The current study included 40 cases of HCCs were treated with radiofrequency ablation (RFA), microwave ablation (MWA), transarterial chemoembolization (TACE), and combined technique. Follow-up PET/CT was done for all cases. It was done during the period from July 2016 till January 2017 and was approved by the local research ethical committee at our University. An informed consent was obtained from all patients.
Any HCC patient, regarding age and sex, was treated with radiofrequency ablation (RFA), microwave ablation (MWA), transarterial chemoembolization (TACE), and combined technique.
1. Patients with contraindication to contrast: patients with disturbed renal function test (if creatinine > 2), patients with glomerular filtration rate < 30 ml per min per 1.73 m2 or any acute renal insufficiency related to the hepato-renal syndrome or perioperative liver transplantation
2. Patients with metastatic HCC
3. Patients with uncontrolled serum glucose level
4. Patients who are pregnant
All patients were asked to fast and rest for a minimum of 6 h before undergoing the examination. Activities including talking, chewing, and walking were restricted. Serum glucose levels were measured 1 h before FDG (fluorodeoxyglucose) injection to ensure that the included patients had a level below 150 mg/dl; the examination was postponed if the level was above 150 mg/dl. No oral contrast agent was administered. In addition, all patients were instructed to void preceding the examination. Patients were placed in a lying down position with raised arms.
18F-FDG PET/CT study and image analysis PET studies were performed after various procedures with unexplained elevated alpha fetoprotein for all patients using a dedicated PET scanner (DST PET/CT; Discovery ST PET-CT, General Electric Medical Systems, Milwaukee, WI, USA). All examinations were carried out using two integrated PET/CT scanners (Ingenuity TF 128; Philips Healthcare, Cleveland, OH, USA) 1 h after intravenous administration of 7–11 mCi of 18F-FDG corresponding to the patient’s body weight. The CT scan component of the PET/CT examination included non-contrast CT acquisition of the liver, arterial phase CT of the liver, portal venous whole-body CT, and equilibrium phase CT of the liver. For the arterial phase, the contrast agent iopromide (Ultravist) (300 mg of iodine/ml) was used at a dose of 100–120 ml corresponding to the patient’s body weight with a 3-ml/s infusion rate, following the administration of 50 ml of a normal saline chaser at a 3-ml/s infusion rate. A 100-HU threshold was set in the region of interest (ROI) at the lower part of the descending thoracic aorta to trigger the start of hepatic arterial phase CT. The portal venous whole-body and equilibrium phases were acquired approximately 65 and 120 s after beginning the contrast medium infusion, respectively. During the portal venous phase, the patients were asked to breathe smoothly. The portal venous whole-body phase images were used for attenuation correction and integration with the PET images.
All CT images, attenuation-corrected PET images, and fused PET/CT images were transferred and viewed centrally on an interactive workstation (IntelliSpace Portal V4.0; Philips Healthcare). The 18F-FDG PET images and contrast-enhanced CT (CECT) images were separated for interpretation (i.e., the 18F-FDG PET image findings were reviewed without knowledge of the CECT findings and vice versa). Two radiologists with 15 and 12 years of experience, respectively, in hepatic CT imaging reviewed all CECT components of the PET/CT scan. Two nuclear medicine physicians with 7 and 5 years of experience, respectively, reviewed all 18F-FDG PET images. All radiologists and nuclear medicine physicians were blinded to any clinical information or the results of the biopsy. Intrahepatic HCC recurrence was noted as newly developed lesions showing hyperenhancement in the arterial phase and washout in the delayed phase of the CECT component. In 18F-FDG PET/CT, disease activity was assessed either qualitatively or semi-quantitatively. Qualitative evaluation was based on the detection of focal 18F-FDG uptake that was higher than the surrounding background and distinct from tracer uptake physiological sites (e.g., bowel and myocardium), whereas semi-quantitative evaluation typically relied on the calculation of the maximum standardized uptake value (SUVmax).
We calculated for each patient the SUVmax of the tumor and the ratio of the tumoral SUVmax to the normal liver SUVmax (TSUVmax/LSUVmax). In order to measure SUVmax for the tumor, we drew a 4 × 4 pixel square region of interest (ROI) and placed it on the area of the highest activity of the tumor but not covering the entire tumor, with the aid of combined CT and measured SUVmax in the ROI. In the case of multiple tumors, the SUVmax of the tumors was defined as the highest SUVmax of the tumors. To measure SUVmax for normal liver, we drew two 50-pixel circular ROIs and placed one on right lobe and one on liver transplantation (LT) lobe at a location where tumor was not detected on combined CT. The SUVmax of the normal liver was defined as the highest SUVmax of the two ROIs drawn on the normal liver. In this combined protocol, we established the diagnosis based on the combined findings from each modality. A finding was considered positive when it was observed in either the CECT or 18F-FDG PET/CT scan or both. We categorized intrahepatic HCC recurrence as either recurrence adjoining the treated site or at a site further than the original tumor site.