Fusion imaging-guided radiofrequency ablation for hepatocellular carcinomas not visible on conventional ultrasound. AJR Am J Roentgenol. 2013;201:1141-1147. [PMID: 24147489 DOI: 10.2214/ajr.13.10532]

Ablation manual for liver cancer

Because of recent advances in energy device technology, ablation has become popular worldwide. It is less invasive and provides faster postoperative recovery compared to surgery, and therefore, it has come to be applied to a wide range of organs, such as liver, lung, kidney, thyroid, and bone/soft tissue tumors. In order to properly guide the needle to the target area, imaging support is necessary, and ultrasound, which has the advantages of high resolution and real-time capability, is the most frequently used modality. In other words, ablation can be said to be a therapeutic method that makes the most of the advantages of ultrasound. This article outlines the role of ultrasound in ablation for liver cancer and its specific usage.

Local Ablation for Hepatocellular Carcinoma: 2024 Expert Consensus-Based Practical Recommendations of the Korean Liver Cancer Association

Local ablation for hepatocellular carcinoma, a non-surgical option that directly targets and destroys tumor cells, has advanced significantly since the 1990s. Therapies with different energy sources, such as radiofrequency ablation, microwave ablation, and cryoablation, employ different mechanisms to induce tumor necrosis. The precision, safety, and effectiveness of these therapies have increased with advances in guiding technologies and device improvements. Consequently, local ablation has become the first-line treatment for early-stage hepatocellular carcinoma. The lack of organized evidence and expert opinions regarding patient selection, preprocedure preparation, procedural methods, swift post-treatment evaluation, and follow-up has resulted in clinicians following varied practices. Therefore, an expert consensus-based practical recommendation for local ablation was developed by a group of experts in radiology and hepatology from the Research Committee of the Korean Liver Cancer Association in collaboration with the Korean Society of Image-Guided Tumor Ablation to provide useful information and guidance for performing local ablation and for the pre- and post-treatment management of patients.

Local Ablation for Hepatocellular Carcinoma: 2024 Expert Consensus-Based Practical Recommendations of the Korean Liver Cancer Association

Local ablation for hepatocellular carcinoma (HCC), a non-surgical option that directly targets and destroys tumor cells, has advanced significantly since the 1990s. Therapies with different energy sources, such as radiofrequency ablation, microwave ablation, and cryoablation, employ different mechanisms to induce tumor necrosis. The precision, safety, and effectiveness of these therapies have increased with advances in guiding technologies and device improvements. Consequently, local ablation has become the first-line treatment for early-stage HCC. The lack of organized evidence and expert opinions regarding patient selection, pre-procedure preparation, procedural methods, swift post-treatment evaluation, and follow-up has resulted in clinicians following varied practices. Therefore, an expert consensus-based practical recommendation for local ablation was developed by a group of experts in radiology and hepatology from the Research Committee of the Korean Liver Cancer Association in collaboration with the Korean Society of Image-guided Tumor Ablation to provide useful information and guidance for performing local ablation and for the pre- and post-treatment management of patients.

Local ablation for hepatocellular carcinoma: 2024 expert consensus-based practical recommendation of the Korean Liver Cancer Association

Local ablation for hepatocellular carcinoma (HCC), a non-surgical option that directly targets and destroys tumor cells, has advanced significantly since the 1990s. Therapies with different energy sources, such as radiofrequency ablation, microwave ablation, and cryoablation, employ different mechanisms to induce tumor necrosis. The precision, safety, and effectiveness of these therapies have increased with advances in guiding technologies and device improvements. Consequently, local ablation has become the firstline treatment for early-stage HCC. The lack of organized evidence and expert opinions regarding patient selection, pre-procedure preparation, procedural methods, swift post-treatment evaluation, and follow-up has resulted in clinicians following varied practices. Therefore, an expert consensus-based practical recommendation for local ablation was developed by a group of experts in radiology and hepatology from the Research Committee of the Korean Liver Cancer Association in collaboration with the Korean Society of Image-guided Tumor Ablation to provide useful information and guidance for performing local ablation and for the pre- and posttreatment management of patients.

Gastrointestinal tract perforation after radiofrequency ablation for hepatic tumor: Incidence and risk factors

OBJECTIVE

We analyzed the incidence and mortality rate of gastrointestinal (GI) tract perforation after radiofrequency ablation (RFA) for hepatic tumors and assess its risk factors.

METHODS

This retrospective cohort study included 4799 patients with malignant tumors who underwent RFA (n = 7206). Sixty-nine cases of thermal injury to the GI tract were identified via a search of the electronic medical record system using index terms and divided into two groups according to the thermal injury with (n = 8) or without (n = 61) GI tract perforation based on follow-up CT reports. The risk factors for GI tract perforation were identified via multivariable logistic regression analysis using clinical, technical, and follow-up CT findings.

RESULTS

The incidence of thermal injury to the GI tract and GI tract perforation was 0.96 % (69/7206) and 0.11 % (8/7206), respectively. The type of adjacent GI tract and history of diabetes mellitus differed significantly between the two groups (p < 0.05). The index tumor being located around the small intestine was the only significant risk factor for GI tract perforation after ablation (Odds ratio, 22.69; 95 % confidence interval, 2.59-198.34; p = 0.005 [reference standard, stomach]). All perforations were not identified on CT images immediately after RFA. The median time to detection was 20 days (range, 3-41 days). Two patients (25 %, 2/8) died due to perforation-related complications.

CONCLUSION

GI tract perforation after RFA for hepatic tumors is rare; however, it is associated with high mortality. Thus, careful follow-up is required after RFA if the index tumor is located around the small intestine.

Examining the Efficacy and Safety of Combined Locoregional Therapy and Immunotherapy in Treating Hepatocellular Carcinoma

More than 800,000 people worldwide are diagnosed with HCC (hepatocellular carcinoma) each year, with approximately 700,000 deaths alone occurring in that same year. Treatment of HCC presents complex therapeutic challenges, particularly in intermediate and advanced stages. LRTs such as transarterial chemoembolization (TACE) and ablations have been the mainstay treatment for early to intermediate-stage HCC, and systemic therapies are used to treat intermediate-late-stage HCC. However, novel literature describing combining LRT with systemic therapies has shown promising results. This review explores recent advances in both liver-directed techniques for hepatocellular carcinoma, including bland transarterial embolization, chemoembolization, radioembolization, and ablative therapies in conjunction as well as with systemic therapies, with a focus on combination therapies, patient selection, procedural technique, periprocedural management, and outcomes. Our findings suggest that LRT combined with systemic therapies is a viable strategy for improving progression-free survival and time to progression for patients with intermediate-to-late-stage HCC. However, further investigation is required to refine treatment protocols and define patient cohorts that would benefit the most.

3D fusion is superior to 2D point-to-point contrast-enhanced US to evaluate the ablative margin after RFA for hepatocellular carcinoma

PURPOSE

To compare the efficiency of three-dimensional (3D) and two-dimensional (2D) contrast-enhanced ultrasound (CEUS)-derived techniques in evaluating the ablative margin (AM) after radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC).

METHODS

In total, 98 patients with 98 HCCs were enrolled. The 2D CEUS point-to-point imaging (2D CEUS-PI) was conducted by comparing the pre- and post-RFA 2D CEUS images manually, and the 3D CEUS fusion imaging (3D CEUS-FI) was conducted by fusing the pre- and post-RFA 3D CEUS images automatically. These two techniques were compared in distinguishing an adequate AM ≥ 5 mm. Risk factors for local tumor progression (LTP) after RFA were analyzed by the Kaplan-Meier method with log-rank test.

