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Mis-estimation and bias of hyperpolarized apparent diffusion coefficient measurements due to slice profile effects.

ABSTRACT: PURPOSEThe purpose of this work was to explore the impact of slice profile effects on apparent diffusion coefficient (ADC) mapping of hyperpolarized (HP) substrates.METHODSSlice profile effects were simulated using a Gaussian radiofrequency (RF) pulse with a variety of flip angle schedules and b-value ordering schemes. A long T1 water phantom was used to validate the simulation results, and ADC mapping of HP [13 C,15 N2 ]urea was performed on the murine liver to assess these effects in vivo.RESULTSSlice profile effects result in excess signal after repeated RF pulses, causing bias in HP measurements. The largest error occurs for metabolites with small ADCs, resulting in up to 10-fold overestimation for metabolites that are in more-restricted environments. A mixed b-value scheme substantially reduces this bias, whereas scaling the slice-select gradient can mitigate it completely. In vivo, the liver ADC of hyperpolarized [13 C,15 N2 ]urea is nearly 70% lower (0.99?±?0.22 vs 1.69?±?0.21?×?10-3 mm2 /s) when slice-select gradient scaling is used.CONCLUSIONSlice profile effects can lead to bias in HP ADC measurements. A mixed b-value ordering scheme can reduce this bias compared to sequential b-value ordering. Slice-select gradient scaling can also correct for this deviation, minimizing bias and providing more-precise ADC measurements of HP substrates. Magn Reson Med 78:1087-1092, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Gordon JW

PROVIDER: S-EPMC5391314 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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Mis-estimation and bias of hyperpolarized apparent diffusion coefficient measurements due to slice profile effects.

Gordon Jeremy W JW Milshteyn Eugene E Marco-Rius Irene I Ohliger Michael M Vigneron Daniel B DB Larson Peder E Z PEZ

Magnetic resonance in medicine 20161013 3

<h4>Purpose</h4>The purpose of this work was to explore the impact of slice profile effects on apparent diffusion coefficient (ADC) mapping of hyperpolarized (HP) substrates.<h4>Methods</h4>Slice profile effects were simulated using a Gaussian radiofrequency (RF) pulse with a variety of flip angle schedules and b-value ordering schemes. A long T<sub>1</sub> water phantom was used to validate the simulation results, and ADC mapping of HP [<sup>13</sup> C,<sup>15</sup> N<sub>2</sub> ]urea was perf ...[more]

PMID: 27735082

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Project description:Background and Purpose- In this era of endovascular therapy (EVT) with early, complete recanalization and reperfusion, we have observed an even more rapid apparent diffusion coefficient (ADC) normalization within the acute ischemic lesion compared with the natural history or IV-tPA-treated patient. In this study, we aimed to evaluate the effect of revascularization on ADC evolution within the core lesion in the first 24 hours in acute ischemic stroke patients. Methods- This retrospective study included anterior circulation acute ischemic stroke patients treated with EVT with or without intravenous tPA (IVT) from 2015 to 2017 compared with a consecutive cohort of IVT-only patients treated before 2015. Diffusion-weighted imaging and ADC maps were used to quantify baseline core lesions. Median ADC value change and core reversal were determined at 24 hours. Diffusion-weighted imaging lesion growth was measured at 24 hours and 5 days. Good clinical outcome was defined as modified Rankin Scale score of 0 to 2 at 90 days. Results- Twenty-five patients (50%) received IVT while the other 25 patients received EVT (50%) with or without IVT. Between these patient groups, there were no differences in age, sex, baseline National Institutes of Health Stroke Scale, interhospital transfer, or IVT rates. Thirty-two patients (64%) revascularized with 69% receiving EVT. There was a significant increase in median ADC value of the core lesion at 24 hours in patients who revascularized compared with further ADC reduction in nonrevascularization patients. Revascularization patients had a significantly higher rate of good clinical outcome at 90 days, 63% versus 9% (P=0.003). Core reversal at 24 hours was significantly higher in revascularization patients, 69% versus 22% (P=0.002). Conclusions- ADC evolution in acute ischemic stroke patients with early, complete revascularization, now more commonly seen with EVT, is strikingly different from our historical understanding. The early ADC normalization we have observed in this setting may include a component of secondary injury and serve as a potential imaging biomarker for the development of future adjunctive therapies. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT00009243.

Dataset Information

Mis-estimation and bias of hyperpolarized apparent diffusion coefficient measurements due to slice profile effects.

Publications

Mis-estimation and bias of hyperpolarized apparent diffusion coefficient measurements due to slice profile effects.

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