Real-Time Monitoring of Hepatocellular Carcinoma Radiofrequency Ablation by Quantitative Temperature MRI

Early detection of hepatocellular carcinoma (HCC) through surveillance programs allows potentially curative therapies such as resection, liver transplantation, and percutaneous ablation to be applied in 40% of the patients. In nonsurgical candidates, percutaneous treatments are the best therapeutic approach and may improve survival in patients with well-preserved liver function and small tumors who achieve initial complete response. Applying these criteria, 5-year survival rates above 50% have been achieved.[1]

Minimally invasive, percutaneous ablative therapies under image guidance with thermal energy sources such as radiofrequency (RF) are increasingly used for tumor ablation because of their efficacy and low cost. Radiofrequency thermal ablation (RFTA) provides better objective response rates than ethanol injection, and a survival advantage has been reported.[2]

Sonography or computed tomography (CT) guidance is most often used for RF needle electrode positioning. However, precise and quantitative on-line control of the thermal ablation is not possible with these imaging modalities. The imaging method used for clinical guidance should ideally have a good spatial, temporal, and thermal resolution and should be easily implemented. In addition, the thermal and spatial resolution should be sufficient to detect temperature rise in the tissue around the lesion to: (1) enable real-time control of the ablation of the complete tumor and of a safety margin of 5 to 10 mm around the tumor and (2) avoid unwanted thermal damage in healthy tissue.

Magnetic resonance imaging (MRI) can monitor temperature changes quantitatively using the temperature-dependent shifts of the proton resonance frequency (PRF).[3] Therefore temperature mapping with MRI can be used to predict the treatment outcome during the heating procedure.

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