Prediction of the ablated area by the spread of microbubbles during radiofrequency ablation of hepatocellular carcinoma

Tips for Preparing and Practicing Thermal Ablation Therapy of Hepatocellular Carcinoma

Thermal ablation therapy, including radiofrequency ablation (RFA) and microwave ablation (MWA), is considered the optimal locoregional treatment for unresectable early-stage hepatocellular carcinomas (HCCs). Percutaneous image-guided ablation is a minimally invasive treatment that is being increasingly performed because it achieves good clinical outcomes with a lower risk of complications. However, the physics and principles of RFA and MWA markedly differ. Although percutaneous thermal ablation under image guidance may be challenging in HCC cases with limited access or a risk of thermal injury, a number of ablative techniques, each of which may be advantageous and disadvantageous for individual cases, are available. Furthermore, even when a HCC is eligible for ablation based on tumor selection and technical factors, additional patient factors may have an impact on whether it is the appropriate treatment choice. Therefore, a basic understanding of the advantages and limitations of each ablation device and imaging guidance technique, respectively, is important. We herein provide an overview of the basic principles of tissue heating in thermal ablation, clinical and laboratory parameters for ablation therapy, preprocedural management, imaging assessments of responses, and early adverse events. We also discuss associated challenges and how they may be overcome using optimized imaging techniques.

Ultrasound single-phase CBE imaging for monitoring radiofrequency ablation of the liver tumor: A preliminary clinical validation

Radiofrequency ablation (RFA) is an alternative treatment for early-stage hepatocellular carcinoma (HCC). The production of gas bubbles by RFA indicates threshold temperature of tissue necrosis and results in changes in backscattered energy (CBE) when ultrasound monitors RFA. In this study, ultrasound single-phase CBE imaging was used as a means of monitoring RFA of the liver tumor by analyzing the backscattering of ultrasound from gas bubbles in the liver. A total of 19 HCC patients were enrolled in the study. An ultrasound system was used during RFA to monitor the ablation process and acquire raw image data consisting of backscattered signals for single-phase CBE imaging. On the basis of single-phase CBE imaging, the area corresponding to the range of gas bubbles was compared with the tumor sizes and ablation zones estimated from computed tomography. During RFA, ultrasound single-phase CBE imaging enabled improved visualization of gas bubbles. Measured gas bubble areas by CBE were related to tumor size (the Spearman correlation coefficient r_s = 0.86; p < 0.05); less dependent on the ablation zone. Approximately 95% of the data fell within the limits of agreement in Bland-Altman plots, and 58% of the data fell within the 95% CI. This study suggests that single-phase CBE imaging provides information about liver tumor size because of the abundant vessels in liver tumors that promote the generation of gas bubbles, which serve as natural contrast agents in RFAs to enhance ultrasound backscattering. Ultrasound single-phase CBE imaging may allow clinicians to determine if the required minimum RFA efficacy level is reached by assessing gas bubbles in the liver tumors.

Can the Entire Ablative Hyperechoic Zone be Regarded as a Necrotic Lesion After Radiofrequency Ablation of the Liver?

Developments in image fusion technology made it possible to visualize the ablative margin on ultrasound (US). The purpose of the present study was to assess the ablative area of radiofrequency ablation for hepatocellular carcinoma and compare it with the ablative hyperechoic zone with a non-enhanced area on contrast-enhanced US/contrast-enhanced computed tomography (CEUS/CECT) in the same cross-section. This retrospective study included 25 patients with 27 hepatocellular carcinomas. The long and short dimensions of the ablative hyperechoic zone were measured using B-mode US, and those of the non-enhanced area were assessed with CEUS/CECT on the same cross-section measured with B-mode US, using image fusion techniques. The technical effectiveness of ablation with an adequate ablative margin in a single session was determined in all patients. The long and short dimensions of the ablative hyperechoic zone ranged between 15.0 and 40.7 mm (mean: 27.3 ± 6.9 mm) and between 14.0 and 33.0 mm (mean: 23.3 ± 5.8 mm), respectively. R values for the long and short dimensions were 0.99 and 0.98, respectively, between B-mode US and CEUS, and 0.96 and 0.92, respectively, between B-mode US and CECT. The ablative hyperechoic zone may be regarded as a necrotic lesion after radiofrequency ablation.

