The impact of echo time on the calibration parameter M
Hannah Hare 1 and Daniel Bulte 1
FMRIB, University of Oxford, Oxford, Oxon,
A calibrated BOLD experiment was performed with a
multi-echo sequence to determine how BOLD response to
hypercapnia and the calibration parameter M vary with
echo time. Theory has predicted these relationships to
be directly proportional, but is based on the assumption
of negligible intravascular signal contribution. We
performed experiments both with and without the use of
intravascular crushers, and show that although M is a
linear function of echo time, the intercept is not zero.
This result has implications for the commonly employed
scaling method used to better compare M values from
experiments with differing echo times.
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