Marci L. Alexander

Percutaneous Microwave Ablation of Hepatocellular Carcinoma with a Gas-Cooled System: Initial Clinical Results with 107 Tumors

PURPOSE To retrospectively review the results of hepatocellular carcinoma (HCC) treatment with a high-power, gas-cooled, multiantenna-capable microwave device. MATERIALS AND METHODS A total of 107 HCCs in 75 patients (65 men) with a mean age of 61 years (range, 44-82 y) were treated via percutaneous approach. Combination microwave ablation and transarterial chemoembolization was performed for 22 tumors in 19 patients with tumors larger than 4 cm (n = 10), tumors larger than 3 cm with ill-defined margins (n = 7), or lesions not identified with ultrasonography (n = 5). Mean tumor size was 2.1 cm (range, 0.5-4.2 cm), with median follow-up of 14 months, for ablation alone; compared with 3.7 cm (range, 1.0-7.0 cm) and 12 months, respectively, for combination therapy. All procedures were performed with a single microwave system (Certus 140) with one to three 17-gauge antennas. RESULTS Mean ablation time was 5.3 minutes (range, 1-11.5 min). All treatments were considered technically successful in a single session. Primary technique effectiveness rates were 91.6% (98 of 107) overall, 93.7% (89 of 95) for tumors 4 cm or smaller, and 75.0% (nine of 12) for tumors larger than 4 cm; and 91.8% (78 of 85) for ablation alone and 90.9% (20 of 22) for combination therapy. There was no major complication or procedure-related mortality. The overall survival rate was 76.0% at a median 14-month clinical follow-up, with most deaths related to end-stage liver disease (n = 11) or multifocal HCC (n = 5). CONCLUSIONS Treating HCC with a gas-cooled, multiantenna-capable microwave ablation device is safe, with promising treatment effectiveness.

Microwave ablation of malignant hepatic tumours: Intraperitoneal fluid instillation prevents collateral damage and allows more aggressive case selection

Abstract Purpose: Theaim of this peper was to retrospectively review our experience utilising protective fluid instillation techniques during percutaneous microwave ablation of liver tumours to determine if fluid instillation prevents non-target injuries and allows a more aggressive case selection. Materials and methods: This institute review board-approved, US Health Insurance Portability and Accountability Act-compliant, retrospective study reviewed percutaneous microwave ablation of 151 malignant hepatic tumours in 87 patients, comparing cases in which protective fluid instillation was performed with those where no fluid was utilised. In cases utilising hydrodisplacement for bowel protection, a consensus panel evaluated eligibility for potential ablation without hydrodisplacement. Patient age, tumour size, local tumour progression rate, length of follow-up, complications, displacement distance/artificial ascites thickness, and treatment power/time were compared. Results: Fluid administration was utilised during treatment in 29/151 of cases: 10/29 for protection of bowel (8/10 cases not possible without fluid displacement), and 19/29 for body wall/diaphragm protection. Local tumour progression was higher when hydrodisplacement was used to protect bowel tissue; this may be due to lower applied power due to operator caution. Local tumour progression was not increased for artificial ascites. There was no difference in complications between the fluid group and controls. Conclusion: Intraperitoneal fluid administration is a safe and effective method of protecting non-target structures during percutaneous hepatic microwave ablation. While hydrodisplacement for bowel protection allows more aggressive case selection, these cases were associated with higher rates of local tumour progression.

Monitoring microwave ablation for liver tumors with electrode displacement strain imaging

