Tissue ablation with radiofrequency: effect of probe size, gauge, duration, and temperature on lesion volume

Temporary liver blood-outflow occlusion increases effectiveness of radiofrequency ablation: An experimental study on pigs

AIM

To evaluate the feasibility of liver blood outflow (LBOF) occlusion and its impact on the effectiveness of radiofrequency ablation (RFA).

METHODS

The experiment was performed on 10 pigs. The animals were divided into groups A and B according to RFA protocol. In group A (n=5) the RFA time was that taken to reach the target temperature of 105 degrees C, whereas group B (n=5) had a constant RFA temperature of 105 degrees C and constant time of 8min. The liver blood flow (LBF) was quantified using Doppler ultrasonography before LBOF occlusion and after that. RFA were performed using an expandable 3cm RF needle. Two liver ablations created in different liver lobes were compared; the first ablation was created before balloon inflation and the second one was created under LBOF occlusion. The time required for RFA procedure, liver ablation volumes, shape and microscopic changes of the thermoablated zones were recorded.

RESULTS

The LBF dropped significantly in all liver vessels after balloon inflation. The volume of the ablated area was 8.2+/-2.2cm(3) and increased significantly after LBOF occlusion to 17.4+/-3.8cm(3) (p<0.001), in group A. A significant enlargement of the ablated area with occluded LBF was registered in group B, it was 6.7+/-2.8cm(3) versus 19.4+/-1.8cm(3) respectively (p<0.01).

CONCLUSIONS

Temporary LBOF occlusion led to a significant reduction in liver blood flow, enlargement of the thermoablated area volume and homogeneity of the coagulated zones.

Percutaneous radiofrequency ablation: relationship between different probe types and procedure time on length and extent of osteonecrosis in dog long bones

PURPOSE

We have been using radiofrequency ablation for the percutaneous treatment of osteoid osteoma since 2001. Frequently, lesions are located near the joint surface, involve the vertebral body or are close to major nerves. We seek to determine whether radiofrequency ablation (RFA) can be used safely in these cases.

MATERIALS AND METHODS

A total of 65 lesions were induced in 4 dogs. Each dog underwent RFA on the diaphysis of long bones, as well as femoral and humeral heads. Four different sessions were carried out by using 1- and 2-cm probes with or without a cool-tip system and by varying the timing of the procedure. Plain film, CT, and MRI were obtained. All bone samples were examined histologically.

RESULTS

The dogs' activity after the procedure was normal. No pathologic fractures occurred despite unrestricted activity of the animals. Cortical bone was always respected; therefore, articular cartilage has not been damaged. Radiological findings were characteristic. There were no significant differences in lesion size, probe type, and the duration of the procedure. The mean lesion diameter perpendicular to the electrode was 18.5 mm.

CONCLUSIONS

Our study confirms the insulative effect of cortical bone. RFA can be safely performed close to the joint surface without damaging the cartilage.

Radiofrequency ablation of renal tumors

Development of cross-sectional imaging has led to a significant increase in diagnosis of small renal tumors. Nephron-sparing surgery has proven to be effective in the management of these small tumors. Could radiofrequency ablation be as effective in the management of these patients, after showing promising results in a selected group of patients? In this article we discuss the principles of radiofrequency ablation and present results in a selected group of patients. We also outline future perspectives of this noninvasive technique.

CT findings after radiofrequency ablation in rabbit livers: comparison of internally cooled electrodes, perfusion electrodes, and internally cooled perfusion electrodes

PURPOSE

To compare the computed tomography (CT) findings of radiofrequency (RF) ablation of rabbit livers with the use of internally cooled electrodes, perfusion electrodes, and internally cooled perfusion (ICP) electrodes.

MATERIALS AND METHODS

RF ablation zones were created in 24 rabbit livers in vivo in three groups, each treated at 30 W for 30 minutes with an electrode with a 1-cm active portion: one group was treated with an internally cooled electrode (group A), one with a perfusion electrode (group B), and one with an ICP electrode (group C). In the latter two groups, 0.9% saline solution mixed with contrast medium (9:1 ratio) was infused at a rate of 1 mL/min. Immediate CT images were ascertained in all groups and follow-up CT was performed in the latter two groups. CT findings of the RF ablation zone and surrounding liver parenchyma were evaluated and compared among groups.

