Rüdiger Hoffmann

Comparison of Four Microwave Ablation Devices: An Experimental Study in ex Vivo Bovine Liver

PURPOSE To compare volume, sphericity, and short-axis diameter of the coagulation zone of four commercially available microwave ablation systems with three technical concepts in an ex vivo setting and to formulate mathematical models to predict these quantities. MATERIALS AND METHODS Two high-power systems (systems A and B), a system that enables simultaneous use of three antennas (system C), and a non-perfusion-cooled system that automatically adapts power and frequency (system D) were tested in ex vivo bovine livers (108 ablations). Coagulation volume, sphericity, and mean short-axis diameter were assessed, and mathematical functions were fitted for each system and assessed with the coefficient of determination (R(2)). Analysis of variance and Tukey post hoc tests were used for interdevice comparison after 5 and 10 minutes and after maximum recommended ablation time. RESULTS Volume and short-axis diameter were determined by using a mathematical model for every system, with coefficients of determination of 0.75-0.98 and 0.70-0.97, respectively. Correlation for determination of sphericity was lower (R(2) = 0.01-0.68). Mean results with ablation performed according to manufacturer recommendations were as follows: Volume, sphericity, and short-axis diameter were 57.5 cm(3), 0.75, and 43.4 mm, respectively, for system A; 72.3 cm(3), 0.68, and 45.5 mm, respectively, for system B; 17.1 cm(3), 0.58, and 26.8 mm, respectively, for system C (one antenna); 76.5 cm(3), 0.89, and 50.6 mm, respectively, for system C (three antennas); and 56.0 cm(3), 0.64, and 40.9 mm, respectively, for system D. Systems A (mean volume, 52.4 cm(3) ± 4.5 [standard deviation]) and B (39.4 cm(3) ± 1.7) reach large ablation zones with 5-minute ablation. CONCLUSION The largest ablation zone is obtained with systems B and C (three antennas) under maximum recommended ablation duration and with system A under short ablation time. The most spherical zone is obtained with system C (three antennas).

Prolonged antibiotic prophylaxis in patients with bilioenteric anastomosis undergoing percutaneous radiofrequency ablation.

PURPOSE To reduce risk of development of a hepatic abscess in patients with preexisting bilioenteric anastomosis (BEA) undergoing radiofrequency (RF) ablation of hepatic tumors by use of prolonged antibiotic prophylaxis over at least 10 days. MATERIALS AND METHODS Between April 2003 and June 2011, 184 patients underwent 206 percutaneous RF ablation procedures for hepatic malignancies. Eight patients presented with BEA and were treated in 10 sessions at 14 tumor locations. These 8 patients were male and ranged in age from 55-73 years. Median follow-up was 34 months. Antibiotic prophylaxis was given before the intervention (n = 9, piperacillin/tazobactam; n = 1, ciprofloxacin). Oral antibiotic prophylaxis after the intervention was continued with ciprofloxacin for at least 10 days. In four cases, prophylaxis after the intervention was extended with additional antibiotics. RESULTS A liver abscess occurred 22 days after 1 of 10 RF ablation sessions in patients with preexisting BEA. The patient who developed an abscess presented with a large hepatocellular carcinoma (59 mm × 54 mm) and underwent transarterial chemoembolization 8 days before RF ablation. No hepatic abscess occurred after 196 RF ablation sessions in 176 patients without BEA. CONCLUSIONS Preexisting BEA is a risk factor for formation of hepatic abscesses after RF ablation. An antibiotic prophylaxis regimen before the intervention and for a prolonged period after the intervention that covers anaerobic bacteria for at least 10 days is presented. Combined therapy of transarterial chemoembolization and RF ablation increases the risk for complications in patients with known BEA.

Image-guided radiofrequency ablation of hepatocellular carcinoma (HCC): Is MR guidance more effective than CT guidance?

