title: Comparing different analysis methods for quantifying the MRI amide proton transfer (APT) effect in hyperacute stroke patients.
abstract: Amide proton transfer (APT) imaging is a pH mapping method based on the chemical exchange saturation transfer phenomenon that has potential for penumbra identification following stroke. The majority of the literature thus far has focused on generating pH-weighted contrast using magnetization transfer ratio asymmetry analysis instead of quantitative pH mapping. In this study, the widely used asymmetry analysis and a model-based analysis were both assessed on APT data collected from healthy subjects (n = 2) and hyperacute stroke patients (n = 6, median imaging time after onset = 2 hours 59 minutes). It was found that the model-based approach was able to quantify the APT effect with the lowest variation in grey and white matter (≤ 13.8 %) and the smallest average contrast between these two tissue types (3.48 %) in the healthy volunteers. The model-based approach also performed quantitatively better than the other measures in the hyperacute stroke patient APT data, where the quantified APT effect in the infarct core was consistently lower than in the contralateral normal appearing tissue for all the patients recruited, with the group average of the quantified APT effect being 1.5 ± 0.3 % (infarct core) and 1.9 ± 0.4 % (contralateral). Based on the fitted parameters from the model-based analysis and a previously published pH and amide proton exchange rate relationship, quantitative pH maps for hyperacute stroke patients were generated, for the first time, using APT imaging.
authors.affiliation: Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK; Centre for Doctoral Training in Healthcare Innovation, University of Oxford, Oxford, UK.
authors.forename: Y K
authors.initials: YK
authors.lastname: Tee
authors.forename: G W J
authors.initials: GW
authors.lastname: Harston
authors.forename: N
authors.initials: N
authors.lastname: Blockley
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Okell
authors.forename: J
authors.initials: J
authors.lastname: Levman
authors.forename: F
authors.initials: F
authors.lastname: Sheerin
authors.forename: M
authors.initials: M
authors.lastname: Cellerini
authors.forename: P
authors.initials: P
authors.lastname: Jezzard
authors.forename: J
authors.initials: J
authors.lastname: Kennedy
authors.forename: S J
authors.initials: SJ
authors.lastname: Payne
authors.forename: M A
authors.initials: MA
authors.lastname: Chappell
mesh_terms: D000369:Aged, 80 and over; D000465:Algorithms; D000577:Amides / Q000737:chemistry*; D001923:Brain Chemistry; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011522:Protons; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020521:Stroke / Q000378:metabolism* / Q000473:pathology*
chemical_list: D000577:Amides; D011522:Protons
keywords: Amide proton transfer (APT) imaging; MRI; chemical exchange saturation transfer (CEST) imaging; magnetization transfer (MT) imaging; pH; stroke