Intra-operative ultrasound elasticity imaging for monitoring of hepatic tumour thermal ablation

The Role of Artificial Intelligence and Texture Analysis in Interventional Radiological Treatments of Liver Masses: A Narrative Review

Liver lesions, including both benign and malignant tumors, pose significant challenges in interventional radiological treatment planning and prognostication. The emerging field of artificial intelligence (AI) and its integration with texture analysis techniques have shown promising potential in predicting treatment outcomes, enhancing precision, and aiding clinical decision-making. This comprehensive review aims to summarize the current state-of-the-art research on the application of AI and texture analysis in determining treatment response, recurrence rates, and overall survival outcomes for patients undergoing interventional radiological treatment for liver lesions. Furthermore, the review addresses the challenges associated with the implementation of AI and texture analysis in clinical practice, including data acquisition, standardization of imaging protocols, and model validation. Future directions and potential advancements in this field are discussed. Integration of multi-modal imaging data, incorporation of genomics and clinical data, and the development of predictive models with enhanced interpretability are proposed as potential avenues for further research. In conclusion, the application of AI and texture analysis in predicting outcomes of interventional radiological treatment for liver lesions shows great promise in augmenting clinical decision-making and improving patient care. By leveraging these technologies, clinicians can potentially enhance treatment planning, optimize intervention strategies, and ultimately improve patient outcomes in the management of liver lesions.

3-D Ultrafast Shear Wave Absolute Vibro-Elastography Using a Matrix Array Transducer

Real-time ultrasound imaging plays an important role in ultrasound-guided interventions. The 3-D imaging provides more spatial information compared to conventional 2-D frames by considering the volumes of data. One of the main bottlenecks of 3-D imaging is the long data acquisition time, which reduces practicality and can introduce artifacts from unwanted patient or sonographer motion. This article introduces the first shear wave absolute vibro-elastography (S-WAVE) method with real-time volumetric acquisition using a matrix array transducer. In S-WAVE, an external vibration source generates mechanical vibrations inside the tissue. The tissue motion is then estimated and used in solving a wave equation inverse problem to provide the tissue elasticity. A matrix array transducer is used with a Verasonics ultrasound machine and a frame rate of 2000 volumes/s to acquire 100 radio frequency (RF) volumes in 0.05 s. Using plane wave (PW) and compounded diverging wave (CDW) imaging methods, we estimate axial, lateral, and elevational displacements over 3-D volumes. The curl of the displacements is used with local frequency estimation to estimate elasticity in the acquired volumes. Ultrafast acquisition extends substantially the possible S-WAVE excitation frequency range, now up to 800 Hz, enabling new tissue modeling and characterization. The method was validated on three homogeneous liver fibrosis phantoms and on four different inclusions within a heterogeneous phantom. The homogeneous phantom results show less than 8% (PW) and 5% (CDW) difference between the manufacturer values and the corresponding estimated values over a frequency range of 80-800 Hz. The estimated elasticity values for the heterogeneous phantom at 400-Hz excitation frequency show the average errors of 9% (PW) and 6% (CDW) compared to the provided average values by magnetic resonance elastography (MRE). Furthermore, both imaging methods were able to detect the inclusions within the elasticity volumes. An ex vivo study on a bovine liver sample shows less than 11% (PW) and 9% (CDW) difference between the estimated elasticity ranges by the proposed method and the elasticity ranges provided by MRE and acoustic radiation force impulse (ARFI).

Can Liver Ultrasound Elastography Predict the Risk of Hepatocellular Carcinoma Recurrence After Radiofrequency Ablation? A Systematic Review and Meta-Analysis

PURPOSE

The role of liver stiffness (LS) on ultrasound elastography in the prediction of hepatocellular carcinoma (HCC) recurrence after treatment with radiofrequency ablation (RFA) is still unclear. Our aim was to perform a systematic review and meta-analysis to assess whether LS can predict the recurrence of HCC after RFA.

MATERIALS AND METHODS

Medline via PubMed, Embase, Scopus, and Cochrane Library databases, and abstracts of international conference proceedings were searched up to June 30, 2020. Cohort studies were included if they assessed the association between LS values measured by ultrasound elastography before RFA and HCC recurrence.

RESULTS

9 studies including 1373 patients with HCC treated by RFA, 643 of whom developed HCC recurrence, were identified. The mean value of LS before RFA was significantly higher in patients who developed HCC recurrence than in those who did not (weighted mean difference=11.98 kPa, 95%CI: 7.60-16.35, I2=63.8%). There was a significant positive association between LS value and HCC recurrence both at univariate (unadjusted HR=1.03, 95%CI: 1.00-1.07, I2=72.7%) and multivariate analysis (adjusted HR=1.03, 95%CI: 1.02-1.04, I2=0). Patients with LS value ≥13-14 kPa or >1.5 m/s have a higher risk of both HCC recurrence (unadjusted HR=2.18, 95%CI: 1.46-3.25, I2=49.7%; adjusted HR=2.41, 95%CI: 1.53-3.79, I2=0) and overall mortality (adjusted HR=4.38; 95%CI: 2.33-8.25, I2=0) in comparison with those with LS below these cutoffs.

