Off-resonance artifacts in magnetic resonance imaging (MRI) are visual distortions that occur when the actual resonant frequencies of spins within the imaging volume differ from the expected frequencies used to encode spatial information. These discrepancies can be caused by a variety of factors, including magnetic field inhomogeneities, chemical shifts, or susceptibility differences within the tissues. Such artifacts can manifest as blurring, ghosting, or misregistration of the reconstructed image, and they often compromise its diagnostic quality. We propose to resolve these artifacts by lifting the 2D MRI reconstruction problem to 3D, introducing an additional "spectral" dimension to model this off-resonance. Our approach is inspired by recent progress in modeling radiance fields, and is capable of reconstructing both static and dynamic MR images as well as separating fat and water, which is of independent clinical interest. We demonstrate our approach in the context of PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) MRI acquisitions, which are popular for their robustness to motion artifacts. Our method operates in a few minutes on a single GPU, and to our knowledge is the first to correct for chemical shift in gradient echo PROPELLER MRI reconstruction without additional measurements or pretraining data.

翻译：磁共振成像（MRI）中的离共振伪影是一种视觉畸变，当成像体积内自旋的实际共振频率与用于编码空间信息的预期频率不一致时产生。这种差异可能由多种因素引起，包括磁场不均匀性、化学位移或组织内的磁敏感性差异。此类伪影可表现为重建图像的模糊、鬼影或配准错误，通常会影响图像的诊断质量。我们提出通过将二维MRI重建问题提升至三维来解决这些伪影，引入额外的"频谱"维度来建模离共振效应。该方法受辐射场建模最新进展的启发，能够重建静态和动态MR图像，并分离脂肪与水——这在临床上具有独立价值。我们在PROPELLER（周期性旋转重叠平行线增强重建）MRI采集场景中验证了该方法，该技术因其对运动伪影的鲁棒性而广受欢迎。我们的方法可在单GPU上数分钟内完成运算，据我们所知，这是首个无需额外测量或预训练数据即可校正梯度回波PROPELLER MRI重建中化学位移的方法。