Sonographically observed echogenic response during intraoperative radiofrequency ablation of cirrhotic livers: pathologic correlation

MR-guided percutaneous microwave coagulation of small breast tumors

BACKGROUND

To evaluate the technical success and patient safety of magnetic resonance-guided percutaneous microwave coagulation (MR-guided PMC) for breast malignancies.

METHODS

From May 2018 to December 2019, 26 patients with breast tumors measuring 2 cm or less were recruited to participate in a prospective, single-institution clinical study. The primary endpoint of this study was the evaluation of treatment efficacy for each patient. Histochemical staining with α-nicotinamide adenine dinucleotide and reduced (NADH)-diaphorase was used to determine cell viability following and efficacy of PMC. The complications and self-reported sensations from all patients during and after ablation were also assessed. The technical success of the PMC procedure was defined when the area of the NADH-diaphorase negative region fully covered the hematoxylin-eosin (H&E) staining region in the tumor.

RESULTS

All patients had a complete response to ablation with no residual carcinoma on histopathological specimen. The mean energy, ablation duration, and procedure duration per tumor were 36.0 ± 4.2 kJ, 252.9 ± 30.9 S, and 104.2 ± 13.5 min, respectively. During the ablation, 14 patients underwent prolonged ablation time, and 1 patient required adjusting of the antenna position. Eleven patients had feelings of subtle heat or swelling, and 3 patients experienced slight pain. After ablation, one patient took two painkillers because of moderate pain, and no patients had postoperative oozing or other complications after PMC. Induration around the ablation area appeared in 16 patients.

CONCLUSION

MR-guided PMC of small breast tumors is feasible and could be applied in clinical practice in the future.

CRITICAL RELEVANCE STATEMENT

MR-guided PMC of small breast tumors is feasible and could be applied in clinical practice in the future.

KEY POINTS

• MR-guided PMC of small breast tumors is feasible. • PMC was successfully performed for all patients. • All patients were satisfied with the final cosmetic result.

Intra-operative High-Intensity Focused Ultrasound in Patients With Colorectal Liver Metastases: A Prospective Ablate-and-Resect Study

OBJECTIVE

High-intensity focused ultrasound (HIFU) is a recent, non-ionizing and non-invasive technology of focal destruction. Independence from the heat-sink effect of blood flow makes HIFU an interesting technique for focal ablation of liver tumors. Current available technology is based on extracorporeal treatment that limits use of HIFU for the treatment of liver tumors, as elementary ablations are small and must be juxtaposed to treat tumors, resulting in long-duration treatment. We developed an HIFU probe with toroidal technology, which increases the volume of ablation, for intra-operative use, and we assessed the feasibility and efficacy of this device in patients with colorectal liver metastasis (CLM) measuring less than 30 mm.

METHODS

This study was an ablate-and-resect, prospective, single-center, phase II study. All ablations were performed in the area of liver scheduled for liver resection to avoid loss of chance of recovery. The primary objective was to ablate CLM with safety margins (>5 mm).

RESULTS

Between May 2014 and July 2020, 15 patients were enrolled and 24 CLM were targeted. The HIFU ablation time was 370 s. In total, 23 of 24 CLM were successfully treated (95.8%). No damage occurred to extrahepatic tissues. HIFU ablations were oblate shaped with an average long axis of 44.3 ± 6.1 mm and an average shortest axis of 35.9 ± 6.7 mm. On pathological examination, the average diameter of the treated metastasis was 12.2 ± 4.8 mm.

CONCLUSION

Intra-operative HIFU can safely and accurately produce large ablations in 6 min with real-time guidance (ClinicalTrials.gov identifier: NCT01489787).

Sensor-Based Automated Detection of Electrosurgical Cautery States

In computer-assisted surgery, it is typically required to detect when the tool comes into contact with the patient. In activated electrosurgery, this is known as the energy event. By continuously tracking the electrosurgical tools' location using a navigation system, energy events can help determine locations of sensor-classified tissues. Our objective was to detect the energy event and determine the settings of electrosurgical cautery-robustly and automatically based on sensor data. This study aims to demonstrate the feasibility of using the cautery state to detect surgical incisions, without disrupting the surgical workflow. We detected current changes in the wires of the cautery device and grounding pad using non-invasive current sensors and an oscilloscope. An open-source software was implemented to apply machine learning on sensor data to detect energy events and cautery settings. Our methods classified each cautery state at an average accuracy of 95.56% across different tissue types and energy level parameters altered by surgeons during an operation. Our results demonstrate the feasibility of automatically identifying energy events during surgical incisions, which could be an important safety feature in robotic and computer-integrated surgery. This study provides a key step towards locating tissue classifications during breast cancer operations and reducing the rate of positive margins.

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

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

Use of Contrast-Enhanced Ultrasound in Ablation Therapy of HCC: Planning, Guiding, and Assessing Treatment Response

Contrast-enhanced ultrasonography (CEUS) plays an important role in the management of patients treated with ablation therapies, in the diagnostic, therapeutic and monitoring phases. Compared to contrast-enhanced computed tomography and contrast-enhanced magnetic resonance imaging, CEUS presents several advantages in imaging HCC, including real time imaging capability, high sensitivity for tumor vascularity, absence of renal toxicity, no ionizing radiation, repeatability of injections, good compliance by the patient and low cost. The purpose of this review is to evaluate the role of CEUS in the management of the patients with HCC treated with ablation therapies and describe how in our protocol CEUS is integrated with the other imaging modalities such as contrast-enhanced computed tomography and contrast-enhanced magnetic resonance imaging.

Feature-based automated segmentation of ablation zones by fuzzy c-mean clustering during low-dose computed tomography

PURPOSE

Intra-procedural monitoring and post-procedural follow-up is necessary for a successful ablation treatment. An imaging technique which can assess the ablation geometry accurately is beneficial to monitor and evaluate treatment. In this study, we developed an automated ablation segmentation technique for serial low-dose, noisy ablation computed tomography (CT) or contrast-enhanced CT (CECT).

METHODS

Low-dose, noisy temporal CT and CECT volumes were acquired during microwave ablation on normal porcine liver (four with non-contrast CT and eight with CECT). Highly constrained backprojection (HYPR) processing was used to recover ablation zone information compromised by low-dose noise. First-order statistic features and normalized fractional Brownian features (NBF) were used to segment ablation zones by fuzzy c-mean clustering. After clustering, the segmented ablation zone was refined by cyclic morphological processing. Automatic and manual segmentations were compared to gross pathology with Dice's coefficient (morphological similarity), while cross-sectional dimensions were compared by percent difference.

