Diffusion-weighted MRI shows promise as a radiation-free alternative for pediatric tumor staging

Image: PD

1. Whole-body diffusion-weighted MRI with ferumoxytol had comparable sensitivity and specificity to 18FDG-PET/CT scans in pediatric lymphoproliferative disorder and malignant sarcoma staging. 

2. The use of IV ferumoxytol as contrast agent was not associated with significant adverse events. 

Evidence Rating Level: 2 (Good)           

Study Rundown: 18FDG-PET/CT scans are the current gold standard in cancer staging. However, their use is associated with substantial exposure to ionizing radiation which increases the lifetime cancer risk, especially in pediatric patients. Whole-body diffusion-weighted MRI (WB-DW MRI), while free of ionizing radiation, shows only limited background information with poor contrast between the highly cellular normal bone marrow and malignant tumor cells. This often leads to misdiagnosis and poor sensitivity for underlying tumors. In the current study, WB-DW MR and T1-weighted MR images with IV ferumoxytol contrast were fused to produce a single image that was comparable to 18FDG-PET/CT scans in tumor staging and identification. The use of IV ferumoxytol was not associated with any significant adverse effects. The fact that WB-DW MRI does not utilize ionizing radiation represents a considerable advantage in the pediatric population. Future research is needed to establish the safety profiles of ferumoxytol in the pediatric population.

This study was limited by the small sample size of 22 patients. The study was funded by Thrasher Research Fund and Clinical Health Research Institute at Stanford University.

Click to read the study, published today in The Lancet Oncology

Relevant Reading: Radiation risks from imaging studies in children with cancer

In-Depth [prospective cohort]: This study investigated the use of radiation-free whole-body diffusion-weighted MRI (WB-DW MRI) scans as an alternative to 18FDG-PET/CT scans for tumor detection and staging. 22 patients between the ages of 8-33 with malignant lymphoma, newly diagnosed lymphoproliferative disorder, or malignant sarcoma who had a previously scheduled or completed 18FDG-PET/CT scan were included in the study. All patients underwent WB-DW MRI at 15–30 min after ferumoxytol injection. Patients then underwent standard ¹⁸F-FDG PET/CT scans within a mean of 8.3 days after their MRI scan. Two experienced radiologists interpreted the whole-body DW-MRI images and two nuclear medicine physicians interpreted the ¹⁸F-FDG PET/CT images. Histopathology, staging outcome, disease history, and other imaging findings were masked from all reviewers.

Image quality was rated as good to excellent for both imaging modalities with an average score of 3.59 (SD 0.50) for WB-DW MRI and 3.36 (SD 0.58) for ¹⁸F-FDG PET/CT images. Ann Arbor tumor staging results for the lymphoma patients showed very good agreement between the two imaging modalities (k=0.93, 95% confidence interval [CI], 0.81-1.00). ¹⁸F-FDG PET/CT was compared to DW-WB MRI with a similar sensitivity of 93.7% (95% CI 89.0–96.8) vs 90.8% (95% CI 85.5–94.7); specificity of 97.7% (95% CI 96.7–98.5) vs 99.5% (95% CI 98.9–99.8); and diagnostic accuracy of 97.2% (95% CI 93.6–99.4) versus 98.3% (95% CI 97.4–99.2).

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