Phase Contrast Imaging Based Microbubble Monitoring of Radiofrequency Ablation: An ex vivo Study

Background

To explore the potential of synchrotron radiation (SR) phase contrast imaging (PCI) for real-time microbubble formation monitoring during radiofrequency ablation (RFA).

Methods

RFA was performed on ex vivo porcine muscle tissue using unipolar and multi-tined expandable electrodes. Images of microbubble formation in the samples were captured by both SR PCI and absorption contrast imaging. The synchronous ablation temperature was recorded. Each RFA electrode type group contained 6 samples. Ablation size was assessed by histologic examination.

Results

Microbubble formation during RFA could be visualized by SR PCI. The diameter of the microbubbles revealed on the image ranged from tens of microns to several millimeters, and these microbubbles first appeared at the edge of the RFA electrode when the target region temperature reached approximately 60°C and rapidly extended outwards. The average microbubble range measured on PCI was 17.66 ± 0.74 mm. The average range of coagulation necrosis measured by histological examination was 17.22 ± 0.38 mm. There was no significant difference between them (P > 0.05). The range of microbubbles corresponded to the ablation zone.

Conclusion

PCI enabled real-time high-resolution visualization of microbubble formation during RFA, indicating a potential for its use in ablation monitoring.

Comparison of switching bipolar ablation with multiple cooled wet electrodes and switching monopolar ablation with separable clustered electrode in treatment of small hepatocellular carcinoma: A randomized controlled trial

OBJECTIVE

A randomized controlled trial was conducted to prospectively compare the therapeutic effectiveness of switching bipolar (SB) radiofrequency ablation (RFA) using cooled-wet electrodes and switching monopolar (SM) RFA using separable clustered (SC) electrodes in patients with hepatocellular carcinomas (HCCs).

MATERIALS AND METHODS

This prospective study was approved by our Institutional Review Board. Between April 2014 and January 2015, sixty-nine patients with 74 HCCs were randomly treated with RFA using either internally cooled-wet (ICW) electrodes in SB mode (SB-RFA, n = 36) or SC electrodes in SM mode (SM-RFA, n = 38). Technical parameters including the number of ablations, ablation time, volume, energy delivery, and complications were evaluated. Thereafter, 1-year and 2-year local tumor progression (LTP) free survival rates were compared between the two groups using the Kaplan-Meier method.

RESULTS

In the SB-RFA group, less number of ablations were required (1.72±0.70 vs. 2.31±1.37, P = 0.039), the ablation time was shorter (10.9±3.9 vs.14.3±5.0 min, p = 0.004), and energy delivery was smaller (13.1±6.3 vs.23.4±12.8 kcal, p<0.001) compared to SM-RFA. Ablation volume was not significantly different between SB-RFA and SM-RFA groups (61.8±24.3 vs.54.9±23.7 cm3, p = 0.229). Technical failure occurred in one patient in the SM-RFA group, and major complications occurred in one patient in each group. The 1-year and 2-year LTP free survival rates were 93.9% and 84.3% in the SB-RFA group and 94.4% and 88.4% in the SM-RFA group (p = 0.687).

CONCLUSION

Both SB-RFA using ICW electrodes and SM-RFA using SC electrodes provided comparable LTP free survival rates although SB-RFA required less ablations and shorter ablation time.

An Image Fusion System for Estimating the Therapeutic Effects of Radiofrequency Ablation on Hepatocellular Carcinoma

Background

During ultrasound-guided radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC), high echoic areas due to RFA-induced microbubbles can help calculate the extent of ablation. However, these areas also decrease visualization of target tumors, making it difficult to assess whether they completely cover the tumors. To estimate the effects of RFA more precisely, we used an image fusion system (IFS).