RESULTS

Automatic and manual segmentations of the ablation zone were very similar to gross pathology (Dice Coefficients: Auto.-Path. = 0.84 ± 0.02; Manu.-Path. = 0.76 ± 0.03, P = 0.11). The differences in ablation area, major diameter and minor diameter were 17.9 ± 3.2%, 11.1 ± 3.2% and 16.2 ± 3.4%, respectively, when comparing automatic segmentation to gross pathology, which were lower than the differences of 32.9 ± 16.8%, 13.0 ± 9.8% and 21.8 ± 5.8% when comparing manual segmentation to gross pathology. Manual segmentations tended to overestimate gross pathology when ablation area was less than 15 cm2 , but the automated segmentation tended to underestimate gross pathology when ablation zone is larger than 20 cm2 .

CONCLUSION

Fuzzy c-means clustering may be used to aid automatic segmentation of ablation zones without prior information or user input, making serial CT/CECT has more potential to assess treatments intra-procedurally.

Gel Phantom Models for Radiofrequency and Microwave Ablation of the Liver

Heat-based percutaneous thermal ablation techniques have emerged as popular and effective treatments for liver cancer. As the technology continues to evolve, there is a need for optimized methods for experimentation to identify advantageous modifications and developments. Given that assessing and comparing resulting ablation zones in animal models are costly and resource-intensive, in vitro gel phantom models can serve an important role for early-stage experimentation. There exist several gel phantom recipes that have been reported in the literature. In this review, we will review the various recipes, the pros and cons to the existing models, and future potential directions.

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.

Physiological Motion Reduction Using Lagrangian Tracking for Electrode Displacement Elastography

Minimally invasive treatments such as microwave ablation (MWA) have been growing in popularity for extending liver cancer survival rates in patients, when surgery is not an option. As a non-ionizing, real-time alternative to contrast-enhanced computed tomography, electrode displacement elastography (EDE) has shown promise as an imaging modality for MWA. Despite imaging efficacy, motion artifacts caused by physiological motion result in unintended speckle pattern variance, thereby inhibiting consistent and accurate ablated region visualization. To combat these unavoidable motion artifacts, a Lagrangian deformation tracking (LDT) approach based on freehand EDE was developed to track tissue movement and better define tissue properties. For validating LDT efficacy, a spherical inclusion phantom as well as seven in vivo data sets were processed, and strain tensor images were compared with identical time sampled images estimated using a traditional Eulerian approach. In vivo results revealed greater consistency among visualized LDT strain tensor images, with segmented ablated regions exhibiting standard deviation reductions of up to 98% when compared with Eulerian strain tensor images. Additionally, Lagrangian strain tensor images provided Dice coefficient improvements up to 25%, and success rates improved from approximately 50% to nearly 100% for ablated region visualization.

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.

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.

Comparison of the Ablation and Hyperechoic Zones in Different Tissues Using Microwave and Radio Frequency Ablation

OBJECTIVES

The aim of this study was to compare the differences between the ablation region and hyperechoic zones in microwave and radio frequency ablation of different tissues.

METHODS

Microwave and radio frequency ablation were performed on fresh porcine muscle and liver with different power levels for 90 seconds. These 2 ablation methods were then performed on rabbit liver in vivo using 20 W for 60 seconds. The volumes of the ablation and hyperechoic zones were compared following different ablation methods.

RESULTS

The ablation zones were significantly greater than the hyperechoic zones (P < .05) with the same power and duration when using 2 ablation methods. The differences of the ablation and hyperechoic zones between muscle and liver tissues were significantly different (P < .05). The difference values of the ablation and hyperechoic zones were also significantly different (P < .05) using 2 ablation methods.

CONCLUSIONS

The hyperechoic zone may have underestimated the extent of ablation using a specified ablation time. In the same tissue, the hyperechoic zone could more accurately estimate the ablation zones using microwave ablation.

Theranostics in Interventional Oncology: Versatile Carriers for Diagnosis and Targeted Image-Guided Minimally Invasive Procedures

We are continuously progressing in our understanding of cancer and other diseases and learned how they can be heterogeneous among patients. Therefore, there is an increasing need for accurate characterization of diseases at the molecular level. In parallel, medical imaging and image-guided therapies are rapidly developing fields with new interventions and procedures entering constantly in clinical practice. Theranostics, a relatively new branch of medicine, refers to procedures combining diagnosis and treatment, often based on patient and disease-specific features or molecular markers. Interventional oncology which is at the convergence point of diagnosis and treatment employs several methods related to theranostics to provide minimally invasive procedures tailored to the patient characteristics. The aim is to develop more personalized procedures able to identify cancer cells, selectively reach and treat them, and to assess drug delivery and uptake in real-time in order to perform adjustments in the treatment being delivered based on obtained procedure feedback and ultimately predict response. Here, we review several interventional oncology procedures referring to the field of theranostics, and describe innovative methods that are under development as well as future directions in the field.

Clinical application of ultrasound-guided percutaneous microwave ablation for benign breast lesions: a prospective study

BACKGROUND

Background: Benign breast lesions are the most common diseases in adult women, which have been treated with minimally invasive therapies in recent years. Little is known about the feasibility of Microwave ablation (MWA) for benign breast lesion treatment. The primary aim of this prospective study was to evaluate the safety and efficiency of MWA as a potential therapeutic option for benign breast lesions in a single-center cohort study.

METHODS

Women with possibly benign breast lesions based on an ultrasound (US) assessment who were scheduled to undergo MWA between November 2014 to July 2018 were included in the study. The patients underwent conventional US to measure the size of the lesion, Doppler US to assess the vascularity of the lesion, elastography to evaluate the stiffness of the mass, core needle biopsy of suspicious lesions, contrast-enhanced US to help determine the treatment plan and eventually MWA of the lesion. Lesions were followed at one, three, six, twelve and eighteen months after treatment to with the same imaging modalities.

RESULTS

A total of 314 women aged 17 to 69 years old (mean = 36.9 ± 9.9 years) with 725 benign breast lesions (mean of maximum diameter = 10.86 ± 5.40 mm) were included. The frequency of palpable mass, pain and nipple discharge significantly decreased after treatment. Complete ablation rate was 97.8%, immediately after ablation, which increased to 100% after supplementary ablation of the 15 cases with incomplete ablation. Blood flow classification and lesion's volume also showed a significant decrease, while both volume reduction ratio and disappearance rate significantly increased following treatment. The elasticity score of the lesions showed fluctuations across different follow-up intervals. None of the patients experienced major complications and the 1% who had mild symptoms were successfully treated.

CONCLUSION

MWA treatment is shown to be safe and efficient and has the potential to be considered as an alternative first line treatment for benign breast lesions.

