Learning‐based motion artifact correction in the Z‐spectral domain for chemical exchange saturation transfer MRI

Abstract Purpose To develop and evaluate a physics‐driven, saturation contrast‐aware, deep‐learning‐based framework for motion artifact correction in CEST MRI. Methods A neural network was designed to correct motion artifacts directly from a Z‐spectrum frequency (Ω) domain rather than an image spatial domain. Motion artifacts were simulated by modeling 3D rigid‐body motion and readout‐related motion during k‐space sampling. A saturation‐contrast‐specific loss function was added to preserve amide proton transfer (APT) contrast, as well as enforce image alignment between motion‐corrected and ground‐truth images. The proposed neural network was evaluated on simulation data and demonstrated in healthy volunteers and brain tumor patients. Results The experimental results showed the effectiveness of motion artifact correction in the Z‐spectrum frequency domain (MOCO Ω ) compared to in the image spatial domain. In addition, a temporal convolution applied to a dynamic saturation image series was able to leverage motion artifacts to improve reconstruction results as a denoising process. The MOCO Ω outperformed existing techniques for motion correction in terms of image quality and computational efficiency. At 3 T, human experiments showed that the root mean squared error (RMSE) of APT images decreased from 4.7% to 2.1% at 1 μT and from 6.2% to 3.5% at 1.5 μT in case of “moderate” motion and from 8.7% to 2.8% at 1 μT and from 12.7% to 4.5% at 1.5 μT in case of “severe” motion, after motion artifact correction. Conclusion The MOCO Ω could effectively correct motion artifacts in CEST MRI without compromising saturation transfer contrast.