MR-guided microwave ablation in hepatic tumours: initial results in clinical routine

Immediate changes in MRI signals after the MRI-guided microwave ablation of malignant liver tumors

OBJECTIVE

To observe the immediate changes in MRI signals after the MRI-guided microwave ablation of malignant liver tumors and to explore the pattern of immediate signal changes post-ablation.

MATERIALS AND METHODS

A retrospective analysis was conducted on 23 patients with 27 lesions who underwent MRI-guided liver microwave ablation at Baoshan people's Hospital from September 2022 to December 2023. The relationship between the changes in MRI signals and time post-ablation was studied. The first scan was performed immediately after ablation (designated as 0 min) and followed by scans at 3 min, 6 min, 10 min, 15 min, 20 min, and 30 min post-ablation. The signal characteristics that changed in each sequence after each scan were measured and recorded.

RESULTS

After ablation, the mean maximum diameter of the high-signal range in 27 T1WI ablation foci varied over a short period of time (0 min: 22.00 mm; at 3 min: 26.58 mm; at 6 min: 26.94 mm; at 10 min: 27.06 mm; at 15 min: 27.12mm; at 20 min: 27.16 mm; and at 30 min: 27.16 mm). The change from 0-10 min was statistically significant (t = -10.326, P < 0.001), whereas the change from 10-30 min was not statistically significant (t = -1.536, P = 0.068). And, the signal intensity increased over time. The signal intensity of the primary lesion remained unchanged while the range decreased. There were minimal differences in the range and intensity changes in the T2-weighted imaging (T2WI) sequence. In diffusion-weighted imaging (DWI), the lesions showed high-signal intensity pre-ablation, but in post-ablation, it exhibited a high-signal surrounding the ablation zone with iso-intense or mixed signals, and the apparent diffusion coefficient (ADC) value increased.

CONCLUSION

The high-signal range observed in the T1WI sequence at the 10th min scan after the ablation completely reflected the true extent of the ablated foci, whereas the low-signal range in the T2WI sequence was stable and unchanged.

MR-Guided Microwave Ablation for Patients with Cirrhosis Complicated by Small Hepatocellular Carcinoma

PURPOSE

To assess the technical effectiveness and therapeutic outcomes of percutaneous magnetic resonance (MR)-guided microwave ablation (MWA) in the treatment of patients with cirrhosis complicated by small hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

A single-center, retrospective analysis of consecutive cases involving 1.5T MR-guided MWA for HCC was performed. Fifty-three patients with cirrhosis, harboring 74 HCC lesions with mean diameter of 13.0 mm (SD ± 6.0; range, 6.0-29.0 mm; median, 10.0 mm), were included in this study. Follow-up MR imaging was performed postprocedurally to assess technical effectiveness, whereas local progression-free survival (LPFS) and overall survival (OS) rates were calculated over the study period.

RESULTS

MR-guided MWA was performed with technical success in all cases with no severe adverse events occurring during the single-session treatment. The mean follow-up duration was 46.1 months (SD ± 17.9; median, 52 months). Local tumor progression was observed in 1 perivascular lesion, accounting for 1.9% of the cases. The mean recurrence-free survival was 31.1 months (SD ± 22.2), with a median of 24.5 months. LPFS rates at 1, 3, and 5 years were 98.1%. The OS rates at 1, 3, and 5 years were 96.2%, 84.9%, and 71.6%, respectively.

CONCLUSIONS

Percutaneous MR-guided MWA for small HCC in patients with cirrhosis demonstrated high technical success, accurate evaluation of ablation margins, and minimal local tumor progression after a single treatment session, resulting in favorable therapeutic outcomes.

A Comparison of the Efficacy and Safety of US-, CT-, and MR-Guided Radiofrequency and Microwave Ablation for HCC: A Systematic Review and Network Meta-Analysis

Objectives: The aim of this study was to compare the efficacy and safety of thermal ablation, focusing on radiofrequency ablation (RFA) and microwave ablation (MWA), for hepatocellular carcinoma (HCC) using US-, CT-, and MR-guidance. Methods: PubMed, EMBASE, Cochrane Library, and Web of Science were searched for studies comparing US, CT, and MR guidance in thermal ablation for HCC. Observational studies and randomized controlled trials (RCTs) were included. Overall survival (OS), local tumor recurrence (LTR), primary technique effectiveness (PTE), and major complications were assessed with network meta-analysis. Results: One RCT and 13 retrospective cohort studies reporting on 2349 patients were included. For OS at 3 years, compared to CT, US had hazard ratios (HRs) of 0.98 (95%CI: 0.77-1.26), and MR had HRs of 1.60 (95%CI: 0.51-5.00); For OS at 5 years, US had HRs of 0.80 (95%CI: 0.64-1.01), and MR had HRs of 1.23 (95%CI: 0.52-2.95) compared to CT. LTR rates, PTE, and major complications did not show statistical significance among the three guidance modalities (LTR: RR = 0.29 (95%CI: 0.08-1.14), p = 0.97 MR vs. CT; RR = 0.25 (95%CI: 0.06-1.02), p = 0.97 MR vs. US; PTE: RR = 1.06 (95%CI: 0.96-1.17), p = 0.90 MR vs. CT; RR = 1.08 (95%CI: 0.98-1.20), p = 0.90 MR vs. US. Major complications: RR = 0.27 (95%CI: 0.13-0.59), p = 0.94 MR vs. CT; RR = 0.41 (95%CI: 0.10-1.74), p = 0.94 MR vs. US). Conclusions: CT-, US-, and MR-guided RFA and MWA are equally effective and safe for HCC patients.

Accuracy of 3D real-time MRI temperature mapping in gel phantoms during microwave heating

BACKGROUND

Interventional magnetic resonance imaging (MRI) can provide a comprehensive setting for microwave ablation of tumors with real-time monitoring of the energy delivery using MRI-based temperature mapping. The purpose of this study was to quantify the accuracy of three-dimensional (3D) real-time MRI temperature mapping during microwave heating in vitro by comparing MRI thermometry data to reference data measured by fiber-optical thermometry.

METHODS

Nine phantom experiments were evaluated in agar-based gel phantoms using an in-room MR-conditional microwave system and MRI thermometry. MRI measurements were performed for 700 s (25 slices; temporal resolution 2 s). The temperature was monitored with two fiber-optical temperature sensors approximately 5 mm and 10 mm distant from the microwave antenna. Temperature curves of the sensors were compared to MRI temperature data of single-voxel regions of interest (ROIs) at the sensor tips; the accuracy of MRI thermometry was assessed as the root-mean-squared (RMS)-averaged temperature difference. Eighteen neighboring voxels around the original ROI were also evaluated and the voxel with the smallest temperature difference was additionally selected for further evaluation.

RESULTS

The maximum temperature changes measured by the fiber-optical sensors ranged from 7.3 K to 50.7 K. The median RMS-averaged temperature differences in the originally selected voxels ranged from 1.4 K to 3.4 K. When evaluating the minimum-difference voxel from the neighborhood, the temperature differences ranged from 0.5 K to 0.9 K. The microwave antenna and the MRI-conditional in-room microwave generator did not induce relevant radiofrequency artifacts.

CONCLUSION

Accurate 3D real-time MRI temperature mapping during microwave heating with very low RMS-averaged temperature errors below 1 K is feasible in gel phantoms.

RELEVANCE STATEMENT

Accurate MRI-based volumetric real-time monitoring of temperature distribution and thermal dose is highly relevant in clinical MRI-based interventions and can be expected to improve local tumor control, as well as procedural safety by extending the limits of thermal (e.g., microwave) ablation of tumors in the liver and in other organs.

KEY POINTS

Interventional MRI can provide a comprehensive setting for the microwave ablation of tumors. MRI can monitor the microwave ablation using real-time MRI-based temperature mapping. 3D real-time MRI temperature mapping during microwave heating is feasible. Measured temperature errors were below 1 °C in gel phantoms. The active in-room microwave generator did not induce any relevant radiofrequency artifacts.

