Limitations of skipping echoes for exponential T2 fitting

Background Exponential fitting of multiecho spin echo sequences with skipped echoes is still commonly used for quantification of transverse relaxation (T2). Purpose To examine the efficacy of skipped echo methods for T2 quantification against computational modeling of the exact signal decay. Study Type Prospective comparison of methods. Subjects/Phantom Eight volunteers were imaged at 4.7T, six volunteers at 1.5T, and phantoms ([MnCl2] = 68–270 mM). Field Strength/Sequence 1.5T and 4.7T; multiple‐echo spin echo. Assessment Exponential fitting for T2 using all echoes, skipping the first echo or skipping all odd echoes, compared with Bloch simulations. Resulting T2 values were examined over a range of T2 (10–150 msec), refocusing flip angles (90–270°), and echo train lengths (ETL = 6–32). Statistical Tests Shapiro–Wilk tests and Q‐Q plots were used to check for normality of data. Paired sample t‐tests and Wilcoxon rank tests were used to compare fitting models using α = 0.05. Multiple comparisons were accounted for with Bonferroni correction. Results In examined regions of interest, typical incorrect estimation of T2 ranged from 23–39% for exponential fitting of all echoes, or 15–32% for skipped echo methods. In vivo, T2 estimation error was reduced to as little as 10% with skipped echo methods using 180° refocusing and ETL = 8, although error varied due to refocusing angle, T2, and ETL. In vivo, skipped echo T2 values were significantly different than all echo exponential fitting (P