RESULTS

On immediate unenhanced CT, infused contrast medium was noted in the center of the ablation zone without extravasation. Marginal linear or tubular low densities of the RF ablation zone were noted only in groups B (n=4) and C (n=3). Liver infarction was more frequently noted in groups B (n=5) and C (n=7) than in group A (n=3). Periportal tracking was noted more frequently in groups B (n=7) and C (n=8) than in group A (n=1). Pericaval or perihepatic tracking was noted only in groups B (n=3) and C (n=3). Extensive portal venous gas was noted in one animal in group C.

CONCLUSIONS

On CT, RF ablation with the perfusion or ICP electrode seemed to show more severe surrounding parenchymal changes than RF ablation with an internally cooled electrode.

Percutaneous radiofrequency ablation of renal tumours: Case series of 11 tumours and review of published work

Detection of renal cell carcinoma (RCC) is increasing with the greater use of cross-sectional imaging and up to two-thirds of RCCs are discovered incidentally in asymptomatic patients. The traditional option of nephrectomy or partial nephrectomy may not always be appropriate. A minimally invasive treatment alternative is radiofrequency ablation (RFA). We retrospectively reviewed the RFA cases for renal tumours at our institution between January 2004 and June 2006. Thirteen RFA treatment sessions were conducted for 11 neoplasms in 11 patients. Mean patient age was 74.4 years (61-88 years). Imaging was carried out after ablation with a mean follow up of 8.0 months (2-26 months). No residual tumour was observed after the first RFA treatment in 82% of patients (nine of 11). Two patients required a second RFA treatment for residual (one) or recurrent tumour (one). RFA is emerging as a useful technique for treatment of small renal tumour. A number of short-term studies reflect this, however, long-term findings are still lacking.

A Newly Developed Perfused Umbrella Electrode for Radiofrequency Ablation: An Ex Vivo Evaluation Study in Bovine Liver

The purpose of this study was to evaluate the effectiveness of a newly developed perfused monopolar radiofrequency (RF) probe with an umbrella-shaped array. A perfused umbrella-shaped monopolar RF probe based on a LeVeen electrode (Boston Scientific Corp., Natick, MA, USA) with a 3-cm array diameter was developed. Five different configurations of this electrode were tested: (a) perfusion channel/endhole, (b) perfusion channel/endhole + sideholes, (c) 1 cm insulation removed at the tip, (d) 1 cm insulation removed at the tip + perfusion channel/endhole, and (e) 1 cm insulation removed at the tip + perfusion channel/endhole + sideholes. An unmodified LeVeen electrode served as a reference standard. RF ablations were performed in freshly excised bovine liver using a commercial monopolar RF system with a 200-W generator (RF 3000; Boston Scientific Corp.). Each electrode was tested 10 times applying the vendor's recommended ablation protocol combined with the preinjection of 2 ml 0.9% saline. Volumes and shapes of the lesions were compared. Lesions generated with the original LeVeen electrode showed a mean volume of 12.74 +/- 0.52 cm(3). Removing parts of the insulation led to larger coagulation volumes (22.65 +/- 2.12 cm(3)). Depending on the configuration, saline preinjection resulted in a further increase in coagulation volume (25.22 +/- 3.37 to 31.28 +/- 2.32 cm(3)). Besides lesion volume, the shape of the ablation zone was influenced by the configuration of the electrode used. We conclude that saline preinjection in combination with increasing the active tip length of the umbrella-shaped LeVeen RF probe allows the reliable ablation of larger volumes in comparison to the originally configured electrode.

Radiofrequency ablation of hepatocellular carcinoma: predicting success using contrast-enhanced sonography

OBJECTIVE

This pilot study compared the utility of immediate postprocedural contrast-enhanced sonography with that of delayed enhanced sonography and CT or MRI in assessing the success of radiofrequency ablation of hepatocellular carcinoma.

