Methodological considerations on segmenting rhabdomyosarcoma with diffusion-weighted imaging—What can we do better?

Abstract

Purpose Diffusion-weighted MRI is a promising technique to monitor response to treatment in pediatric rhabdomyosarcoma. However, its validation in clinical practice remains challenging. This study aims to investigate how the tumor segmentation strategy can affect the apparent diffusion coefficient (ADC) measured in pediatric rhabdomyosarcoma. Materials and methods A literature review was performed in PubMed using search terms relating to MRI and sarcomas to identify commonly applied segmentation strategies. Seventy-six articles were included, and their presented segmentation methods were evaluated. Commonly reported segmentation strategies were then evaluated on diffusion-weighted imaging of five pediatric rhabdomyosarcoma patients to assess their impact on ADC. Results We found that studies applied different segmentation strategies to define the shape of the region of interest (ROI)(outline 60%, circular ROI 27%), to define the segmentation volume (2D 44%, multislice 9%, 3D 21%), and to define the segmentation area (excludes edge 7%, excludes other region 19%, specific area 27%, whole tumor 48%). In addition, details of the segmentation strategy are often unreported. When implementing and comparing these strategies on in-house data, we found that excluding necrotic, cystic, and hemorrhagic areas from segmentations resulted in on average 5.6% lower mean ADC. Additionally, the slice location used in 2D segmentation methods could affect ADC by as much as 66%. Conclusion Diffusion-weighted MRI studies in pediatric sarcoma currently employ a variety of segmentation methods. Our study shows that different segmentation strategies can result in vastly different ADC measurements, highlighting the importance to further investigate and standardize segmentation.

Diagnostic magnetic resonance imaging characteristics of congenital mesoblastic nephroma: a retrospective multi-center International Society of Pediatric Oncology-Renal Tumor Study Group (SIOP-RTSG) radiology panel study

“…Furthermore, in international studies, variability on the level of the patient and the MRI, reflected in the heterogeneity of reported scan parameters, has to be taken into consideration [ 57 ]. While this might not influence the reported results, it limits the possibility for statistical analysis in DWI data, given non-comparable ADC maps based on a variety of b -values [ 58 ]. Concerning clinical characteristics of the patients, this study was not designed to report on prenatal imaging or outcome, therefore lacking information on prenatal diagnoses and survival of the included patients.…”

Monoexponential, biexponential, stretched exponential and diffusion kurtosis models of diffusion-weighted imaging: A quantitative differentiation of solitary pulmonary lesion

“…These factors may result in more restricted diffusion of water molecules in both extracellular and intracellular spaces, whereas benign SPL has lower cell density and larger extracellular space, resulting in larger ADC values. Study had shown that the diffusion of water molecules in tumors is mainly affected by tumor cell density and the movement of water molecules in the stroma [15]. The cell density of malignant SPL is higher than that of benign SPL, with an increased number of cells per unit volume and a relatively reduced extracellular space, resulting in more restricted diffusion of water molecules and lower ADC values.…”