Body-Mounted MR-Conditional Robot for Minimally Invasive Liver Intervention

MR-guided microwave ablation (MWA) has proven effective in treating hepatocellular carcinoma (HCC) with small-sized tumors, but the state-of-the-art technique suffers from sub-optimal workflow due to the limited accuracy provided by the manual needle insertions. This paper presents a compact body-mounted MR-conditional robot that can operate in closed-bore MR scanners for accurate needle guidance. The robotic platform consists of two stacked Cartesian XY stages, each with two degrees of freedom, that facilitate needle insertion pose control. The robot is actuated using 3D-printed pneumatic turbines with MR-conditional bevel gear transmission systems. Pneumatic valves and control mechatronics are located inside the MRI control room and are connected to the robot with pneumatic transmission lines and optical fibers. Free-space experiments indicated robot-assisted needle insertion error of 2.6 ± 1.3 mm at an insertion depth of 80 mm. The MR-guided phantom studies were conducted to verify the MR-conditionality and targeting performance of the robot. Future work will focus on the system optimization and validations in animal trials.

Improved visualization of hepatic tumors in magnetic resonance-guided thermoablation using T1-inversion-recovery imaging with variable inversion time

OBJECTIVES

In magnetic resonance (MR)-guided interventions, visualization of hepatic lesions may be difficult using standard unenhanced T1-weighted gradient-echo volume-interpolated breath-hold (VIBE) sequence due to low contrast. Inversion recovery (IR) imaging may have the potential to improve visualization without the necessity to apply contrast agent.

METHODS

Forty-four patients (mean age 64 years, female 33%) scheduled for MR-guided thermoablation due to liver malignancies (hepatocellular carcinoma or metastases) were prospectively included in this study between March 2020 and April 2022. Fifty-one liver lesions were intra-procedurally characterized before treatment. Unenhanced T1-VIBE was acquired as part of the standard imaging protocol. Additionally, T1-modified look-locker images were acquired with eight different inversion times (TI) between 148 and 1743 ms. Lesion-to-liver contrast (LLC) was compared between T1-VIBE and IR images for each TI. T1 relaxation times for liver lesions and liver parenchyma were calculated.

RESULTS

Mean LLC in T1-VIBE sequence was 0.3 ± 0.1. In IR images, LLC was highest at TI 228 ms (1.04 ± 1.1) and significantly higher compared to T1-VIBE (p < 0.001). In subgroup analysis, lesions of colorectal carcinoma showed the highest LLC at 228 ms (1.14 ± 1.4), and hepatocellular carcinoma showed the highest LLC at 548 ms (1.06 ± 1.16). T1-relaxation times in liver lesions were higher compared to the adjacent liver parenchyma (1184 ± 456 vs. 654 ± 96 ms, p < 0.001).

CONCLUSIONS

IR imaging is promising to provide improved visualization during unenhanced MR-guided liver interventions compared to standard T1-VIBE sequence when using specific TI. Low TI between 150 and 230 ms yields the highest contrast between liver parenchyma and malignant liver lesions.

CLINICAL RELEVANCE STATEMENT

Improved visualization of hepatic lesions during MR-guided percutaneous interventions using inversion recovery imaging without the necessity to apply contrast agent.

KEY POINTS

• Inversion recovery imaging is promising to provide improved visualization of liver lesions in unenhanced MRI. • Planning and guidance during MR-guided interventions in the liver can be performed with greater confidence without necessity to apply contrast agent. • Low TI between 150 and 230 ms yields the highest contrast between liver parenchyma and malignant liver lesions.

Dual-Applicator MR Imaging-Guided Microwave Ablation with Real-Time MR Thermometry: Phantom and Porcine Tissue Model Experiments

PURPOSE

To investigate the effect of simultaneous use of dual applicators on the image quality of real-time magnetic resonance (MR) thermometry and to characterize the dual-applicator treatment zone pattern during MR imaging-guided microwave ablation (MWA).

MATERIALS AND METHODS

MWA experiments were performed on a 1.5-T MR scanner with 2 commercial microwave systems (902-928 MHz). Phantom experiments were first performed to evaluate the effect of dual-applicator MWA on the image quality of MR. Then, porcine tissue model experiments were conducted with real-time MR thermometry using either a single applicator or dual applicators inserted 2.6, 3.6, and 4.6 cm apart. Fiberoptic thermal probes were used to measure the temperature changes at the tissue surface.

RESULTS

Simultaneous use of dual applicators resulted in a decrease in the relative signal-to-noise ratio (SNR) in the MR thermometry images to 55% ± 2.9% when compared with that of a single applicator (86.2% ± 2.0%). Despite the lower SNR, the temperature and ablation zone maps were of adequate quality to allow visualization of the ablation zone(s). The extents of increase in the temperature at the tissue surface using dual applicators (19.7 °C ± 2.6 °C) and a single applicator (18.2 °C ± 3.3 °C) were not significantly different (P = .40). Treatment zones were significantly larger (P < .05) in dual-applicator ablations (29.4 ± 0.4, 39.9 ± 0.6, and 42.6 ± 0.9 cm² with 2.6-, 3.6-, and 4.6-cm spacing, respectively) at the end of the ablation procedure than in the single-applicator MWA (18.6 ± 0.9 cm²).

CONCLUSIONS

MR imaging-guided dual-applicator MWA produced larger ablation zones while allowing adequate real-time MR thermometry image quality for monitoring the evolution of the treatment zone.

3.0-T closed MR-guided microwave ablation for HCC located under the hepatic dome: a single-center experience

PURPOSE

To analyze the clinical safety and efficacy of 3.0-T closed MR-guided microwave ablation (MWA) for the treatment of HCC located under the hepatic dome.

METHODS

From May 2018 to October 2020, 49 patients with 74 HCCs located under the hepatic dome underwent MWA using 3.0-T closed MR guidance. The technical success rate, operative time, complete ablation (CA) rate, complications, local tumor progression (LTP), tumor-free survival (TFS) and overall survival (OS) were examined. Routine blood analysis, liver/kidney function and alpha fetoprotein (AFP) and protein induced by vitamin k absent or antagonist (PIVKA) levels were compared before and 2 months after MWA.

RESULTS

All patients underwent MWA successfully, including 10 patients who underwent general anesthesia. The technical success rate was 100% without major complications. The CA rate was 95.9% (71/74) at the 2-month evaluation. The LTP rate was 2.7% during the median follow-up of 17.8 months (range: 4-43 months); the 6-, 12-, 18-month TFS rates were 97.8, 90.6, 68.1%, respectively, and the 6-, 12-, 18-month OS rates were 100, 97.6, 92.1%, respectively. There were no significant changes in routine blood tests and liver/kidney function (p > 0.05), while the AFP and PIVKA level decreased significantly at 2 months (p < 0.05).

CONCLUSION

3.0-T MR-guided MWA is safe and feasible for HCC lesions located under the hepatic dome.

Interventional oncology of liver tumors: how it all started and where are we now

Liver was the very first organ for which interventional procedures were applied for the local treatment of primary and secondary malignancies. In this paper, the history of Interventional Oncology of liver, from the very beginning to the current situation, is summarized, including both percutaneous and intravascular procedures, and together with the evolution of the techniques for image guidance. The main ongoing developments, such as new techniques, combined interventional treatments and association of local interventions with new drugs are briefly described, too.

Detection of Ablation Boundaries Using Different MR Sequences in a Swine Liver Model

PURPOSE

To determine the magnetic resonance (MR) sequences best suited for the assessment of ablation zones after radiofrequency ablation (RFA).

METHODS

Three percutaneous MR-guided RFA of the liver were performed on three swine. Four pre-contrast and two hepatobiliary post-contrast sequences were obtained after ablation. Tissue samples were extracted and stained for nicotinamide adenine dinucleotide diaphorase hydride (NADH) and with hematoxylin and eosin. Post-ablation MR images and NADH slides were segmented to determine the total ablation zone, their Dice similarity coefficient (DSC), and the contrast-to-noise ratio (CNR) of the visible ablation boundary to normal liver tissue.

RESULTS

Two distinct layers were combined to determine the ablation zone: an inner layer of coagulation necrosis and an outer layer defined as the peripheral transition zone. Corresponding zones could be found in the MR images as well. Compared to histology, the total area of the MR ablation zone was significantly smaller on the pre-contrast T1 images (p < 0.01) and significantly larger with T2 turbo spin-echo (p = 0.025). No significant difference in size of the ablation zone depiction could be found between histology, post-contrast T1 volumetric interpolated breath-hold examination (VIBE), and post-contrast T1 3D Turboflash (TFL) as well as T2 SPACE images. All sequences but the pre-contrast T1 VIBE sequence showed a DSC above 80% and a high CNR.

