Simultaneous R 2 *, R 2 , and R 2 ′ quantification by combining S 0 estimation of the free induction decay with a single spin echo: A single acquisition method for R 2 insensitive quantification of holmium‐166–loaded microspheres

Purpose To present a new method, S 0 estimation of the free induction decay combined with a single spin echo measurement (SOFIDSE), that enables simultaneous measurements of R 2 *, R 2 , and R 2 ′ in order to quantify the local concentration of holmium microspheres (Ho‐MS) for radioembolization. Theory and Methods SOFIDSE estimates R 2 * and the signal magnitude at time point 0, S 0 , from a multigradient echo readout of the free induction decay and subsequently estimates R 2 using S 0 and a single spin echo, from which R 2 ′ is deducted. The method was evaluated by comparing SOFIDSE R 2 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 R 2 values compared with SSE independent of the microsphere concentration. R 2 ′ values determined by subtraction of either SOFIDSE R 2 or SSE R 2 from R 2 * showed excellent agreement (correlation coefficient = 1; P = 9 · 10 −11 ). The Ho‐MS–induced R 2 ′ values obtained by SOFIDSE were insensitive to the R 2 value of the tissue in which they resided. Conclusion SOFIDSE enables quantification of Ho‐MS, in media with spatially or temporally varying R 2 values, in a single acquisition. Magn Reson Med 73:273–283, 2015. © 2014 Wiley Periodicals, Inc.