CONCLUSION

Liver ultrasound elastography appears to be a reliable tool to predict HCC recurrence and overall survival after RFA. This technique may be useful for the management of patients with HCC treated by RFA.

Subregion Radiomics Analysis to Display Necrosis After Hepatic Microwave Ablation-A Proof of Concept Study

OBJECTIVES

The aim of this study was to improve the visualization of coagulation necrosis after computed tomography (CT)-guided microwave ablation (MWA) in routine postablational imaging.

MATERIALS AND METHODS

Ten MWAs were performed in 8 pigs under CT guidance. After each ablation, we obtained contrast-enhanced CT scans in venous phase. Ablations were then resected as a whole, and histologic slices were obtained orthogonally through the ablation center. Subsequently, a vital stain was applied to the sections for visualization of coagulation necrosis. Computed tomography images were reformatted to match the histologic slices. Afterwards, quantitative imaging features were extracted from the subregions of all images, and binary classifiers were used to predict the presence of coagulation necrosis for each subregion. From this, heatmaps could be created, which visually represented the extent of necrosis in each CT image. Two independent observers evaluated the extent of coagulative necrosis between the heat maps and histological sections.

RESULTS

We applied 4 different classifiers, including a generalized linear mixed model (GLMM), a stochastic gradient boosting classifier, a random forest classifier, and a k-nearest neighbor classifier, out of which the GLMM showed the best performance to display coagulation necrosis. The GLMM resulted in an area under the curve of 0.84 and a Jaccard index of 0.6 between the generated heat map and the histologic reference standard as well as a good interobserver agreement with a Jaccard index of 0.9.

CONCLUSIONS

Subregion radiomics analysis may improve visualization of coagulation necrosis after hepatic MWA in an in vivo porcine model.

Geometrically variable three-dimensional ultrasound for mechanically assisted image-guided therapy of focal liver cancer tumors

PURPOSE

Image-guided focal ablation procedures are first-line therapy options in the treatment of liver cancer tumors that provide advantageous reductions in patient recovery times and complication rates relative to open surgery. However, extensive physician training is required and image guidance variabilities during freehand therapy applicator placement limit the sufficiency of ablation volumes and the overall potential of these procedures. We propose the use of three-dimensional ultrasound (3D US) to provide guidance and localization of therapy applicators, augmenting current ablation therapies without the need for specialized procedure suites. We have developed a novel scanning mechanism for geometrically variable 3D US images, a mechanical tracking system, and a needle applicator insertion workflow using a custom needle applicator guide for targeted image-guided procedures.

METHODS

A three-motor scanner was designed to use any commercially available US probe to generate accurate, consistent, and geometrically variable 3D US images. The designed scanner was mounted on a counterbalanced stabilizing and mechanical tracking system for determining the US probe orientation, which was assessed using optical tracking. Further exploiting the utility of the motorized scanner, an image-guidance workflow was developed that moved the probe to any identified target within an acquired 3D US image. The complete 3D US guidance system was used to perform mock targeted interventional procedures on a phantom by selecting a target in a 3D US image, navigating to the target, and performing needle insertion using a custom 3D-printed needle applicator guide. Registered postinsertion 3D US images and cone-beam computed tomography (CBCT) images were used to evaluate tip targeting errors when using the motors, tracking system, or mixed navigation approaches. Two 3D US image geometries were investigated to assess the accuracy of a small-footprint tilt approach and a large field-of-view hybrid approach for a total of 48 targeted needle insertions. 3D US image quality was evaluated in a healthy volunteer and compared to a commercially available matrix array US probe.

RESULTS

A mean positioning error of 1.85 ± 1.33 mm was observed when performing compound joint manipulations with the mechanical tracking system. A combined approach for navigation that incorporated the motorized movement and the in-plane tracking system corrections performed the best with a mean tip error of 3.77 ± 2.27 mm and 4.27 ± 2.47 mm based on 3D US and CBCT images, respectively. No significant differences were observed between hybrid and tilt image acquisition geometries with all mean registration errors ≤1.2 mm. 3D US volunteer images resulted in clear reconstruction of clinically relevant anatomy.

CONCLUSIONS

A mechanically tracked system with geometrically variable 3D US provides a utility that enables enhanced applicator guidance, placement verification, and improved clinical workflow during focal liver tumor ablation procedures. Evaluations of the tracking accuracy, targeting capabilities, and clinical imaging feasibility of the proposed 3D US system, provided evidence for clinical translation. This system could provide a workflow for improving applicator placement and reducing local cancer recurrence during interventional procedures treating liver cancer and has the potential to be expanded to other abdominal interventions and procedures.

