CT examination :
The advances in multidetector CT, have given the radiologist unique imaging capabilities that provide the opportunity to revolutionize the evaluation of liver tumors. The use of subsecond multidetector CT with ability to acquire multiple well-timed sets of image data has increased the ability to detect hepatic tumors and recurrences after treatment. A minimum of two phases of data acquisition are needed: an arterial phase (25-30-second delay) and a (portal) venous phase (60-second delay). CT examinations of the liver for suspected metastatic or primary tumor are performed with a multidetector CT (Somatom Volume Zoom/ Siemens) 2.5-mm collimation and reconstruction thickness (mm)/interval (mm) of 5/5 or 5/3. Computed tomography (CT) is used most frequently to determine whether the ablation is complete and to screen for early recurrences that may benefit from reablation. Complete ablation creates an area of necrosis that, at CT, is of low attenuation compared with the surrounding liver tissue, is often homogeneous, and has smooth margins. The disadvantages of CT are: potential radiation dose, the need of contrast-agent injection with it's usual inconvenient, timing of scanning is more critical as the increased speed of multidetector CT narrows the "temporal window" for desirable phase of enhancement.
Successful treatment of a small metastasis from colon cancer. Contrast-enhanced CT scan obtained 10 days after RF ablation with insertion of a single infused electrode shows a hypoattenuation without contrast enhancement, suggestive of a complete response.
Treatment of a large HCC lesion. Transverse contrast-enhanced arterial phase CT scan obtained 10 days after radio-frequency ablation shows an ablation defect with a diffuse, ill-defined enhancement around the defect. These findings are indeterminate.