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.