Patients and methods

We enrolled patients with a single HCC who received RFA with or without the IFS. In the IFS group, we drew a spherical marker along the contour of a target tumor on reference images immediately after administering RFA so that the synchronized spherical marker represented the contour of the target tumor on real-time ultrasound images. When the high echoic area completely covered the marker, we considered the ablation to be complete. We compared outcomes between the IFS and control groups.

Results

We enrolled 25 patients and 20 controls, and the baseline characteristics were similar between the two groups. The complete ablation rates during the first RFA session were significantly higher in the IFS group compared with those in the control group (88.0% vs. 60.0%, P = 0.041). The number of RFA sessions was significantly smaller in the IFS group compared with that in the control group (1.1 ± 0.3 vs. 1.5 ± 0.7, P = 0.016).

Conclusions

The study suggested that the IFS enables a more precise estimation of the effects of RFA on HCC, contributing to enhanced treatment efficacy and minimized patient burden.

Application of radiofrequency ablation for the treatment of intermediate-stage hepatocellular carcinoma

BACKGROUND AND AIM

Transcatheter arterial chemoembolization (TACE) is a standard therapy for the treatment of intermediate-stage hepatocellular carcinoma (HCC). In this study, we tried to elucidate the possibility of using radiofrequency ablation (RFA) as an alternative treatment of intermediate-stage HCC.

METHODS

Among 246 patients who were initially diagnosed with intermediate-stage HCC, 76 who were treated with TACE (TACE group) and 91 who were treated with RFA (RFA group) were enrolled in this study. The risk for survival was analyzed with the Cox Proportional Hazard Model, and the survival rates were compared using propensity score matching.

RESULTS

About half (50.6%) of the intermediate-stage HCC patients in the RFA group were diagnosed with Barcelona Clinic Liver Cancer substage-B1 (BCLC-B1) compared with only 19.7% of the patients in the TACE group. Survival of the RFA group was longer than that of TACE group in patients with BCLC-B1 and BCLC-B2. In contrast, no difference between groups was observed in patients with BCLC-B3/4. Multivariate analysis revealed that large tumor size (>30 mm, hazard ratio = 1.685, P = 0.043), high des-γ-carboxyprothrombin (>100 mAU/mL, hazard ratio = 1.920, P = 0.012), and TACE group (hazard ratio = 1.896, P = 0.016) were significant risk factors for survival. Overall 3-year survival of the patients in the RFA group (69.5%) was significantly longer than that of patients in the TACE group (51.5%) after propensity score matching (P = 0.032). No significant adverse events were observed in either group.

CONCLUSIONS

RFA was useful for the treatment of less advanced intermediate-stage HCC and could be an alternative to TACE in selected cases.

High-intensity focused ultrasound ablation assisted using color Doppler imaging for the treatment of hepatocellular carcinomas

PURPOSE

We evaluated the usefulness of color Doppler flow imaging to compensate for the inadequate resolution of the ultrasound (US) monitoring during high-intensity focused ultrasound (HIFU) for the treatment of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

US-guided HIFU ablation assisted using color Doppler flow imaging was performed in 11 patients with small HCC (<3 lesions, <3 cm in diameter). The HIFU system (Chongqing Haifu Tech) was used under US guidance. Color Doppler sonographic studies were performed using an HIFU 6150S US imaging unit system and a 2.7-MHz electronic convex probe.

RESULTS

The color Doppler images were used because of the influence of multi-reflections and the emergence of hyperecho. In 1 of the 11 patients, multi-reflections were responsible for the poor visualization of the tumor. In 10 cases, the tumor was poorly visualized because of the emergence of a hyperecho. In these cases, the ability to identify the original tumor location on the monitor by referencing the color Doppler images of the portal vein and the hepatic vein was very useful. HIFU treatments were successfully performed in all 11 patients with the assistance of color Doppler imaging.

CONCLUSION

Color Doppler imaging is useful for the treatment of HCC using HIFU, compensating for the occasionally poor visualization provided by B-mode conventional US imaging.

