Background <p>Effect of radiation on [¹⁸F]FDG-uptake in non-tumorous liver tissue after radioembolization is sparsely investigated, despite the liver being the most common reference for assessment of metabolic response (e.g., PET Response Criteria In Solid Tumors). The study aims to evaluate changes in mean standardized uptake value corrected for lean body mass in treated and untreated non-tumorous liver after unilobar radioembolization with ⁹⁰Y-glass microspheres in patients with colorectal liver metastases.</p> Results <p>Eighteen patients were included. Median mean standardized uptake value corrected for lean body mass in the treated lobe increased from baseline 2.88 (range 2.24–3.81) to posttreatment 2.98 (range 2.53–3.53). In the untreated lobe, the median mean standardized uptake value corrected for lean body mass changed from 2.95 (range 2.23–4.02) to 2.88 (range 2.39–3.71), respectively. The median mean standardized uptake value corrected for lean body mass of the ratio treated/untreated liver changed from 0.96 (range .77–1.23) to 1.00 (range .88–1.26) after treatment (p = 0.147)). The correlation for the ratio (mean standardized uptake value corrected for lean body mass in treated liver divided by mean standardized uptake value corrected for lean body mass in untreated liver) before and after radioembolization was nonsignificant. No trend was seen between [¹⁸F]FDG-uptake and treated or untreated non-tumorous liver absorbed dose.</p> Conclusions <p>This study shows no significant increase in [¹⁸F]FDG-uptake in both treated and untreated non-tumorous liver in patients with liver metastases of colorectal carcinoma, three months after lobar ⁹⁰Y-glass microsphere radioembolization. This non-significant increase suggests that using background SUL in the non-tumorous liver (treated and untreated) is reliable and appropriate as a reference to assess metabolic response three months after unilobar radioembolization.</p>