OBJECTIVES The purpose of the study was to retrospectively compare technique effectiveness of computed tomography (CT)-guided versus magnetic resonance (MR)-guided radiofrequency (RF) ablation of hepatocellular carcinoma (HCC). MATERIALS AND METHODS In 35 consecutive patients 53 CT-guided (n=29) or MR-guided (n=24) ablation procedures were performed in the treatment of 56 (CT: 29; MR: 27) HCC. The entire ablation procedure was performed at a multislice CT-scanner or an interventional 0.2-Tesla MR-scanner. Assessment of treatment response was based on dynamic MR imaging at 1.5Tesla. The mean follow-up was 22.9 months. Primary technique effectiveness was assessed 4 months after ablation therapy. Secondary technique effectiveness was assessed 4 months after a facultative second ablation procedure. Primary and secondary technique effectiveness of CT-guided and MR-guided RF ablation was compared by using Chi-Square (likelihood ratio) test. RESULTS Primary technique effectiveness after a single session was achieved in 26/27 (96.3%) HCC after MR-guided RF ablation and 23/29 (79.3%) HCC after CT-guided RF ablation (Chi-Square: p=0.04). Secondary technique effectiveness was achieved in 26/27 (96.3%) HCC after MR-guided RF ablation and in 26/29 (89.7%) HCC after CT-guided RF ablation (Chi-Square: p=0.32). A local tumor progression was detected in 8/52 (15.4%) tumors after initial technique effectiveness. Major complications were detected after 3/53 (5.7%) ablation procedures. CONCLUSIONS CT-guided and MR-guided RF ablations are locally effective therapies in the treatment of HCC. Due to a higher rate of primary technique effectiveness MR-guided RF ablation may reduce the number of required sessions for complete tumor treatment.

Diffusion-weighted imaging during MR-guided radiofrequency ablation of hepatic malignancies: analysis of immediate pre- and post-ablative diffusion characteristics.

Background Previous studies have shown a benefit of magnetic resonance (MR)-diffusion-weighted imaging (DWI) for follow-up after liver radiofrequency (RF) ablation. However, no data are available concerning acute changes of DWI characteristics immediately after RF ablation. Purpose To analyze and compare the MR-diffusion characteristics of pre-interventional hepatic malignancies and the ablation zone during successful MR-guided RF ablation. Material and Methods This retrospective study was conducted in accordance with the guidelines of the local institutional review board. Forty-seven patients with 29 HCC (24 patients) and 30 hepatic metastases (23 patients) underwent MR-guided radiofrequency ablation including DWI before and immediately after ablation (b = 50, 400, 800 s/mm2). Two reviewers (A and B) analyzed DWI with focus on detectability of the tumor before ablation and characteristics of the coagulative area after treatment. Mean apparent diffusion coefficient (ADC) was compared between liver, untreated tumor, and hyperintense areas in post-ablative DWI (b = 800 s/mm2) with the paired Student’s t-test. Results Pre-ablative: the reviewers classified 19/29 (A) and 23/29 (B) HCC and 25/30 (A and B) metastases as detectable in DWI. Post-ablative: a hyperintense rim surrounding the ablation zone was observed in 28/29 treated HCC and 30/30 treated metastases (A and B). A homogenous hypointense central ablation zone was found in 18/29 (A) and 20/29 (B) treated HCC and 17/30 (A & B) treated metastases in DWI. ADC of the rim was significantly lower than ADC of the liver (P < 0.001). Conclusion DWI enables visualization of the target tumor in MR-guided liver radiofrequency ablation in most cases. A common post-ablative DWI finding is a hyperintense rim with decreased ADC surrounding the ablation zone.

Multipolar radiofrequency ablation using internally cooled electrodes in ex vivo bovine liver: Correlation between volume of coagulation and amount of applied energy

