Transverse relaxometry with transmit field-constrained stimulated echo compensation

• Published in: Magma (New York, N.Y.) Vol. 32; no. 6; pp. 669 - 677
• Main Authors: Basiri, Reza, Federico, Paolo, Lebel, Robert Marc
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2019
• Subjects: Adult; Algorithms; Biomedical Engineering and Bioengineering; Brain - diagnostic imaging; Brain Mapping - methods; Computer Appl. in Life Sciences; Computer Simulation; Female; Health Informatics; Healthy Volunteers; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Imaging; Magnetic Resonance Imaging; Male; Medicine; Medicine & Public Health; Models, Theoretical; Phantoms, Imaging; Radiology; Reproducibility of Results; Research Article; Solid State Physics; Magnetic resonance imaging; Stimulated echo correction; Relaxometry; Extended phase graph; Spin echo imaging
• ISSN: 0968-5243; 1352-8661
• DOI: 10.1007/s10334-019-00769-9

Objective Purely exponential decay is rarely observed in conventional mono-exponential T 2 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 T 2 relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T 2 mapping using SEC. Methods 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. Results Simulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T 2 variance with tSEC relative to SEC. Average T 2 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. Discussion The proposed method generates reliable and reproducible quantitative T 2 maps and should be considered for future relaxometry studies.