Elastography for characterization of focal liver lesions: current evidence and future perspectives

Focal liver lesions (FLLs) are a common finding during routine abdominal ultrasound (US). The differential diagnosis between diverse types of FLLs, especially between benign and malignant ones, is extremely important and can often be particularly challenging. Radiological techniques with contrast administration and/or liver biopsy are mostly necessary for establishing diagnosis, but they have several contraindications or complications. Due to limitations of these tools, there is urgent and still unmet need to develop a first line, non-invasive and simple method to diagnose FLLs. Elastography is an US-based imaging modality that provides information about the physical parameter corresponding to the tissue stiffness and can be considered a virtual biopsy. Several elastographic approaches have been developed, such as transient elastography, strain imaging and share wave imaging, which include point shear wave elastography and 2D shear wave elastography. These tools are already in use for evaluating liver fibrosis and in the assessment of focal lesions in other organs, like breast and thyroid gland. This review aims to assess the current evidence of different techniques based on elastography in the setting of FLLs, in order to evaluate accuracy, limitations and future perspectives. In particular, we focused on two contexts: the ability of discriminating between benign and malignant lesions, especially hepatocellular carcinoma and liver metastasis, and the surveillance after percutaneous therapy. This could have a high clinical impact making elastography crucial to identify the appropriate management of FLLs.

Outcomes of Resectability Assessment of the Dutch Colorectal Cancer Group Liver Metastases Expert Panel

BACKGROUND

Decision making on optimal treatment strategy in patients with initially unresectable colorectal cancer liver metastases (CRLM) remains complex because uniform criteria for (un)resectability are lacking. This study reports on the feasibility and short-term outcomes of The Dutch Colorectal Cancer Group Liver Expert Panel.

STUDY DESIGN

The Expert Panel consists of 13 hepatobiliary surgeons and 4 radiologists. Resectability assessment is performed independently by 3 randomly assigned surgeons, and CRLM are scored as resectable, potentially resectable, or permanently unresectable. In absence of consensus, 2 additional surgeons are invited for a majority consensus. Patients with potentially resectable or unresectable CRLM at baseline are evaluated every 2 months of systemic therapy. Once CRLM are considered resectable, a treatment strategy is proposed.

RESULTS

Overall, 398 panel evaluations in 183 patients were analyzed. The median time to panel conclusion was 7 days (interquartile range [IQR] 5-11 days). Intersurgeon disagreement was observed in 205 (52%) evaluations, with major disagreement (resectable vs permanently unresectable) in 42 (11%) evaluations. After systemic treatment, 106 patients were considered to have resectable CRLM, 84 of whom (79%) underwent a curative procedure. R0 resection (n = 41), R0 resection in combination with ablative treatment (n = 26), or ablative treatment only (n = 4) was achieved in 67 of 84 (80%) patients.

CONCLUSIONS

This study analyzed prospective resectability evaluation of patients with CRLM by a panel of radiologists and liver surgeons. The high rate of disagreement among experienced liver surgeons reflects the complexity in defining treatment strategies for CRLM and supports the use of a panel rather than a single-surgeon decision.

The Place of Elastography in Evaluating the Efficacy of Radiofrequency Ablation of Thyroid Nodules

The usage of radiofrequency ablation (RFA) therapy and elastography to treat thyroid nodules has been increasing recently. Elastography specifically measures the stiffness of tissue using ultra-sonography (US). The aim of the present study was to evaluate the relationship between the elastography values of thyroid nodules and the efficacy of RFA therapy. Ultrasonography was performed on 49 patients who had a thyroid nodule with a diameter of 1 cm or greater before RFA therapy. The RFA was performed under local anesthesia, and elastography was used to measure the stiffness of the normal thyroid tissue, sternocleidomastoid muscle (SCM) and thyroid nodules three months after RFA. The nodule diameter significantly decreased three months after RFA (P < 0.05). According to a cross-evaluation of the mean elastography rates, the thyroid/SCM and nodule/thyroid elastography rates had an inverse relationship (P: 0.009). However, the thyroid/ SCM elastography rates and nodule/SCM elastography rates (P: 0.022) and the thyroid/SCM elastography rates and the rates of reduction (%) of the nodule diameter before and three months after RFA (P: 0.016) had positive relationships. In conclusion, RFA therapy is more effective in patients with thyroid nodules if there are high thyroid tissue/SCM rates in elastography.

Delineation of Post-Procedure Ablation Regions with Electrode Displacement Elastography with a Comparison to Acoustic Radiation Force Impulse Imaging

We compared a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), with acoustic radiation force impulse imaging (ARFI) for monitoring microwave ablation (MWA) procedures on patients diagnosed with liver neoplasms. Forty-nine patients recruited to this study underwent EDE and ARFI with a Siemens Acuson S2000 system after an MWA procedure. On the basis of visualization results from two observers, the ablated region in ARFI images was recognizable on 20 patients on average in conjunction with B-mode imaging, whereas delineable ablation boundaries could be generated on 4 patients on average. With EDE, the ablated region was delineable on 40 patients on average, with less imaging depth dependence. Study of tissue-mimicking phantoms revealed that the ablation region dimensions measured on EDE and ARFI images were within 8%, whereas the image contrast and contrast-to-noise ratio with EDE was two to three times higher than that obtained with ARFI. This study indicated that EDE provided improved monitoring results for minimally invasive MWA in clinical procedures for liver cancer and metastases.

