Transverse relaxometry with transmit field-constrained stimulated echo compensation
Purely exponential decay is rarely observed in conventional mono-exponential T2 mapping due to transmit field inhomogeneity and calibration errors, which collectively introduce stimulated and indirect echo pathways. Stimulated echo correction (SEC) requires an additional fit parameter for the transmit field, resulting in greater uncertainty in T2 relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T2 mapping using SEC.
The proposed method, called two-step SEC (tSEC), leverages spatial correlations in the transmit field to reduce the number of fully independent fitting parameters from three to two. The method involves a two-pass fit: the first pass involves a fast but standard SEC fit. The initially estimated transmit field is smoothed and provided as a fixed input to the second pass.
Simulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T2 variance with tSEC relative to SEC. Average T2 values were unchanged between tSEC and SEC fits. The proposed method uses the same input data as SEC and exponential fits, so it is applicable to existing data.
The proposed method generates reliable and reproducible quantitative T2 maps and should be considered for future relaxometry studies.
KeywordsMagnetic resonance imaging Spin echo imaging Stimulated echo correction Relaxometry Extended phase graph
RB: study conception and design, acquisition of data, analysis and interpretation of data, drafting of manuscript, and critical revision. PF: study conception and design, and critical revision. RML: study conception and design, acquisition of data, analysis and interpretation of data, and critical revision.
Compliance with ethical standards
Conflict of interest
Dr. Lebel is an employee of GE Healthcare. The remaining authors have no conflicts of interest or financial ties.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
- 6.Syed MA, Raman SV, Simonetti OP (2015) Basic principles of cardiovascular magnetic resonance imaging: physics and imaging techniques. Springer, New YorkGoogle Scholar
- 13.Jones C, Xiang Q, Whittall K, Mackay A (2003) Calculating T2 and B1 from decay curves collected with non-180 degree refocusing pulses. In: Proceedings of 11th annual meeting ISMRM. Toronto, Canada, p 1018Google Scholar
- 15.Hennig J (1988) Multiecho imaging sequences with low refocusing flip angles. J Magn Reson 78:397–407Google Scholar
- 21.Basiri R, Lebel M, Federico P (2016) Transverse relaxometry with B1+ constrained stimulated echo correction. In: Proceedings of 24th annual meeting ISMRM. Singapore, Singapore, p 1529Google Scholar
- 30.Lee CE, Baker EH, Thomasson DM (2006) Normal regional T1 and T2 relaxation times of the brain at 3T. In: Proceedings of 14th annual meeting ISMRM. Seattle, USA, p 959Google Scholar
- 33.Alecci M, Collins CM, Smith MB, Jezzard P (2000) BI field plots for a 3 tesla birdcage coil: concordance of experimental and theoretical results. In: Proceedings of 8th Annual Meeting ISMRM. Colorado, USA, p 1391Google Scholar