Hepatocellular carcinoma is one of the most common malignant tumors worldwide. Early detection and treatment of recurrent HCC after loco-regional interventional treatment is crucial to patient survival .
Percutaneous techniques such as TACE are now available to manage localized HCC. Tumoral response assessment after TACE is important to determine whether the tumor is completely eradicated or needs additional treatment .
CT and MRI are the most widely used tools to assess the patients who underwent loco-regional intervention procedures such as TACE. Both can determine not only reduction in tumoral size, but also detect the change in the internal structure and enhancement pattern that most investigators rely on as a non-separable adjunct to size change when it comes to evaluation of treatment response. As using size criteria, based on the Response Evaluation Criteria in Solid Tumors (RECIST), does not apply well to post-chemoembolization of HCC .
CT has been long used for post chemoembolized HCC follow-up assessment depending on the presence or absence of contrast enhancement; however, the beam-hardening artifact of the high-attenuation lipiodol on CT can surely hinder the intralesional viable tumor detection. Not to mention that after TACE, the feeding arteries of the residual tumor are significantly thinner that will affect the degree of enhancement of the tumor .
PET/CT is a unique combination of the cross-sectional anatomical data provided by CT and the metabolic data provided by PET. It also has the advantage of local therapy assessment as well as detection of extrahepatic spread of HCC which is crucial before patient planning for liver transplantation. In contrast to morphological image diagnosis, FDG PET evaluates viability based on glucose metabolism and is not influenced by tumor morphology or lipiodol deposition .
In agreement with Ali et al. , our study concluded that the chemoembolized lesions that become completely photopenic immediately after embolization are suggestive of successful ablation. Focal, nodular, and intense uptake of FDG within the ablated zone is suggestive of residual viable HCC while a uniform low-grade FDG uptake depicted at the periphery of the ablated lesion is suggestive of reactive tissue changes as inflammation and hyperemia.
In our study, the median value of tumor SUVmax in positive cases was 6.6 (ranged from 1.4 to 24), most of them were poorly differentiated HCCs, yet a single case measured about 1.4 SUVmax (well-differentiated HCC type). In the study done by Ahn et al. , the median value of tumor SUVmax was 4.3 (ranged from 2.0 to 11.6).
In a study done by Myeong Jun Song et al.  over 83 patients with HCC to investigate the correlation of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) with clinical features and the prediction of treatment response, he found the TSUVmax/LSUVmax in his study was 1.36 (ranged from 0.77 to 7.64) with cut off value of 1.45 which is comparable with our study which revealed TSUVmax/LSUVmax 2.9 (ranged from 1.06 to 7.2) with cut off value of 1.
Kim et al.  stated that HCCs with high 18F-FDG uptake are reported to be more aggressive than HCCs with low 18F-FDG uptake. This is concordant with Ho et al.  who stated that poorly and moderately differentiated HCC have avid FDG uptake of these tumors on PET. These results are coinciding with our results where almost all positive cases of HCC were of moderately or poorly differentiated types, showing increased FDG uptake and SUV max values > 3, while the single case of well-differentiated type we encountered showed relatively low 18F-FDG uptake and 1.4 SUVmax value.
The false positive interpretations of PET/CT can be attributed to physiological uptake, infection, and recent chemotherapy, whereas false negative results can be found with well-differentiated HCC and small lesion below the scanner resolution (< 10 mm) Tsurusaki et al. . Therefore, we waited in our study for at least 6 weeks after TACE to get the most accurate characterization of loco-regional response after chemoembolization.
Small lesions <10 mm that are below the scanner resolution might be missed unless they show avid FDG uptake on top of limited background activity so we excluded lesions less than 10 mm from our study.
The diameter of lesions in our study ranged between 1 and 8.5 cm (with mean diameter of 4.2 cm) which is comparable to the study done by Ahn et al.  where the diameter of lesions ranged between 2.5 and 10.5 cm (with mean diameter of 5.5 cm).
Our study demonstrated higher sensitivity of PET/CT over triphasic CT in detection of local tumor residue/recurrence following TACE which may be masked by lipiodol artifact. Not to mention its ability to detect extrahepatic spread of HCC in a single whole-body examination that can be crucial for patient preparation for liver transplantation. PET/CT showed sensitivity, specificity, and accuracy of 96.3%, 66.7%, and 93.3%, respectively, in comparison to 74%, 100.0%, and 76 % for triphasic CT. These results are comparable to many studies as mentioned before.
Song et al.  reported that PET/CT sensitivity, specificity, and accuracy for detection of viable HCC after TACE were 89.29%, 65.71%, and 80.22%, respectively, in comparison to 60.71%, 77.1%, and 67.03% for contrast-enhanced computed tomography (CECT).
Kim et al.  found that the respective values for sensitivity, specificity, and accuracy of PET/CT in the evaluation of early treatment response after interventional therapy for hepatocellular carcinoma were 87.5 %, 71.4%, and 80.0 %.
Our results are also correlated with the results of Jinpeng et al.  when he studied the recurrence of HCC after (TACE) in 29 patients; the sensitivity of the PET was 95.4% while the sensitivity of CECT was 63.8%.
Our results are nearly matched with Kim et al.  who studied evaluation of metabolic characteristics and viability of lipidolized hepatocellular carcinomas using 18F-FDG PET/CT with sensitivity and specificity 97% and 63% for PET/CT in comparison to 87% and 100% for CECT, respectively, also Ali et al.  studied the role of 18F-FDG PET/CT in the detection of local tumor residue/recurrence in hepatocellular carcinoma (HCC) post hepatic therapeutic intervention on 40 patients; the sensitivity of triphasic CT and PET were 76.7% and 96.7%, respectively.