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, 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. (c) 2014 Wiley Periodicals, Inc.