Superb Microvascular Imaging Compared with Contrast-Enhanced Ultrasound for Assessing Laser Ablation Treatment of Benign Thyroid Nodules

Purpose

To compare superb microvascular imaging (SMI) with contrast-enhanced ultrasonography (CEUS) for evaluating the ablation of benign thyroid nodules.

Methods

225 Patients with 256 benign thyroid nodules underwent conventional ultrasound, color Doppler flow imaging (CDFI), CEUS, and SMI before and after laser ablation. They were routinely followed up at 1, 3, 6, and 12 months. The volume and volume reduction rate of the ablated nodules was calculated.

Results

On SMI, the complete ablated nodules had no microvascular perfusion, while the incompletely ablated nodules had microvascular perfusion at the edge of the nodule. The percentages of the detected incompletely ablated nodules of SMI (37/256, 14.45%) and CEUS (41/256, 16.02%) were comparable, and both were significantly higher than CDFI (P< 0.001). CEUS was used as the criterion to determine whether the nodules were completely ablated. The sensitivity, specificity, and accuracy of SMI for detecting incompletely ablated nodules were 90.2, 98.2, and 100%, respectively. The volume of ablated nodules, as measured on ultrasound, was greater than that on CEUS or SMI (both P< 0.001), while CEUS and SMI were similar. The average volume reduction rate of nodules at 1, 3, 6, and 12 months was 40.25, 54.98, 76.83, and 95.43%, respectively.

Conclusion

SMI sensitively detected the capillaries within residual thyroid nodules after laser ablation. The lesion size and detection rate of incompletely ablated nodules via SMI was consistent with that of CEUS. SMI may replace CEUS in certain cases for monitoring the curative effect of laser ablation for benign thyroid nodules.

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.

Time and temperature dependence of radiofrequency ablation in the human placenta

OBJECTIVE

The objective of the study is to compare radiofrequency (RF) effects on fresh placentae with varying levels of sustained time (Ts) and degrees of target temperature (°t).

METHOD

A total of 108 pieces of fresh placentae were coagulated with a 2-cm RF needle at 60 W in an organ bath. The vertical and horizontal diameters (Vd, Hd) of tissue coagulation visualized by ultrasound were measured. The impacts of 12 different Ts-°t combinations on the ablation size ascertained on pathological examination (Vd_p , Hd_p ) were compared using 2-way ANOVA. The agreement between sonographic and pathological findings was assessed using Bland-Altman analysis.

RESULTS

Considerable changes in the Vd_p and Hd_p were associated with increasing the Ts and °t. The impact of RF on tissue coagulation was greatest when the °t was set at 100°C, with further destruction as the Ts progressed to 7 minutes of exposure. The ablation size estimated by ultrasound exhibited an overestimation by an average of 5.65% and 21.02% for Vd and Hd, respectively.

CONCLUSION

A prolonged Ts at a higher °t contributes to progressive placental tissue destruction by RF, with maximum destruction at 100°C for 7 minutes in an ex vivo nonperfused placenta. Tissue injury that is apparent on ultrasound may extend beyond pathological damage.

Ultrasound-ultrasound image overlay fusion improves real-time control of radiofrequency ablation margin in the treatment of hepatocellular carcinoma

OBJECTIVES

To assess the clinical feasibility of US-US image overlay fusion with evaluation of the ablative margin in radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC).

METHODS

Fifty-three patients with 68 HCCs measuring 0.9-4.0 cm who underwent RFA guided by US-US overlay image fusion were included in this retrospective study. By an overlay of pre-/postoperative US, the tumor image could be projected onto the ablative hyperechoic zone. Therefore, the ablative margin three-dimensionally could be shown during the RFA procedure. US-US image overlay was compared to dynamic CT a few days after RFA for assessment of early treatment response. Accuracy of graded response was calculated, and the performance of US-US image overlay fusion was compared with that of CT using a Kappa agreement test.

RESULTS

Technically effective ablation was achieved in a single session, and 59 HCCs (86.8 %) succeeded in obtaining a 5-mm margin on CT. The response with US-US image overlay correctly predicted early CT evaluation with an accuracy of 92.6 % (63/68) (k = 0.67; 95 % CI: 0.39-0.95).

CONCLUSION

US-US image overlay fusion can be proposed as a feasible guidance in RFA with a safety margin and predicts early response of treatment assessment with high accuracy.

KEY POINTS

• US-US image overlay fusion visualizes the ablative margin during RFA procedure. • Visualizing the margin during the procedure can prompt immediate complementary treatment. • US image fusion correlates with the results of early evaluation CT.

Ablation zone visualization enhancement by periodic contrast-enhancement computed tomography during microwave ablation

PURPOSE

Intra-procedural contrast-enhanced computed tomography (CECT) has been proposed to monitor the growth of thermal ablations. The primary challenge with multiple CT acquisitions is reducing radiation dose while maintaining sufficient image quality. The purpose of this study was to evaluate the feasibility of applying local highly constrained backprojection reconstruction (HYPR-LR) on periodic CECT images acquired with low-dose protocols, and to determine whether the ablations visible on CT were commensurate to gross pathology.

METHODS

Low-dose (CTDIvol≤1.49mGy), temporal CECT volumes were acquired during microwave ablation on normal porcine liver. HYPR processing was performed on each volume after image registration. Ablation signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were collected to evaluate the degree of enhancement of image quality and ablation zone visualization. Ablation zones were manually segmented on HYPR and non-HYPR images and compared spatially using Dice's coefficient. The dimensions of ablation zones were also compared to gross pathology by correlation and dimensional differences.

RESULTS

The SNR and CNR of ablation zones were increased after HYPR processing. The manually segmented ablation zone was highly similar to gross pathology with a Dice coefficient of 0.81 ± 0.03, while the low-dose CECT had a smaller Dice coefficient of 0.72 ± 0.05. Both HYPR and low-dose CECT had high correlation to gross pathology (0.99 and 0.94, respectively), but the variance of measurements were lower after HYPR processing compared to unprocessed images. The relative difference in area, length of long axis, and length of short axis for HYPR image were 13.1 ± 5.6%, 9.7 ± 4.2%, and 15.2 ± 2.8%, which were lower than those for low-dose CECT at 37.5 ± 6.0%, 17.7 ± 2.8%, and 28.9 ± 5.4%.

CONCLUSION

HYPR processing applied to periodic CECT images can enhance ablation zone visualization. HYPR processing may potentially enable CECT in real-time ablation monitoring under strict regulation of radiation dose.

Chronological changes of radiofrequency ablation zone in rabbit liver: an in vivo correlation between gross pathology and histopathology

OBJECTIVE

To examine the gross pathology and histopathology of ablation zones created from radiofrequency (RF) ablation and to correlate their chronological changes.

