Quantitative Ischemic Lesions of Portable Low–Field Strength MRI Using Deep Learning–Based Super-Resolution

BACKGROUND: Deep learning–based synthetic super-resolution magnetic resonance imaging (SynthMRI) may improve the quantitative lesion performance of portable low–field strength magnetic resonance imaging (LF-MRI). The aim of this study is to evaluate whether SynthMRI improves the diagnostic performance of LF-MRI in assessing ischemic lesions. METHODS: We retrospectively included 178 stroke patients and 104 healthy controls with both LF-MRI and high–field strength magnetic resonance imaging (HF-MRI) examinations. Using HF-MRI as the ground truth, the deep learning–based super-resolution framework (SCUNet) was pretrained using large-scale open-source data sets to generate SynthMRI images from LF-MRI images. Participants were split into a training set (64.2%) to fine-tune the pretrained SCUNet, and a testing set (35.8%) to evaluate the performance of SynthMRI. Sensitivity and specificity of LF-MRI and SynthMRI were assessed. Agreement with HF-MRI for Alberta Stroke Program Early Computed Tomography Score in the anterior and posterior circulation (diffusion-weighted imaging–Alberta Stroke Program Early Computed Tomography Score and diffusion-weighted imaging–posterior circulation Alberta Stroke Program Early Computed Tomography Score) was evaluated using intraclass correlation coefficients (ICCs). Agreement with HF-MRI for lesion volume and mean apparent diffusion coefficient (ADC) within lesions was assessed using both ICCs and Pearson correlation coefficients. RESULTS: SynthMRI demonstrated significantly higher sensitivity and specificity than LF-MRI (89.0% [83.3%–94.6%] versus 77.1% [69.5%–84.7%]; P <0.001 and 91.3% [84.7%–98.0%] versus 71.0% [60.3%–81.7%]; P <0.001, respectively). The ICCs of diffusion-weighted imaging–Alberta Stroke Program Early Computed Tomography Score between SynthMRI and HF-MRI were also better than that between LF-MRI and HF-MRI (0.952 [0.920–0.972] versus 0.797 [0.678–0.876], P <0.001). For lesion volume and mean apparent diffusion coefficient within lesions, SynthMRI showed significantly higher agreement ( P <0.001) with HF-MRI (ICC>0.85, r >0.78) than LF-MRI (ICC>0.45, r >0.35). Furthermore, for lesions during various poststroke phases, SynthMRI exhibited significantly higher agreement with HF-MRI than LF-MRI during the early hyperacute and subacute phases. CONCLUSIONS: SynthMRI demonstrates high agreement with HF-MRI in detecting and quantifying ischemic lesions and is better than LF-MRI, particularly for lesions during the early hyperacute and subacute phases.