RESULTS

The mean registration time of 3D CEUS-FI and 2D CEUS-PI was 5.0 and 9.3 min, respectively (p < 0.0001). The kappa coefficient was 0.680 for agreement between 2D CEUS-PI and 3D CEUS-FI in the evaluation of AM (p < 0.0001). Tumors with AM < 5 mm by 2D CEUS-PI were all identified as AM < 5 mm by 3D CEUS-FI. Nonetheless, 16 (26%) tumors identified as AM ≥ 5 mm by 2D CEUS-PI were re-classified as AM < 5 mm by 3D CEUS-FI. During a median follow-up time of 31.2 months (range, 3.2-66.0 months), LTP was identified in 8 tumors. The estimated 1-/2-/3-year cumulative incidence of LTP was 4.4%, 8.1%, and 10.3%, respectively. Higher estimated cumulative incidence of LTP was identified in tumors with AM < 5 mm by 2D CEUS-PI (at 3-year, 27.2% vs 0%; p < 0.001), and by 3D CEUS-FI (at 3-year, 20.7% vs 0%; p = 0.004).

CONCLUSION

3D CEUS-FI excelled in the evaluation of AM when compared with 2D CEUS-PI. With equivalent efficacy in the prediction of LTP, 3D CEUS-FI was superior to 2D CEUS-PI for its automatic and time-saving procedure.

CLINICAL RELEVANCE STATEMENT

3D CEUS fusion imaging may serve as an effective tool in evaluating ablative margin and predicting local tumor progression after RFA in HCC.

KEY POINTS

• Both 2D and 3D CEUS-derived techniques could evaluate ablative margin (AM) after RFA for hepatocellular carcinoma. • 3D CEUS fusion imaging was more precise in the evaluation of AM compared to 2D CEUS point-to-point imaging, with advantages of its automatic and time-saving procedure. • An inadequate AM < 5 mm evaluated by CEUS-derived techniques was the only risk factor of LTP after RFA for hepatocellular carcinoma (p < 0.001 for 2D CEUS point-to-point imaging, and p = 0.004 for 3D CEUS fusion imaging).

Clinical Impact of a Protocol Involving Cone-Beam CT (CBCT), Fusion Imaging and Ablation Volume Prediction in Percutaneous Image-Guided Microwave Ablation in Patients with Hepatocellular Carcinoma Unsuitable for Standard Ultrasound (US) Guidance

PURPOSE

to evaluate the clinical impact of a protocol for the image-guided percutaneous microwave ablation (MWA) of hepatocellular carcinoma (HCC) that includes cone-beam computed tomography (CBCT), fusion imaging and ablation volume prediction in patients with hepatocellular carcinoma unsuitable for standard ultrasound (US) guidance.

MATERIALS AND METHODS

this study included all patients with HCC treated with MWA between January 2021 and June 2022 in a tertiary institution. Patients were divided into two groups: Group A, treated following the protocol, and Group B, treated with standard ultrasound (US) guidance. Follow-up images were reviewed to assess residual disease (RD), local tumor progression (LTP) and intrahepatic distant recurrence (IDR). Ablation response at 1 month was also evaluated according to mRECIST. Baseline variables and outcomes were compared between the groups. For 1-month RD, propensity score weighting (PSW) was performed.

RESULTS

80 consecutive patients with 101 HCCs treated with MWA were divided into two groups. Group A had 41 HCCs in 37 patients, and Group B had 60 HCCs in 43 patients. Among all baseline variables, the groups differed regarding their age (mean of 72 years in Group A and 64 years in Group B, respectively), new vs. residual tumor rates (48% Group A vs. 25% Group B, p < 0.05) and number of subcapsular tumors (56.7% Group B vs. 31.7% Group A, p < 0.05) and perivascular tumors (51.7% Group B vs. 17.1% Group A, p < 0.05). The protocol led to repositioning the antenna in 49% of cases. There was a significant difference in 1-month local response between the groups measured as the RD rate and mRECIST outcomes. LTP rates at 3 and 6 months, and IDR rates at 1, 3 and 6 months, showed no significant differences. Among all variables, logistic regression after PSW demonstrated a protective effect of the protocol against 1-month RD.

CONCLUSIONS

The use of CBCT, fusion imaging and ablation volume prediction during percutaneous MWA of HCCs provided a better 1-month tumor local control. Further studies with a larger population and longer follow-up are needed.

Radiofrequency ablation for pediatric recurrent hepatocellular carcinoma: a single-center experience

PURPOSE

To summarize our single-center experience with percutaneous ultrasound (US)-guided radiofrequency ablation (RFA) for pediatric recurrent hepatocellular carcinoma (RHCC).

METHODS

From September 2007 to September 2021, patients under 18 who underwent percutaneous US-guided RFA for RHCC were retrospectively enrolled in this study. Local effectiveness, complications, local tumor progression (LTP), progression free survival (PFS), and overall survival (OS) were evaluated.

RESULTS

A total of 10 patients (9 male and 1 female; mean age, 11.7 ± 4 years ; age range, 6-17 years) with 15 intrahepatic RHCC lesions were enrolled in this study. Complete ablation (CA) was achieved in 14 out of 15 lesions (93.3%) after the first RFA. During the follow-up (mean, 63.1 ± 18 months; range, 5.3-123.3 months), LTP did not occur. Five patients died including three with tumor progression and one with liver failure. The accumulative one- and three-year PFS rates were 30% and 10%, respectively. The accumulative one- and three-year OS rates were 77.8% and 44.4%, respectively.

CONCLUSIONS

Our single-center experience suggests the safety and feasibility of percutaneous US-guided RFA for pediatric RHCC.

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.

No-Touch Radiofrequency Ablation for Early Hepatocellular Carcinoma: 2023 Korean Society of Image-Guided Tumor Ablation Guidelines

Radiofrequency ablation (RFA) has been widely used to manage hepatocellular carcinomas (HCCs) equal to or smaller than 3 cm. No-touch RFA has gained attention and has recently been implemented in local ablation therapy for HCCs, despite its technical complexity, as it provides improved local tumor control compared to conventional tumor-puncturing RFA. This article presents the practice guidelines for performing no-touch RFA for HCCs, which have been endorsed by the Korean Society of Image-Guided Tumor Ablation (KSITA). The guidelines are primarily designed to assist interventional oncologists and address the limitations of conventional tumor-puncturing RFA with describing the fundamental principles, various energy delivery methods, and clinical outcomes of no-touch RFA. The clinical outcomes include technical feasibility, local tumor progression rates, survival outcomes, and potential complications.

Percutaneous Microwave Ablation of Hepatocellular Carcinoma with "Double Fusion" Technique: Technical Note and Single-Center Preliminary Experience

Percutaneous image-guided thermal ablation is included in most society guidelines for treatment of hepatocellular carcinoma (HCC). The results of this treatment in terms of efficacy depend on the ability to precisely place the device into the target tumor. Ultrasound (US) is a commonly used imaging guidance modality for its real-time feedback. However, an accurate device deployment remains challenging in some clinical scenarios, including cases of tumors that are undetectable or not clearly visible by US. To overcome this problem, fusion imaging techniques have been developed, which combine images from different modalities. The most widely known technique combines pre-procedural contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) with real-time US scans. Cone beam CT (CBCT) is a technology that can provide intra-procedural cross-sectional images, which can be registered to images from other modalities, including preprocedural CT/MR scans. The aim of our study is to report the preliminary experience on percutaneous microwave ablation (MWA) of patients with HCC that were treated using the "double fusion" technique, which combines the use of US fusion imaging and CBCT fusion imaging. We describe the technical details, feasibility, safety and short-term efficacy of this technique in a small series of eight patients with 11 HCCs.