CONCLUSIONS

Post-contrast T1 3DTFL performs best when assessing ablation zones after RFA. Since the sequence requires a long acquisition time, T1 VIBE post-contrast offers the best compromise between acquisition time and estimation accuracy.

Development of a novel MR-conditional microwave needle for MR-guided interventional microwave ablation at 1.5T

PURPOSE

To develop an MR-conditional microwave needle that generates a spherical ablation zone and clear MRI visibility for MR-guided microwave ablation.

METHODS

An MR-conditional microwave needle consisting of zirconia tip and TA18 titanium alloy tube was investigated. The numerical model was created to optimize the needle's geometry and analyze its performance. A geometrically optimized needle was produced using non-magnetic materials based on the electromagnetics simulation results. The needle's mechanical properties were tested per the Chinese pharmaceutical industry standard YY0899-2013. The MRI visibility performance and ablation characteristics of the needle was tested both in vitro (phantom) and in vivo (rabbit) at 1.5T. The RF-induced heating was evaluated in ex vivo porcine liver.

RESULTS

The needle's mechanical properties met the specified requirements. The needle susceptibility artifact was clearly visible both in vitro and in vivo. The needle artifact diameter (A) was small in in vivo (A_shaft: 4.96 ± 0.18 mm for T1W-FLASH, 3.13 ± 0.05 mm for T2-weighted fast spin-echo (T2W-FSE); A_tip: 2.31 ± 0.09 mm for T1W-FLASH, 2.29 ± 0.08 mm for T2W-FSE; tip location error [TLE]_: -0.94 ± 0.07 mm for T1W-FLASH, -1.10 ± 0.09 mm for T2W-FSE). Ablation zones generated by the needle were nearly spherical with an elliptical aspect ratio ranging from 0.79 to 0.90 at 30 W, 50 W for 3, 5, 10 min duration ex vivo ablations and 0.86 at 30 W for 10 min duration in vivo ablations.

CONCLUSION

The designed MR-conditional microwave needle offers excellent mechanical properties, reliable MRI visibility, insignificant RF-induced heating, and a sufficiently spherical ablation zone. Further clinical development of MR-guided microwave ablation appears warranted.

Fluid-based augmentation of magnetic resonance visualization of interventional devices

PURPOSE

To evaluate the transient artifact augmentation of microtubes in magnetic resonance imaging by fluid injection.

METHODS

Twenty-one fluorinated ethylene propylene catheters (inner diameter 760 μm) were filled with three different contrast media at various concentrations (Ferucarbotran, Resovist®, Bayer Schering Pharma; Manganese dichloride, MnCl2, Sigma-Aldrich; Gadobutrol, Gadovist®, Bayer Schering Pharma). Artifact appearance was determined in an ex vivo phantom at 1.5 T using three different sequences: T1-weighted three-dimensional volume interpolated breath-hold examination, T2-weighted turbo spin echo, and T1-weighted fast low angle shot. Catheter angulation to the main magnetic field (B0) was varied. Influence of parameters on artifact diameters was assessed with a multiple linear regression similar to an analysis of variance.

RESULTS

Artifact diameter was significantly influenced by the contrast agent (p < 0.001), concentration of the contrast agent (p < 0.001), angulation of the phantom to B0 with the largest artifact at 90° (p < 0.001), and encoding direction with a larger diameter in phase encoding direction (PED, p < 0.001). Mean artifact diameters at 90° angulation to B0 in PED were 18.5 ± 5.4 mm in 0.5 mmol/ml Ferucarbotran, 8.7 ± 2.5 mm in 1 mmol/ml Gadobutrol, and 11.6 ± 4.6 mm in 5 mmol/ml MnCl2 .

CONCLUSIONS

Fluid-based contrast agents might be applied to interventional devices and thus temporarily augment the artifact ensuring both visibility and safe navigation.

Image-Guided Ablation for Colorectal Liver Metastasis: Principles, Current Evidence, and the Path Forward

Image-guided ablation can provide effective local tumor control in selected patients with CLM. A randomized controlled trial suggested that radiofrequency ablation combined with systemic chemotherapy resulted in a survival benefit for patients with unresectable CLM, compared to systemic chemotherapy alone. For small tumors, ablation with adequate margins can be considered as an alternative to resection. The improvement of ablation technologies can allow the treatment of tumors close to major vascular structures or bile ducts, on which the applicability of thermal ablation modalities is challenging. Several factors affect the outcomes of ablation, including but not limited to tumor size, number, location, minimal ablation margin, RAS mutation status, prior hepatectomy, and extrahepatic disease. Further understanding of the impact of tumor biology and advanced imaging guidance on overall patient outcomes might help to tailor its application, and improve outcomes of image-guided ablation.

Differential Imaging of Liver Tumors before and after Microwave Ablation with Electrode Displacement Elastography

Liver cancer is a leading cause of cancer-related deaths; however, primary treatment options such as surgical resection and liver transplant may not be viable for many patients. Minimally invasive image-guided microwave ablation (MWA) provides a locally effective treatment option for these patients with an impact comparable to that of surgery for both cancer-specific and overall survival. MWA efficacy is correlated with accurate image guidance; however, conventional modalities such as B-mode ultrasound and computed tomography have limitations. Alternatively, ultrasound elastography has been used to demarcate post-ablation zones, yet has limitations for pre-ablation visualization because of variability in strain contrast between cancer types. This study attempted to characterize both pre-ablation tumors and post-ablation zones using electrode displacement elastography (EDE) for 13 patients with hepatocellular carcinoma or liver metastasis. Typically, MWA ablation margins of 0.5-1.0 cm are desired, which are strongly correlated with treatment efficacy. Our results revealed an average estimated ablation margin inner quartile range of 0.54-1.21 cm with a median value of 0.84 cm. These treatment margins lie within or above the targeted ablative margin, indicating the potential to use EDE for differentiating index tumors and ablated zones during clinical ablations. We also obtained a high correlation between corresponding segmented cross-sectional areas from contrast-enhanced computed tomography, the current clinical gold standard, when compared with EDE strain images, with r2 values of 0.97 and 0.98 for pre- and post-ablation regions.

Stereotactic Thermal Ablation of Liver Tumors: 3D Planning, Multiple Needle Approach, and Intraprocedural Image Fusion Are the Key to Success-A Narrative Review

Thermal ablation is an emerging, potentially curative approach in treating primary and metastatic liver cancer. Different technologies are available, with radiofrequency ablation (RFA) and microwave ablation (MWA) being the most widely used. Regardless of the technique, destruction of the entire tumor, including an adequate safety margin, is key. In conventional single-probe US- or CT-guided thermal ablation, the creation of such large necrosis zones is often hampered by technical limitations, especially for large tumors (i.e., >2-3 cm). These limitations have been overcome by stereotactic RFA (SRFA): a multiple needle approach with 3D treatment planning and precise stereotactic needle placement combined with intraprocedural image fusion of pre- and post-interventional CT scans for verification of treatment success. With these sophisticated tools and advanced techniques, the spectrum of locally curable liver malignancies can be dramatically increased. Thus, we strongly believe that stereotactic thermal ablation can become a cornerstone in the treatment of liver malignancies, as it offers all the benefits of a minimally invasive method while providing oncological outcomes comparable to surgery. This article provides an overview of current stereotactic techniques for thermal ablation, summarizes the available clinical evidence for this approach, and discusses its advantages.

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.

MR-Guided Microwave Ablation in T1 Renal Cell Carcinoma: Initial Results in Clinical Routine

Objective

Percutaneous tumor ablation is usually performed using computed tomography (CT) or ultrasound (US) guidance, although reliable visualization of the target tumor could be challenging. Magnetic resonance- (MR-) guided ablation provides more reliable visualization of the target tumors and allows multiplanar imaging of the treatment process, making it the modality of choice, in particular if lesions are small.

