A case of dual-energy computed tomography (CT) being useful for detecting recurrence after radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC)
Tokyo Medical University Hospital
Takafumi Yamada, Dept. of Radiology
DATE : 2021
Introduction
Patient’s background
Female; 40s; body weight: 72 kg; HCC
Assessment objectives
Monitoring after RFA for HCC
Contrast agent used
Iopromide 370 injection syringe 100 mL, “BYL” / 98 mL
Case explanation
The patient was a woman in her 40s. She developed HCC during monitoring of chronic hepatitis C, and percutaneous RFA was performed. Dynamic contrast CT during post-treatment monitoring showed nodular early dark staining in the margin of the treated region of S8 of the liver, and the region with dark staining in the arterial phase was delineated as a low-absorption region in the equilibrium phase, suggesting recurrence.
Imaging findings
Post-RFA changes were observed as a faint low-absorption region.
Fig. 1. Simple CT at 70 keV
Faint, early dark staining was seen.
Fig. 2. Arterial phase at 70 keV
Early dark staining was seen, and was more distinct than at 70 keV.
Fig. 3. Arterial phase at 50 keV
Wash-out was indistinct.
Fig. 4. Equilibrium phase at 70 keV
Wash-out can be clearly observed.
Fig. 5. Equilibrium phase at 50 keV
Photography protocol
| Equipment used | CT device model | Revolution CT (GE Healthcare) |
| Number of CT detector rows / number of slices | 256/256 | |
| Workstation | Synapse Vincent (Fujifilm) |
| Imaging conditions | Imaging phase | A,P,D |
| Tube voltage (kV) | Dual 80-140kv | |
| AEC | Auto mA ON | |
| AEC settings | 8 | |
| Beamwidth (mm) | 80mm | |
| Imaging slice thickness (mm) | 5.0mm | |
| Focal-spot size | L | |
| Scan mode | Helical | |
| Scan speed (s/rotation) | 0.50 s | |
| Pitch | 0.508 | |
| Scan range | Abdomen | |
| Imaging duration (s) | 6.37 s | |
| Imaging direction | Head to foot |
| Reconstruction conditions | A,P,D | |
| Routine: Reconstructed slice thickness / interval (mm/mm) | 5.0mm/5.0mm | |
| Routine: Reconstruction function / iterative approximation method | std/DLIR:Low | |
| 3D / multiplanar reformation: Reconstructed slice thickness / interval (mm/mm) | 1.25mm/1.25mm | |
| 3D / multiplanar reformation: Reconstruction function / iterative approximation method | std/DLIR:Medium |
| Contrast conditions | A,P,D | |
| Automatic injector model and manufacturer | Dual Shot GX7 (Nemoto Kyorindo) | |
| Contrast agent used | Iopromide 370 injection syringe 100 mL, “BYL” | |
| Contrast agent: Dose | 600mgI/kg | |
| Contrast agent: Injection speed, injection duration | 30-s injection | |
| Physiological saline solution: Dose | 20mL | |
| Physiological saline solution: Injection speed, injection duration | In accordance with the contrast agent injection speed | |
| Scan timing | Fixed for 43 s | |
| Delay time | None | |
| Indwelling needle size (G) | 22G | |
| Injection pressure limit (kg/cm2) | 10kg/cm2 |
Explanation about the photography protocol
Usually, 62 mL of the above contrast medium stock solution was used, but co-injection was performed in a 6:4 ratio (contrast medium : physiological saline solution).
Role of contrast CT in diagnosis of this disease
Various mass shadow lesions, including primary, metastatic and inflammatory lesions, may occur in the liver. Dynamic contrast CT is an indispensable test for differential diagnosis of hepatic tumor lesions for evaluation of intra-tumor blood flow. Apart from primary HCC (the present patient’s lesion), lesions such as cavernous hemangioma and metastatic hepatic tumor, which are frequently encountered in routine medical treatment, can usually be differentiated on the basis of the contrast pattern. HCC is an epithelial malignant tumor that develops in the background in association with chronic hepatitis and/or hepatic cirrhosis. Highly to moderately differentiated HCC (i.e. classical HCC) is characterized by early dark staining in the arterial phase and wash-out in the equilibrium phase, and signs of this type were found with the present patient’s recurrent lesion. In comparison with a 70-keV image (corresponding to a tube voltage of 120 kVp in conventional CT), a 50-keV image using virtual monochromatic X-rays (detailed below) gives clearer contrast between the hepatic parenchyma and tumor, facilitating detection of early enhancement and wash-out.
CT techniques and imaging protocol settings
Revolution CT (GE Healthcare Co., Ltd.), which can perform dual-energy CT, has been introduced at the author’s hospital. Unlike conventional, single-energy CT, in which imaging is performed at a single tube voltage (most commonly 120 kVp), and information about CT values is obtained, dual-energy CT uses two tube voltages (140 and 80 kVp at the author’s hospital), and two different types of X-ray energy are obtained. By analyzing the two types of X-ray energy, virtual monochromatic X-ray images, that is, CT images prepared by virtual monoenergetic X-radiography ranging from low to high energy, can be reconstructed as wished. With iodine-based contrast agents, contrast is strengthened by use of low-energy virtual monochromatic X-ray images, so early dark staining of the HCC becomes more distinct, and can be identified more readily. However, attention should be paid to the fact that enhancement of image noise also occurs.
- *The case introduced is just one clinical case, so the results are not the same as for all cases.
- *Please refer to the Package Insert for the effects and indications, dosage and administration method, and warnings, contraindications, and other precautions with use.