Minimally invasive ablative therapies have become important alternatives to surgical treatment of both hepatocellular carcinoma (HCC) and liver metastases. Image based guidance and monitoring are therefore essential. Although ultrasound (US) imaging suffers from inadequate echogenic contrast between ablated and normal tissue, US based elasticity imaging has shown remarkable ability to depict ablated regions and delineate margins. The purpose of this study is to apply “electrode displacement elastography,” or EDE for monitoring clinical microwave ablation (MWA) treatments for HCC and liver metastases. EDE images were acquired from 10 patients who underwent MWA for their liver tumors. The MWA system used was a Neuwave Medical Certus 140 (Madison, WI, USA) operating at 2.45 GHz. The MWA power and duration was adjusted for each patient, with typical values of 65 watts and 5 minutes. A Siemens S2000 scanner equipped with a curvilinear array transducer (VFX 6C1) pulsed at 4 MHz was used to acquire radiofrequency echo data. Electrode displacement was applied manually by the physician. A multi-seed two-dimensional tracking algorithm, with kernel dimensions of 0.096 mm × 3 A-lines was used to estimate local displacements between consecutive data frames. Strain images were computed as the gradient of the local displacement estimates. The average contrast of the ablated region was 0.23±0.07 (0.14-0.35) on B-mode images and 0.73±0.08 (0.56-0.82) on EDE. The average contrast improvement with EDE over B mode was about 230%. The average tumor size was 2.2±0.8 (0.7-3.5) cm on pre-treatment diagnostic images (CT or MRI). The average size of the ablated region was 3.8±0.7 (2.6-4.9) cm on EDE, with an average ablation margin of 1.6 cm which is within the clinically suggested ablated margin (>0.5 cm).

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.

Comparison of Displacement Tracking Algorithms for in Vivo Electrode Displacement Elastography

Hepatocellular carcinoma and liver metastases are common hepatic malignancies presenting with high mortality rates. Minimally invasive microwave ablation (MWA) yields high success rates similar to surgical resection. However, MWA procedures require accurate image guidance during the procedure and for post-procedure assessments. Ultrasound electrode displacement elastography (EDE) has demonstrated utility for non-ionizing imaging of regions of thermal necrosis created with MWA in the ablation suite. Three strategies for displacement vector tracking and strain tensor estimation, namely coupled subsample displacement estimation (CSDE), a multilevel 2-D normalized cross-correlation method, and quality-guided displacement tracking (QGDT) have previously shown accurate estimations for EDE. This paper reports on a qualitative and quantitative comparison of these three algorithms over 79 patients after an MWA procedure. Qualitatively, CSDE presents sharply delineated, clean ablated regions with low noise except for the distal boundary of the ablated region. Multilevel and QGDT contain more visible noise artifacts, but delineation is seen over the entire ablated region. Quantitative comparison indicates CSDE with more consistent mean and standard deviations of region of interest within the mass of strain tensor magnitudes and higher contrast, while Multilevel and QGDT provide higher CNR. This fact along with highest success rates of 89% and 79% on axial and lateral strain tensor images for visualization of thermal necrosis using the Multilevel approach leads to it being the best choice in a clinical setting. All methods, however, provide consistent and reproducible delineation for EDE in the ablation suite.

Improved delineation rate of thermally ablated liver tumors with electrode displacement elastography compared to commercial acoustic radiation force impulse imaging

Ultrasound elastography is an effective modality for the delineation of thermally ablated regions after liver tumor treatments. Image contrast in elasticity imaging is based on differences in the Youngs modulus of local tissue. In this work, we compare our previously introduced electrode displacement elastography (EDE) with a commercially available acoustic radiation force impulse imaging (ARFI) technique, for delineating the post ablation regions. Forty-seven patients diagnosed with either hepatocellular carcinoma (HCC) or metastases underwent microwave ablation (MWA) procedures with a typical setting of 65 W for 5 minutes. EDE and ARFI images were acquired with a Siemens Acuson S2000 system and 6C1 HD transducer. EDE images were generated from a continuous loop of ultrasound radiofrequency (RF) data using a 2D cross-correlation algorithm. ARFI images were obtained using the ‘Virtual Touch’ function available on the Siemens Acuson S2000 system. Delineation of the ablated region was performed by two observers. Imaging depth dependence of EDE and ARFI was evaluated using tissue mimicking (TM) phantoms with the inclusion positioned at different depths. Delineation results from the two observers indicate that the ablated region in ARFI images was recognizable on an average of 19 patients, while delineable ablation boundaries could be generated on an average of 4 patients. With EDE strain images, delineable ablation boundaries were generated on an average of 39 patients, without obvious imaging depth dependence. The TM phantom studies show that differences in inclusion dimensions measured with EDE and ARFI images were within 8%, while image contrast and contrast to noise ratio (CNR) with EDE was 2–3 times higher than that obtained with ARFI. This study showed that monitoring MWA in terms of the delineation rate and CNR was higher with EDE when compared to the commercially available ARFI approach. EDE could therefore become an alternative imaging modality for monitoring MWA procedures for liver tumor treatments in the ablation suite. EDE is also feasible for deeper tumor locations beyond the evaluated imaging depth for ARFI.