SUBJECTS AND METHODS

Twenty-two lesions (1.5-3.7 cm) were studied in 19 patients. Enhanced sonography was performed before and within 1 hr after radiofrequency ablation. At routine 2-week follow-up CT or MRI, additional enhanced sonography was performed. The findings of preablation CT or MRI and enhanced sonography were compared with those of postprocedural and follow-up enhanced sonography by three radiologists experienced in these techniques. The reviewers were unaware of the follow-up CT or MRI results (reference standard). Technical adequacy, ablation zone targeting, and identification of residual disease were assessed by each reviewer, and the results were analyzed by consensus.

RESULTS

One postprocedural sonographic study was considered technically inadequate. Postprocedural sonography predicted the follow-up CT or MRI results in 76% (16/21) of subjects (sensitivity, 88%; specificity, 40%; positive predictive value [PPV], 82%; negative predictive value, [NPV] 50%). Follow-up CT or MRI identified accurate targeting in 17 of 22 subjects. Follow-up sonography agreed with CT or MRI in 82% (18/22) of subjects (sensitivity, 88%; specificity, 67%; PPV, 88%; NPV, 67%). Postprocedural sonography predicted the follow-up CT or MRI results in 81% (17/21) of subjects (sensitivity, 40%; specificity, 94%; PPV, 66%; NPV, 83%). Follow-up CT or MRI detected residual disease in six subjects. Follow-up sonography agreed with CT or MRI in 91% (20/22) of subjects (sensitivity, 83%; specificity, 94%; PPV, 83%; NPV, 94%).

CONCLUSION

Postprocedural enhanced sonography has the potential to guide completion of radiofrequency ablation at the time of initial therapy when residual disease is detected. The procedure is less accurate in detection of residual disease than is either delayed enhanced sonography or CT or MRI.

Radiofrequency ablation in a porcine liver model: Effects of transcatheter arterial embolization with iodized oil on ablation time, maximum output, and coagulation diameter as well as angiographic characteristics

AIM: To evaluate the effects of combined radiofrequency ablation and transcatheter arterial embolization with iodized oil on ablation time, maximum output, coagulation diameter, and portal angiography in a porcine liver model.

METHODS: Radiofrequency ablation (RFA) was applied to in vivo livers of 10 normal pigs using a 17-gauge 3.0 cm expandable LeVeen RF needle electrode with or without transcatheter arterial embolization (TAE) with iodized oil (n = 5). In each animal, 2 areas in the liver were ablated. Direct portography was performed before and after RFA. Ablation was initiated at an output of 30 W, and continued with an increase of 10 W per minute until roll-off occurred. Ablation time and maximum output until roll-off, and coagulated tissue diameter were compared between the 2 groups. Angiographic changes on portography before and after ablation were also reviewed.

RESULTS: For groups with and without TAE with iodized oil, the ablation times until roll-off were 320.6 ± 30.9 seconds and 445.1 ± 35.9 seconds, respectively, maximum outputs were 69.0 ± 7.38 W and 87.0 ± 4.83 W and maximal diameters of coagulation were 41.7 ± 3.85 mm and 33.2 ± 2.28 mm. Significant reductions of ablation time and maximum output, and significantly larger coagulation diameter were obtained with RFA following TAE with iodized oil compared to RFA alone. Portography after RFA following TAE with iodized oil revealed more occlusion of the larger portal branches than with RFA alone.

CONCLUSION: RFA following TAE with iodized oil can increase the volume of coagulation necrosis with lower output and shorter ablation time than RFA alone in normal pig liver tissue.

CT-guided radiofrequency ablation for lung cancer

Recently, percutaneous radiofrequency (RF) ablation has been increasingly performed as a local treatment for lung malignancies. In RF ablation, the application of radiofrequency agitates ions in the tissues surrounding the electrode, causing them to fluctuate at high speed, and this generates frictional heat. The generated heat coagulates the tissues. Puncture is carried out under computed tomography (CT) guidance in the same manner as that for needle biopsy. In animal studies, it was speculated that air functioned as an insulator and that the heat did not damage normal surrounding lung parenchyma to any great extent, because lung is filled with air. An experimental VX2 tumor in rabbits was well controlled by RF ablation. Since the clinical use of RF ablation for lung malignancies was first reported in 2000, many series have been published. The patients reported in these studies were not candidates for surgical treatment, either because of poor cardiopulmonary function and comorbidities, or because they refused surgery. With RF ablation, complete necrosis can be expected for tumors with a diameter of 3 cm or less. Palliative RF ablation may be indicated for large tumors. The most frequent complication associated with puncture was pneumothorax, with a frequency higher for RF ablation compared with that for needle biopsy. The initial results have been promising, but we await future reports for long-term results.

