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

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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.

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