Comparison study of displacement estimation methods for microwave ablation procedures using electrode displacement elastography

Minimally invasive procedures such as microwave ablation (MWA) are growing in popularity as a substitute for surgical resection of hepatocellular carcinomas. Ultrasound electrode displacement elastography (EDE) has demonstrated the potential to provide a feasible non-ionizing approach for monitoring the region of thermal necrosis. We present results on a comparison of the contrast, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios for two displacement estimation algorithms; namely the Quality-Guided Displacement Tracking (QGDT) and the Coupled Subsample Displacement Estimation (CSDE) methods. Twenty patients with EDE strain images estimated from the same radiofrequency frame pair using both algorithms are presented. CSDE depicts well delineated ablated regions, while QGDT in many instances depicts noisy boundaries. Quantitatively, the SNR, contrast, and CNR obtained using CSDE were higher than those obtained with QGDT. The axial SNR, contrast, and CNR for QGDT were found to be 34.6 ± 11.9 dB, 7.8 ± 4.2 dB, and 2.7 ± 6.4 dB, while the CSDE presented with values of 56.9 ± 20.4 dB, 22.5 ± 12.3, and 3.8 ± 2.5 dB, respectively. This study indicates that EDE using CSDE provides improved strain images however, both approaches produced reproducible results.

Delineation of microwave ablated hepatocellular carcinoma tumor regions using electrode displacement elastography

An effective imaging modality to delineate the ablated region after microwave ablation (MWA) therapy is crucial to yield promising treatment outcomes. Ultrasound B mode imaging is widely used to guide the ablation needle. However, the image quality suffers from relatively low imaging contrast due to the similar echogenicity between the ablated and surrounding liver tissue. In this study, we applied a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), to delineate the thermally ablated regions for patients diagnosed with hepatocellular carcinoma (HCC) treated with MWA procedures.

Delineation of microwave ablated hepatocellular carcinomass using electrode displacement elastography

An effective imaging modality to delineate ablated regions after microwave ablation (MWA) therapy is crucial to yield successful treatment outcomes. Ultrasound B-mode imaging is widely used to guide the ablation antenna placement. However, the image quality suffers from relatively low imaging contrast due to the similar echogenicity between the ablated and surrounding tissue. In this study, we applied a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), to delineate the thermally ablated regions for patients diagnosed with hepatocellular carcinoma (HCC) and treated with minimally invasive MWA procedures. Under our approved institutional review board (IRB) protocol, EDE was used for monitoring MWA on fifty-one patients. MWA was performed using a NeuWave Certus 140 system, with a typical setting of 65 W and 5 minutes. Ultrasound B-mode and radiofrequency (RF) data loops for EDE were acquired using a Siemens Acuson S2000 system and a 6C1 HD transducer. RF data loops were acquired simultaneously with a manual perturbation of the ablation antenna performed by a physician. EDE strain images were generated with a 2D cross-correlation based displacement tracking algorithm with a kernel size of 1.35 mm × 3.29 mm along the axial and lateral direction. Ablation area, contrast and contrast to noise ratio (CNR) of EDE strain and ultrasound B-mode images were compared. Delineable ablation regions were obtained using EDE for 45 patients, with a success rate of 88.2%. The area of the ablation region in EDE images was 13.3 ± 5.0 cm2, when compared to 7.7 ± 3.2 cm2 with B-mode images. Contrast and CNR obtained with EDE was on the order of 236% and 102%, respectively, significantly higher than values measured in B-mode images (p <0.001). This study showed that thermally ablated regions were delineated in EDE strain images with enhanced detectability. Potential application of EDE for real-time monitoring of the MWA procedure may improve the treatment outcome.