Ultrasound fusion imaging for improving diagnostic and therapeutic strategies of focal liver lesions: A preliminary study

PURPOSE

To assess the effect of ultrasound (US) fusion imaging on the clinical diagnostic and therapeutic strategies of focal liver lesions, which are difficult to detect or diagnose by conventional US.

METHODS

From November 2019 to June 2022, 71 patients with invisible or undiagnosed focal liver lesions who underwent fusion imaging combining US with CT or MR were included in this retrospective study. The reasons for US fusion imaging were as follows: (1) lesions that were undetectable or inconspicuous on B-mode US; (2) post-ablation lesions that could not be assessed accurately by B-mode US; (3) to evaluate whether the lesions detected by B-mode US that were consistent with those presented on MRI/CT images.

RESULTS

Of the 71 cases, 43 cases were single lesions, and 28 cases were multiple lesions. Among the 46 cases which were invisible on conventional US, the display rate of lesions using US-CT/MRI fusion imaging was 30.8%, and that combined with CEUS was 76.9%. US-guided biopsy was performed in 30 patients after the detection and localization determined by fusion imaging, with a positive rate of 73.3%. Six patients with recurrence after ablation therapy were all detected and located accurately after fusion imaging, and 4 of them successfully underwent ablation therapy again.

CONCLUSION

Fusion imaging contributes to the understanding of the anatomical relationship between lesion location and blood vessels. Additionally, fusion imaging can improve the diagnostic confidence, be helpful to guide interventional operations, and hence be conducive to clinical therapeutic strategies.

Ultrasound-Tomographic Image Fusion - A Novel Tool for Follow up After Acute Complicated Appendicitis

BACKGROUND

Computerized tomography (CT) is an integral part of the follow-up and decision-making process in complicated acute appendicitis (AA) treated non-operatively. However, repeated CT scans are costly and cause radiation exposure. Ultrasound-tomographic image fusion is a novel tool that integrates CT images to an Ultrasound (US) machine, thus allowing accurate assessment of the healing process compared to CT on presentation. In this study, we aimed to assess the feasibility of US-CT fusion as part of the management of appendicitis.

MATERIALS AND METHODS

We retrospectively collected data of consecutive patients with complicated AA managed non-operatively and followed up with US Fusion for clinical decision-making. Patients demographics, clinical data, and follow-up outcomes were extracted and analyzed.

RESULTS

Overall, 19 patients were included. An index Fusion US was conducted in 13 patients (68.4%) during admission, while the rest were performed as part of an ambulatory follow-up. Nine patients (47.3%) had more than 1 US Fusion performed as part of their follow-up, and 3 patients underwent a third US Fusion. Eventually, 5 patients (26.3%) underwent elective interval appendectomy based on the outcomes of the US Fusion, due to a non-resolution of imaging findings and ongoing symptoms. In 10 patients (52.6%), there was no evidence of an abscess in the repeated US Fusion, while in 3 patients (15.8%), it significantly diminished to less than 1 cm in diameter.

CONCLUSION

Ultrasound-tomographic image fusion is feasible and can play a significant role in the decision-making process for the management of complicated AA.

Multimodal registration of ultrasound and MR images using weighted self-similarity structure vector

PROPOSE

Multimodal registration of 2D Ultrasound (US) and 3D Magnetic Resonance (MR) for fusion navigation can improve the intraoperative detection accuracy of lesion. However, multimodal registration remains a challenge because of the poor US image quality. In the study, a weighted self-similarity structure vector (WSSV) is proposed to registrate multimodal images.

METHOD

The self-similarity structure vector utilizes the normalized distance of symmetrically located patches in the neighborhood to describe the local structure information. The texture weights are extracted using the local standard deviation to reduce the speckle interference in the US images. The multimodal similarity metric is constructed by combining a self-similarity structure vector with a texture weight map.

RESULTS

Experiments were performed on US and MR images of the liver from 88 groups of data including 8 patients and 80 simulated samples. The average target registration error was reduced from 14.91 ± 3.86 mm to 4.95 ± 2.23 mm using the WSSV-based method.

CONCLUSIONS

The experimental results show that the WSSV-based registration method could robustly align the US and MR images of the liver. With further acceleration, the registration framework can be potentially applied in time-sensitive clinical settings, such as US-MR image registration in image-guided surgery.

Comparative Study of Application of Computed Tomography/Ultrasound and Computed Tomography Imaging Guidance Methods in the Microwave Ablation of Liver Cancer

PURPOSE

The aim of the study is to assess the clinical value of the combined computed tomography (CT)/ultrasound (US) guidance in microwave ablation (MWA) for hepatocellular carcinoma (HCC).

METHODS

From July 16, 2016, to June 20, 2021, medical records of 150 HCC patients treated with MWA were retrospectively analyzed. Ninety-two patients with 115 liver tumors underwent MWA under combined CT/US guidance, and 58 patients with 73 liver tumors received MWA under CT guidance alone. The clinical efficacy of combined CT/US-guided MWA was analyzed. We compared the complications, procedure time, and CT scan times between the 2 groups.

RESULTS

The total complete ablation rate and complete ablation rate of high-risk location tumors were significantly higher in the group treated with combined CT/US guidance ( P = 0.0471 and P = 0.0347, respectively), the imaging guidance modality (odds ratio, 0.303; 95% confidence interval [CI], 0.095-0.970; P = 0.044) was an independent factor for ablation efficacy. These 2 groups also had significant differences in the procedure time ( P = 0.0171), the incidence rate of pneumothorax ( P = 0.0209), abdominal pain ( P = 0.0196), nausea or vomiting ( P = 0.0026), and intraoperative CT scan times ( P < 0.001). The overall complication rates ( P = 0.4023) and recurrence rates ( P = 0.5063) between the 2 groups were not statistically significant. However, CT/US group has a better short-term progressive free survival (log-rank P = 0.103, Breslow P = 0.030). In multivariate analysis, guidance modality (hazard ratio, 0.586; 95% CI, 0.368-0.934; P = 0.025) and Barcelona Clinic Liver Cancer stage (hazard ratio, 2.933; 95% CI, 1.678-5.127; P < 0.001) were risk factor for progressive free survival.

CONCLUSIONS

Percutaneous MWA under the combined CT/US guidance for HCC can improve clinical benefits.

Image Fusion Involving Real-Time Transabdominal or Endoscopic Ultrasound for Gastrointestinal Malignancies: Review of Current and Future Applications

Image fusion of CT, MRI, and PET with endoscopic ultrasound and transabdominal ultrasound can be promising for GI malignancies as it has the potential to allow for a more precise lesion characterization with higher accuracy in tumor detection, staging, and interventional/image guidance. We conducted a literature review to identify the current possibilities of real-time image fusion involving US with a focus on clinical applications in the management of GI malignancies. Liver applications have been the most extensively investigated, either in experimental or commercially available systems. Real-time US fusion imaging of the liver is gaining more acceptance as it enables further diagnosis and interventional therapy of focal liver lesions that are difficult to visualize using conventional B-mode ultrasound. Clinical studies on EUS guided image fusion, to date, are limited. EUS-CT image fusion allowed for easier navigation and profiling of the target tumor and/or surrounding anatomical structure. Image fusion techniques encompassing multiple imaging modalities appear to be feasible and have been observed to increase visualization accuracy during interventional and diagnostic applications.