PURPOSE To evaluate the relationship between applied energy and volume of coagulation induced by multipolar radiofrequency (RF) ablation. METHODS AND MATERIALS Multipolar RF ablations (n=80) were performed in ex vivo bovine liver. Three bipolar applicators with two electrodes located on each applicator shaft were placed in a triangular array. The power-output (75-225 W) and the distance between the different applicators (2, 3, 4, 5 cm) were systematically varied. The volume of confluent white coagulation and the amount of applied energy were assessed. Based on our experimental data the relationship between the volume of coagulation and applied energy was assessed by nonlinear regression analysis. The variability explained by the model was determined by the parameter r(2). RESULTS The volume of coagulation increases with higher amounts of applied energy. The maximum amount of energy was applied at a power-output of 75 W and an applicator distance of 5 cm. The corresponding maximum volume of coagulation was 324 cm(3) and required an application of 453 kJ. The relationship between amount of applied energy (E) and volume (V) of coagulation can be described by the function, V=4.39E(0.7) (r(2)=0.88). By approximation the volume of coagulation can be calculated by the linear function V=0.61E+40.7 (r(2)=0.87). CONCLUSION Ex vivo the relationship between volume of coagulation and amount of applied energy can be described by mathematical modeling. The amount of applied energy correlates to the volume of coagulation and may be a useful parameter to monitor multipolar RF ablation.

Transarterial chemoembolization using drug eluting beads and subsequent percutaneous MR-guided radiofrequency ablation in the therapy of intermediate sized hepatocellular carcinoma

OBJECTIVE To evaluate safety, efficacy, survival and recurrence-free survival of transarterial chemoembolization (TACE) with drug eluting (DC) beads combined with MR-guided radiofrequency (RF) ablation for the treatment of hepatocellular carcinomas (HCC) larger than 3 cm. MATERIALS AND METHODS This retrospective study was approved by the institutional review board. 20 patients (69.6 years ± SD 8.8) with HCC underwent DC Bead TACE and subsequent MR-guided RF ablation. Treatment interval varied between 5 and 15 days. Mean HCC diameter was 39 mm ± SD 7 mm (range 31-50mm). Rates of recurrence-free survival and overall survival were estimated using the Kaplan-Meier method. RESULTS Technical success rate, primary and secondary technical effectiveness rate were 100%, 90% and 95%, respectively. Local tumour progression developed in one patient. Cumulative survival rates at 1, 3 and 5 years were 90% (Confidence Interval [CI]: 67%-97%), 50% (CI: 29%-70%), 27% (CI: 11%-51%) respectively. Median survival time was 37.4 months. During follow up (mean: 39.1 months ± SD 22.4; range 5-84 months), tumour progression in untreated liver developed in 14 cases. Cumulative recurrence-free survival rates at 1, 3 and 5 years were 48% (CI: 27-69%), 16% (5-39%), 16% (5-39%) respectively. Median recurrence-free survival time was 10.7 months. One major complication occurred due to misdiagnosed local recurrence. CONCLUSION In conclusion, we demonstrated that MR-guided RF ablation with subsequent DC Bead TACE is safe and effective in local tumour control in patients with intermediate sized HCC.

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

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.

Therapy monitoring of magnetic resonance-guided radiofrequency ablation using T1- and T2-weighted sequences at 1.5 T: reliability of estimated ablation zones.

PurposeThe aim of this study was to compare the size and shape of the indicated ablation zone using magnetic resonance (MR) imaging with different contrast weightings after MR-guided radiofrequency ablation (RFA) at 1.5 T. Materials and MethodsMagnetic resonance images of 50 patients treated for hepatic malignancies using MR-guided RFA were retrospectively evaluated. Areas indicating ablation zones in contrast-enhanced images were compared with nonenhanced T1- and T2-weighted images acquired after the intervention and 1 and 7 months after therapy. Corresponding slices were selected and registered to each other. Regions indicating ablation zones were segmented and compared. Areas in cm2, positive predictive value, and sensitivity of native T1- and T2-weighted images were calculated with regard to their accordance with the contrast-enhanced images. ResultsDirectly after the intervention, the ratios between the areas of the ablation zone in the contrast-enhanced and the tested sequences were 1.02 ± 0.12 in the T1-weighted images and 2.03 ± 0.78 in the T2-weighted images. Sensitivity (portion of the coagulation zone that was correctly detected based on the tested sequences) was 0.88 ± 0.08 using the T1-weighted and 0.54 ± 0.20 using the T2-weighted images. The positive predictive values were 0.89 ± 0.06 (T1 weighted) and 0.93 ± 0.06 (T2 weighted). One month after therapy, the ratios between the areas in the contrast-enhanced and the tested sequences were 1.02 ± 0.12 in the T1-weighted images and 1.04 ± 0.25 in the T2-weighted images. Seven months after therapy, the ratios were 1.04 ± 0.16 in the T1-weighted and 1.18 ± 0.22 in the T2-weighted images. ConclusionIn examinations performed directly after the intervention, the T2-weighted images tend to underestimate the ablation zone, whereas T1-weighted images clearly better reflect the ablation zone. T1-weighted images therefore seem more adequate for repetitive monitoring of MR-guided RFA at 1.5 T.