METHODS

A total of 48 in vivo ablation zones (16 rabbit livers) were obtained immediately after and also 30 min, 1 h and 2 h after RF ablation and were subjected to haematoxylin and eosin (H&E) staining, nicotinamide adenine dinucleotide (NADH) diaphorase staining, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. Chronological changes in gross pathology and histopathology were evaluated and correlated with each other.

RESULTS

Peripheral red zones on gross pathology correlated with peripheral zones on H&E staining, lightly stained peripheral zones on NADH staining and peripheral positive zones on TUNEL staining. Central white zones on gross pathology correlated with combined central and border zones on H&E staining, central negative zones on NADH staining and combined central-positive and middle-negative zones on TUNEL staining. Boundary visibility between central white and peripheral red zones on gross pathology was significantly higher at 1 and 2 h than immediately after RF ablation. As time increased after RF ablation, visibility of the border zone on H&E staining and the grade of positively stained hepatocytes in the peripheral zone on TUNEL staining increased.

CONCLUSION

Chronological changes in gross pathology of RF ablation zones correlated well with histopathology. The boundary between the central white and peripheral red zones tended to become clear at 1 h after RF ablation. Advances in knowledge: (1) RF ablation zones show chronological changes on gross pathology and histopathology. (2) Gross pathology and histopathology correlate well with each other.

A clinical study of thermal monitoring techniques of ultrasound-guided microwave ablation for hepatocellular carcinoma in high-risk locations

To confirm the safety and effectiveness of the minimally invasive thermal monitor technique on percutaneous ultrasound-guided microwave ablation (MWA) for hepatocellular carcinoma (HCC) in high-risk locations, a total of 189 patients with 226 HCC nodules in high-risk locations were treated with MWA. The real-time temperature of the tissue between the lesion margin and the vital structures was monitored by inserting a 21G thermal monitoring needle. The major indexes of technical success, technique effectiveness, local tumour progression and complications were observed during the follow-up period. Technical success was acquired in all patients. Technique effectiveness was achieved with one session in 119 lesions based on contrast-enhanced ultrasound (CEUS) 3-5 days after treatment. An additional 95 lesions achieved technique effectiveness at the second session. Within the follow-up period of 6-58 months (median 38 months), the 1-, 2-, 3-, and 4-year local tumour progression rate was 11.1%, 18.1%, 19.1%, and 19.9%, respectively. There were no major complications in all the patients except for the common side effects. These results indicate that the thermal monitor technique can be applied to prevent major complications in vulnerable structures and allow percutaneous MWA to achieve satisfactory technique effectiveness in the treatment of HCC in high-risk locations.

US-US Fusion Imaging in Radiofrequency Ablation for Liver Metastases

OBJECTIVE

Radiofrequency ablation (RFA) induces gas bubbles in ablation zones, and the ablative margin cannot be evaluated accurately on ultrasound (US) during and immediately after RFA. This study assessed the usefulness of US-US fusion imaging to visualize the ablative margin of RFA for liver metastasis.

METHODS

RFA guided by US-US fusion imaging was performed on 12 targeted tumors in 10 patients. Secondary hepatic malignancies included patients with colorectal cancer (n = 4), breast cancer (n = 2), lung cancer (n = 1), gastrointestinal stromal tumor (n = 1), pancreatic neuroendocrine tumor (n = 1), and adrenocortical carcinoma (n = 1). The maximal diameter of the tumors ranged from 0.8 to 4.0 cm (mean ± SD 1.6 ± 0.9 cm).

RESULTS

The mean number of electrode insertions was 1.6 per session (range 1-3). Technically, effective ablation was achieved in a single session in all patients, and safety ablative margins were confirmed on contrast-enhanced CT for early assessment of tumor response. There were no serious adverse events or procedure-related complications. During the follow-up period (median 220 days, range 31-417 days), none of the patients showed local tumor progression.

CONCLUSION

US-US fusion imaging could show the tumor images before ablation and the ablative area on US in real time. The image overlay of US-US fusion imaging made it possible to evaluate the ablative margin three dimensionally according to the US probe action. Therefore, US-US fusion imaging can contribute to RFA therapy with a safety margin, that is, the so-called precise RFA.

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

OBJECTIVES

Evaluation of the technical success, patient safety and technical effectiveness of magnetic resonance (MR)-guided microwave ablation of hepatic malignancies.

METHODS

Institutional review board approval and informed patient consent were obtained. Fifteen patients (59.8 years ± 9.5) with 18 hepatic malignancies (7 hepatocellular carcinomas, 11 metastases) underwent MR-guided microwave ablation using a 1.5-T MR system. Mean tumour size was 15.4 mm ± 7.7 (7-37 mm). Technical success and ablation zone diameters were assessed by post-ablative MR imaging. Technique effectiveness was assessed after 1 month. Complications were classified according to the Common Terminology Criteria for Adverse Events (CTCAE). Mean follow-up was 5.8 months ± 2.6 (1-10 months).

RESULTS

Technical success and technique effectiveness were achieved in all lesions. Lesions were treated using 2.5 ± 1.2 applicator positions. Mean energy and ablation duration per tumour were 37.6 kJ ± 21.7 (9-87 kJ) and 24.7 min ± 11.1 (7-49 min), respectively. Coagulation zone short- and long-axis diameters were 31.5 mm ± 10.5 (16-65 mm) and 52.7 mm ± 15.4 (27-94 mm), respectively. Two CTCAE-2-complications occurred (pneumothorax, pleural effusion). Seven patients developed new tumour manifestations in the untreated liver. Local tumour progression was not observed.

CONCLUSIONS

Microwave ablation is feasible under near real-time MR guidance and provides effective treatment of hepatic malignancies in one session.

KEY POINTS

• Planning, applicator placement and therapy monitoring are possible without using contrast enhancement • Energy transmission from the generator to the scanner room is safely possible • MR-guided microwave ablation provides effective treatment of hepatic malignancies in one session • Therapy monitoring is possible without applicator retraction from the ablation site.

Analysis of iodinated contrast delivered during thermal ablation: is material trapped in the ablation zone?

