Simultaneous R2, R2, and R2′ quantification by combining S0 estimation of the free induction decay with a single spin echo: A single acquisition method for R2 insensitive quantification of holmium-166-loaded microspheres

Purpose To present a new method, S0 estimation of the free induction decay combined with a single spin echo measurement (SOFIDSE), that enables simultaneous measurements of R2*, R2, and R2′ in order to quantify the local concentration of holmium microspheres (Ho‐MS) for radioembolization. Theory and Methods SOFIDSE estimates R2* and the signal magnitude at time point 0, S0, from a multigradient echo readout of the free induction decay and subsequently estimates R2 using S0 and a single spin echo, from which R2′ is deducted. The method was evaluated by comparing SOFIDSE R2 values with values obtained from shifted spin echo (SSE) measurements on a phantom setup containing Ho‐MS and from dual spin echo measurements on a healthy volunteer. Results On average, SOFIDSE showed a small overestimation of R2 values compared with SSE independent of the microsphere concentration. R2′ values determined by subtraction of either SOFIDSE R2 or SSE R2 from R2* showed excellent agreement (correlation coefficient = 1; P = 9 · 10−11). The Ho‐MS–induced R2′ values obtained by SOFIDSE were insensitive to the R2 value of the tissue in which they resided. Conclusion SOFIDSE enables quantification of Ho‐MS, in media with spatially or temporally varying R2 values, in a single acquisition. Magn Reson Med 73:273–283, 2015. © 2014 Wiley Periodicals, Inc.