Study of Common Quantification Methods of Amide Proton Transfer Magnetic Resonance Imaging for Ischemic Stroke Detection

Purpose: To assess the correlation and differences between common amide proton transfer (APT) quantification methods in ischemic stroke diagnosis. Methods: Five APT quantification methods, including asymmetry analysis and its variants as well as two Lorentzian model-based methods, were applied on data acquired from six rats that underwent middle cerebral artery occlusion scanned at 9.4 T . Diffusion and perfusion weighted images, and water relaxation time maps were also acquired to study the relationship of these conventional imaging modalities with the different APT quantification methods. Results: The APT ischemic area estimates had varying sizes (Jaccard index: 0.544 ≤ J ≤ 0.971) and had varying correlations in their distributions (Pearson correlation coefficient: 0.104 ≤ r ≤ 0.995), revealing discrepancies in the quantified ischemic areas. The Lorentzian methods produced the highest CNRs (1.427 ≤ CNR ≤ 2.002), but generated APT ischemic areas that were comparable in size to CBF deficit area; asymmetry analysis and its variants produced APT ischemic areas that were smaller than CBF but larger than ADC deficit areas although having lower CNRs (0.561 ≤ CNR ≤ 1.083). Conclusion: There is a need to further investigate the accuracy and correlation of each quantification method with the pathophysiology using a larger scale multi-imaging modality and multi-time point clinical study. Future studies should include the MTRasym results alongside the findings of their study, in order to facilitate the comparison of results between different centers and also the published literature.