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

Abstract

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.