Intraoperative ultrasound and tissue elastography measurements do not predict the size of hepatic microwave ablations

RATIONALE AND OBJECTIVES

Image-guided thermal ablation is used to treat primary and secondary liver cancers. Evaluating completeness of ablation is difficult with standard intraoperative B-mode ultrasound. This study evaluates the ability of B-mode ultrasound (US) and tissue elastography to adequately measure the extent of ablation compared to pathologic assessment.

MATERIALS AND METHODS

An in vivo porcine model was used to compare B-mode ultrasonography and elastography to pathologic assessment of the microwave ablation zone area. In parallel, intraoperative ablations in patients were used to assess the ability of B-mode US and elastographic measures of tissue strain immediately after ablation to predict ablation size, compared to postprocedural computed tomography (CT).

RESULTS

In the animal model, ablation zones appeared to decrease in size when monitored with ultrasound over a 10-minute span with both B-mode US and elastography. Both techniques estimated smaller zones than gross pathology, however, the differences did not reach statistical significance. Biopsies from the edges of the ablation zone, as assessed by US, contained viable tissue in 75% of the cases. In the human model, B-mode US and elastography estimated similar ablation sizes; however, they underestimate the final size of the ablation defect as measured on postprocedure CT scan (median area [interquartile range]: CT, 7.3 cm(2) [5.2-9.5] vs. US 3.6 cm(2) [1.7-6.3] and elastography 4.1 cm(2) [1.4-5.1]; P = .005).

CONCLUSIONS

Ultrasound and elastography provide an accurate gross estimation of ablation zone size but are unable to predict the degree of cellular injury and significantly underestimate the ultimate size of the ablation.

Usefulness of the extracted-overlay function in CT/MR-ultrasonography fusion imaging for radiofrequency ablation of hepatocellular carcinoma

OBJECTIVES

We developed a novel technique of the extracted-overlay function in CT/MR-ultrasonography (US) fusion imaging for radiofrequency ablation (RFA), in which only a tumor extracted from CT/MR images with a virtual ablative margin of arbitrary thickness is overlaid on US. The usefulness of this function is investigated in this preliminary report.

METHODS

The volume data of the extracted tumor with a virtual ablative margin were created on an image-processing workstation, and transported into a US unit equipped with a CT/MR-US fusion imaging system. After the positional registration of US and transported images, the extracted tumor with an ablative margin could be overlaid on US. In RFA, using this function, an electrode was inserted targeting the overlaid tumor with an ablative safety margin of 5 mm on US, and the treatment effect was evaluated by dynamic CT. Treatment results of 23 consecutive hepatocellular carcinomas (HCCs) that underwent RFA using this function were retrospectively analyzed.

RESULTS

Complete tumor ablation was achieved in 22 (95.7%) and 1 (4.3%) HCCs in 1 and 2 treatment sessions, respectively.

CONCLUSIONS

Due to the visualization of an extracted tumor with an ablative safety margin on a US image, even during and after ablation, this function is useful for treatment planning and guidance of RFA.

Contrast-enhanced ultrasound in the preoperative, intraoperative and postoperative assessment of liver lesions

The use of contrast agents (CA) with liver ultrasound (US) has gained recently an established role for the diagnosis of various hepatic diseases due to their safety, high versatility and low costs (contrast-enhanced ultrasound: CEUS). The purpose of this review is to provide a state-of-the-art summary of the available evidence for their use in the characterization of focal liver lesions. A published work search was conducted for all preclinical and clinical studies involving CA on hepatic US imaging. CEUS increases the sensitivity for lesion detection and the specificity to differentiate between benign and malignant diseases due to the enhanced visualization of the tumor microcirculation. Results achieved seem at least equivalent to those of spiral computed tomography or magnetic resonance imaging. The association of CA with intraoperative ultrasound has changed the surgical approach in 25% of patients and guarantees complete ablations by a single session in most of them. CEUS provides detailed information about tumor vasculature, improves the preoperative characterization and therefore the therapeutic strategy, and can evaluate the intraoperative completeness of the ablation.