Methods

From March 2016 to January 2018, 32 patients scheduled for percutaneous treatment of T1 RCC underwent MR-guided MWA. Complications were classified according to the Clavien grade. Kaplan–Meier survival estimates were calculated to evaluate progression-free survival (PFS).

Results

Technical success was achieved in all lesions. The mean energy and procedure duration were 61.6 ± 8.7 kJ and 118.2 ± 26.7 min, respectively. The glomerular filtration rate (GFR) dropped rapidly after 1 month of treatment and slowly recovered within three months (P < 0.05). Postoperative pain and fever were the most common adverse events after treatment. Perirenal hematoma, thermal injury of the psoas muscle, and abdominal distension were common complications after MWA, and the incidence rates were 9.4% (3/32), 6.3% (2/32), and 6.3% (2/32), respectively. According to the Clavien grade classification, serious complications include hydrothorax, bowel injury, and renal failure, all of which have a probability of 3.1%. Of note, the three serious complications occurred in one patient. The 1-, 2-, and 3-year PFS rates were 96.9%, 93.8%, and 83.9%, respectively. The mean PFS rates were 33.972 months (95% CI: 33.045, 35.900).

Conclusion

Microwave ablation is feasible under MR guidance and provides effective treatment of RCC in one session.

Microwave Ablation of Small Hepatic Metastases Using MR Guidance and Monitoring: Clinical Safety and Efficacy

Background

To evaluate the technical success and clinical safety of magnetic resonance (MR)-guided microwave ablation (MWA) of small hepatic metastases.

Materials and Methods

Institutional review board approval and informed patient consent were obtained. A retrospective analysis of the patient data revealed 50 patients with small hepatic metastases (34 men, 16 women) who underwent MWA under MR guidance and monitoring. After the procedure, the intervention-related complications were classified according to the Common Terminology Criteria for Adverse Events (CTCAE) and Society of Interventional Radiology (SIR) classification system. Furthermore, the overall survival (OS) and local tumor-free survival (LTP) of the patients were analyzed.

Results

The patients who underwent MR-guided MWA achieved technical success. The mean energy, ablation duration per tumor, and procedure duration were 55.3 ± 9.4 kJ, 11.7 ± 5.6 min and 89.5 ± 30.9 min, respectively. Most adverse events and complications were CTCAE grade 1 or 2 or SIR classification grade A or B. The 1-, 2-, and 3-year local tumor progression (LTP) rates were 65.9%, 31.5% and 18.5%, respectively, with a mean LTP of 19.216 months (95% CI: 16.208, 22.224); and the 1-, 2- and 3-year overall survival (OS) rates were 81.8%, 60.8% and 44.7%, respectively, with a mean OS of 26.378 months (95% CI: 23.485, 29.270). Multivariate Cox’s regression analysis further illustrated that tumor location (challenging locations vs ordinary locations) and the anesthesia (general anesthesia VS local anesthesia) were important factors affecting LTP and OS.

Conclusion

MR-guided MWA can successfully treat small hepatic metastases with potentially favorable safety and technical efficacy.

Advanced Techniques in the Percutaneous Ablation of Liver Tumours

Percutaneous ablation is an accepted treatment modality for primary hepatocellular carcinoma (HCC) and liver metastases. The goal of curative ablation is to cause the necrosis of all tumour cells with an adequate margin, akin to surgical resection, while minimising local damage to non-target tissue. Aside from the ablative modality, the proceduralist must decide the most appropriate imaging modality for visualising the tumour and monitoring the ablation zone. The proceduralist may also employ protective measures to minimise injury to non-target organs. This review article discusses the important considerations an interventionalist needs to consider when performing the percutaneous ablation of liver tumours. It covers the different ablative modalities, image guidance, and protective techniques, with an emphasis on new and advanced ablative modalities and adjunctive techniques to optimise results and achieve satisfactory ablation margins.

Feasibility and efficacy study of microwave ablation of recurrent small HCC guided by enhanced liver-specific magnetic resonance imaging contrast agent

OBJECTIVES

To investigate the feasibility and efficacy of liver-specific magnetic resonance imaging (MRI) with gadolinium-containing contrast agent guidance for microwave ablation (MWA) of recurrent small hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

The Ethics Committee of the First Affiliated Hospital of Fujian Medical University approved this study. Eighteen patients presented with 30 recurrent small HCCs, at least one lesion per patient was undetectable on unenhanced MRI, but this was clearly demonstrated in the hepatobiliary phase after liver-specific MRI contrast agent administration. Gd-BOPTA (16 cases) or Gd-EOB-DTPA (2 cases) were injected half an hour before the procedure, and MWA was performed by percutaneous puncture of the target lesion with a magnetic resonance-compatible microwave antenna under 1.5 T MRI guidance.

RESULTS

The technical success rate was 100%. The mean maximum diameter of the lesions was 9.7 ± 2.8 mm (5.0-15.4 mm). The mean follow-up time was 11.6 ± 4.7 months (range, 4-19 months), and no local recurrence was observed.

CONCLUSIONS

MWA of small HCCs guided by enhanced liver-specific MRI contrast agent is a safe and effective technique.

MR-guided microwave ablation in hepatic malignancies: clinical experiences from 50 procedures

Purpose: To investigate technical success, technique efficacy, safety and outcome of MR-guided microwave ablation (MWA) in hepatic malignancies.Material and methods: In this prospective IRB-approved study, patients scheduled for percutaneous treatment of hepatic malignancies underwent MR-guided MWA in a closed-bore 1.5 T MR system. Technical success was assessed on post-procedural MR control imaging. Technique efficacy was evaluated 4 weeks after the procedure on multi-parametric MRI. Assessment of safety followed the Society of Interventional Radiology grading system. Kaplan-Meier survival estimates were calculated to evaluate overall survival (OS), time to local tumor progression (TLTP), and time to non-target progression (TNTP).Results: Between 2015 and 2019, 47 patients (60.5 ± 12.2 years; 39 male) underwent 50 procedures for 58 hepatic tumors (21 hepatocellular carcinomas; 37 metastases). Mean target tumor size was 16 ± 7mm (range: 6-39 mm). Technical success and technique efficacy were 100% and 98%, respectively. Lesions were treated using 2.6 applicator positions (range: 1-6). Mean energy, ablation duration per tumor, and procedure duration were 43.2 ± 23.5 kJ, 26.7 ± 13.1 min and 211.2 ± 68.7 min, respectively. 10 minor (20%) and 3 major (6%) complications were observed. Median post-interventional hospital admission was 1 day (range: 1-19 days). Median OS was 41.6 (IQR: 26.4-) months. Local recurrence occurred after 4 procedures (8%) with TLTP ranging between 3.1 and 41.9 months. Non-target recurrence was observed in 64% of patients after a median TNTP of 13.8 (IQR 2.3-) months.Conclusion: MR-guided MWA allows for safe and successful treatment of hepatic malignancies with a high technique efficacy however with relatively long procedure durations.

Percutaneous radiofrequency ablation for small hepatocellular carcinoma in hepatic dome under MR-guidance: clinical safety and efficacy

Purpose: To evaluate the clinical safety and efficacy of percutaneous radiofrequency ablation (RFA) using multitined expandable electrodes under magnetic resonance imaging (MRI) guidance in the treatment of small hepatocellular carcinomas (HCCs) in the hepatic dome.Materials and methods: The data of 49 patients with 50 HCC lesions in the hepatic dome who underwent MRI-guided RFA from April 2010 to January 2018 were retrospectively analyzed. Planning, targeting, and controlling were performed under MR-guidance during the procedure. The complications after RFA were observed. Follow-up MRI was performed to evaluate the curative effect. The local progression-free survival, recurrence-free survival, and overall survival rates were calculated using the Kaplan-Meier survival curve.Results: The procedures were successfully accomplished in all patients without major complications. The mean follow-up time was 36.9 ± 25.8 months (range, 3-99 months). Technical success was 100% after one RFA session with MRI assessment after 1 month. Local tumor progression was observed in one patient (2%) with the lesion located in the hepatic dome at 4 months on a subsequent follow-up MRI. The progression-free survival time was 25.0 ± 22.7 months (median, 17.0 months). The 1-,3-, and 5-year local tumor progression-free survival rates were all 98.0%. The 1-,3-, and 5-year recurrence-free survival rates were 68.1%, 39.9%, and 28.5%, respectively, and the estimated overall survival rates were 93.7%, 76.3%, and 54.3%, respectively.Conclusion: Planning, targeting, and controlling of RFA were well supported by MRI with acceptable time. MRI-guided RFA for small HCCs in the hepatic dome is safe and effective with fewer RF sessions.