Recent Advances in Tracking Devices for Biomedical Ultrasound Imaging Applications

With the rapid advancement of tracking technologies, the applications of tracking systems in ultrasound imaging have expanded across a wide range of fields. In this review article, we discuss the basic tracking principles, system components, performance analyses, as well as the main sources of error for popular tracking technologies that are utilized in ultrasound imaging. In light of the growing demand for object tracking, this article explores both the potential and challenges associated with different tracking technologies applied to various ultrasound imaging applications, including freehand 3D ultrasound imaging, ultrasound image fusion, ultrasound-guided intervention and treatment. Recent development in tracking technology has led to increased accuracy and intuitiveness of ultrasound imaging and navigation with less reliance on operator skills, thereby benefiting the medical diagnosis and treatment. Although commercially available tracking systems are capable of achieving sub-millimeter resolution for positional tracking and sub-degree resolution for orientational tracking, such systems are subject to a number of disadvantages, including high costs and time-consuming calibration procedures. While some emerging tracking technologies are still in the research stage, their potentials have been demonstrated in terms of the compactness, light weight, and easy integration with existing standard or portable ultrasound machines.

The usefulness of three-dimensional ultrasound fusion imaging for precise needle placement in liver thermal ablation: a phantom and an in vivo simulation study

PURPOSE

To investigate the value of three-dimensional ultrasound fusion imaging (3DUS-FI) in real-time guiding needle placement by phantom models and in vivo simulations.

MATERIALS AND METHODS

Two radiologists (beginner and expert) performed needle placement using two-dimensional ultrasound (2DUS) and 3DUS-FI, respectively. In the phantom study, single-needle placement was performed by puncturing the center point of each ball and assessed based on the specimen length. Multiple-needles placement was performed by placing three needles in each ball, and their locations were confirmed by computed tomography, and assessed based on the distance deviation between needles. In the in vivo simulation study, simulated-needle placement was performed by placing a virtual ablation needle in each liver tumor and assessed by the simulated ablative cover rate and margin.

RESULTS

Specimen length was significantly longer with 3DUS-FI in the beginner, whereas no significant difference was observed in the expert (2DUS vs. 3DUS-FI: beginner, 14.60 ± 2.60 mm vs. 16.25 ± 1.38 mm, p = .017; expert, 16.78 ± 1.40 mm vs. 16.95 ± 1.15 mm, p = .668). Distance deviation between needles was significantly smaller with 3DUS-FI (2DUS vs. 3DUS-FI: beginner, 25.06 ± 16.07 mm vs. 3.72 ± 1.99 mm, p < .001; expert, 11.70 ± 7.79 mm vs. 2.89 ± 1.52 mm, p < .001). The simulated ablative cover rate and margin were significantly larger with 3DUS-FI for the beginner, whereas only the latter was significantly larger for the expert (2DUS vs. 3DUS-FI: beginner, 73.55 ± 8.73% vs. 81.38 ± 11.84%, p = .001, 0.82 ± 0.97 mm vs. 2.65 ± 1.23 mm, p < .001; expert, 78.60 ± 9.91% vs. 83.24 ± 11.69%, p = .059; 1.65 ± 1.15 mm vs. 2.95 ± 1.13 mm, p < .001).

CONCLUSIONS

3DUS-FI is useful for real-time guiding precise needle placement and may be further use to improve the efficacy of liver thermal ablation.

Combined transarterial chemoembolization and radiofrequency ablation for subphrenic versus nonsubphrenic hepatocellular carcinoma: a propensity score matched study

PURPOSE

To compare therapeutic outcomes of combined transarterial chemoembolization (TACE) and radiofrequency ablation (RFA) treatment for small hepatocellular carcinoma (HCC) in subphrenic versus nonsubphrenic locations by propensity score matching.

METHODS

This retrospective study included 293 patients with single HCC (≤ 3 cm) ineligible for ultrasound-guided RFA who received iodized oil TACE and subsequent RFA between June 2010 and January 2017. The patients were divided into two groups according to the tumor location: subphrenic (n = 99) and nonsubphrenic (n = 194). Subphrenic HCC was defined as a tumor abutting the diaphragm. Local tumor progression (LTP) and overall survival (OS) rates were compared by propensity score matching. Procedure-related complications were also assessed.

RESULTS

Matching yielded 93 matched pairs of patients. In the matched cohorts, cumulative 1-, 3-, and 5-year LTP rates were 5.4%, 12.1%, and 12.1% in the subphrenic group and 1.1%, 7.5%, and 8.6% in the nonsubphrenic group, respectively, with no significant differences (p = 0.278). Corresponding OS rates were 100%, 80.2%, and 71.3% in the subphrenic group and 97.9%, 88.1%, and 75.6% in the nonsubphrenic group, respectively, with no significant differences (p = 0.308). The subphrenic location was not a significant risk factor for LTP and OS in multivariate analysis. There were no significant differences in complication rates between the two groups (p > 0.05).

CONCLUSION

The therapeutic outcomes of combined TACE and RFA for small subphrenic HCC were similar to those for nonsubphrenic HCC. The combination therapy seems to be an effective and safe method in treating small subphrenic HCC.

Deep learning-based motion tracking using ultrasound images

PURPOSE

Ultrasound (US) imaging is an established imaging modality capable of offering video-rate volumetric images without ionizing radiation. It has the potential for intra-fraction motion tracking in radiation therapy. In this study, a deep learning-based method has been developed to tackle the challenges in motion tracking using US imaging.

METHODS

We present a Markov-like network, which is implemented via generative adversarial networks, to extract features from sequential US frames (one tracked frame followed by untracked frames) and thereby estimate a set of deformation vector fields (DVFs) through the registration of the tracked frame and the untracked frames. The positions of the landmarks in the untracked frames are finally determined by shifting landmarks in the tracked frame according to the estimated DVFs. The performance of the proposed method was evaluated on the testing dataset by calculating the tracking error (TE) between the predicted and ground truth landmarks on each frame.

RESULTS

The proposed method was evaluated using the MICCAI CLUST 2015 dataset which was collected using seven US scanners with eight types of transducers and the Cardiac Acquisitions for Multi-structure Ultrasound Segmentation (CAMUS) dataset which was acquired using GE Vivid E95 ultrasound scanners. The CLUST dataset contains 63 2D and 22 3D US image sequences respectively from 42 and 18 subjects, and the CAMUS dataset includes 2D US images from 450 patients. On CLUST dataset, our proposed method achieved a mean tracking error of 0.70 ± 0.38 mm for the 2D sequences and 1.71 ± 0.84 mm for the 3D sequences for those public available annotations. And on CAMUS dataset, a mean tracking error of 0.54 ± 1.24 mm for the landmarks in the left atrium was achieved.

CONCLUSIONS

A novel motion tracking algorithm using US images based on modern deep learning techniques has been demonstrated in this study. The proposed method can offer millimeter-level tumor motion prediction in real time, which has the potential to be adopted into routine tumor motion management in radiation therapy.

Operator Evaluation of Ultrasound Fusion Imaging Usefulness in the Percutaneous Ablation of Hepatic Malignancies: A Prospective Study

The purpose of the work described here was to evaluate the use of ultrasound fusion imaging (US-FI) in percutaneous ablation of hepatic malignancies with respect to its global usefulness, improvement of conspicuity, confidence increment, needle route changes, and time savings. Thirty-four hepatic tumors (28 hepatocellular carcinomas, 6 metastases) were prospectively ablated in 16 consecutive patients (64 ± 11 y, 75% males), first simulating B-mode-only planning and then synchronizing computed tomography/magnetic resonance images with US and proceeding to needle insertion and tumor ablation under US-FI guidance. Surveys were administered to the operators to evaluate their perception of US-FI advantages. First treatment and local recurrence were also compared. US-FI was judged useful in 91% of cases and more useful when the tumor was not conspicuous in B-mode (p < 0.001), in particular for ablation of local recurrences (p = 0.021). Forty-one percent of tumors were undetectable at B-mode evaluation, and 93% of them were completely ablated under US-FI guidance. The confidence of the operator was highly increased by US-FI in 68% of cases. In 71% of cases, the radiologist saved time using US-FI, especially in treatment of local recurrences (p = 0.024). In conclusion, US-FI significantly increases the detection of target tumors, improves the confidence of the operator and is a time-saving method, especially in the treatment of local recurrences.