Imaging patterns and focal lesions in fatty liver: a pictorial review

Non-alcoholic fatty liver disease is the most common cause of chronic liver disease and affects nearly one-third of US population. With the increasing trend of obesity in the population, associated fatty change in the liver will be a common feature observed in imaging studies. Fatty liver causes changes in liver parenchyma appearance on imaging modalities including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) and may affect the imaging characteristics of focal liver lesions (FLLs). The imaging characteristics of FLLs were classically described in a non-fatty liver. In addition, focal fatty change and focal fat sparing may also simulate FLLs. Knowledge of characteristic patterns of fatty change in the liver (diffuse, geographical, focal, subcapsular, and perivascular) and their impact on the detection and characterization of FLL is therefore important. In general, fatty change may improve detection of FLLs on MRI using fat suppression sequences, but may reduce sensitivity on a single-phase (portal venous) CT and conventional ultrasound. In patients with fatty liver, MRI is generally superior to ultrasound and CT for detection and characterization of FLL. In this pictorial essay, we describe the imaging patterns of fatty change in the liver and its effect on detection and characterization of FLLs on ultrasound, CT, MRI, and PET.

Planned Treatment of Advanced Metastatic Disease with Completion Ablation After Hepatic Resection

PURPOSE

The aim of this study is to describe a modified treatment strategy with image-guided percutaneous ablation after hepatic resection as a completion method to surgical eradication of liver metastases ("completion ablation [CA]").

METHODS

We conducted a retrospective analyses of patients who underwent CA within 180 days from the liver surgical resection to eradicate liver metastases present on the pre-surgical cross-sectional imaging or identified during intraoperative ultrasound that were not resected due to various reasons. Lesions treated with CA were evaluated for local tumor progression (LTP). Patients were evaluated for hepatic- and overall-recurrence-free survivals (hepatic-RFS and overall-RFS, respectively) and overall survival (OS).

RESULTS

Sixteen patients (10 females; median age 55 years, range 28-69) underwent CA of 21 lesions (median size 8 mm, range 6 to 22). Indications for the use of CA were small future liver remnant in 10 (63%), inability to identify the lesion during surgical exploration in 3 (19%), and technical difficulty of resection in 3 (19%) patients. No liver-related complications were recorded following the surgical resection or the CA procedures. Primary and secondary CA efficacy rates were 95 and 100%, respectively. LTP was 0% at a median clinical follow-up of 27 months (range 4.0-108 months). Five-year hepatic-RFS, overall-RFS, and OS were 36, 16, and 51%, respectively.

CONCLUSION

The use of CA as a complement to surgical resection is safe and effective. Such approach could potentially expand the surgical candidacy for patients with limited liver functional reserve and reduce postoperative morbidity and mortality in this selected patient population with more advanced disease.

Comparison of elastography, contrast-enhanced ultrasonography, and computed tomography for assessment of lesion margin after radiofrequency ablation in livers of healthy dogs

OBJECTIVE To assess by use of various diagnostic imaging modalities acute changes in livers of healthy dogs after radiofrequency ablation (RFA) and determine the capability of each imaging modality to monitor ablation lesion changes.

ANIMALS 6 healthy Beagles.

PROCEDURES 12 ablation lesions were created in the liver of the dogs (2 lesions/dog). Ablation lesions were evaluated by use of conventional ultrasonography, strain elastography, and contrast-enhanced ultrasonography immediately after (time 0), 30 to 60 minutes after, and 3 days after RFA, and by use of CT 30 minutes and 3 days after RFA. Three dogs were euthanized shortly after RFA, and the other 3 dogs were euthanized on day 3. Lesion size measured by each imaging modality was compared with necropsy findings.

RESULTS Immediately after RFA, clear margins were more visible with elastography and contrast-enhanced ultrasonography than with conventional ultrasonography, which had acoustic shadowing. On triphasic contrast CT, the ablation zone, which indicated necrosis and hemorrhage, was not enhanced and could be measured. Marked enhancement of the periablation rim was observed during the venous phase and was identified as granulation tissue. Size of the ablation area measured on enhanced CT images was strongly correlated with actual lesion size.

CONCLUSIONS AND CLINICAL RELEVANCE For dogs of this study, CT was the most reliable method for lesion size determination. Although ultrasonographic imaging measurements underestimated lesion size, all modalities could be used to provide additional real-time guidance for RFA procedures of the liver as well as for other RFA procedures.