Transcatheter CT Hepatic Arteriography Compared with Conventional CT Fluoroscopy Guidance in Percutaneous Thermal Ablation to Treat Colorectal Liver Metastases: A Single-Center Comparative Analysis of 2 Historical Cohorts

PURPOSE

To evaluate safety and efficacy of CT hepatic arteriography compared with conventional CT fluoroscopy guidance in percutaneous radiofrequency (RF) and microwave (MW) ablation to treat colorectal liver metastases (CRLM).

MATERIALS AND METHODS

This single-center comparative, retrospective study analyzed data of 108 patients treated with 156 percutaneous ablation procedures (42 CT fluoroscopy guidance [25 RF ablation, 17 MW ablation]; 114 CT hepatic arteriography guidance [18 RF ablation, 96 MW ablation]) for 260 CRLM between January 2009 and May 2019. Local tumor progression-free survival (LTPFS) was assessed using univariate and multivariate Cox proportional hazard regression analyses. LTPFS and overall survival (OS) were estimated using the Kaplan-Meier method.

RESULTS

There were no complications related to the transarterial catheter procedure. CT hepatic arteriography proved superior to CT fluoroscopy regarding 2-year LTPFS (18/202 [8.9%] vs 19/58 [32.8%]; P < .001, respectively). CT hepatic arteriography versus CT fluoroscopy (hazard ratio = 0.28; 95% confidence interval, 0.15-0.54; P < .001) and MW ablation versus RF ablation (hazard ratio = 0.52; 95% confidence interval, 0.24-1.12; P = .094) were positive predictors for longer LTPFS. Multivariate analysis revealed that CT hepatic arteriography versus CT fluoroscopy (hazard ratio = 0.41; 95% confidence interval, 0.19-0.90; P = .025) was associated with a significantly superior LTPFS. OS was similar between the 2 cohorts (P = .3).

CONCLUSIONS

While adding procedure time and marginal patient burden, transcatheter CT hepatic arteriography-guided ablation was associated with increased local disease control and superior LTPFS compared with conventional CT fluoroscopy. CT hepatic arteriography represents a safe and valid alternative to CT fluoroscopy, as it reduces the number of repeat ablations required without adding risk or detrimental effect on survival.

Ultrasound-guided percutaneous microwave ablation for hepatocellular carcinoma adjacent to large vessels: a propensity score matching analysis

PURPOSE

This study aimed to compare the efficacy and safety of ultrasound-guided percutaneous microwave ablation (MWA) for hepatocellular carcinoma (HCC) adjacent to large vessels with those far from large vessels.

METHODS

The clinical data of patients who underwent ultrasound-guided percutaneous MWA for HCC were retrospectively analyzed between January 2011 and December 2018 in Shengjing Hospital. Patients with HCC adjacent to large vessels were included in the Vessel group, the remaining patients were included in the Control group. Propensity score matching analysis was used to reduce confounding bias. The rates of complete ablation, local recurrence, recurrence-free survival (RFS), overall survival (OS) and complications were compared between the two groups.

RESULTS

A total of 134 patients with 157 nodules (size range, 0.6-3.8 cm) were enrolled in this study, 23 in the Vessel group and 111 in the Control group. A total of 21 patients in the Vessel group (91.3%) and 105 patients in the Control group (94.6%) achieved complete ablation (p = .902). Following 1:2 propensity score matching, 22 patients were included in the Vessel group and 40 patients were enrolled in the Control group. Local recurrence was observed in 2 (9.1%) patients in the Vessel group and 5 (12.5%) in the Control group (p = .86). No significant difference in local recurrence rate, RFS and OS were observed between the two groups.

CONCLUSIONS

Ultrasound-guided percutaneous MWA appears to be a safe procedure and can achieve comparable oncological efficacy for HCC abutting large vessels.

MR-Guided High-Power Microwave Ablation in Hepatic Malignancies: Initial Results in Clinical Routine

PURPOSE

Evaluation of technique effectiveness, patient safety and ablation parameters of MR-guided microwave ablation in hepatic malignancies using an MR-conditional high-power microwave ablation system.

MATERIALS AND METHODS

Institutional review board approval and informed patient consent were obtained. Patients who underwent MR-guided microwave ablation of hepatic malignancies in a 1.5T wide-bore scanner using a perfusion-cooled high-power microwave ablation system with a maximum generator power of 150 W were included. Ablation parameters comprising procedure durations, net ablation duration, applicator positions and ablation zone dimensions were recorded. Adverse events were classified according to the CIRSE classification system. Technique effectiveness was assessed after 1 month. Follow-up was conducted with contrast-enhanced MRI and ranged from 1 to 20 months (mean: 6.1 ± 5.4 months).

RESULTS

Twenty-one consecutive patients (age: 63.4 ± 10.5 years; 5 female) underwent 22 procedures for 28 tumours (9 hepatocellular carcinomas, 19 metastases) with a mean tumour diameter of 14.6 ± 5.4 mm (range: 6-24 mm). Technique effectiveness was achieved in all lesions. Tumours were treated using 1.7 ± 0.7 applicator positions (range: 1-3). Mean energy and ablation duration per tumour were 75.3 ± 35.4 kJ and 13.3 ± 6.2 min, respectively. Coagulation zone short- and long-axis diameters were 29.1 ± 6.4 mm and 39.9 ± 7.4 mm, respectively. Average procedure duration was 146.4 ± 26.2 min (range: 98-187 min). One minor complication was reported. Five patients developed new tumour manifestations in the untreated liver. Local tumour progression was not observed during initial follow-up.

CONCLUSION

MR-guided high-power microwave ablation provides safe and effective treatment of hepatic malignancies with short ablation times and within acceptable procedure durations.

Adaptation of Dictionary Learning for Electrode Displacement Elastography. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020;2020:2023-2026. [PMID: 33018401 PMCID: PMC7538652 DOI: 10.1109/embc44109.2020.9175319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Microwave ablation has become a common treatment method for liver cancers. Unfortunately, microwave ablation success is correlated with clinician's ability for proper electrode placement and assess ablative margins, requiring accurate imaging of liver tumors and ablated zones. Conventionally, ultrasound and computed tomography are utilized for this purpose, yet both have their respective drawbacks. As an alternate approach, electrode displacement elastography offers promise but is still plagued by decorrelation artifacts reducing lesion depiction and visualization. A recent filtering method, namely dictionary representation, has improved contrast-to-noise ratios without reducing delineation contrast. As a supplement to this recent work, this paper evaluates adaptations on this initial dictionary-learning algorithm and applies them to an EDE phantom and 15 in-vivo patient datasets. Two new adaptations of dictionary representations were evaluated, namely a combined dictionary and magnitude-based dictionary representation. When comparing numerical results, the combined dictionary representation algorithm outperforms the previous developed dictionary representation in signal-to-noise (1.54 dB) and contrast-to-noise (0.67 dB) ratios, while a magnitude dictionary representation produces higher noise levels, but improves visualized strain tensor resolution.

Simulated accuracy assessment of small footprint body-mounted probe alignment device for MRI-guided cryotherapy of abdominal lesions

PURPOSE

Magnetic resonance imaging (MRI)-guided percutaneous cryotherapy of abdominal lesions, an established procedure, uses MRI to guide and monitor the cryoablation of lesions. Methods to precisely guide cryotherapy probes with a minimum amount of trial-and-error are yet to be established. To aid physicians in attaining precise probe alignment without trial-and-error, a body-mounted motorized cryotherapy-probe alignment device (BMCPAD) with motion compensation was clinically tested in this study. The study also compared the contribution of body motion and organ motion compensation to the guidance accuracy of a body-mounted probe alignment device.

