QIMP Team, Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
Med Phys. 2022 Sep;49(9):5819-5829. doi: 10.1002/mp.15853. Epub 2022 Jul 25.
Hybrid imaging (e.g., positron emission tomography [PET]/computed tomography [CT], PET/magnetic resonance imaging [MRI]) helps one to visualize and quantify morphological and physiological tumor characteristics in a single study. The noninvasive characterization of tumor heterogeneity is essential for grading, treatment planning, and following-up oncological patients. However, conventional (CONV) image-based parameters, such as tumor diameter, tumor volume, and radiotracer activity uptake, are insufficient to describe tumor heterogeneities. Here, radiomics shows promise for a better characterization of tumors. Nevertheless, the validation of such methods demands imaging objects capable of reflecting heterogeneities in multi-modality imaging. We propose a phantom to simulate tumor heterogeneity repeatably in PET, CT, and MRI.
The phantom consists of three 50-ml plastic tubes filled partially with acrylic spheres of S1: 1.6 mm, S2: 50%(1.6 mm)/50%(6.3 mm), or S3: 6.3-mm diameter. The spheres were fixed to the bottom of each tube by a plastic grid, yielding one sphere free homogeneous region and one heterogeneous (S1, S2, or S3) region per tube. A 3-tube phantom and its replica were filled with a fluorodeoxyglucose (18F) solution for test-retest measurements in a PET/CT Siemens TPTV and a PET/MR Siemens Biograph mMR system. A number of 42 radiomic features (10 first order and 32 texture features) were calculated for each phantom region and imaging modality. Radiomic features stability was evaluated through coefficients of variation (COV) across phantoms and scans for PET, CT, and MRI. Further, the Wilcoxon test was used to assess the capability of stable features to discriminate the simulated phantom regions.
The different patterns (S1-S3) did present visible heterogeneity in all imaging modalities. However, only for CT and MRI, a clear visual difference was present between the different patterns. Across all phantom regions in PET, CT, and MR images, 10, 16, and 21 features out of 42 evaluated features in total had a COV of 10% or less. In particular, CONV, histogram, and gray-level run length matrix features showed high repeatability for all the phantom regions and imaging modalities. Several of repeatable texture features allowed the image-based discrimination of the different phantom regions (p < 0.05). However, depending on the feature, different pattern discrimination capabilities were found for the different imaging modalities.
The proposed phantom appears suitable for simulating heterogeneities in PET, CT, and MRI. We demonstrate that it is possible to select radiomic features for the readout of the phantom. Most of these features had been shown to be relevant in previous clinical studies.
混合成像（例如正电子发射断层扫描[PET]/计算机断层扫描[CT]、PET/磁共振成像[MRI]）有助于在单次研究中可视化和量化形态和生理肿瘤特征。肿瘤异质性的无创特征对于分级、治疗计划和随访肿瘤患者至关重要。然而，常规（CONV）基于图像的参数，例如肿瘤直径、肿瘤体积和放射性示踪剂摄取，不足以描述肿瘤异质性。 在这里，放射组学有望更好地描述肿瘤。然而，此类方法的验证需要能够反映多模态成像中异质性的成像对象。我们提出了一种可以在 PET、CT 和 MRI 中重复模拟肿瘤异质性的体模。
该体模由三个装满部分丙烯酸球体的 50 毫升塑料管组成，球体 S1：1.6 毫米、S2：50%（1.6 毫米）/50%（6.3 毫米）或 S3：6.3 毫米直径。球体通过塑料网格固定在每个管的底部，每个管产生一个球体自由均匀区域和一个异质（S1、S2 或 S3）区域。一个 3 管体模及其复制品被充满氟脱氧葡萄糖（18F）溶液，以便在 PET/CT 西门子 TPTV 和 PET/MR 西门子 Biograph mMR 系统中进行测试-重测测量。为每个体模区域和成像方式计算了 42 个放射组学特征（10 个一阶特征和 32 个纹理特征）。通过体模间和扫描间的变异系数（COV）评估放射组学特征的稳定性，用于 PET、CT 和 MRI。此外，使用 Wilcoxon 检验评估稳定特征区分模拟体模区域的能力。
不同模式（S1-S3）在所有成像方式中均呈现出明显的异质性。然而，只有 CT 和 MRI 显示出不同模式之间存在明显的视觉差异。在 PET、CT 和 MR 图像的所有体模区域中，在总共有 42 个评估特征中，有 10、16 和 21 个特征的 COV 为 10%或更低。特别是，CONV、直方图和灰度游程矩阵特征在所有体模区域和成像方式中均具有很高的重复性。一些可重复的纹理特征允许基于图像区分不同的体模区域（p<0.05）。然而，取决于特征，不同的成像方式发现了不同模式的不同区分能力。
所提出的体模似乎适合模拟 PET、CT 和 MRI 中的异质性。我们证明了可以选择放射组学特征来读取体模。其中大多数特征在以前的临床研究中已经被证明是相关的。