Intra-procedural contrast-enhanced CT (CECT) has been proposed to evaluate treatment efficacy of thermal ablation. We hypothesized that contrast material delivered concurrently with thermal ablation may become trapped in the ablation zone, and set out to determine whether such an effect would impact ablation visualization. CECT images were acquired during microwave ablation in normal porcine liver with: (A) normal blood perfusion and no iodinated contrast, (B) normal perfusion and iodinated contrast infusion or (C) no blood perfusion and residual iodinated contrast. Changes in CT attenuation were analyzed from before, during and after ablation to evaluate whether contrast was trapped inside of the ablation zone. Visualization was compared between groups using post-ablation contrast-to-noise ratio (CNR). Attenuation gradients were calculated at the ablation boundary and background to quantitate ablation conspicuity. In Group A, attenuation decreased during ablation due to thermal expansion of tissue water and water vaporization. The ablation zone was difficult to visualize (CNR  =  1.57  ±  0.73, boundary gradient  =  0.7  ±  0.4 HU mm(-1)), leading to ablation diameter underestimation compared to gross pathology. Group B ablations saw attenuation increase, suggesting that iodine was trapped inside the ablation zone. However, because the normally perfused liver increased even more, Group B ablations were more visible than Group A (CNR  =  2.04  ±  0.84, boundary gradient  =  6.3  ±  1.1 HU mm(-1)) and allowed accurate estimation of the ablation zone dimensions compared to gross pathology. Substantial water vaporization led to substantial attenuation changes in Group C, though the ablation zone boundary was not highly visible (boundary gradient  =  3.9  ±  1.1 HU mm(-1)). Our results demonstrate that despite iodinated contrast being trapped in the ablation zone, ablation visibility was highest when contrast is delivered intra-procedurally. Therefore, CECT may be feasible for real-time thermal ablation monitoring.

Percutaneous Image-guided Radiofrequency Ablation of Tumors in Inoperable Patients - Immediate Complications and Overall Safety

INTRODUCTION

Percutaneous destruction of cancer cells using a radiofrequency energy source has become an accepted part of the modern armamentarium for managing malignancies. Radiofrequency ablation (RFA) is a relatively novel procedure for treating recurrent and metastatic tumors. It is used for debulking tumors and as adjuvant therapy for palliative care apart from its role as a pain management tool. Its use in the third world countries is limited by various factors such as cost and expertise. In the remotest parts of India, where economic development has been slow, abject poverty with poor health care facilities advanced malignancies present a challenge to health care providers. We undertook this study to assess the safety of the percutaneous RFA tumor ablation as a therapeutic or palliative measure in patients where surgery was not possible. We observed that RFA may be an effective, alternative therapeutic modality for some inoperable tumors where other therapeutic modalities cannot be considered.

CONTEXT

Palliative and therapeutic image-guided RFAs of tumors may be the only treatment option in patients who are inoperable for a variety of reasons. To assess the safety and complications of RFA in such a patient population is important before embarking upon any interventions given their physically, mentally, and socially compromised status in a country such as India.

AIMS

To assess the safety of percutaneous image-guided radiofrequency tumor ablation and to note the various immediate and early complications of the intervention.

SETTINGS AND DESIGN

This was a prospective, observational study conducted in Tata Main Hospital, Jamshedpur, Jharkhand, India.

SUBJECTS AND METHODS

After approval by the Hospital Approval Committee all patients who consented for percutaneous RFA of their tumor admitted in the hospital were included after taking fully informed consent from patient/close relative keeping the following criteria in view.

INCLUSION CRITERIA

Patients who were likely to derive a direct benefit in the survival or as a palliative measure for relief in their symptoms and patients who were inoperable because of any of the following reasons: (1) Exhausted conventional treatment options, (2) technical and anatomical contraindications to conventional treatment, (3) medical comorbidities precluding surgery, (4) patient refusal, (5) recurrent tumors, and (6) advanced tumor stage. Conventional Treatment has been defined as surgical resection, radiotherapy, and/or chemotherapy, although the patient eligibility for each treatment may vary.

EXCLUSION CRITERIA

Patients with the following were excluded: (1) Severe coagulopathy, (2) heart, renal, or liver failure, (3) lesions within 1 cm of gall bladder, hilum, bowel wall, and major blood vessels, (4) patient with any metal implant, (5) patients in sepsis, and (6) tumor adjacent to structures at risk (main bile ducts, pericardium, stomach, or bowel).

RESULTS

The duration of procedure as well as ablation of tumor free margin was significantly related to the size of the tumor. As the size of tumor increased, duration of procedure increased significantly. A good tumor-free margin also needs to be ablated for optimum results as it prevents residual tumors and recurrences in the future. We observed that tumors sized <3.1 cm were optimal in this regard. Most common adverse event in postprocedure period was pain in and around ablation site. Post-RFA syndrome is also a common and benign self-limiting side effect. Patient counseling and proper selection of patients in the early stages of malignancy can enhance the efficacy of the procedure and patient satisfaction.

CONCLUSIONS

Percutaneous image-guided RFA is an option in patients where most other tumor management modalities have been exhausted or rejected. RFA may not be free from side effects such as postablation syndrome, pain, and there may be other serious complications such as bleeding, but based on our observations, percutaneous image-guided RFA of tumors is a safe palliative and therapeutic treatment option.

A novel electrode with electromagnetic tip tracking in ultrasonography-guided radiofrequency ablation: a phantom, ex vivo, and in vivo experimental study

OBJECTIVES

The objective of this study was to compare the targeting and ablation performance between a newly developed radiofrequency (RF) electrode embedded with an electromagnetic position sensor (EMPS) at the electrode tip and a conventional RF electrode.

MATERIALS AND METHODS

The institutional animal care and use committee approved this study. The targeting of paint balls within phantoms was performed under ultrasonography guidance by 2 radiologists (beginner vs expert) with an "in-plane" and "out-of-plane" approaches using the new RF electrode and a conventional RF electrode (n = 20 for each method). To evaluate the targeting performance, the electrode placement time and the number of electrode pullbacks for redirection were compared between the 2 electrodes. The ablation performance was also compared by analyzing the ablation volumes in ex vivo bovine and in vivo porcine livers (n = 30 and n = 24, respectively) and the cellular viability of the ablation zone in in vivo specimens.

RESULTS

In the phantom study, the RF electrode embedded with an EMPS showed a significantly shorter electrode placement time compared with the conventional RF electrode in both the in-plane and out-of-plane approaches by both radiologists (P < 0.05). The electrode pullback rate for both radiologists was lower in the new RF electrode than in the conventional RF electrode, but it did not reach statistical significance in the in-plane approach by the expert (P = 0.059). The ablation volumes analyzed with and without cellular viability in the ex vivo and in vivo studies were not significantly different between the 2 electrodes (P > 0.05).

CONCLUSIONS

The RF electrode embedded with an EMPS is faster than the conventional electrode in the electrode placement into the target lesions. The ablation performance is not significantly different between the 2 electrodes.