METHODS

The accuracy of guidance using the BMCPAD was prospectively measured during MRI-guided percutaneous cryotherapies before insertion of the probes. Clinical parameters including patient age, types of anesthesia, depths of the target, and organ sites of target were collected. By using MR images of the target organs and fiducial markers embedded in the BMCPAD, we retrospectively simulated the guidance accuracy with body motion compensation, organ motion compensation, and no compensation. The collected data were analyzed to test the impact of motion compensation on the guidance accuracy.

RESULTS

Thirty-seven physical guidance of probes were prospectively recorded for sixteen completed cases. The accuracy of physical guidance using the BMCPAD was 13.4 ± 11.1 mm. The simulated accuracy of guidance with body motion compensation, organ motion compensation, and no compensation was 2.4 ± 2.9 mm, 2.2 ± 1.6 mm, and 3.5 ± 2.9 mm, respectively. Data analysis revealed that the body motion compensation and organ motion compensation individually impacted the improvement in the accuracy of simulated guidance. Moreover, the difference in the accuracy of guidance either by body motion compensation or organ motion compensation was not statistically significant. The major clinical parameters impacting the accuracy of guidance were the body and organ motions. Patient age, types of anesthesia, depths of the target, and organ sites of target did not influence the accuracy of guidance using BMCPAD. The magnitude of body surface movement and organ movement exhibited mutual statistical correlation.

CONCLUSIONS

The BMCPAD demonstrated guidance accuracy comparable to that of previously reported devices for CT-guided procedures. The analysis using simulated motion compensation revealed that body motion compensation and organ motion compensation individually impact the improvement in the accuracy of device-guided cryotherapy probe alignment. Considering the correlation between body and organ movements, we also determined that body motion compensation using the ring fiducial markers in the BMCPAD can be solely used to address both body and organ motions in MRI-guided cryotherapy.

Microwave ablation of hepatic malignant tumors using 1.5T MRI guidance and monitoring: feasibility and preliminary clinical experience

Purpose: To evaluate the feasibility and therapeutic efficacy of 1.5-T MRI-guided and monitored microwave ablation in patients with hepatic malignant tumors.Materials and Methods: This retrospective study was approved by the ethics committee of the First Affiliated Hospital of Fujian Medical University. Thirty-five patients (32 men, three women) with 48 lesions (maximum diameter < 3 cm) underwent microwave ablation under the guidance and monitoring of a 1.5-T MRI. The MRI-compatible microwave generator was appended with a magnetic shield case, and the cable was combined with a choke coil for shielding the Larmor processing frequency. The average age of the patients was 56.51 ± 11.36 years (31-77 years). Twenty-eight patients (37 lesions) displayed hepatocellular carcinoma and seven patients (11 lesions) had metastatic liver carcinoma. The mean maximum tumor diameter was 12.31 ± 4.72 mm (range 5.0-25.7 mm).Results: MRI scans were performed simultaneously without electromagnetic interference during ablation. The average maximum diameter of the hypointense zone of the last monitored T2WI sequence, hypointense zone of post-procedure T2WI sequence, and hyperintense zone of post-procedure T1WI were 28.82 ± 7.58 mm, 29.79 ± 7.91 mm, and 28.28 ± 8.37 mm, respectively, with no observed statistical difference (F = 0.434, p = .649). The technical success rate was 100%. The average follow-up duration was 11.43 ± 5.29 (4-33) months. The technique efficacy rate was 100%.Conclusion: MRI-guided and monitored microwave ablation of hepatic malignant tumors is feasible and potentially safe and effective.Key pointsMRI-guided microwave ablation of hepatic malignant tumors is feasible.The MRI monitoring scan could accurately reflect the scope of ablation lesion.On T1WI, the ablation lesions of liver showed the 'target sign'.

A novel microwave tool for robotic liver resection in minimally invasive surgery

Introduction: During the last two decades, many surgical procedures have evolved from open surgery to minimally invasive surgery (MIS). This limited invasiveness has motivated the development of robotic assistance platforms to obtain better surgical outcomes. Nowadays, the da Vinci robot is a commercial tele-robotic platform widely used for different surgical applications.Material and methods: In this work, the da Vinci Research Kit (dVRK), namely the research version of the da Vinci, is used to manipulate a novel microwave device in a teleoperation scenario. The dVRK provides an open source platform, so that the novel microwave tool, dedicated to prevention bleeding during hepatic resection surgery, is mechanically integrated on the slave side, while the software interface is adapted in order to correctly control tool pose. Tool integration is validated through in-vitro and ex-vivo tests performed by expert surgeons, meanwhile the coagulative efficacy of the developed tool in a perfused liver model was proved in in-vivo tests.Results and conclusions: An innovative microwave tool for liver robotic resection has been realized and integrated into a surgical robot. The tool can be easily operated through the dVRK without limiting the intuitive and friendly use, and thus easily reaching the hemostasis of vessels.

Improved MR-thermometry during hepatic microwave ablation by correcting for intermittent electromagnetic interference artifacts

MRI-guided microwave ablation (MWA) is a minimally invasive treatment for localized cancer. MR thermometry has been shown to be able to provide vital information for monitoring the procedure in real-time. However, MRI during active MWA can suffer from image quality degradation due to intermittent electromagnetic interference (EMI). A novel approach to correct for EMI-contaminated images is presented here to improve MR thermometry during clinical hepatic MWA. The method was applied to MR-thermometry images acquired during four MR-guided hepatic MWA treatments using a commercially available MRI-configured microwave generator system. During the treatments MR thermometry data acquisition was synchronized to respiratory cycle to minimize the impact of motion. EMI was detected and corrected using uncontaminated k-space data from nearby frames in k-space. Substantially improved temperature and thermal damage maps have been obtained and the treatment zone can be better visualized. Our ex vivo tissue sample study shows the correction introduced minimal errors to the temperature maps and thermal damage maps.

In vivo ultrasound thermal ablation control using echo decorrelation imaging in rabbit liver and VX2 tumor

The utility of echo decorrelation imaging feedback for real-time control of in vivo ultrasound thermal ablation was assessed in rabbit liver with VX2 tumor. High-intensity focused ultrasound (HIFU) and unfocused (bulk) ablation were performed using 5 MHz linear image-ablate arrays. Treatments comprised up to nine lower-power sonications, followed by up to nine higher-power sonications, ceasing when the average cumulative echo decorrelation within a control region of interest exceeded a predefined threshold (- 2.3, log10-scaled echo decorrelation per millisecond, corresponding to 90% specificity for tumor ablation prediction in previous in vivo experiments). This threshold was exceeded in all cases for both HIFU (N = 12) and bulk (N = 8) ablation. Controlled HIFU trials achieved a significantly higher average ablation rate compared to comparable ablation trials without image-based control, reported previously. Both controlled HIFU and bulk ablation trials required significantly less treatment time than these previous uncontrolled trials. Prediction of local liver and VX2 tumor ablation using echo decorrelation was tested using receiver operator characteristic curve analysis, showing prediction capability statistically equivalent to uncontrolled trials. Compared to uncontrolled trials, controlled trials resulted in smaller thermal ablation regions and higher contrast between echo decorrelation in treated vs. untreated regions. These results indicate that control using echo decorrelation imaging may reduce treatment duration and increase treatment reliability for in vivo thermal ablation.

Practical implementation of robust MR-thermometry during clinical MR-guided microwave ablations in the liver at 1.5 T

Practical non-invasive equipment modifications and effective acquisition methods to achieve robust and reliable real-time MR thermometry for monitoring of clinical hepatic microwave ablations were implemented. These included selection of the microwave generator location (inside versus outside the MR scan room), the number of radiofrequency chokes added to the microwave generator's coaxial lines, and the use of copper wool to maximize their electrical grounding. Signal-to-noise ratio (SNR) of MR thermometry images of a small fluid-filled phantom acquired during activation of microwave antenna were used to evaluate image quality as a function of each modification. SNR measurements corresponding to both locations of the microwave generator were comparable and so it was located outside the MR scan room. For this location, addition of one RF choke on the power and four chokes on the sensor coaxial lines was found to be optimal, corresponding to a 68% increase in SNR. Furthermore, image quality strongly depended on the proper electrical grounding of the power and sensor lines. SNR ratio (relative to SNR of baseline images) during activation of microwave generator was found to be 0.49 ± 0.28 without adequate grounding, and 0.88 ± 0.08 with adequate grounding (p = 0.002, Student's t-test). These SNR measurements were sufficiently sensitive to detect issues related to equipment performance and hence formed part of the quality assurance testing performed prior to each clinical treatment. Incorporating these non-invasive approaches resulted in significant improvements to image quality and, importantly while maintaining the clinical integrity of the microwave system which is of paramount importance in a highly regulated healthcare environment.

