M4Raw: A multi-contrast, multi-repetition, multi-channel MRI k-space dataset for low-field MRI research [V1.6]

V1.6 release notes: The test subset is released, which contains T1w (6 repetitions/subject), T2w (6 repetitions/subject), and FLAIR (4 repetitions/subject) data from 25 new subjects. These data have passed motion inspection, but one should note that due to the doubled repetition numbers, the average inter-contrast motions are around twice larger than those in the training and validation subsets. To facilitate users, we release the ground truth images as well, but please do not use them during hyperparameter tuning. V1.5 release notes: T1w Gradient echo (GRE) data for all 183 subjects are released. Note that the phase encoding direction for GRE data is in the AP direction, different from other contrasts. These GRE data were not checked for motions. A few incorrect records of patient_id were corrected in the H5 files. Scans 2022062708 and 2022062709 were removed due to duplication. Two new scans were added to replace them. V1.1 release notes: Please refer to https://www.nature.com/articles/s41597-023-02181-4 for details.V1.6 版本更新说明：本次发布测试子集，包含25名新增受试者的T1加权成像（T1w）、T2加权成像（T2w）及液体衰减反转恢复序列（FLAIR）数据，其中T1w、T2w各重复采集6次/受试者，FLAIR重复采集4次/受试者。该批次数据已通过运动伪影检查，但需注意：由于重复采集次数翻倍，各序列间的平均运动伪影幅度约为训练与验证子集的两倍。为便利用户使用，我们同步发布了真值图像，但请勿在超参数调优阶段使用该真值图像。 V1.5 版本更新说明：本次发布全部183名受试者的T1加权梯度回波（Gradient Echo, GRE）数据。需注意：GRE数据的相位编码方向为前后（Anterior-Posterior, AP）方向，与其他成像序列不同。该批次GRE数据未进行运动伪影检查。H5文件中若干错误的受试者ID记录已完成修正。因存在重复扫描，编号为2022062708与2022062709的扫描数据已被移除，同时新增两条扫描数据予以替换。 V1.1 版本更新说明：详细信息请参阅 https://www.nature.com/articles/s41597-023-02181-4。