New frontiers in liver ultrasound: From mono to multi parametricity

Modern liver ultrasonography (US) has become a "one-stop shop" able to provide not only anatomic and morphologic but also functional information about vascularity, stiffness and other various liver tissue properties. Modern US techniques allow a quantitative assessment of various liver diseases. US scanning is no more limited to the visualized plane, but three-dimensional, volumetric acquisition and consequent post-processing are also possible. Further, US scan can be consistently merged and visualized in real time with Computed Tomography and Magnetic Resonance Imaging examinations. Effective and safe microbubble-based contrast agents allow a real time, dynamic study of contrast kinetic for the detection and characterization of focal liver lesions. Ultrasound can be used to guide loco-regional treatment of liver malignancies and to assess tumoral response either to interventional procedures or medical therapies. Microbubbles may also carry and deliver drugs under ultrasound exposure. US plays a crucial role in diagnosing, treating and monitoring focal and diffuse liver disease. On the basis of personal experience and literature data, this paper is aimed to review the main topics involving recent advances in the field of liver ultrasound.

Iodized oil computed tomography versus ultrasound-guided radiofrequency ablation for early hepatocellular carcinoma

BACKGROUND AND PURPOSE

Radiofrequency ablation (RFA) is the standard of care for early stage hepatocellular carcinoma (HCC). However, the clinical outcomes of iodized oil computed tomography (IoCT) versus ultrasound (US)-guided RFA for HCC remain unclear.

METHODS

We retrospectively analyzed consecutive treatment-naïve patients who received curative RFA for HCC within Milan criteria from January 2016 to December 2018. Patients who underwent either IoCT-guided RFA (IoCT group) or US-guided RFA (US group) were included. Various clinical factors, including tumor location, were adjusted with a 1:1 propensity score matching. Subsequently, the cumulative incidence rates for recurrence and hazard ratios for survival were calculated.

RESULTS

We included 184 (37.9%) and 301 (62.1%) patients who received IoCT- and US-guided RFA, respectively. Before propensity score matching, IoCT guidance was significantly associated with multiple tumors, higher body mass index, lower albumin level, and tumors located at S8. After matching, the 1-, 2-, and 3-year local tumor progression rates of the IoCT group were significantly lower than those of the US group (4.4%, 6.9%, and 7.5% vs. 14.4%, 16.3%, and 16.3%, respectively, at p = 0.002, 0.009, and 0.016, respectively). In univariate analyses and multivariate analyses that adjusted for clinical and tumor location-related parameters, the IoCT group had better recurrence-free survival (hazard ratio = 0.581, 95% confidence interval 0.375-0.899) than those with US guidance but not overall survival.

CONCLUSION

IoCT-guided RFA had a lower local tumor progression rate and better recurrence-free survival than did US-guided RFA for HCC within the Milan criteria. CT-guide RFA is a safe and effective alternative to US-guided with similar overall survival. IoCT-guided RFA might have a better local tumor control than US-guided. IoCT-guided RFA may be more suitable for male patients, aged < 70 years, a single tumor measuring 2-5 cm, and a tumor located at the subdiaphragmatic/subcardiac region.

Assessing the value of volume navigation during ultrasound-guided radiofrequency- and microwave-ablations of liver lesions

Purpose

The goal of our study was to determine the influence of ultrasound (US)-coupled volume navigation on the use of computed tomography (CT) during minimally-invasive radiofrequency and microwave ablation procedures of liver lesions.

Method

Twenty-five patients with 40 liver lesions of different histological origin were retrospectively analysed. Lesions were ablated following standard protocol, using 1) conventional US-guidance, 2) manual registered volume navigation (mVNav), 3) automatic registered (aVNav) or 4) CT-guidance. In case of ultrasonographically inconspicuous lesions, conventional US-guidance was abandoned and mVNav was used. If mVNav was also unsuccessful, the procedure was either continued with aVNav or CT-guidance. The number, size and location of the lesions targeted using the different approaches were documented.

Results

Of the 40 lesions, sixteen (40.0 %) could be targeted with conventional US-guidance only, sixteen (40.0 %) with mVNav, three (7.5 %) with aVNav and five (12.5 %) only through the use of CT-guidance. Of the three alternatives (mVNav, aVNav and CT only) the mean size of the lesions targeted using mVNav (9.1 ± 4.6 mm) was significantly smaller from those targeted using US-guidance only (20.4 ± 9.4 mm; p < 0.001). The location of the lesions did not influence the selection of the modality used to guide the ablation.

Conclusions

In our cohort, mVNav allowed the ablation procedure to become less dependent on the use of CT. mVNav supported the ablation of lesions smaller than those that could be ablated with US only and doubled the application of minimally-invasive US-guided ablations.

Challenges Facing Percutaneous Ablation in the Treatment of Hepatocellular Carcinoma: Extension of Ablation Criteria

As an emerging minimally invasive treatment method, percutaneous ablation is more and more widely used in the treatment of liver tumors. It has been recommended by guidelines for diagnosis and treatment of hepatocellular carcinoma (HCC) as a curative treatment alongside surgical resection and liver transplantation. In recent years, with the continuous advancement and innovation of percutaneous ablation technologies, their clinical efficacy and safety have been significantly improved, which has led to the expanded application of percutaneous ablation in the treatment of HCC—more and more patients who were previously considered unsuitable for ablation therapies are now being treated with percutaneous ablation. Obviously, percutaneous ablation can reduce the risk of treatment changes from curative strategies to palliative strategies. Based on clinical practice experience, this review enumerates the advantages and disadvantages of different ablative modalities and summarizes the existing combinations of ablation techniques, thus will help clinicians choose the most appropriate ablative modality for each patient and will provide scientific guidance for improving prognosis and making evidence-based treatment decisions. In addition, we point out the challenges and future prospects of the ablation therapies, thereby providing direction for future research.

Real-time virtual sonography-assisted radiofrequency ablation in liver tumors with conspicuous or inconspicuous images or peritumoral landmarks under ultrasonography

Objectives

The objectives of this study were to determine the primary technique effectiveness (PTE), to compare the complete response and local recurrence rates between conspicuous and inconspicuous tumors using single and switching electrodes of real-time virtual sonography (RVS)-assisted radiofrequency ablation (RFA) in conspicuous and inconspicuous hepatic tumors under conventional ultrasonography (US).

Subjects and method

We compared the complete ablation of inconspicuous tumors with and without anatomical landmark (N = 54) with conspicuous liver tumors (N = 272). Conventional US imaging was done initially, and then these images were fused with CT or MRI arterial-venous-wash-out cross-sectional studies and synchronized with real-time US images.

Results

RVS-assisted RFA was technically feasible in all patients. The PTE rate after the first ablation was 94% (245/261) for conspicuous tumors, 88% (7/8) in inconspicuous tumors with landmark, and 78% (36/46) in inconspicuous tumors without landmark. The complete response (p = 0.1912 vs. p = 0.4776) and local recurrence rate (p = 0.1557 vs. p = 0.7982) were comparable in conspicuous tumors of both HCC and liver metastasis group when single or multiple switching was used. The cumulative local recurrence in the conspicuous and inconspicuous tumors of the HCC group (p = 0.9999) was almost parallel after 12 (10% vs. 4%) and 24 (13% vs. 4%) months of follow-up. In the liver metastasis group, the cumulative local recurrence for conspicuous tumors (p = 0.9564) was nearly equal after 12 and 24 months of monitoring (24% vs. 27%) while no recurrence was incurred for the inconspicuous tumors.