Experimental and Clinical Radiofrequency Ablation: Proposal for Standardized Description of Coagulation Size and Geometry

BACKGROUND

Radiofrequency (RF) ablation is used to obtain local control of unresectable tumors in liver, kidney, prostate, and other organs. Accurate data on expected size and geometry of coagulation zones are essential for physicians to prevent collateral damage and local tumor recurrence. The aim of this study was to develop a standardized terminology to describe the size and geometry of these zones for experimental and clinical RF.

METHODS

In a first step, the essential geometric parameters to accurately describe the coagulation zones and the spatial relationship between the coagulation zones and the electrodes were defined. In a second step, standard terms were assigned to each parameter.

RESULTS

The proposed terms for single-electrode RF ablation include axial diameter, front margin, coagulation center, maximal and minimal radius, maximal and minimal transverse diameter, ellipticity index, and regularity index. In addition a subjective description of the general shape and regularity is recommended.

CONCLUSIONS

Adoption of the proposed standardized description method may help to fill in the many gaps in our current knowledge of the size and geometry of RF coagulation zones.

Effects of blood flow and/or ventilation restriction on radiofrequency coagulation size in the lung: an experimental study in swine

The purpose of this study was to investigate how the restriction of blood flow and/or ventilation affects the radiofrequency (RF) ablation coagulation size in lung parenchyma. Thirty-one RF ablations were done in 16 normal lungs of 8 living swine with 2-cm LeVeen needles. Eight RF ablations were performed as a control (group G1), eight with balloon occlusion of the ipsilateral mainstem bronchus (G2), eight with occlusion of the ipsilateral pulmonary artery (G3), and seven with occlusion of both the ipsilateral bronchus and pulmonary artery (G4). Coagulation diameters and volumes of each ablation zone were compared on computed tomography (CT) and gross specimen examinations. Twenty-six coagulation zones were suitable for evaluation: eight in G1, five in G2, seven in G3, and six in G4 groups. In G1, the mean coagulation diameter was 21.5 +/- 3.5 mm on CT and 19.5 +/- 1.78 mm on gross specimen examination. In G2, the mean diameters were 26.5 +/- 5.1 mm and 23.0 +/- 2.7 mm on CT and gross specimen examination, respectively. In G3, the mean diameters were 29.4 +/- 2.2 mm and 27.4 +/- 2.9 mm on CT and gross specimen examination, respectively, and in G4, they were 32.6 +/- 3.33 mm and 28.8 +/- 2.6 mm, respectively. The mean coagulation volumes were 3.39 +/- l.52 cm(3) on CT and 3.01 +/- 0.94 cm(3) on gross examinations in G1, 6.56 +/- 2.47 cm(3) and 5.22 +/- 0.85 cm(3) in G2, 10.93 +/- 2.17 cm(3) and 9.97 +/- 2.91 cm(3) in G3, and 13.81 +/- 3.03 cm(3) and 11.06 +/- 3.27 cm(3) in G4, respectively. The mean coagulation diameters on gross examination and mean coagulation volumes on CT and gross examination with G3 and G4 were significantly larger than those in G1 (p < 0.0001, p < 0.0001, p < 0.0001, respectively) or in G2 (p < 0.05, p < 0.005, p < 0.005, respectively). Pulmonary collapse occurred in one lung in G2 and pulmonary artery thrombus in two lungs of G3 and two lungs of G4. The coagulation size of RF ablation of the lung parenchyma is increased by ventilation and particularly by pulmonary artery blood flow restriction. The value of these restrictions for potential clinical use needs to be explored in experimentally induced lung tumors.