Usefulness of the hyperechoic rim for assessing the therapeutic efficacy of radiofrequency ablation in hepatocellular carcinoma patients

AIM

During radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC), a hyperechoic rim develops around the HCC nodules. The usefulness of the hyperechoic rim to guide treatment was assessed.

METHODS

RFA was first performed in pig livers to determine the significance of the hyperechoic rim. Fifty-five patients with 75 HCC nodules had received RFA for the treatment of HCC. For those patients, we evaluated whether conventional ultrasonography (US) could be used instead of contrast-enhanced computed tomography (CECT) and contrast-enhanced ultrasonography (CEUS) using virtual imaging. Finally, 31 patients with 45 HCC nodules received RFA, and the degree of ablation was assessed based on the hyperechoic rim. Repeated RFA was done when ablation appeared incomplete.

RESULTS

In the pig livers, the hyperechoic rim was found to be related to the presence of dead cells. The preliminary study showed that US could be used instead of CECT and CEUS to evaluate the degree of ablation caused by RFA. Because hepatic vessels in the back side of the hyperechoic rim were not clear by the artifact, we used the distance from the surface of the liver to the hyperechoic rim for evaluation. By analyzing the extent of the hyperechoic rim, it was noted that incomplete ablation was achieved in 17 of 31 patients (21 of 45 HCC nodules). These patients were re-treated with RFA within 5-15 min of the first RFA.

CONCLUSION

This study shows that the hyperechoic rim is related to the presence of dead and necrotic tissues. Thus, assessment of the hyperechoic rim's characteristics allows one to evaluate the efficacy of RFA.

Major complications of ultrasound-guided percutaneous radiofrequency ablations for liver malignancies: single center experience

BACKGROUND AND AIM

Despite radiofrequency ablation (RFA) for malignant liver nodular lesions having promising therapeutic effects, the trade-off between the risks and benefits must be acceptable. This study analyzed the major complications of ultrasound (US)-guided percutaneous RFA procedures encountered at a single center, by a single physician.

METHODS

A total of 104 patients (total 183 tumors) underwent 172 US-guided percutaneous RFA sessions between May 2003 and March 2006. The definition of major complications was according to the standardized Society of Interventional Radiology grading system (classification C-E).

RESULTS

Eighty-six patients had hepatocellular carcinoma (HCC) and 18 patients had hepatic metastatic tumors. Nine major complications occurred from 172 RFA sessions (9/172, incidence of 5.2% per session); namely, two cases of transient liver function impairment, two cases of infection (liver abscess and septicemia), two cases of tumor seeding along the ablated track, one case of colon perforation, one case of acalculous cholecystitis and, lastly, a case of hemocholecyst. We further analyzed the possible risk factors precipitating these complications, and found that only tumor size (Pearson's correlation coefficient, 0.324; P < 0.05) and baseline liver function reserve (compensated 0%, 0/148 vs decompensated 8.3%, 2/24; P = 0.019) were significant factors for the complication of transient liver function impairment.

CONCLUSION

Radiofrequency ablation for liver malignancy is a safe procedure with acceptable incidence of complications. Decompensated baseline liver function reserve and large tumor size are precipitating factors for transient liver function impairment after RFA and warrant a close follow up.

Risk factors for local and distant recurrence of hepatocellular carcinomas after local ablation therapies

BACKGROUND AND AIM

Hepatocellular carcinoma (HCC) recurs frequently after local ablation therapies. Recurrence following the therapies may be of two types: local recurrence and distant recurrence. The aim of the current study is to separately elucidate the predisposing factors for each recurrence.

METHODS

Among the 2141 consecutive patients with HCC who were admitted to our institute and affiliated hospital between May 1997 and April 2004, 621 patients who had undergone local ablation therapies as the initial treatment were enrolled. Correlations between the clinical backgrounds of the patients and the type of recurrence were analyzed by the Cox proportional hazard model.

