In this work we aim to mitigate the bias in the quantification of T1 and T2 caused by macromolecules when using magnetic resonance fingerprinting (MRF).
METHOD AND MATERIALSMagnetization transfer (MT) effects can bias the estimation of T1 and T2 in MR and are caused by dipolar effects and chemical exchange between free water and macromolecules. We used a radial MRF sequence to measure the T1 and T2 in the brain of a healthy volunteer at 3T. The same measurement was performed with three different RF pulse durations (5 ms, 2 ms, and an interleaved mix of both). The first two measurements were reconstructed using the traditional method, whereas the last scan was reconstructed using a new prototype algorithm which includes a specialized MT model.
RESULTSIn the conventional fingerprinting sequence, the white-matter T2 values show a dependence on the RF pulse duration (48 ms for the long and 35 ms the short pulses). Moreover, compared to the values reported in the literature (~60 ms), both configurations significantly underestimate the true T2. Using a mix of different RF pulse durations in combination with the proposed algorithm, an MT bias map can be extracted which enables a more accurate measurement of T2 (~60ms).
CONCLUSIONHere we demonstrate that the quantification of relaxation parameters using fingerprinting is sensitive to MT effects and show that this bias can be mitigated by varying the RF pulse duration in the sequence and incorporating a MT model into the reconstruction process.
CLINICAL RELEVANCE/APPLICATIONUnlike weighted images, quantitative imaging enables intra- and inter-subject comparison. Unbiased quantitative measures promise benefits to diagnosis, staging and monitoring of pathology and therapy.