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T2* Measurement bias due to concomitant gradient fields.

ABSTRACT: To demonstrate that concomitant magnetic fields can cause significant spatially dependent biases in T2* relaxometry measurements with implications for clinical applications such as BOLD and dynamic susceptibility contrast-enhanced MRI.After developing a theoretical framework for intravoxel dephasing and signal loss from concomitant magnetic fields, this framework and the effect of concomitant fields on T2* are validated with phantom experiments and numerical simulation. In lower leg and renal T2* mapping, we quantify measurement bias for imaging protocols with high gradient amplitude multiecho readouts, comparable to those used in clinical applications.Concordance between phantom experiment and numerical simulation validate the theoretical framework. Changes in T2* measured in the lower leg and kidney varied by up to 15% and 35%, respectively, as a result of concomitant gradient effects when compared with the control measurements.Concomitant magnetic fields produced by imaging gradient coils can cause clinically significant T2* mapping errors when high amplitude, long duration gradient waveforms are used. While we have shown that measurement biases can be quite large, modification of imaging parameters can potentially reduce concomitant field-induced measurement errors to acceptable levels. Magn Reson Med 77:1562-1572, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Hofstetter LW

PROVIDER: S-EPMC5266676 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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T2* Measurement bias due to concomitant gradient fields.

Hofstetter Lorne W LW Morrell Glen G Kaggie Joshua J Kim Daniel D Carlston Kristi K Lee Vivian S VS

Magnetic resonance in medicine 20160517 4

<h4>Purpose</h4>To demonstrate that concomitant magnetic fields can cause significant spatially dependent biases in T2* relaxometry measurements with implications for clinical applications such as BOLD and dynamic susceptibility contrast-enhanced MRI.<h4>Theory and methods</h4>After developing a theoretical framework for intravoxel dephasing and signal loss from concomitant magnetic fields, this framework and the effect of concomitant fields on T2* are validated with phantom experiments and nume ...[more]

PMID: 27186845

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Project description:BackgroundThere is now clear systematic review evidence that measurement can affect the people being measured; much of this evidence focusses on how asking people to complete a questionnaire can result in changes in behaviour. Changes in measured behaviour and other outcomes due to this reactivity may introduce bias in otherwise well-conducted randomised controlled trials (RCTs), yielding incorrect estimates of intervention effects. Despite this, measurement reactivity is not currently adequately considered in risk of bias frameworks. The present research aims to produce a set of guidance statements on how best to avoid or minimise bias due to measurement reactivity in studies of interventions to improve health, with a particular focus on bias in RCTs.MethodsThe MERIT study consists of a series of systematic and rapid reviews, a Delphi study and an expert workshop to develop guidance on how to minimise bias in trials due to measurement reactivity. An existing systematic review on question-behaviour effects on health-related behaviours will be updated and three new rapid reviews will be conducted to identify (1) existing guidance on measurement reactivity; (2) systematic reviews of studies that have quantified the effects of measurement on outcomes relating to behaviour and affective outcomes in health and non-health contexts and (3) trials that have investigated the effects of objective measurements of behaviour on concurrent or subsequent behaviour itself. A Delphi procedure will be used to combine the views of experts with a view to reaching agreement on the scope of the guidance statements. Finally, a workshop will be held in autumn 2018, with the aim of producing a set of guidance statements that will form the central part of new MRC guidance on how best to avoid bias due to measurement reactivity in studies of interventions to improve health.DiscussionOur ambition is to produce MRC guidance on measurement reactions in trials which will be used by future trial researchers, leading to the development of trials that are less likely to be at risk of bias.

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T2* Measurement bias due to concomitant gradient fields.

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T2* Measurement bias due to concomitant gradient fields.

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