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Abstract:
Signal from balanced steady-state free precession is affected by magnetization transfer. To investigate the possible effects on derived T2 values using variable nutation steady-state free precession, magnetization transfer-effects were modulated by varying the radiofrequency pulse duration only or in combination with variable pulse repetition time. Simulations reveal a clear magnetization transfer dependency of T2 when decreasing radiofrequency pulse duration, reaching maximal deviation of 34.6 underestimation with rectangular pulses of 300 μs duration. The observed T2 deviation evaluated in the frontal white matter and caudate nucleus shows a larger underestimation than expected by numerical simulations. However, this observed difference between simulation and measurement is also observed in an aqueous probe and can therefore not be attributed to magnetization transfer: it is an unexpected sensitivity of derived T2 to radiofrequency pulse modulation. As expected, the limit of sufficiently long radiofrequency pulse duration to suppress magnetization transfer-related signal modulations allows for proper T2 estimation with variable nutation steady-state free precession.
