Abstract
BackgroundMyocardial T1-mapping methods such as MOLLI use SSFP readout and are prone to frequency-dependent error in T1-measurement. A significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without banding artifacts.MethodsThe sensitivity of T1-estimates based on the SSFP based MOLLI sequence to errors in center frequency are calculated by means of a Bloch simulation and validated by phantom measurements. Typical off-resonance errors following local cardiac shimming are determined by field mapping at both 1.5 and 3.0T. In vivo examples demonstrate the artifactual appearance of T1-maps in the presence of off-resonance variation.ResultsOff-resonance varied 61.8 ± 15.5 Hz (mean ± SD, n = 18) across the heart at 1.5T and 125.0 ± 40.6 Hz (mean ± SD, n = 18) at 3.0T. For T1 = 1000 ms, the variation in T1 due to off-resonance variation was approximately 20 ms at 62 Hz, and > 50 ms at 125 Hz.ConclusionsRegional variations due to the inability to completely shim the B0-field variation around the heart appear as regional variation in T1, which is artifactual.
Highlights
Myocardial T1-mapping methods such as modified Look-Locker inversion recovery (MOLLI) use steady state free precession (SSFP) readout and are prone to frequency-dependent error in T1-measurement
Simulation results are provided for a specific MOLLI protocol which used a 5(3s)3 sampling scheme which uses 2 inversions with images acquired for 5 heartbeats following the first inversion, followed by a 3 second recovery period, and images acquired for 3 heartbeats following the second inversion
The use of single shot SSFP imaging for T1-mapping in the heart is accompanied by an off-resonance sensitivity of the T1 estimates
Summary
Myocardial T1-mapping methods such as MOLLI use SSFP readout and are prone to frequency-dependent error in T1-measurement. A significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without banding artifacts. The frequency response of steady state free precession (SSFP) sequences is well known and results in dark band artifacts [1,2,3]. Myocardial T1-mapping methods such as the modified Look-Locker inversion recovery method (MOLLI) [4,5] use SSFP readout and are prone to frequency dependent errors in T1-measurements. The off-resonance response becomes dependent on the initial condition, which is in turn dependent on the inversion recovery time. It is not well appreciated that a significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without
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