RESULTS

A multivariate analysis revealed that tumor size (>30 mm; risk ratio 2.80; 95% confidence interval, 1.77-4.45; P < 0.0001), tumor number (> or =2; 1.74, 1.23-2.47, P = 0.002), and the serum alpha-fetoprotein level (>100 ng/mL; (1.62, 1.09-2.41, P = 0.014), which were classified as "tumor factors", were significant predisposing factors for the local recurrence of HCC. In contrast, a low platelet count (<100,000/microL; 1.34, 1.04-1.74, P = 0.03) and the presence of ascites (1.73, 1.16-2.57, P = 0.008), which were classified as "background factors", as well as tumor size (1.83, 1.11-3.01, P = 0.02) and tumor number (2.23, 1.72-3.00, P < 0.0001) were predisposing factors for distant recurrence.

CONCLUSION

The predisposing factors for local and distant recurrence of HCC differ and different precautions must be observed to prevent recurrence, depending on the HCC status and background liver functions.

Treatment of hepatocellular carcinoma using internally cooled electrodes. A prospective comparison of modified automated vs. manual pulsed radiofrequency algorithms

OBJECTIVES

To compare the effectiveness of modified automated and manual pulsed radiofrequency (RF) algorithms using internally cooled electrodes for hepatocellular carcinoma (HCC).

METHODS

Seventy-seven treatment-naive cirrhotic patients with 102 HCC (< or =4 cm) underwent 109 sessions of ultrasound-guided percutaneous RF ablation using a 17-gauge, 20-cm-long, single internally cooled electrode. Patients were assigned alternatively: 40 patients to the modified automated algorithm group and 37 patients to the manual algorithm group. The mean tumor diameters were 2.34 +/- 0.9 and 2.25 +/- 0.7 cm in the automated and manual groups, respectively (p = 0.56). Primary technique effectiveness and local tumor progression were compared between the two groups.

RESULTS

More overlapping ablations (n = 112) were required in the manual than in the automated group (n = 82) to achieve similar primary technique effectiveness rates of 96.1 and 94.1%, respectively. After a mean follow-up period of 26.7 +/- 1.1 months, the local tumor progression rates at 12 and 18 months were 4 and 20% in the manual group and 12 and 24% in the modified automated group (p = 0.3). Only tumors >3 cm were independently associated with local tumor progression (odds ratio 1.25; 95% CI 1.06-2.34, p = 0.03).

CONCLUSIONS

The manual algorithm requires more overlapping ablations and treatment sessions in order to achieve similar primary technique effectiveness and local tumor progression rates compared with the modified automated algorithm.

Factors limiting complete tumor ablation by radiofrequency ablation

The purpose of this study was to determine radiological or physical factors to predict the risk of residual mass or local recurrence of primary and secondary hepatic tumors treated by radiofrequency ablation (RFA). Eighty-two patients, with 146 lesions (80 hepatocellular carcinomas, 66 metastases), were treated by RFA. Morphological parameters of the lesions included size, location, number, ultrasound echogenicity, computed tomography density, and magnetic resonance signal intensity were obtained before and after treatment. Parameters of the generator were recorded during radiofrequency application. The recurrence-free group was statistically compared to the recurrence and residual mass groups on all these parameters. Twenty residual masses were detected. Twenty-nine lesions recurred after a mean follow-up of 18 months. Size was a predictive parameter. Patients' sex and age and the echogenicity and density of lesions were significantly different for the recurrence and residual mass groups compared to the recurrence-free group (p < 0.05). The presence of an enhanced ring on the magnetic resonance control was more frequent in the recurrence and residual mass groups. In the group of patients with residual lesions, analysis of physical parameters showed a significant increase (p < 0.05) in the time necessary for the temperature to rise. In conclusion, this study confirms risk factors of recurrence such as the size of the tumor and emphasizes other factors such as a posttreatment enhanced ring and an increase in the time necessary for the rise in temperature. These factors should be taken into consideration when performing RFA and during follow-up.