Magnetic resonance imaging assessment of effective ablated volume following high intensity focused ultrasound

Under magnetic resonance (MR) guidance, high intensity focused ultrasound (HIFU) is capable of precise and accurate delivery of thermal dose to tissues. Given the excellent soft tissue imaging capabilities of MRI, but the lack of data on the correlation of MRI findings to histology following HIFU, we sought to examine tumor response to HIFU ablation to determine whether there was a correlation between histological findings and common MR imaging protocols in the assessment of the extent of thermal damage. Female FVB mice (n = 34), bearing bilateral neu deletion tumors, were unilaterally insonated under MR guidance, with the contralateral tumor as a control. Between one and five spots (focal size 0.5 × 0.5 × 2.5 mm³) were insonated per tumor with each spot receiving approximately 74.2 J of acoustic energy over a period of 7 seconds. Animals were then imaged on a 7T MR scanner with several protocols. T1 weighted images (with and without gadolinium contrast) were collected in addition to a series of T2 weighted and diffusion weighted images (for later reconstruction into T2 and apparent diffusion coefficient maps), immediately following ablation and at 6, 24, and 48 hours post treatment. Animals were sacrificed at each time point and both insonated/treated and contralateral tumors removed and stained for NADH-diaphorase, caspase 3, or with hematoxylin and eosin (H&E). We found the area of non-enhancement on contrast enhanced T1 weighted imaging immediately post ablation correlated with the region of tissue receiving a thermal dose CEM43 ≥ 240 min. Moreover, while both tumor T2 and apparent diffusion coefficient values changed from pre-ablation values, contrast enhanced T1 weighted images appeared to be more senstive to changes in tissue viability following HIFU ablation.

First clinical experience of intra-operative high intensity focused ultrasound in patients with colorectal liver metastases: a phase I-IIa study

BACKGROUND

Surgery is the only curative treatment in patients with colorectal liver metastases (CLM), but only 10-20% of patients are eligible. High Intensity Focused Ultrasound (HIFU) technology is of proven value in several indications, notably prostate cancer. Its intra-operative use in patients with CLM has not previously been studied. Preclinical work suggested the safety and feasibility of a new HIFU device capable of ablating volumes of up to 2cm x 2cm in a few seconds.

METHODS

We conducted a prospective, single-centre phase I-IIa trial. HIFU was delivered immediately before scheduled hepatectomy. To demonstrate the safety and efficacy of rapidly ablating liver parenchyma, ablations were performed on healthy tissue within the areas scheduled for resection.

RESULTS

In total, 30 ablations were carried out in 15 patients. These ablations were all generated within 40 seconds and on average measured 27.5mm x 21.0mm. The phase I study (n = 6) showed that use of the HIFU device was feasible and safe and did not damage neighbouring tissue. The phase IIa study (n = 9) showed both that the area of ablation could be precisely targeted on a previously implanted metallic mark (used to represent a major anatomical structure) and that ablations could be undertaken deliberately to avoid such a mark. Ablations were achieved with a precision of 1-2 mm.

CONCLUSION

HIFU was feasible, safe and effective in ablating areas of liver scheduled for resection. The next stage is a phase IIb study which will attempt ablation of small metastases with a 5 mm margin, again prior to planned resection.

TRIAL REGISTRATION

ClinicalTrials.govNCT01489787.

First clinical experience of intra-operative high intensity focused ultrasound in patients with colorectal liver metastases: a phase I-IIa study

Background

Surgery is the only curative treatment in patients with colorectal liver metastases (CLM), but only 10–20% of patients are eligible. High Intensity Focused Ultrasound (HIFU) technology is of proven value in several indications, notably prostate cancer. Its intra-operative use in patients with CLM has not previously been studied. Preclinical work suggested the safety and feasibility of a new HIFU device capable of ablating volumes of up to 2cm x 2cm in a few seconds.

Methods

We conducted a prospective, single-centre phase I-IIa trial. HIFU was delivered immediately before scheduled hepatectomy. To demonstrate the safety and efficacy of rapidly ablating liver parenchyma, ablations were performed on healthy tissue within the areas scheduled for resection.

Results

In total, 30 ablations were carried out in 15 patients. These ablations were all generated within 40 seconds and on average measured 27.5mm x 21.0mm. The phase I study (n = 6) showed that use of the HIFU device was feasible and safe and did not damage neighbouring tissue. The phase IIa study (n = 9) showed both that the area of ablation could be precisely targeted on a previously implanted metallic mark (used to represent a major anatomical structure) and that ablations could be undertaken deliberately to avoid such a mark. Ablations were achieved with a precision of 1–2 mm.

Conclusion

HIFU was feasible, safe and effective in ablating areas of liver scheduled for resection. The next stage is a phase IIb study which will attempt ablation of small metastases with a 5 mm margin, again prior to planned resection.

Trial Registration

ClinicalTrials.govNCT01489787

Radiofrequency ablation for colorectal liver metastases

The management of hepatic metastases from colorectal cancer (HMCRC) is multimodal including chemotherapy, surgical resection, radiation therapy, and focused destruction technologies. Radiofrequency ablation (RFA) is the most commonly used focused destruction technology. It represents a therapeutic option that may be potentially curative in cases where surgical excision is contra-indicated. It also increases the number of candidates for surgical resection among patients whose liver metastases were initially deemed unresectable. This article explains the techniques, indications, and results of radiofrequency ablation in the treatment of hepatic colorectal metastases.

In vivo thermal ablation monitoring using ultrasound echo decorrelation imaging

Previous work indicated that ultrasound echo decorrelation imaging can track and quantify changes in echo signals to predict thermal damage during in vitro radiofrequency ablation (RFA). In the in vivo studies reported here, the feasibility of using echo decorrelation imaging as a treatment monitoring tool was assessed. RFA was performed on normal swine liver (N = 5), and ultrasound ablation using image-ablate arrays was performed on rabbit liver implanted with VX2 tumors (N = 2). Echo decorrelation and integrated backscatter were computed from Hilbert transformed pulse-echo data acquired during RFA and ultrasound ablation treatments. Receiver operating characteristic (ROC) curves were employed to assess the ability of echo decorrelation imaging and integrated backscatter to predict ablation. Area under the ROC curves (AUROC) was determined for RFA and ultrasound ablation using echo decorrelation imaging. Ablation was predicted more accurately using echo decorrelation imaging (AUROC = 0.832 and 0.776 for RFA and ultrasound ablation, respectively) than using integrated backscatter (AUROC = 0.734 and 0.494).

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

RATIONALE AND OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Liver lesion conspicuity during real-time MR-guided radiofrequency applicator placement using spoiled gradient echo and balanced steady-state free precession imaging

PURPOSE

To retrospectively evaluate the conspicuity of liver lesions in a fluoroscopic spoiled gradient echo (GRE) and a balanced steady-state free precession (SSFP) magnetic resonance imaging (MRI) sequence.

