- Workshop presentation
- Open Access
Myocardial T1 mapping at 3.0T using inversion recovery FLASH readout
© Shao et al; licensee BioMed Central Ltd. 2015
- Published: 3 February 2015
- Balance Steady State Free Precession
- Balance Steady State
- Banding Artifact
- MOLLI Sequence
- Inversion Factor
Myocardial T1 mapping methods such as modified Look-Locker inversion-recovery (MOLLI) typically use balanced steady state free precession (bSSFP) readout, which is known to be particularly sensitive to off resonance and thus limits its utility at higher field strengths. Fast low angle shot (FLASH) imaging is known to be more robust against susceptibility artifacts than bSSFP. However, the T1 mapping algorithms that have been developed for bSSFP readout are not directly applicable to FLASH-based T1 mapping sequences at 3.0T. We sought to develop a FLASH-based MOLLI T1 mapping technique for 3.0T and validate it on a cohort of healthy volunteers.
The FLASH-MOLLI sequence was developed by modifying the standard MOLLI sequence to use FLASH readout, incorporating a modified T1 estimation algorithm. The proposed algorithm calculates the one dimensional longitudinal signal evolution of the FLASH-MOLLI sequence based on Bloch equations, considering the incomplete inversion using inversion factor δ and the saturation effects of each RF excitation using apparent flip angle α. The 3-parameters (M0, T1, and α, assuming δ is known) or 4-parameters fitting can be performed by using the Levenberg-Marquardt algorithm such that the calculated signal matches best with the measured signal for each pixel.
The FLASH-MOLLI was evaluated against the standard bSSFP-MOLLI based on studies over six phantoms and 10 healthy volunteers in a 3.0T MR scanner, using the same 5-(3)-3 acquisition scheme. For T1 estimation, the proposed 3-parameters fitting was applied to FLASH-MOLLI, and the standard MOLLI fitting with inversion factor correction was applied to bSSFP-MOLLI. Reference T1 values of phantoms were determined by spin-echo experiments. The average inversion factors for phantoms and in vivo were determined by "FLASH-MOLLI+M0" with 4-parameters-fitting, which acquires additional M0 weighted image 5 seconds following the 5-(3)-3 acquisition. Based on results measured by the "FLASH-MOLLI+M0" sequence, the inversion factor was set to be 0.955 for phantom studies and 0.88 for in vivo studies for both the FLASH-MOLLI and bSSFP-MOLLI.
The FLASH-MOLLI approach yields more accurate T1 estimation than the standard bSSFP-MOLLI, and eliminates the banding artifacts associated with bSSFP at 3.0T.
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