumstantial, as it only occurs because the error due to MTC has the opposite sign compared to the error due to the stimulated echo contribution. Conclusion: Use of a multiecho, multislice sequence for cartilage T2 measurements should be undertaken with the caution that substantial inaccuracy is introduced from stimulated echoes and MTC.