Conclusion

RVS-assisted RFA is an effective tool for the treatment of conspicuous and inconspicuous HCC and hepatic metastasis.

Image Guidance in Ablation for Hepatocellular Carcinoma: Contrast-Enhanced Ultrasound and Fusion Imaging

The ultrasound (US) imaging technology, including contrast-enhanced US (CEUS) and fusion imaging, has experienced radical improvement, and advancement in technology thus overcoming the problem of poor conspicuous hepatocellular carcinoma (HCC). On CEUS, the presence or absence of enhancement distinguishes the viable portion from the ablative necrotic portion. Using volume data of computed tomography (CT) or magnetic resonance imaging (MRI), fusion imaging enhances the three-dimensional relationship between the liver vasculature and HCC. Therefore, CT/MR-US fusion imaging provides synchronous images of CT/MRI with real-time US, and US-US fusion imaging provides synchronous US images before and after ablation. Moreover, US-US overlay fusion can visualize the ablative margin because it focuses the tumor image onto the ablation zone. Consequently, CEUS and fusion imaging are helpful to identify HCC with little conspicuity, and with more confidence, we can perform ablation therapy. CEUS/fusion imaging guidance has improved the clinical effectiveness of ablation therapy in patients with poor conspicuous HCCs. Therefore; this manuscript reviews the status of CEUS/fusion imaging guidance in ablation therapy of poor conspicuous HCC.

Virtual navigation-guided radiofrequency ablation for recurrent hepatocellular carcinoma invisible on ultrasound after hepatic resection

BACKGROUND

No reports are available on the technical efficiency and therapeutic response of virtual navigation (VN)-guided radiofrequency ablation (RFA) for patients with recurrent hepatocellular carcinoma (HCC) after hepatic resection. The aim of this study was to investigate the overall technical performance and outcome of VN-guided RFA in recurrent HCC patients. In addition, a nomogram model was developed to predict the factors influencing the overall survival (OS).

METHODS

This was a prospective study on 76 recurrent HCC patients who underwent VN-guided RFA between June 2015 and February 2018. The technical feasibility, success, and efficiency, OS, local tumor progression, and complications were evaluated. A multivariate Cox regression analysis was conducted to predict the significant factors, and a nomogram including independent predictive factors was subsequently plotted to predict OS.

RESULTS

The technical feasibility, success, and efficiency rates of VN-guided RFA were 86.4%, 94.7%, and 97.4%, respectively. The cumulative OS rates at 1-, 2-, and 3-year were 88.1%, 79.7%, and 71.0%, respectively. The cumulative local tumor progression rates at 1-, 2-, and 3-year were 5.5%, 8.7%, and 14.0%, respectively. In addition, the minor and major complication rates were 5.3% and 3.9%, respectively. No intervention-related deaths occurred during the follow-up period. The C-index of the OS nomogram in this study was 0.737.

CONCLUSIONS

VN-guided RFA is an effective therapeutic option in recurrent HCC patients and improves the long-term outcomes especially for the lesions that cannot be detected in the two-dimensional ultrasound. Besides, the nomogram may be a useful supporting tool in predicting OS to estimate the individual survival probability, optimize treatment options, and facilitate decision-making.

Advanced Fusion Imaging and Contrast-Enhanced Imaging (CT/MRI-CEUS) in Oncology

Fusion imaging depicts an innovative technique that facilitates combining assets and reducing restrictions of advanced ultrasound and cross-sectional imaging. The purpose of the present retrospective study was to evaluate the role of fusion imaging for assessing hepatic and renal lesions. Between 02/2011-08/2020, 92 patients in total were included in the study, of which 32 patients had hepatic lesions, 60 patients had renal lesions. Fusion imaging was technically successful in all patients. No adverse side effects upon intravenous (i.v.) application of SonoVue® (Bracco, Milan, Italy) were registered. Fusion imaging could clarify all 11 (100%) initially as indeterminate described hepatic lesions by computed tomography/magnetic resonance imaging (CT/MRI). Moreover, 5/14 (36%) initially suspicious hepatic lesions could be validated by fusion imaging, whereas in 8/14 (57%), malignant morphology was disproved. Moreover, fusion imaging allowed for the clarification of 29/30 (97%) renal lesions initially characterized as suspicious by CT/MRI, of which 19/30 (63%) underwent renal surgery, histopathology revealed malignancy in 16/19 (84%), and benignity in 3/19 (16%). Indeterminate findings could be elucidated by fusion imaging in 20/20 (100%) renal lesions. Its accessibility and repeatability, even during pregnancy and in childhood, its cost-effectiveness, and its excellent safety profile, make fusion imaging a promising instrument for the thorough evaluation of hepatic and renal lesions in the future.

Locoregional Therapy Approaches for Hepatocellular Carcinoma: Recent Advances and Management Strategies

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and third leading cause of cancer-related mortality worldwide. While surgical resection and transplantation are the standard first-line treatments for early-stage HCC, most patients do not fulfill criteria for surgery. Fortunately, catheter-directed and percutaneous locoregional approaches have evolved as major treatment modalities for unresectable HCC. Improved outcomes have been achieved with novel techniques which can be employed for diverse applications ranging from curative-intent for small localized tumors, to downstaging or bridging to resection and transplantation for early and intermediate disease, and locoregional control and palliation for advanced disease. This review explores recent advances in liver-directed techniques for HCC including bland transarterial embolization, chemoembolization, radioembolization, and ablative therapies, with a focus on patient selection, procedural technique, periprocedural management, and outcomes.

A closer look to the new frontier of artificial intelligence in the percutaneous treatment of primary lesions of the liver

The purpose of thermal ablation is induction of tumor death by means of localized hyperthermia resulting in irreversible cellular damage. Ablative therapies are well-recognized treatment modalities for HCC lesions and are considered standard of care for HCC nodules < 3 cm in diameter in patients not suitable for surgery. Effective lesion treatment rely on complete target volume ablation. Technical limitations are represented by large (> 3 cm) or multicentric nodules as well as complex nodule location and poor lesion conspicuity. Artificial Intelligence (AI) is a general term referred to computational algorithms that can analyze data and perform complex tasks otherwise prerogative of Human Intelligence. AI has a variety of application in percutaneous ablation procedures such as Navigational software, Fusion Imaging, and robot-assisted ablation tools. Those instruments represent relative innovations in the field of Interventional Oncology and promising strategies to overcome actual limitations of ablative therapy in order to increase feasibility and technical results. This work aims to review the principal application of Artificial Intelligence in the percutaneous ablation of primary lesions of the liver with special focus on how AI can impact in the treatment of HCC especially on potential advantages on the drawbacks of the conventional technique.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

Current role of ultrasound in the diagnosis of hepatocellular carcinoma

Ultrasonography (US) is a major, sustainable hepatocellular carcinoma (HCC) surveillance method as it provides inexpensive, real-time, and noninvasive detection. Since US findings are based on pathological features, knowledge of pathological features is essential for delivering a correct US diagnosis. Recent advances in US equipment have made it possible to provide more information, such as malignancy potential and accurate localization diagnosis of HCC. Evaluation of malignancy potential is important to determine the treatment strategy, especially for small HCC. Diagnosis of blood flow dynamics using color Doppler and contrast-enhanced US is one of the most definitive approaches for evaluating HCC malignancy potential. Recently, a new Doppler microvascular imaging technique, superb microvascular imaging, which can detect Doppler signals generated by low-velocity blood flow, was developed. A fusion imaging system, another innovative US technology, has already become an indispensable technology over the last few years not only for US-guided radiofrequency ablation but also for the detection of small, invisible HCC. This article reviews the evidence on the use of ultrasound and contrast-enhanced ultrasound with Sonazoid for the practical management of HCC.