Internally gas-cooled radiofrequency applicators as an alternative to conventional radiofrequency and microwave ablation devices: An in vivo comparison

PURPOSE To test the efficacy of internally CO2-cooled radiofrequency (RF) ablation in vivo and to compare its effectiveness to a standard water-cooled RF probe and to a gas-cooled microwave (MW) device. METHOD AND MATERIALS 49 ablations were performed on 15 pigs under general anesthesia using 15G monopolar CO2-cooled RF applicators, 17G monopolar water-cooled RF applicators and 15G internally CO2-cooled microwave devices. The power of the MW device was 45W, the current of the gas-cooled RF device was 1200-1600mA. At the water-cooled RF probe, maximum power of 200W was set. Ablation time was 15min. The short and long axes of the ablation zone were measured. Histological analyses and NADH-staining were performed. The diameters and the ablation volumes were compared using an analysis of variance. RESULTS No spots of untreated tissue were observed close to the cooled needle track in any of the ablation zones. The largest short axis diameter was 3.4±0.5cm achieved with the gas-cooled monopolar applicator. With the water-cooled applicators, short axis diameter was significantly smaller, reaching 2.5±0.4cm. Gas-cooled MW probes achieved 2.9±1.0cm. The largest ablation volume was 31.5±12ml (gas-cooled RF), and the smallest was 12.7±4ml (water-cooled RF). Short/long axis ratio was largest for gas-cooled RF probes with 0.73±0.08 versus 0.64±0.04 for the water-cooled probes and 0.49±0.25 for the microwave applicator. CONCLUSION Gas-cooled RF applicators may have a higher potential for effective destruction of liver lesions than comparable water-cooled RF systems, and may be an alternative to standard RF and MW ablation devices.

A comparison of internally water-perfused and cryogenically cooled monopolar and bipolar radiofrequency applicators in ex vivo liver samples.

RATIONALE AND OBJECTIVES To evaluate the ex vivo ablation zones created in hepatic tissue using monopolar and bipolar gas- and water-cooled radiofrequency (RF) applicators. MATERIALS AND METHODS RF ablations were performed on ex vivo bovine liver tissue using closed circuit water-cooled and closed circuit cryogenically cooled (via CO₂ enthalpy) 15-ga linear-needle applicators. Both monopolar and bipolar electrode applicators were used, with the electric current administered ranging in 50-mA increments from 1100 to 1300 mA for the monopolar case, and from 500 to 700 mA for the bipolar case. Total ablation time was 15 minutes. Six tissue samples were ablated per setting. The ablated volumes were assumed to have a three-dimensional ellipsoid shape, with one long major axis and two smaller minor axes. Gross histology was used to measure the dimensions of the ablated regions to quantify the ablated volume, the dimensions of the axis, and the ratio between the long axis and the smallest minor axis, which was termed the ellipticity index. RESULTS The gas-cooled monopolar applicator achieved the largest short-axis ablation diameter (4.05 ± 0.4 cm), followed by the water-cooled monopolar applicator (3.18 ± 0.29 cm). With the bipolar applicator, the gas-cooled applicators also achieved larger short-axis ablation diameters (3.02 ± 0.15 cm) than the water-cooled applicators (2.72 ± 0.29 cm). The gas-cooled monopolar applicator also provided the largest ablation volume (42.7 ± 10.7 mL) and the most spherically shaped lesions (ellipticity index: 1.21 ± 0.10). Lesion size increased with injected current up to a threshold current of 1200/1250 mA (monopolar water-/gas-cooled) and 600/650 mA (bipolar water-/gas-cooled), but dropped at greater values. CONCLUSIONS Gas-cooled monopolar applicators were superior to the other tested applicators in terms of both volume and sphericity of the ablation zone.