Comparative study evaluating the efficiency of cooled and uncooled single-treatment MWA in thyroid nodules after a 3-month follow up

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cMWA and uMWA both lead to a significant reduction of thyroid nodule volume.

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Patient pain level during uMWA is significantly higher than during cMWA.

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cMWA reduces the risk of side effects.

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Single-treatment session shows comparable results to multiple treatment sessions.

Objective

The aim of this study was to evaluate and compare the efficacy of single-treatment cooled and uncooled microwave ablation in thyroid nodules.

Methods

Eighteen patients (11 women) with an average age of 62 years (range: 41–80) with 18 cold, mainly solid or solid thyroid nodules were treated with cooled or uncooled microwave ablation. Pain during the treatment was measured on a 10-point score. Side effects revealed by ultrasound or patients’ complaints were documented. Laboratory data was evaluated before, 24 h and three months after MWA. Nodule volumes were measured before and three months after MWA.

Results

Cooled MWA was better tolerated than uncooled MWA. A significant reduction of thyroid nodule volume was observed in all cases. The reduction after cMWA was higher (40%) than after uMWA (29%). Pain intensity during cMWA was significantly lower than after uMWA. CMWA and uMWA led to a significant decrease of nodule blood circulation and echogenicity and to a significant increase of nodule elasticity. Thyroid function remained intact in all cases. The energy (kJ/s) administered into the nodules in relation to the ablation time during cMWA was higher than during uMWA.

Conclusions

CMWA leads to a slightly higher but statistically not significant nodule volume reduction than uMWA. Patient comfort during cMWA is higher than during uMWA. The risk of unintended side effects is less in cMWA. A Single-treatment provides sufficient results.

Cooled microwave ablation of thyroid nodules: Initial experience

OBJECTIVE

To evaluate if internally cooled microwave ablation (cMWA) is a safe and effective method for treatment of benign and malign thyroid nodules.

METHODS

9 patients with 11 symptomatic cold benign thyroid nodules and 1 recurrent thyroid carcinoma ranging in volume from 9.1 to 197ml (mean size 52± 57ml) were treated with cMWA. The mean age of the patients was 59 years. Pain during the treatment was measured on a 10-point scale. Side effects revealed by ultrasound or patients' complaints were documented. Periablative efficacy was measured 24h after cMWA as change (Δ) in serum thyreoglobulin (Tg). Nodule elasticity was measured on a 4-point scale, blood circulation and echogenicity on a 3-point scale.

RESULTS

All patients tolerated cMWA well. Median pain intensity averaged 2.1±0.8 (range: 1-3). Postablative hematoma was observed in all cases. In no cases ablation led to hoarseness, superficial burns, nodule ruptures, vagal reactions or dysphagia. cMWA lead to a significant decrease of blood circulation, nodule echogenicity and a significant increase of elasticity (Δ = 1.1 ± 0.33; 0.8 ± 0.4 and 1.1 ± 0.6 points)(p<0.05). An average increase of 4495ng/ml Tg was measured (p<0.05).

CONCLUSIONS

cMWA is an effective and secure method for treatment of thyroid nodules.

Monitoring Radiofrequency Ablation Using Ultrasound Envelope Statistics and Shear Wave Elastography in the Periablation Period: An In Vitro Feasibility Study

Radiofrequency ablation (RFA) is a minimally invasive method for treating tumors. Shear wave elastography (SWE) has been widely applied in evaluating tissue stiffness and final ablation size after RFA. However, the usefulness of periablation SWE imaging in assessing RFA remains unclear. Therefore, this study investigated the correlation between periablation SWE imaging and final ablation size. An in vitro porcine liver model was used for experimental validation (n = 36). During RFA with a power of 50 W, SWE images were collected using a clinical ultrasound system. To evaluate the effects of tissue temperature and gas bubbles during RFA, changes in the ablation temperature were recorded, and image echo patterns were measured using B-mode and ultrasound statistical parametric images. After RFA, the gross pathology of each tissue sample was compared with the region of change in the corresponding periablation SWE image. The experimental results showed that the tissue temperature at the ablation site varied between 70°C and 100°C. Hyperechoic regions and changes were observed in the echo amplitude distribution induced by gas bubbles. Under this condition, the confounding effects (including the temperature increase, tissue stiffness increase, and presence of gas bubbles) resulted in artifacts in the periablation SWE images, and the corresponding region correlated with the estimated final ablation size obtained from the gross pathology (r = 0.8). The findings confirm the feasibility of using periablation SWE imaging in assessing RFA.

2D shear-wave ultrasound elastography (SWE) evaluation of ablation zone following radiofrequency ablation of liver lesions: is it more accurate?

OBJECTIVE

To evaluate the usefulness of two-dimensional quantitative ultrasound shear-wave elastography (2D-SWE) [i.e. virtual touch imaging quantification (VTIQ)] in assessing the ablation zone after radiofrequency ablation (RFA) for ex vivo swine livers.