MATERIALS AND METHODS

In all, 103 patients with hepatocellular carcinomas (HCC) (41) or liver metastases (67) were treated using MR-guided radiofrequency ablation in a wide-bore 1.5 T scanner. A multislice real-time spoiled GRE sequence allowing for a T1 weighting (T1W) and a balanced SSFP sequence allowing for a T2/T1W contrast were used for MR guidance. The contrast-to-noise-ratio (CNR) of the lesions was calculated and lesion conspicuity was assessed retrospectively (easily detectable / difficult to detect / not detectable).

RESULTS

HCC was easily detectable in 33/52% (GRE/SSFP), difficult to detect in 30/18%, and not detectable in 37/30% of the cases. Mean CNR varied widely (9.1 for GRE vs. 16.4 for SSFP). Liver metastases were easily detectable in 58/41% (GRE/SSFP), difficult to detect in 14/21%, and not detectable in 28/38% of the cases. Mean CNR for liver metastases was 11.5 (GRE) vs. 12.7 (SSFP). Twenty percent of all lesions could not be detected with either of the MR fluoroscopy sequences.

CONCLUSION

MR fluoroscopy using GRE and SSFP contrast enabled real-time detectability of 80% of the liver lesions.

Contrast enhanced ultrasound: Roles in immediate post-procedural and 24-h evaluation of the effectiveness of thermal ablation of liver tumors

PURPOSE

To retrospectively assess the diagnostic accuracy of immediate post-procedural CEUS, 24-h CEUS, and 24-h CT in verifying the effectiveness of thermal ablation of liver tumors ablation, using the combined results of 3-month post-procedure CEUS and MDCT as the reference standard.

MATERIALS AND METHODS

From our database, we selected patients who had immediate post-procedural CEUS and 24-h CEUS and MDCT examinations after undergoing thermal ablation of a liver tumor between January 2009 and March 2010. The study population consisted of 53 subjects and 55 tumors (44 HCC and 11 metastasis) were evaluated. Thirty-seven tumors were treated with radiofrequency and 18 with microwave ablation. Post-procedural CEUS, 24-h CEUS and MDCT, and 3-month follow-up CEUS and MDCT images were blindly reviewed by two radiologists, who measured the size of the ablation area on the post-procedural and 24-h studies. They also evaluated the ability of each of these three index tests to predict the outcome (residual tumor vs. no residual tumor) using imaging studies done at the 3-month follow-up as the reference standard.

RESULTS

Mean tumor diameter on preablation CEUS (the day before treatment) was 20 ± 9 mm. Mean diameter of the necrotic area was 29 ± 9 mm on post-procedural CEUS, 34 ± 11 mm on 24-h CEUS, and 36 ± 11 mm on 24-h MDCT. Diameters of the necrotic area (mean and maximum) on post-procedural CEUS were significantly smaller than those measured on 24-h CEUS or 24-h MDCT, which were not significantly different. For predicting the presence of residual tumor at the 3-month follow-up, post-procedural CEUS, 24-h CEUS, and 24-h MDCT displayed sensitivity of 33%, 33%, and 42%; specificity of 92%, 97%, and 97%; negative predictive value of 84%, 85%, and 83%. The accuracy parameters of these three imaging modalities were not significantly different from one another.

CONCLUSIONS

In patients undergoing thermal ablation for liver tumors, the immediate post-procedural CEUS seems comparable to 24-h CEUS and MDCT in terms of detecting residual disease.

Image-guided liver surgery: intraoperative projection of computed tomography images utilizing tracked ultrasound

BACKGROUND

Ultrasound (US) is the most commonly used form of image guidance during liver surgery. However, the use of navigation systems that incorporate instrument tracking and three-dimensional visualization of preoperative tomography is increasing. This report describes an initial experience using an image-guidance system with navigated US.

METHODS

An image-guidance system was used in a total of 50 open liver procedures to aid in localization and targeting of liver lesions. An optical tracking system was employed to localize surgical instruments. Customized hardware and calibration of the US transducer were required. The results of three procedures are highlighted in order to illustrate specific navigation techniques that proved useful in the broader patient cohort.

RESULTS

Over a 7-month span, the navigation system assisted in completing 21 (42%) of the procedures, and tracked US alone provided additional information required to perform resection or ablation in six procedures (12%). Average registration time during the three illustrative procedures was <1 min. Average set-up time was approximately 5 min per procedure.

CONCLUSIONS

The Explorer™ Liver guidance system represents novel technology that continues to evolve. This initial experience indicates that image guidance is valuable in certain procedures, specifically in cases in which difficult anatomy or tumour location or echogenicity limit the usefulness of traditional guidance methods.

Contrast enhanced ultrasound: Should it play a role in immediate evaluation of liver tumors following thermal ablation?

PURPOSE

To compare the accuracy of immediate CEUS with results of 24-h CEUS and MDCT in early evaluation of liver tumors following thermal ablation, using the combined results of a 3 month follow-up MDCT and CEUS as a reference standard.

SUBJECTS AND METHODS

From our database, we selected patients who underwent a thermal ablation immediately followed by CEUS (within 5-10min) between February 2009 and February 2011. There were 92 patients (median age 73 years), two of whom had repeat ablation during the study period for a total of 94 tumors. Sixty tumors were treated with radiofrequency and 34 with microwave ablation. All patients underwent CEUS and CT examinations at 24h. For patients with more than one treated tumor in the same session, the lesion imaged post-procedural and at 24-h with CEUS in all vascular phases was selected. All measurements of the necrotic zone, as an avascular zone, were performed during the portal-venous phase. Immediate post-procedural CEUS and 24h CEUS and MDCT were blindly reviewed by two radiologists. One radiologist blindly reviewed the follow-up imaging. The mean diameters of the necrotic zone at post-procedural CEUS, and CEUS and MDCT at 24h were compared and diagnostic accuracy to detect residual tumor calculated for each index tests compared to 3-months follow-up imaging.

RESULTS

The mean diameter of the necrotic zone was: 29±9mm at post-procedural CEUS, 34±10mm at 24h CEUS and 35±11mm at 24h MDCT. Mean diameter of the necrotic zone was significantly smaller at post-procedural CEUS compared to either CEUS or MDCT at 24h (p<0.001 for all). With a 95% confidence interval, the sensitivity was 25% (11-47%) for immediate CEUS, 20% (8-42%) for CEUS at 24-h, and 40% (22-61%) for CT at 24-h. Specificity was 96% (89-99%) for immediate CEUS, 97% (91-99%) for CEUS at 24-h, and 97% (91-99%) for CT at 24-h.