Ultrasound fusion imaging technologies for guidance in ablation therapy for liver cancer

With advances in imaging technology, images from ultrasound (US) and computed tomography (CT) or magnetic resonance imaging (MRI) can be displayed simultaneously and in real time, according to the angle of the transducer. CT/MR-US fusion imaging improves the visualization of inconspicuous hepatocellular carcinoma (HCC) and helps us to understand the three-dimensional relationship between the liver vasculature and HCC. US fusion imaging guidance facilitates improvement in the treatment response for HCC with poor conspicuity, and the rates of technical success of ablation and local tumor progression for inconspicuous HCC range from 94.4 to 100% and 0 to 8.3%, respectively. Moreover, the development of image fusion has made it possible to compare and overlay pre- and post-ablation US images. This US-US fusion imaging allows side-by-side comparison of the ablative margin, while US-US overlay fusion can visualize the ablative margin because the tumor image is projected onto the ablative hyperechoic zone. Thus, US-US overlay fusion guidance is highly effective for safety margin achievement in local ablation therapy for HCC, providing a lower risk of local tumor progression. This manuscript reviews the current status of ultrasound fusion imaging for percutaneous ablation therapy of HCC.

Electromagnetic tracking-based ultrasound/computed tomography fusion imaging in dogs: preliminary application to ocular and periocular regions

In ultrasound/computed tomography (CT) fusion images, ultrasound allows visualization of the target in real time. CT provides a navigation for ultrasound scanning and improves the overview in areas of limited visualization with ultrasound. This study was performed to investigate the feasibility of ultrasound/CT fusion based on an electromagnetic tracking technique using external fiducial markers for canine ocular and periocular regions. In 7 Beagle dogs, contrast-enhanced CT images of the head were obtained with placing external fiducial markers over the frontal region and both sides of the forepaws of the dog. Ultrasonography was performed under a magnetic field by installing a position sensor in the linear probe, without changing the dog's position. The positions of the external fiducial markers were adjusted and matched, based on the CT images. The execution time of co-registration and the distance between the regions of interest and the co-registration points, the frontal bone, cornea, retina, and optic nerve, were estimated. Approximately 60% of external fiducial markers were properly recognized in all dogs. After adjustment, all external fiducial markers were precisely matched. The co-registration execution time was less than 1 min. The distances between the regions of interest and co-registration points were less than 3 mm in all dogs. The electromagnetic tracking technique using external fiducial markers was a simple and applicable method for fusion imaging of a canine head using real-time ultrasonography and CT. This technique can be useful for interventional procedures of retrobulbar and periorbital lesions.

Radiofrequency ablation for hepatocellular carcinoma: Clinical value of ultrasound-ultrasound overlay fusion for optimal ablation and local controllability

AIM

To retrospectively investigate the potential benefit of ultrasound-ultrasound (US-US) overlay fusion guidance for local controllability of radiofrequency ablation (RFA) in the treatment of hepatocellular carcinoma (HCC).

METHODS

Patients (n = 101) with 121 HCCs (mean ± SD, 1.8 ± 0.7 cm) who underwent RFA guided by US-US overlay fusion were included in the retrospective study. By overlaying pre/postoperative US, the tumor image could be projected onto the ablative hyperechoic zone. The ablative margin could thereby be evaluated three-dimensionally during the RFA procedure. As a control group, all 325 patients with 453 HCCs who underwent conventional RFA during the same study period were selected.

RESULTS

The total number of RF needle insertions per tumor for ablation was significantly more in the US overlay fusion group (mean 1.9 vs. 1.2; P < 0.01). The technical success rates of ablation after a single session were 100% (101/101) and 96.6% (314/325) for the US overlay fusion group and the control group, respectively. For early assessment of RFA response, 5-mm safety margins were achieved in 89.3% (108/121) and 47.0% (213/453) of nodules in the US overlay fusion group and the control group, respectively (P < 0.01). During the follow-up period (median 19 months), the 2-year local tumor progression rates were 0.8% (1/121) and 6.0% (27/453) in the US overlay fusion group and the control group, respectively (P = 0.022, log-rank test).

CONCLUSIONS

US-US overlay fusion guidance can be highly effective for safety margin achievement in RFA for HCC, providing a lower risk of local tumor progression.

Investigating the Accuracy of Ultrasound-Ultrasound Fusion Imaging for Evaluating the Ablation Effect via Special Phantom-Simulated Liver Tumors

The goal of this study was to investigate the accuracy of ultrasound-ultrasound (US-US) fusion imaging for evaluating the ablation effect via phantom-simulated liver tumors. Twenty special phantom models were established, ablated and divided into a complete ablation group (n = 10) and an incomplete ablation group (n = 10). US-US fusion imaging was performed to evaluate the ablation effect. Gross specimens were observed as a standard reference. In this US-US fusion imaging study, the registration success rate was 100% (20/20), and the assessment time was 3.8 ± 0.9 min. The accuracy rate of the evaluation was 100% (20/20). There was no significant difference in the residual pseudo-tumoral area between the evaluation with US-US fusion imaging and gross specimen observation (p = 0.811), and the measurement error was 1.1 ± 0.6 mm. In conclusion, the feasibility and accuracy of US-US fusion imaging when evaluating the ablation effect can be investigated with this phantom-simulated liver tumor ablation model in an ideal state.

3-D Contrast-Enhanced Ultrasound Fusion Imaging: A New Technique to Evaluate the Ablative Margin of Radiofrequency Ablation for Hepatocellular Carcinoma

To investigate the feasibility of assessing the ablative margin (AM) of radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC) with 3-D contrast-enhanced ultrasound fusion imaging (3-DCEUS-FI), pre- and post-RFA 3-DCEUS images of 84 patients with HCC were fused for two radiologists to independently assess the AMs. The success rate, duration and influencing factors for registration; inter-observer agreement for AM classification; and local tumor progression (LTP) rate were evaluated. The success rate of the automatic registration (AR), which was completed within 4-12 s, was 57.1% (48/84). The duration and success rate of the interactive registration (IR) were 4.2 ± 1.8 min and 91.7% (77/84) for radiologist A and 4.8 ± 2.1 min and 91.7% (77/84) for radiologist B, respectively. The multivariate analysis demonstrated that the pre-RFA image quality, number of vessels (≥3 mm) and presence of acoustic shadow were independent factors for AR (p < 0.05), while the number of vessels was an independent factor for IR (p = 0.001). The agreement between observers was excellent (kappa = 0.914). LTP rate was significantly higher for AMs <5 mm than for AMs ≥5 mm (p = 0.024). Quantitatively evaluating the AM immediately after RFA for HCC with 3-DCEUS-FI was feasible.

Thermal ablation with fusion imaging guidance of hepatocellular carcinoma without conspicuity on conventional or contrast-enhanced US: surrounding anatomical landmarks matter

AIM

Evaluating clinical and technical factors affecting thermal ablation of B-Mode/CEUS inconspicuous HCC nodules, relying only on fusion imaging (FI) performed under conscious sedation and using previously acquired CT or MR.

MATERIALS AND METHODS

Among 367 HCC nodules treated in the study period, data of 37 B-mode/CEUS undetectable HCC nodules treated with FI-guided ablation were extracted from our prospectively collected institutional database. Analyzed variables included patients' sex, age, cirrhosis etiology, Child-Pugh status, size of the lesion, liver segment, subcapsular or central liver site, type of imaging used for fusion (MR/CT), and the presence of surrounding anatomical landmarks (SAL) < 3 cm from the index lesion.