METHODS

RFA was performed in 10 pieces of fresh ex vivo swine livers with a T20 electrode needle and 20-W output power. Conventional ultrasound, conventional strain elastography (SE) and VTIQ were performed to depict the ablation zone 0 min, 10 min, 30 min and 60 min after ablation. On VTIQ, the ablation zones were evaluated qualitatively by evaluating the shear-wave velocity (SWV) map and quantitatively by measuring the SWV. The ultrasound, SE and VTIQ results were compared against gross pathological and histopathological specimens.

RESULTS

VTIQ SWV maps gave more details about the ablation zone, the central necrotic zone appeared as red, lateral necrotic zone as green and transitional zone as light green, from inner to exterior, while the peripheral unablated liver appeared as blue. Conventional ultrasound and SE, however, only marginally depicted the whole ablation zone. The volumes of the whole ablation zone (central necrotic zone + lateral necrotic zone + transitional zone) and necrotic zone (central necrotic zone + lateral necrotic zone) measured by VTIQ showed excellent correlation (r = 0.915, p < 0.001, and 0.856, p = 0.002, respectively) with those by gross pathological specimen, whereas both conventional ultrasound and SE underestimated the volume of the whole ablation zone. The SWV values of the central necrotic zone, lateral necrotic zone, transitional zone and unablated liver parenchyma were 7.54-8.03 m s(-1), 5.13-5.28 m s(-1), 3.31-3.53 m s(-1) and 2.11-2.21 m s(-1), respectively (p < 0.001 for all the comparisons). The SWV value for each ablation zone did not change significantly at different observation times within an hour after RFA (all p > 0.05).

CONCLUSION

The quantitative 2D-SWE of VTIQ is useful for the depiction of the ablation zone after RFA and it facilitates discrimination of different areas in the ablation zone qualitatively and quantitatively. This elastography technique might be useful for the therapeutic response evaluation instantly after RFA.

ADVANCES IN KNOWLEDGE

A new quantitative 2D-SWE (i.e. VTIQ) for evaluation treatment response after RFA is demonstrated. It facilitates discrimination of the different areas in the ablation zone qualitatively and quantitatively and may be useful for the therapeutic response evaluation instantly after RFA in the future.

The role of intraoperative ultrasonography in the diagnosis and management of focal hepatic lesions

Intraoperative ultrasonography (IOUS) has been widely utilized in hepatic surgery both as a diagnostic technique and in the course of treatment. Since IOUS involves direct-contact imaging of the target organ, it can provide high spatial resolution without interference from the surrounding structures. Therefore, IOUS may improve the detection, characterization, localization, and local staging of hepatic tumors. IOUS is also a real-time imaging modality capable of providing interactive information and valuable guidance in a range of procedures. Recently, contrast-enhanced IOUS, IOUS elastography, and IOUS-guided hepatic surgery have attracted increasing interest and are expected to lead to the broader implementation of IOUS. Herein, we review the various applications of IOUS in the diagnosis and management of focal hepatic lesions.

Monitoring radiofrequency ablation using real-time ultrasound Nakagami imaging combined with frequency and temporal compounding techniques

Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone.

Usefulness of evaluating hepatic elasticity using artificial acoustic radiation force ultrasonography before hepatectomy

AIM

To evaluate hepatic fibrosis and tumor diagnosis preoperatively, we investigated the elasticity calculated by the new parameter of ultrasonography, acoustic radiation force impulse (ARFI).

METHODS

We examined ARFI of the non-tumorous right and left lateral liver and in the tumor by push pulse of probe in 95 patients with hepatic malignancies undergoing hepatectomy. Measurement of ARFI as hepatic stiffness was indicated as the Vs (m/s).

RESULTS

Measuring the Vs in the non-tumor region was achieved in the right liver in 99% and at the left lateral liver in 94%. The Vs in the right liver was significantly lower than in the left lateral liver, and the Vs of the liver tumor was significantly higher than in the non-tumorous liver. The Vs in the right and left lateral liver was correlated with the platelet count, aspartate aminotransferase, fibrotic indices and indocyanine green test. The Vs in the right liver was significantly correlated with the fibrotic marker or index. The Vs of liver cirrhosis and histological stage 4 in the right and left liver was significantly the highest compared to the others. The Vs in the right liver showed a high area under the receiver-operator curve value predicting histological fibrosis. The Vs in the right was significantly correlated with blood loss and postoperative complications, particularly uncontrolled ascites.

CONCLUSION

Non-invasive ARFI imaging elastography is useful in evaluating impaired liver function or in the differential diagnosis of liver malignancies, highly hepatic fibrosis and in predicting posthepatectomy morbidity.