Lung cancer and radiofrequency ablation

Radiofrequency (RF) ablation is a recently developed technique for image-guided local destruction of selected tumors. Because the lung is a common site for cancer and usually has substantial functional reserve, RF ablation of lung cancers is an attractive option for minimally invasive treatment. The primary goal of the present review is to describe the natural history, staging systems, and conventional therapies for primary and secondary treatment of lung cancer, as well as the results of RF ablation in animal models and in humans for pulmonary applications, to clarify the appropriate role and limitations of this technology. The secondary goals are to review the principles of how RF works and to describe RF ablation techniques to familiarize interventionalists who may consider incorporating this technology into their practice and inform diagnostic radiologists of expected imaging findings and clinicians of their patients' anticipated courses and outcomes.

Hepatic resection using heat coagulative necrosis. First report of successful trisegmentectomy after hypertrophy induction

INTRODUCTION

Intraoperative blood loss has been identified as one of the major mortality predictors for liver surgery. Different strategies have been used in the past to minimize blood loss during resection. A new method using heat coagulative necrosis in healthy tissue at the resection plane to achieve a bloodless resection has been described 3 years ago and has already gained acceptance for peripheral resections. A further developmental stage of this method is now available with the so-called Habib 4x sealer. So far, only resections ranging from segmentectomies to hemihepatectomies are reported.

MATERIALS AND METHODS

In the case reported here, the new method was challenged to perform an extended hepatic resection in a patient suffering from colorectal liver metastases. The resection was performed in a hybrid technique of regular hilar preparation and parenchymal dissection using the sealer.

CONCLUSION

The method showed to be safe and efficient even for an extended resection.

Kinetics of indocyanine green removal from blood can be used to predict the size of the area removed by radiofrequency ablation of hepatic nodules

BACKGROUND AND AIM

The size of radiofrequency ablation (RFA) in the liver can be negatively influenced by the surrounding blood flow. The indocyanine green (ICG) test can be used to evaluate the effective blood flow in the liver, and distance from the hilus can affect local blood flow. The aim of this study was to assess whether the ICG test or distance from the hilus could be used to predict the size of the ablated area in liver by RFA treatment of hepatocellular carcinoma (HCC) nodules.

METHODS

The RFA measurements of 44 HCC nodules in 39 patients were retrospectively studied. Cases were included if they met the following criteria: (i) no catheter treatment before RFA; (ii) no movement of the RFA device; (iii) strict ablation time; and (iv) only one ablation. In all patients, ICG-R15 testing was done immediately before RFA and the initial therapeutic efficacy was evaluated by dynamic computed tomography scanning 2-5 days after RFA. The correlation between the maximum size of the RFA area and the ICG test results or the distance of the target area from the hilus (site of first portal vein divergence) were analyzed statistically.

RESULTS

The ICG-R15 result was significantly correlated with the maximum diameter of the ablated area both in 2 cm-electrode tip length (R2 = 0.35, P = 0.0012), and in 3 cm-tip length (R2 = 0.26, P = 0.0377). Multiple-regression analysis showed that the electrode tip length (P = 0.0010) and ICG-R15 (P = 0.0046) were independent factors that could predict the maximum diameter of the RFA area.

CONCLUSION

The results of ICG testing can be used to predict the size of the area that will be ablated at a target liver site before RFA treatment.

The role of contrast-enhanced sonography of focal liver lesions before percutaneous biopsy

OBJECTIVE

The objective of our study was to evaluate the clinical utility of performing contrast-enhanced sonography before percutaneous biopsy of focal liver lesions.

SUBJECTS AND METHODS

One hundred eighty-six patients with focal liver lesions detected on either sonography or contrast-enhanced CT were randomly divided into two groups: a group who underwent contrast-enhanced sonography and another who underwent unenhanced sonography. The contrast-enhanced sonography group (79 patients, 129 lesions) underwent SonoVue-enhanced sonography before biopsy, and the unenhanced sonography group (107 patients, 143 lesions) did not undergo contrast-enhanced sonography before biopsy. Conventional sonography was used in all patients to guide the biopsy procedures. The pathologic diagnosis was considered definitive and final if the biopsy result was malignant. If the initial biopsy result was benign or negative for malignancy, then the result was either confirmed or denied on the basis of contrast-enhanced CT, MRI, angiography, serum alpha-fetoprotein level, or clinical follow-up over a period of 6 months. In some patients with suspected malignancy, biopsy was repeated when considered necessary during the follow-up. The diagnostic accuracy of the initial biopsy was defined as the percentage of the total number of lesions that were correctly diagnosed at the initial biopsy. The difference in diagnostic accuracy between the two groups was analyzed to evaluate the value of performing contrast-enhanced sonography before biopsy.

