Rudy Rizzo1 and Roland Kreis1
1Department of Radiology and Biomedical Research, University of Bern, Bern, Switzerland
1Department of Radiology and Biomedical Research, University of Bern, Bern, Switzerland
Limiting
the parameter space to meaningful values when fitting MR spectra introduces
bias in cohort averaging. A correction term can reduce this bias whereas extending
the parameter space can eliminate it.
Figure 2: Top: cohort distribution with unbounded
fitting algorithm and pertinent formulae. µ: ground truth mean, σ: ground
truth std. µTR: mean
of right truncated distribution, µTL:
mean of left truncated distribution.
Bottom: cohort distribution with 0+ fitting
boundary. Limiting parameter space skews the Gaussian distribution. The
negative tail is mapped to a small interval around 0+. Assuming its contribution
to equal 0, the true mean can be reconstructed from its distorted version.
Figure 3: histogram of estimated concentrations for
GABA in three different parameter space settings. Cohort 1 is depicted in the
left column and cohort 2 in the right. µGT: ground truth concentration. µdistr: distribution estimated concentration.
