Viscoelastic profiling of rare pediatric extracranial tumors using multifrequency MR elastography: a pilot study

Magnetic resonance elastography (MRE) is a noninvasive technique for assessing viscoelastic properties of soft biological tissues in vivo, with potential relevance for tumor evaluation. This exploratory study aimed to assess the feasibility of multifrequency MRE in pediatric extracranial solid tumors and to investigate potential associations between viscoelastic parameters and different rare pediatric tumor entities. Ten pediatric patients (mean age, 5.7 ± 4.8 years; four female) with extracranial solid tumors underwent multifrequency MRE in this prospective study. Shear waves at 30-70 Hz were subsequently generated and measured with a phase-sensitive single-shot spin-echo planar imaging sequence. The obtained shear wave fields were processed by wavenumber (k-)based multi-frequency inversion to reconstruct tumor stiffness and fluidity. Viscoelastic properties within the tumors were quantified and correlated with the apparent diffusion coefficient (ADC). Differences in stiffness and fluidity were assessed across histopathologically confirmed tumor entities, stratified into malignancy-based groups. MRE was successfully performed in all patients within less than five minutes. Viscoelastic properties varied among tumor entities, with a tendency toward higher stiffness, fluidity, and spatial heterogeneity in tumors assigned to higher malignancy groups (all p < 0.05). Stiffness (p > 0.05) and fluidity (p < 0.05) showed inverse associations with tumor ADC values. Multifrequency MRE can be integrated into pediatric MRI examinations and provides quantitative information on tumor viscoelastic properties. Differences in stiffness and fluidity were observed across pediatric extracranial solid tumors with higher values in tumors assigned to higher risk groups. These preliminary findings suggest that MRE-derived parameters may provide complementary information for tumor characterization.