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Background
Transarterial radioembolization with 90Y microspheres (RE) has developed into a competitive and complementary locoregional therapy for patients with primary and secondary liver cancer. Due to the unique properties of RE, the expected appearance of posttreatment tumors differs from other therapies. It is essential to understand these differences and their expected evolution for the accurate evaluation of treatment response. Sequential magnetic resonance imaging (MRI) provides crucial information to differentiate tumor necrosis from viable tumor and to evaluate potential posttreatment complications.

Educational Goals / Teaching Points
Basics of and MRI appearance of liver cancer including hepatocellular carcinoma, intrahepatic cholangiocarcinoma, and most common liver metastasis. Society guidelines and common practices for use of RE in liver cancer. Physical properties and mechanism of action of RE. Comparison of expected evolution of lesions treated with RE versus other locoregional therapies. Response evaluation guidelines, limitations, and unique considerations in RE. Essential MRI sequences for posttreatment follow-up. Expected early MRI findings. Expected intermediate to late MRI findings. Tumor recurrence and its differentiating features. Unexpected findings and evaluation of treatment related complications.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The imaging techniques and essential MRI sequences for accurate evaluation of tumor response in primary and secondary liver cancer will be reviewed.

Conclusion
Transarterial radioembolization with 90Y microspheres of primary and secondary liver cancer presents unique challenges for the interpreting radiologist. Detailed knowledge of expected and unexpected findings with MRI is an invaluable tool for the accurate assessment of tumor response.