Department of Diagnostic and Interventional Radiology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
Magn Reson Med. 2019 Dec;82(6):2077-2089. doi: 10.1002/mrm.27891. Epub 2019 Jul 17.
Quantitative susceptibility mapping (QSM) is heavily impacted by phase processing of gradient echo imaging data. So far, phase unwrapping algorithms have mostly been developed and tested for neuroimaging applications. In this work, a numerical human abdomen phantom was created and used to assess the feasibility of different phase unwrapping algorithms in abdominal QSM. Furthermore, in vivo data were acquired to evaluate consistency with the simulations.
Laplacian-based, quality-guided region growing and graph-cuts unwrapping techniques were evaluated using the numerical phantom as well as an in vivo measurement. As a quality metric, root mean square error (RMSE) was calculated in order to analyze the performance of the examined unwrapping algorithms. Subsequently, susceptibility maps were generated from the resulting phase maps and compared to the ground truth. The evaluation was carried out on the whole phantom as well as individual organs.
Graph-cuts led to the most accurate and robust results among the investigated unwrapping methods. The other algorithms showed severe errors in regions with large susceptibility changes (i.e., around the lungs). Deviations from the ground-truth susceptibility were higher than in the previous brain simulations for all tested algorithms.
Graph-cuts-based unwrapping algorithms should be preferred in QSM studies in the human abdomen, where large susceptibility changes occur. For further improvement of QSM studies, unwrapping algorithms should be optimized for abdominal applications.
定量磁化率映射（QSM）受到梯度回波成像数据相位处理的严重影响。到目前为止，相位解缠算法主要是为神经影像学应用而开发和测试的。在这项工作中，创建了一个数值人体腹部模拟体，并用于评估不同相位解缠算法在腹部 QSM 中的可行性。此外，还采集了体内数据以评估与模拟的一致性。
使用数值模拟体和体内测量评估基于拉普拉斯的、质量引导的区域生长和图割解缠技术。作为质量指标，计算均方根误差（RMSE）以分析所检查的解缠算法的性能。随后，从所得相位图生成磁化率图，并与真实值进行比较。在整个模拟体和各个器官上进行了评估。
在研究的解缠方法中，图割法得到了最准确和最稳健的结果。其他算法在磁化率变化较大的区域（即肺部周围）显示出严重的误差。与所有测试算法的大脑模拟相比，对于所有测试算法，从真实磁化率的偏差都更高。
在人体腹部出现大磁化率变化的 QSM 研究中，应优先选择基于图割的解缠算法。为了进一步改进 QSM 研究，应针对腹部应用优化解缠算法。