A survey of ultrasound elastography approaches to percutaneous ablation monitoring

Percutaneous thermal ablation has been widely used as a minimally invasive treatment for tumors. Treatment monitoring is essential for preventing complications while ensuring treatment efficacy. Mechanical testing measurements on tissue reveal that tissue stiffness increases with temperature and ablation duration. Different types of imaging methods can be used to monitor ablation procedures, including temperature or thermal strain imaging, strain imaging, modulus imaging, and shear modulus imaging. Ultrasound elastography demonstrates the potential to become the primary imaging modality for monitoring percutaneous ablation. This review briefly presented the state-of-the-art ultrasound elastography approaches for monitoring radiofrequency ablation and microwave ablation. These techniques were divided into four groups: quasi-static elastography, acoustic radiation force elastography, sonoelastography, and applicator motion elastography. Their advantages and limitations were compared and discussed. Future developments were proposed with respect to heat-induced bubbles, tissue inhomogeneities, respiratory motion, three-dimensional monitoring, multi-parametric monitoring, real-time monitoring, experimental data center for percutaneous ablation, and microwave ablation monitoring.

Real time shear waves elastography monitoring of thermal ablation: in vivo evaluation in pig livers

BACKGROUND

Thermal ablation is a widely used minimally invasive treatment modality for different cancers. However, lack of a real-time imaging system for accurate evaluation of the procedure is one of the reasons of local recurrences. Shear waves elastography (SWE) is a new ultrasound (US) imaging modality to quantify tissue stiffness. The aim of the study was to assess the feasibility and accuracy of US elastography for quantitative monitoring of thermal ablation and to determine the elasticity threshold predictive of coagulation necrosis.

METHODS

A total of 29 in vivo thermal lesions were performed in pig livers with radiofrequency system. SWE and B-mode images were acquired simultaneously. Liver elasticity was quantified by using SWE data and expressed in kilopascal. After the procedure, pathologic analysis of treated tissues was compared with US images. The sensitivity and positive predictive value of the SWE maps of tissue elasticity were calculated and compared with the boundaries of the pale coagulation necrosis areas found at pathology.

RESULTS

The liver mean elasticity values before and after thermal therapy were 6.4 ± 0.3 and 38.1 ± 2.5 kPa, respectively (P < 0.0001). For a threshold of 20 kPa, sensitivity (i.e., the rate of pixels correctly detected as necrosed tissue) was 0.8, and the positive predictive value (i.e., the rate of pixels in the elastographic map >20 kPa that actually developed coagulation necrosis) was 0.83.

CONCLUSIONS

Tissue areas with coagulation necrosis are significantly stiffer than the surrounding tissue. SWE permits the real-time detection of coagulation necrosis produced by radiofrequency and could potentially be used to monitor US-guided thermal ablation.

Visualization, imaging and new preclinical diagnostics in radiation oncology

Innovative strategies in cancer radiotherapy are stimulated by the growing knowledge on cellular and molecular tumor biology, tumor pathophysiology, and tumor microenvironment. In terms of tumor diagnostics and therapy monitoring, the reliable delineation of tumor boundaries and the assessment of tumor heterogeneity are increasingly complemented by the non-invasive characterization of functional and molecular processes, moving preclinical and clinical imaging from solely assessing tumor morphology towards the visualization of physiological and pathophysiological processes. Functional and molecular imaging techniques allow for the non-invasive characterization of tissues in vivo, using different modalities, including computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, positron emission tomography (PET) and optical imaging (OI). With novel therapeutic concepts combining optimized radiotherapy with molecularly targeted agents focusing on tumor cell proliferation, angiogenesis, and cell death, the non-invasive assessment of tumor microcirculation and tissue water diffusion, together with strategies for imaging the mechanisms of cellular injury and repair is of particular interest. Characterizing the tumor microenvironment prior to and in response to irradiation will help to optimize the outcome of radiotherapy. These novel concepts of personalized multi-modal cancer therapy require careful pre-treatment stratification as well as a timely and efficient therapy monitoring to maximize patient benefit on an individual basis. Functional and molecular imaging techniques are key in this regard to open novel opportunities for exploring and understanding the underlying mechanisms with the perspective to optimize therapeutic concepts and translate them into a personalized form of radiotherapy in the near future.

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.

Recurrence after microwave ablation of liver malignancies: a single institution experience

BACKGROUND

Microwave ablation (MWA) is increasingly used to achieve local control for liver tumours. This study sought to examine a monocentric experience with MWA, with a primary hypothesis that primary tumour histology was a significant predictor of early recurrence.

METHODS

Retrospective single-institution review identified consecutive patients with liver tumours treated by MWA. Cox proportional hazards models assessed significance of prognostic variables.