Artefact and ablation performance of an MR-conditional high-power microwave system in bovine livers: an ex vivo study

Background

We evaluated a magnetic resonance (MR)-conditional high-power microwave ablation system.

Methods

An exvivo 1.5-T evaluation was conducted by varying the sequence (T1-weighted volume interpolated breath-hold examination, T1w-VIBE; T1-weighted fast low-angle shot, T1w-FLASH; T2-weighted turbo spin-echo, T2w-TSE), applicator angulation to B₀ (A-to-B₀), slice orientation, and encoding direction. Tip location error (TLE) and artefact diameters were measured, and influence of imaging parameters was assessed with analysis of variance and post hoc testing. Twenty-four exvivo ablations were conducted in three bovine livers at 80 W and 120 W. Ablation durations were 5, 10, and 15 min. Ablation zones were compared for short-axis diameter (SAD), volume, and sphericity index (SI) with unpaired t test.

Results

The artefact pattern was similar for all sequences. The shaft artefact (4.4 ± 2.9 mm, mean ± standard deviation) was dependent on the sequence (p = 0.012) and the A-to-B₀ (p < 0.001); the largest shaft diameter was measured with T1w-FLASH (6.3 ± 3.4 mm) and with perpendicular A-to-B₀ (6.7 ± 2.4 mm). The tip artefact (1.6 ± 0.7 mm) was dependent on A-to-B₀ (p = 0.001); TLE was -2.6 ± 1.0 mm. Ablation results at the maximum setting (15 min, 120 W) were SAD = 42.0 ± 1.41 mm; volume = 56.78 ± 3.08 cm³, SI = 0.68 ± 0.05. In all ablations, SI ranged 0.68–0.75 with the smallest SI at 15 min and 120 W (p = 0.048).

Conclusion

The system produced sufficiently large ablation zones and the artefact was appropriate for MR-guided interventions.

A variable flip angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonant frequency shift and T1 -based thermometry

PURPOSE

To develop and evaluate a variable-flip-angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonance frequency shift (PRF) and T₁ -based thermometry in aqueous and adipose tissues, respectively.

METHODS

The proposed technique acquires multiecho radial k-space data in segments with alternating flip angles to measure 3D temperature maps dynamically on the basis of PRF and T₁ . A sliding-window k-space weighted image contrast filter is used to increase temporal resolution. PRF is measured in aqueous tissues and T₁ in adipose tissues using fat/water masks. The accuracy for T₁ quantification was evaluated in a reference T₁ /T₂ phantom. In vivo nonheating experiments were conducted in healthy subjects to evaluate the stability of PRF and T₁ in the brain, prostate, and breast. The proposed technique was used to monitor high-intensity focused ultrasound (HIFU) ablation in ex vivo porcine fat/muscle tissues and compared to temperature probe readings.

RESULTS

The proposed technique achieved 3D coverage with 1.1-mm to 1.3-mm in-plane resolution and 2-s to 5-s temporal resolution. During 20 to 30 min of nonheating in vivo scans, the temporal coefficient of variation for T₁ was <5% in the brain, prostate, and breast fatty tissues, while the standard deviation of relative PRF temperature change was within 3°C in aqueous tissues. During ex vivo HIFU ablation, the temperatures measured by PRF and T₁ were consistent with temperature probe readings, with an absolute mean difference within 2°C.

CONCLUSION

The proposed technique achieves simultaneous PRF and T₁ -based dynamic 3D MR temperature mapping in aqueous and adipose tissues. It may be used to improve MRI-guided thermal procedures.

Monitoring Microwave Ablation Using Ultrasound Echo Decorrelation Imaging: An ex vivo Study

In this study, a microwave-induced ablation zone (thermal lesion) monitoring method based on ultrasound echo decorrelation imaging was proposed. A total of 15 cases of ex vivo porcine liver microwave ablation (MWA) experiments were carried out. Ultrasound radiofrequency (RF) signals at different times during MWA were acquired using a commercial clinical ultrasound scanner with a 7.5-MHz linear-array transducer. Instantaneous and cumulative echo decorrelation images of two adjacent frames of RF data were calculated. Polynomial approximation images were obtained on the basis of the thresholded cumulative echo decorrelation images. Experimental results showed that the instantaneous echo decorrelation images outperformed conventional B-mode images in monitoring microwave-induced thermal lesions. Using gross pathology measurements as the reference standard, the estimation of thermal lesions using the polynomial approximation images yielded an average accuracy of 88.60%. We concluded that instantaneous ultrasound echo decorrelation imaging is capable of monitoring the change of thermal lesions during MWA, and cumulative ultrasound echo decorrelation imaging and polynomial approximation imaging are feasible for quantitatively depicting thermal lesions.

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.

Optimized Echo Decorrelation Imaging Feedback for Bulk Ultrasound Ablation Control

Feasibility of controlling bulk ultrasound (US) thermal ablation using echo decorrelation imaging was investigated in ex vivo bovine liver. The first of two ablation and control procedures used a sequence of constant-intensity sonication cycles, ceased when the minimum echo decorrelation within a control region of interest (ROI) exceeded a predetermined threshold. The second procedure used a variable-intensity sonication sequence, with spatially averaged decorrelation as the stopping criterion. US exposures and echo decorrelation imaging were performed by a linear image-ablate array. Based on preliminary experiments, control ROIs and thresholds for the minimum-decorrelation and average-decorrelation criteria were specified. Controlled trials for the minimum-decorrelation and average-decorrelation criteria were compared with uncontrolled trials employing 9 or 18 cycles of matching sonication sequences. Lesion dimensions, treatment times, ablation rates, and areas under receiver operating characteristic curves were statistically compared. Successfully controlled trials using both criteria required significantly shorter treatment times than corresponding 18-cycle treatments, with better ablation prediction performance than uncontrolled 9-cycle and 18-cycle treatments. Either control approach resulted in greater ablation rate than corresponding 9-cycle or 18-cycle uncontrolled approaches. A post hoc analysis studied the effect of exchanging control criteria between the two series of controlled experiments. For either group, the average time needed to exceed the alternative decorrelation threshold approximately matched the average duration of successfully controlled experimental trials. These results indicate that either approach, using minimum-decorrelation or average-decorrelation criteria, is feasible for control of bulk US ablation. In addition, use of a variable-intensity sonication sequence for bulk US thermal ablation can result in larger ablated regions compared to constant-intensity sonication sequences.

Feasibility, efficacy, and safety of percutaneous MR-guided ablation of small (≤12 mm) hepatic malignancies

BACKGROUND

Percutaneous tumor ablation is commonly performed using computed tomography (CT) or ultrasound (US) guidance, although reliable visualization of the target tumor may be challenging. MRI guidance provides more reliable visualization of target tumors and allows for real-time imaging and multiplanar capabilities, making it the modality of choice, in particular if lesions are small.

PURPOSE

To investigate the feasibility, technical success, and safety of percutaneous MR-guided ablation (RFA n = 27 / MWA n = 16) of small (≤12 mm) hepatic malignancies.

STUDY TYPE

Retrospective case study.

POPULATION

In all, 45 patients (age: 61.1 ± 11.8) with hepatic malignancies and a lesion diameter of ≤12 mm scheduled for percutaneous MR-guided tumor ablation based on a tumor board decision were included.

FIELD STRENGTH

A 1.5T MR system was used for planning, targeting, and monitoring.

ASSESSMENT

Feasibility assessment included the detection of the target tumor, tumor delineation during MR-fluoroscopy guided targeting, and the number of attempts needed for precise applicator placement. Technical success was defined as successful performance of the procedure including a safety margin of 5 mm. Safety evaluation was based on procedure-related complications.

STATISTICAL TEST

Frequency.