RESULTS

The primary efficacy was 59.4% (22/37 nodules); nine lesions (24.3%) were partially ablated (PA), six lesions (16.7%) were mistargeted (MA). Eight nodules were retreated with a CA obtained in all cases (100% CA, secondary efficacy in 30/37-81.1%). LTP was observed in 2/30 cases (6.7%). Two minor complications were registered (Clavien-Dindo, Grade1, CIRSE Classification Grade 2). SAL were related to a better ablation outcome (37.5% vs 84.6% p = 0.01). No differences were observed between CA group and PA-MA group in terms of lesion size (15.4 mm vs 14.9 mm p = 0.63), liver segment (p = 0.58), subcapsular or central liver site (8/22 36% vs 4/15 26.7% p = 0.84), and imaging (MR vs CT, p = 0.72).

CONCLUSION

Even in the presence of potentially critical conditions (completely B-Mode/CEUS inconspicuous nodules, spontaneous breathing, and previously acquired CT or MRI), FI-only guidance is safe and allows having good primary, secondary efficacy and LTP rates. The outcome of the procedure is heavily affected by the presence of SAL.

Intraprocedural computed tomography/magnetic resonance-contrast-enhanced ultrasound fusion imaging improved thermal ablation effect of hepatocellular carcinoma: Comparison with conventional ultrasound

AIM

To retrospectively compare the treatment effect of intraprocedural computed tomography/magnetic resonance-contrast-enhanced ultrasound (CT/MR-CEUS) fusion imaging (FI) with that of conventional ultrasound (US) in the guidance and assessment of thermal ablation of hepatocellular carcinoma (HCC).

METHODS

The FI group (112 patients with 129 HCC) was treated between April 2010 and December 2012, whereas the US group (83 patients with 90 HCC) was treated between January 2008 and March 2010. Either CT/MR-CEUS FI or US was used to guide puncture, provide immediate assessment, and guide supplementary ablation. Technical efficacy, cumulative local tumor progression rate (LTP), recurrence-free survival (RFS), and overall survival (OS) were evaluated and compared during follow-up. Technical success rate of CT/MR-CEUS FI was also recorded.

RESULTS

Technical efficacy was significantly higher in the FI group than in the US group (100% vs. 86.7%, P < 0.001). The 1-, 2-, 3-, 4-, 5-, and 6-year cumulative LTP rates in the FI group were significantly lower than in the US group (3.8%, 4.9%, 6.0%, 6.0%, 7.2%, and 7.2% vs. 16.9%, 20.1%, 25%, 25%, 25%, and 25%, respectively; P < 0.001); RFS and OS were significantly higher in the FI group than in the US group (P = 0.027 and P = 0.049, respectively). The technical success rate of FI was 85.3%.

CONCLUSIONS

Intraprocedural CT/MR-CEUS FI improved the treatment effect of thermal ablation of HCC by immediately assessing treatment response and guiding supplementary ablation relative to those resulting from the use of conventional US.

Abdominal applications of ultrasound fusion imaging technique: liver, kidney, and pancreas

Fusion imaging allows exploitation of the strengths of all imaging modalities simultaneously, eliminating or minimizing the weaknesses of every single modality. Ultrasound (US) fusion imaging provides benefits in real time from both the dynamic information and spatial resolution of the normal US and the high-contrast resolution and wider field of view of the other imaging methods. US fusion imaging can also be associated with the use of different ultrasound techniques such as color Doppler US, elastography, and contrast-enhanced US (CEUS), for better localization and characterization of lesions. The present paper is focused on US fusion imaging technologies and clinical applications describing the possible use of this promising imaging technique in the liver, kidney, and pancreatic pathologies.

Management of sub-centimeter recurrent hepatocellular carcinoma after curative treatment: Current status and future

Hepatocellular carcinomas (HCCs) frequently recur despite initial successful surgical resection or local ablation therapy. Diagnostic methods for small HCCs have improved with the introduction of gadoxetic acid-enhanced liver magnetic resonance imaging and diffusion-weighted imaging (DWI). Currently, sub-centimeter recurrent nodules showing typical hallmark imaging findings of HCC are frequently detected in patients with a treatment history for HCC. With five typical magnetic resonance findings, including arterial enhancement, washout on portal or transitional phase, high signal intensity on both T2-weighted image and DWI, and low signal intensity on hepatobiliary phase, sub-centimeter recurrent HCC can be diagnosed with high accuracy. Although more information is needed to determine the treatment of choice, local ablation therapy under fusion imaging and/or contrast-enhanced ultrasound guidance or cone-beam computed tomography-guided chemoembolization seem to be promising as they are effective and safe for the management of sub-centimeter recurrent HCCs.

Comparison of Combined Therapy Using Conventional Chemoembolization and Radiofrequency Ablation Versus Conventional Chemoembolization for Ultrasound-Invisible Early-Stage Hepatocellular Carcinoma (Barcelona Clinic Liver Cancer Stage 0 or A)

Objective

To compare the therapeutic efficacy between conventional transarterial chemoembolization (cTACE) and combined therapy using cTACE and radiofrequency ablation (RFA) in ultrasound (US)-invisible early stage hepatocellular carcinoma (HCC).

Materials and Methods

From January 2008 to June 2016, 167 patients with US-invisible early stage HCCs were treated with cTACE alone (cTACE group; n = 85) or cTACE followed by immediate fluoroscopy-guided RFA targeting intratumoral iodized oil retention (combined group; n = 82). Procedure-related complications, local tumor progression (LTP), time to progression (TTP), and overall survival (OS) were compared between the two groups. Multivariate analyses were performed to identify prognostic factors.

Results

There was no major complication in either group. The cTACE group showed higher 1-, 3-, and 5-year LTP rates than the combined group; i.e., 12.5%, 31.7%, and 37.0%, respectively, in the cTACE group; compared to 7.3%, 16.5%, and 16.5%, respectively, in the combined group; p = 0.013. The median TTP was 18 months in the cTACE group and 24 months in the combined group (p = 0.037). Cumulative 1-, 3-, and 5-year OS rates were 100%, 93.2%, and 87.7%, respectively, in the cTACE group and 100%, 96.6%, and 87.4%, respectively, in the combined group (p = 0.686). Tumor diameter > 20 mm and cTACE monotherapy were independent risk factors for LTP and TTP.

Conclusion

Combined therapy using cTACE followed by fluoroscopy-guided RFA is a safe and effective treatment in US-invisible early stage HCCs. It provides less LTP and longer TTP than cTACE alone.

Development of a robust MRI fiducial system for automated fusion of MR-US abdominal images

We present the development of a two‐component magnetic resonance (MR) fiducial system, that is, a fiducial marker device combined with an auto‐segmentation algorithm, designed to be paired with existing ultrasound probe tracking and image fusion technology to automatically fuse MR and ultrasound (US) images. The fiducial device consisted of four ~6.4 mL cylindrical wells filled with 1 g/L copper sulfate solution. The algorithm was designed to automatically segment the device in clinical abdominal MR images. The algorithm's detection rate and repeatability were investigated through a phantom study and in human volunteers. The detection rate was 100% in all phantom and human images. The center‐of‐mass of the fiducial device was robustly identified with maximum variations of 2.9 mm in position and 0.9° in angular orientation. In volunteer images, average differences between algorithm‐measured inter‐marker spacings and actual separation distances were 0.53 ± 0.36 mm. “Proof‐of‐concept” automatic MR‐US fusions were conducted with sets of images from both a phantom and volunteer using a commercial prototype system, which was built based on the above findings. Image fusion accuracy was measured to be within 5 mm for breath‐hold scanning. These results demonstrate the capability of this approach to automatically fuse US and MR images acquired across a wide range of clinical abdominal pulse sequences.