Evaluation of acidosis in brain infarction with magnetization transfer ratio asymmetry (MTRasym) and magnetization transfer and relaxation-normalized amide proton transfer rate (MRAPTR) in amide proton transfer-weighted MRI and its influencing factors.

PURPOSE: To investigate the sensitivity of the magnetization transfer ratio asymmetry (MTRasym) and magnetization transfer and relaxation-normalized APT rate (MRAPTR) in detecting the tissue acidosis in ischemic stroke, and to assess the influence of infarct volume, apparent diffusion coefficient (ADC), and regions of interest (ROI) position. METHOD: Ischemic stroke patients who met the inclusion criteria had a comprehensive MRI scan within 3 days of admission, including the APT sequence on a 3T MRI system. MTRasym and MRAPTR were obtained through the post-processing of APT data. The infarct volume, ADC, and ROI positions were also collected. McNemar's test was used to compare the pH sensitivity of two APT metrics. Spearman correlation analysis was used to compare the relationships between infarct volume, ADC, and ROI position with MTRasym and MRAPTR. One-way ANOVA was used to assess differences of both metrics across three ROI locations. RESULTS: 147 patients (mean age, 62.17 years ± 0.92 [SD], 97 men) were evaluated. MRAPTR showed obviously better pH sensitivity than MTRasym for infarction (p<0.001). The pH sensitivity of MTRasym appeared compromised by larger infarct volume and elevated ADC values, even the ROIs position (p<0.05). In contrast, MRAPTR effectively mitigated the impact of these confounding factors, resulting in higher pH sensitivity. CONCLUSIONS: MRAPTR demonstrated a higher sensitivity to tissue acidosis compared to MTRasym in APTw MRI. While MRAPTR effectively eliminates confounding influences from non-pH factors, but might still sensitive to the magnetic field inhomogeneities.