RESULTS

Tumor ablation (mean diameter 9.0 ± 2.1 mm) was successfully completed in 43/45 patients. Planning imaging was conducted without a contrast agent in 79% (n = 37). In 64% (n = 30), the target tumors were visible with MR-fluoroscopy. In six patients (13%), planning imaging revealed new, unexpected small lesions, which were either treated in the same session (n = 4) or changed therapy management (n = 2) due to diffuse tumor progress. Postprocedural imaging revealed a technical success of 100% (43/43), with no major complications. During follow-up, no local tumor progression was observed (mean follow-up 24.7 ± 14.0 months) although 28% (12) patients developed new hepatic lesions distant to the ablation zone. No major complications were observed.

DATA CONCLUSION

MR-guided ablation is a feasible approach for an effective and safe treatment of small hepatic malignancies.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2019;49:374-381.

Microwave ablation combined with doxorubicin enhances cell death via promoting reactive oxygen species generation in breast cancer cells

PURPOSE

To evaluate the mechanism for enhancing cell death induced by microwave ablation (MWA) combined with doxorubicin treatment in breast cancer cells.

MATERIALS AND METHODS

Different temperatures of heat treatment were used to mimic the tumor affected by sublethal heat during MWA in vitro. Breast cancer cells were treated at 43°C and 45°C, with or without doxorubicin. Cell viability, apoptosis, and intracellular reactive oxygen species (ROS) were evaluated in MDA-MB-231 and SUM-1315 cells. Nude mice breast cancer models were randomly divided into control, MWA, doxorubicin, and combined treatment groups. Tumor apoptosis and DNA damage were evaluated in these groups.

RESULTS

The combined group had lower cell viability than the heat or doxorubicin group (all P<0.05), and enhanced apoptosis rate was observed in the combined group compared to others (all P<0.01) in MDA-MB-231 and SUM-1315. Increased capase3 (all P<0.01) and decreased Bcl-Xl (all P<0.01) were detected after combined therapy compared to single treated group in vitro. The raisedCaspase3 and DNA damage marker histone H2A.X induced by combined treatment were also approved in the nude mice models. Combined treatment promoted ROS generation compared to doxorubicin or MWA treatment (all P < 0.01). NF-κB expression in the combined group was higher than that of the single treatment group (all P<0.05). N-acetylcysteine (NAC), a ROS scavenger, partly restrained the combined treatment induced cell proliferation inhibition, Caspase3 and NF-κB compared to doxorubicin treatment (all P<0.05).

CONCLUSION

MWA combined with doxorubicin promote cell death via ROS induced cell apoptosis and DNA damage. Increasing ROS has potential for improving the efficiency of combined treatment.

Percutaneous Liver Tumour Ablation: Image Guidance, Endpoint Assessment, and Quality Control

Liver tumour ablation nowadays represents a routine treatment option for patients with primary and secondary liver tumours. Radiofrequency ablation and microwave ablation are the most widely adopted methods, although novel techniques, such as irreversible electroporation, are quickly working their way up. The percutaneous approach is rapidly gaining popularity because of its minimally invasive character, low complication rate, good efficacy rate, and repeatability. However, matched to partial hepatectomy and open ablations, the issue of ablation site recurrences remains unresolved and necessitates further improvement. For percutaneous liver tumour ablation, several real-time imaging modalities are available to improve tumour visibility, detect surrounding critical structures, guide applicators, monitor treatment effect, and, if necessary, adapt or repeat energy delivery. Known predictors for success are tumour size, location, lesion conspicuity, tumour-free margin, and operator experience. The implementation of reliable endpoints to assess treatment efficacy allows for completion-procedures, either within the same session or within a couple of weeks after the procedure. Although the effect on overall survival may be trivial, (local) progression-free survival will indisputably improve with the implementation of reliable endpoints. This article reviews the available needle navigation techniques, evaluates potential treatment endpoints, and proposes an algorithm for quality control after the procedure.

A Radiologist's View of Tumor Ablation in the Radiology Suite

Image-guided percutaneous, minimally invasive ablation techniques offer a wide variety of new modalities to treat tumors in some of the most medically complicated patients coming to our hospitals. The use of computed tomography, PET, ultrasound imaging, and MRI to guide radiofrequency ablation, microwave ablation, and cryoablation techniques now makes it possible to treat patients on a short stay or outpatient basis with very good immediate outcomes. This rapid expansion of new tumor ablation techniques often presents challenges for the non-operating room anesthesia team. Collaboration and communication between the radiologist and anesthesiologist are key to safety and excellent patient outcomes.

[Percutaneous renal ablation: Pre-, per-, post-interventional evaluation modalities and adapted management]

OBJECTIVES

Ablative treatment (AT) rise is foreseen, validation of steps to insure good proceedings is needed. By looking over the process of the patient, this study evaluates the requirements and choices needed in every step of the management.

METHODS

We searched MEDLINE^®, Embase^®, using (MeSH) words and we looked for all the studies. Investigators graded the strength of evidence in terms of methodology, language and relevance.

RESULTS

Explanations of AT proposal rather than partial nephrectomy or surveillance have to be discussed in a consultation shared by urologist and interventional radiologist. Per-procedure choices depend on predictable ballistic difficulties. High volume, proximity of the hilum or of a risky organ are in favor of general anesthesia, cryotherapy and computed tomography/magnetic resonance imaging (CT/MRI). Percutaneous approach should be privileged, as it seems as effective as the laparoscopic approach. Early and delayed complications have to be treated both by urologist and radiologist. Surveillance by CT/MRI insure of the lack of contrast-enhanced in the treated area. Patients and tumors criteria, in case of incomplete treatment or recurrence, are the key of the appropriate treatment: surgery, second session of AT, surveillance.

CONCLUSION

AT treatments require patient's comprehension, excellent coordination of the partnership between urologist and radiologist and relevant choices during intervention.

[Image-guided tumor ablation]

INTRODUCTION

Ablatives techniques for destroying in situ a tumoral process aim tissular necrosis by the application of several physical principles.

MATERIAL AND METHODS

We searched MEDLINE^®, Embase^®, using (MeSH) words; from January 2005 through May 2017, and we looked for all the studies. Investigators graded the strength of evidence in terms of methodology, language and relevance.

RESULTS

Forty-seven articles were analyzed. We described ablative techniques and sorted them in thermal and non-thermal therapies according to the used physical principle and their frequency of use in the urological pathology.

CONCLUSION

Percutaneous ablative therapies are mini-invasive techniques, which have an important role in tumors focal treatment. This article is a review of the ablative therapies and describes their physical principles, their equipment and their recent technological modifications, which have been developed to improve the clinical success of these techniques.

Early assessment of coagulation necrosis after hepatic microwave ablation: a comparison of non-enhanced and enhanced T1-weighted images

PURPOSE

To compare the technical success and accuracy of hepatic microwave ablation (MWA) using non-enhanced and enhanced T1-weighted imaging early after ablation. Patients were evaluated with regard to the ablation zone and local tumor progression (LTP).

METHODS

This retrospective study conducted between September 2014 and December 2015 which consisted of 56 patients with 56 hepatic malignant lesions who underwent percutaneous MWA. Non-enhanced and contrast-enhanced T1-weighted imagings were performed within 2 days after tumor ablation. The efficacy of ablation assessed according to the hyperintense middle zone on non-enhanced T1-weighted images and the non-enhanced area on contrast-enhanced T1-weighted images were compared. The development of LTP during ≥7 months of follow-up served as the end point.

RESULTS

On the non-enhanced T1-weighted images, the ablated region had a characteristic two-zone structure featuring a hyperintense middle zone and a surrounding hypointense band. Among the 56 patients, LTP developed in ten including seven lesions, in which both the non-enhanced T1-weighted and portal-phase images showed incomplete tumor ablation. In two of the remaining three patients, incomplete tumor ablation was detected on the non-enhanced T1-weighted images, whereas the corresponding portal-phase images showed complete ablation. In the remaining patient, no residual tumor was detected on either the non-enhanced T1-weighted or the portal-phase images. In the 46 patients without LTP, there was no evidence of residual tumor on the non-enhanced T1-weighted or portal-phase images obtained early after ablation.

CONCLUSIONS

Non-enhanced T1-weighted images are useful in assessing the therapeutic efficacy of MWA of liver tumors early after the procedure.