RESULTS

Seventy-two patients (43 female, 60%) underwent 83 MWA procedures for 157 tumours. Tumour histologies included hepatocellular cancer (10 operations), colorectal metastases (39), metastatic carcinoid (20) and other (14). The median tumour size was 2.0 cm. A concomitant liver resection was performed in 50 cases (60%). Crude peri-operative morbidity and mortality rates were 16% and 1%, respectively. The median follow-up was 16 months. Ablations were complete for 149 out of 157 tumours (95%). The median overall and recurrence-free survivals were 36 and 18 months, respectively. There was no difference in time to recurrence between the primary tumour types. In multivariable models, recurrence-free survival was independently associated with the use of neoadjuvant [hazard ratio (HR): 2.90, 95% confidence interval (CI): 1.09-7.76, P = 0.034] and adjuvant chemotherapy (HR: 0.36, 95% CI: 0.15-0.82, P = 0.016).

CONCLUSIONS

MWA is a safe and feasible approach for local control of liver tumours. While chemotherapy administration was associated with time to recurrence after MWA, larger studies are needed to corroborate these findings.

Ultrasound elastography in liver

Conventional imaging techniques cannot provide information about tissue mechanical properties. Many injuries can cause changes in tissue stiffness, especially tumors and fibrosis. In recent years, various non-invasive ultrasound methods have been developed to study tissue elasticity for a large number of applications (breast, thyroid, prostate, kidneys, blood vessels, liver…). For non-invasive assessment of liver diseases, several ultrasound elastography techniques have been investigated: Transient elastography (the most extensively used), Real Time Elastography (RTE), Acoustic Radiation Force Impulse Imaging (ARFI) and more recently Shear Wave Elastography (SWE). Even if evaluation of liver fibrosis in chronic liver disease remains the principal application, there are many others applications for liver: predicting cirrhosis-related complications; monitoring antiviral treatments in chronic viral liver disease; characterizing liver tumors; monitoring local treatments, etc. The aim of this article is to report on the different hepatic ultrasound elastography techniques, their advantages and disadvantages, their diagnostic accuracy, their applications in clinical practice.

[Preclinical imaging in animal models of radiation therapy]

CLINICAL/METHODICAL ISSUE

Modern radiotherapy benefits from precise and targeted diagnostic and pretherapeutic imaging.

STANDARD RADIOLOGICAL METHODS

Standard imaging modalities, such as computed tomography (CT) offer high morphological detail but only limited functional information on tumors.

METHODICAL INNOVATIONS

Novel functional and molecular imaging modalities provide biological information about tumors in addition to detailed morphological information.

PERFORMANCE

Perfusion magnetic resonance imaging (MRI) CT or ultrasound-based perfusion imaging as well as hybrid modalities, such as positron emission tomography (PET) CT or MRI-PET have the potential to identify and precisely delineate viable and/or perfused tumor areas, enabling optimization of targeted radiotherapy. Functional information on tissue microcirculation and/or glucose metabolism allow a more precise definition and treatment of tumors while reducing the radiation dose and sparing the surrounding healthy tissue.

ACHIEVEMENTS

In the development of new imaging methods for planning individualized radiotherapy, preclinical imaging and research plays a pivotal role, as the value of multimodality imaging can only be assessed, tested and adequately developed in a preclinical setting, i.e. in animal tumor models.

PRACTICAL RECOMMENDATIONS

New functional imaging modalities will play an increasing role for the surveillance of early treatment response during radiation therapy and in the assessment of the potential value of new combination therapies (e.g. combining anti-angiogenic drugs with radiotherapy).

Robot-assisted laparoscopic ultrasonography for hepatic surgery

INTRODUCTION

This study describes and evaluates a novel, robot-assisted laparoscopic ultrasonographic device for hepatic surgery. Laparoscopic liver surgery is being performed with increasing frequency. One major drawback of this approach is the limited capability of intraoperative ultrasonography (IOUS) using standard laparoscopic devices. Robotic surgery systems offer the opportunity to develop new tools to improve techniques in minimally invasive surgery. This study evaluates a new integrated ultrasonography (US) device with the da Vinci Surgical System for laparoscopic visualization, comparing it with conventional handheld laparoscopic IOUS for performing key tasks in hepatic surgery.

METHODS

A prototype laparoscopic IOUS instrument was developed for the da Vinci Surgical System and compared with a conventional laparoscopic US device in simulation tasks: (1) In vivo porcine hepatic visualization and probe manipulation, (2) lesion detection accuracy, and (3) biopsy precision. Usability was queried by poststudy questionnaire.

RESULTS

The robotic US proved better than conventional laparoscopic US in liver surface exploration (85% success vs 73%; P = .030) and tool manipulation (79% vs 57%; P = .028), whereas no difference was detected in lesion identification (63 vs 58; P = .41) and needle biopsy tasks (57 vs 48; P = .11). Subjects found the robotic US to facilitate better probe positioning (80%), decrease fatigue (90%), and be more useful overall (90%) on the post-task questionnaire.

CONCLUSION

We found this robot-assisted IOUS system to be practical and useful in the performance of important tasks required for hepatic surgery, outperforming free-hand laparoscopic IOUS for certain tasks, and was more subjectively usable to the surgeon. Systems such as this may expand the use of robotic surgery for complex operative procedures requiring IOUS.