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Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T2 mapping.

ABSTRACT: PURPOSE:Quantitative MRI may require correcting for nuisance parameters which can or must be constrained to independently measured or assumed values. The noise and/or bias in these constraints propagate to fitted parameters. For example, the case of refocusing pulse flip angle constraint in multiple spin echo T2 mapping is explored. METHODS:An analytical expression for the mean-squared error of a parameter of interest was derived as a function of the accuracy and precision of an independent estimate of a nuisance parameter. The expression was validated by simulations and then used to evaluate the effects of flip angle (?) constraint on the accuracy and precision of T?2 for a variety of multi-echo T2 mapping protocols. RESULTS:Constraining ? improved T?2 precision when the ?-map signal-to-noise ratio was greater than approximately one-half that of the first spin echo image. For many practical scenarios, constrained fitting was calculated to reduce not just the variance but the full mean-squared error of T?2, for bias in ???6%. CONCLUSION:The analytical expression derived in this work can be applied to inform experimental design in quantitative MRI. The example application to T2 mapping provided specific cases, depending on ?? accuracy and precision, in which ?? measurement and constraint would be beneficial to T?2 variance or mean-squared error. Magn Reson Med 79:673-682, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Lankford CL

PROVIDER: S-EPMC5650597 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T<sub>2</sub> mapping.

Lankford Christopher L CL Does Mark D MD

Magnetic resonance in medicine 20170420 2

<h4>Purpose</h4>Quantitative MRI may require correcting for nuisance parameters which can or must be constrained to independently measured or assumed values. The noise and/or bias in these constraints propagate to fitted parameters. For example, the case of refocusing pulse flip angle constraint in multiple spin echo T<sub>2</sub> mapping is explored.<h4>Methods</h4>An analytical expression for the mean-squared error of a parameter of interest was derived as a function of the accuracy and precis ...[more]

PMID: 28426147

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Project description:Background and purposeThere is a paucity of literature that supports the Consortium of Multiple Sclerosis Centers guideline that proton density MR imaging is a core spinal cord sequence. We hypothesized that proton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. This study compared the detection rate and conspicuity of cervical cord MS lesions on sagittal 1.5T proton density fast spin-echo and T2 fast spin-echo MR imaging.Materials and methodsOne hundred consecutive patients with MS imaged with 1.5T sagittal proton density fast spin-echo and T2 fast spin-echo cervical cord MR imaging between September 2012 and October 2013 were retrospectively included. The number of MS lesions detected on each sequence was recorded; conspicuity was assessed quantitatively with the lesion-to-cord contrast ratio and lesion-contrast-to-noise ratio. Statistical analysis was performed by using the Wilcoxon signed rank test.ResultsSeventy-eight patients had MS cord lesions detected. Proton density fast spin-echo imaging detected a greater number of lesions (n = 181) compared with T2 fast spin-echo imaging (n = 137, P < .001). Fifteen patients (19%) with abnormal findings on proton density fast spin-echo imaging had normal findings on T2 fast spin-echo imaging; no patient with abnormal T2 fast spin-echo imaging findings had normal proton density fast spin-echo imaging findings. Although proton density fast spin-echo and T2 fast spin-echo imaging had similar lesion-to-cord contrast ratios (proton density fast spin-echo, 0.32 ± 0.01, versus T2 fast spin-echo, 0.33 ± 0.01; P = .43), proton density fast spin-echo had greater lesion-contrast-to-noise ratio (proton density fast spin-echo, 82 ± 3.0, versus T2 fast spin-echo, 64 ± 2.6; P < .001).ConclusionsProton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. Proton density fast spin-echo detects cord lesions in patients in whom T2 fast spin-echo findings appear normal. This study forms the evidentiary base for the current Consortium of Multiple Sclerosis Centers guideline that proton density imaging is a core spinal cord sequence.

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Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T2 mapping.

Publications

Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T<sub>2</sub> mapping.

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