CONCLUSIONS

Diagnostic accuracy of post-procedural CEUS in early evaluation of liver tumors following thermal ablation is comparable to both CEUS and MDCT performed at 24h. Therefore, post-procedural CEUS can be used to detect and retreat residual viable tissue in the same ablation session.

The current role of minimally invasive therapies in the management of liver tumors

This is a review of minimally invasive therapy options for liver tumors, such as highly focused ultrasound, microwave ablation, and irreversible electroporation, as well as new aspects of radiofrequency ablation. Radiofrequency ablation is recommended for patients with early-stage HCC with up to 3 lesions with a tumor diameter within 3 cm and for patients with non-resectable liver metastasis. Indications and contraindications to treatment are designated, and different modalities for image-based therapy guidance are compared. Options for therapy monitoring and controlling are reviewed, namely intraprocedural tools, imaging and functional parameters and their evolution during therapy. Prevention and control of local recurrences is discussed. We also present a short review of current clinical results in treating liver metastasis and primary liver tumors.

Threshold-based prediction of the coagulation zone in sequential temperature mapping in MR-guided radiofrequency ablation of liver tumours

OBJECTIVE

To evaluate different cut-off temperature levels for a threshold-based prediction of the coagulation zone in magnetic resonance (MR)-guided radiofrequency (RF) ablation of liver tumours.

METHODS

Temperature-sensitive measurements were acquired during RF ablation of 24 patients with primary (6) and secondary liver lesions (18) using a wide-bore 1.5 T MR sytem and compared with the post-interventional coagulation zone. Temperature measurements using the proton resonance frequency shift method were performed directly subsequent to energy application. The temperature maps were registered on the contrast-enhanced follow-up MR images acquired 4 weeks after treatment. Areas with temperatures above 50°, 55° and 60°C were segmented and compared with the coagulation zones. Sensitivity and positive predictive value were calculated.

RESULTS

No major complications occurred and all tumours were completely treated. No tumour recurrence was observed at the follow-up examination after 4 weeks. Two patients with secondary liver lesions showed local tumour recurrence after 4 and 7 months. The 60°C threshold level achieved the highest positive predictive value (87.7 ± 9.9) and the best prediction of the coagulation zone.

CONCLUSIONS

For a threshold-based prediction of the coagulation zone, the 60°C cut-off level achieved the best prediction of the coagulation zone among the tested levels.

KEY POINTS

• Temperature monitoring can be used to survey MR-guided radiofrequency ablation • The developing ablation zone can be estimated based on post-interventional temperature measurements • A 60°C threshold level can be used to predict the ablation zone • The 50°C and 55°C temperature zones tend to overestimate the ablation zone.

Image-based monitoring of magnetic resonance-guided thermoablative therapies for liver tumors

Minimally invasive treatment options for liver tumor therapy have been increasingly used during the last decade because their benefit has been proven for primary and inoperable secondary liver tumors. Among these, radiofrequency ablation has gained widespread consideration. Optimal image-guidance offers precise anatomical information, helps to position interventional devices, and allows for differentiation between already-treated and remaining tumor tissue. Patient safety and complete ablation of the entire tumor are the overriding objectives of tumor ablation. These may be achieved most elegantly with magnetic resonance (MR)-guided therapy, where monitoring can be performed based on precise soft-tissue imaging and additional components, such as diffusion-weighted imaging and temperature mapping. New MR scanner types and newly developed sequence techniques have enabled MR-guided intervention to move beyond the experimental phase. This article reviews the current role of MR imaging in guiding radiofrequency ablation. Signal characteristics of primary and secondary liver tumors are identified, and signal alteration during therapy is described. Diffusion-weighted imaging (DWI) and temperature mapping as special components of MR therapy monitoring are introduced. Practical information concerning coils, sequence selection, and parameters, as well as sequence gating, is given. In addition, sources of artifacts are identified and techniques to decrease them are introduced, and the characteristic signs of residual tumor in T1-, T2-, and DWI are described. We hope to enable the reader to choose MR sequences that allow optimal therapy monitoring depending on the initial signal characteristics of the tumor as well as its size and location in the liver.

Four-dimensional transcatheter intraarterial perfusion MRI monitoring of radiofrequency ablation of rabbit VX2 liver tumors

PURPOSE

To investigate the hypothesis that four-dimensional (4D) transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) can quantify immediate perfusion changes after radiofrequency (RF) ablation in rabbit VX2 liver tumors.

MATERIALS AND METHODS

Nine New Zealand White rabbits were used to surgically implant VX2 liver tumors. During ultrasound-guided RF ablation, tumors received either a true or sham ablation. After selective catheterization of the left hepatic artery under x-ray fluoroscopy, we acquired pre- and post-RF ablation 4D TRIP MR images using 3 mL of 2.5% intraarterial gadopentetate dimeglumine. Two regions-of-interest were drawn upon each tumor to generate signal-intensity time curves. Area under the curve (AUC) was calculated to provide semiquantitative perfusion measurements that were compared using a paired t-test (α = 0.05). Ablated tissue was visually confirmed on pathology using Evans blue dye.

RESULTS

Mean AUC perfusion of VX2 tumors for the true ablation group decreased by 92.0% (95% confidence interval [CI]: 83.3%-100%), from 1913 (95% CI: 1557, 2269) before RF ablation to 76.6 (95% CI: 18.4, 134.8) after RF ablation (a.u., P < 0.001). Sham-ablated tumors demonstrated no significant perfusion changes.

CONCLUSION

4D TRIP MRI can quantify liver tumor perfusion reductions in VX2 rabbits after RF ablation. This MRI technique can potentially be used to improve tumor response assessment at the time of RF ablation.

Emerging local ablation techniques

Local ablation technologies for hepatic malignancy have developed rapidly in the past decade, with advances in several percutaneous or externally delivered treatment methods including radiofrequency ablation, microwave ablation, laser ablation, and high-intensity focused ultrasound. Research has focused on increasing the size of the ablation zone and minimizing heat-sink effects. More recent developments include improvements in treatment planning and navigation with integration of several imaging modalities, as well as automated delivery of the ablation through robotics. These improvements will allow increased consistency in treatment delivery and will facilitate translation to the community setting. Combination therapies with multimodality guidance are on the cutting edge of image-guided, minimally invasive cancer therapies. Local ablation is being combined with regional therapies, such as arterial chemoembolization and local activation of systemically administered drugs, with promising results. Potential combinations with local ablation also include external radiation therapy and antitumor immune modulation. Image-guided oncology is emerging as an important part of the interventional radiology practice, thanks in part to the innovation and imaging background that lies at the roots of our discipline.