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Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T2
Christopher L Lankford1,2, Mark D Does1,2,3,4
1Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
Magnetic Resonance in Medicine
|April 21, 2017
Summary
Constraining the flip angle (θ) in quantitative MRI T2 mapping improves T2 precision and reduces mean-squared error, especially when θ accuracy is high. This method enhances experimental design for more reliable MRI parameter estimation.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Quantitative Imaging
- Biomedical Engineering
Background:
- Quantitative MRI requires correcting for nuisance parameters, where noise or bias in constraints affects fitted parameters.
- Refocusing pulse flip angle (θ) constraint in multi-spin echo T2 mapping is a key example of such a parameter.
Purpose of the Study:
- To derive an analytical expression for the mean-squared error of a parameter of interest.
- To evaluate the impact of flip angle (θ) constraint on T2 accuracy and precision in multi-echo T2 mapping protocols.
Main Methods:
- Derived an analytical expression for mean-squared error based on nuisance parameter accuracy and precision.
- Validated the expression using simulations.
- Applied the expression to assess flip angle constraint effects on T2 mapping.
Main Results:
- Constraining θ improved T2 precision when the θ-map signal-to-noise ratio exceeded half that of the first spin echo image.
- Constrained fitting reduced T2 variance and mean-squared error for biases in θ up to approximately 6%.
Conclusions:
- The derived analytical expression aids in designing quantitative MRI experiments.
- Flip angle measurement and constraint can be beneficial for T2 variance and mean-squared error in T2 mapping, depending on θ accuracy and precision.