RESULTS

Of the 129 lesions in the contrast-enhanced sonography group, 28 (21.7%) were benign and 101 (78.3%) were malignant. Of the 143 lesions in the unenhanced sonography group, 36 (25.2%) were benign and 107 (74.8%) were malignant. There was no significant difference in the distribution of malignant and benign lesions in these two groups (p > 0.05). There was no statistically significant difference in the distribution of lesions by size between the contrast-enhanced and unenhanced sonography groups (chi(2) = 0.619, p > 0.05). The diagnostic accuracy of the initial biopsy was significantly higher in the contrast-enhanced sonography group than in the unenhanced sonography group (95.3% vs 87.4%, respectively; p < 0.05). The diagnostic accuracy of the initial biopsy for malignant lesions < or = 2.0 cm was also significantly higher in the contrast-enhanced sonography group than in the unenhanced sonography group (97.1% vs 78.8%, respectively; p < 0.05). No major complications occurred in our study except one case of pneumothorax in the unenhanced sonography group.

CONCLUSION

Contrast-enhanced sonography before percutaneous focal liver lesion biopsy improved the diagnostic accuracy of the procedure by providing important intralesional information for differentiating viable, denaturalized, or necrotic tissue; consequently, by providing more accurate information about the site of biopsy even in lesions < or = 2.0 cm, contrast-enhanced sonography before biopsy reduced the number of puncture attempts.

Comparison of expandable electrodes in percutaneous radiofrequency ablation of renal cell carcinoma

OBJECTIVE

To compare two different expandable electrodes in radiofrequency ablation of renal cell carcinoma.

METHODS

Percutaneous ablation was performed at two centers using either an expandable 7F umbrella-shaped LeVeen probe (diameter 2-4 cm) and a 200-W generator (group A), or an expandable Starburst XL electrode with a 150-W generator (group B). From each center, eight patients with one tumor each were matched retrospectively with regard to tumor volume, which was 9.71+/-6.43 cm3 for group A and 8.74+/-4.35 cm3 for group B (mean tumor diameter: 2.47+/-0.9 cm versus 2.50+/-0.4 cm, respectively). An unpaired t-test showed no significant difference in tumor volume between the two groups (p=0.820).

RESULTS

Sixteen patients with 16 tumors were treated. The primary technical success of radiofrequency ablation was 94% (15 of 16 patients). After retreatment of residual tumor in one patient from group B, secondary technical success was 100%. No major complications were observed. The resulting mean volume of the almost spherical necroses was 21.1+/-9.1 cm3 versus 14.6+/-6.7 cm3 for groups A and B (diameter of necrosis: 3.5+/-0.7 cm versus 3.1+/-0.6 cm, respectively). A Mann-Whitney U-test showed no significant difference in necrosis volume between the two groups (CI [-0.215; 0.471]; p=0.2892). The calculated shape value of S (ratio of length to height of the coagulation necrosis) was 0.9+/-0.1 and 1.0+/-0.1 for groups A and B, respectively. No local recurrence was observed during a mean follow-up of 14.8+/-11.6 months, while extrarenal tumor progression occurred in three patients.

CONCLUSIONS

No significant differences in coagulation volume and shape were found after RF ablation of renal cell carcinoma using two different expandable electrodes. To avoid local recurrence, however, accurate placement of probes and appropriate expansion of the electrode is necessary.

Renal tumors: technical success and early clinical experience with radiofrequency ablation of 18 tumors

PURPOSE

To evaluate the feasibility, safety, and technical efficacy of image-guided radiofrequency ablation (RFA) for the treatment of small peripheral renal tumors and to report our early results with this treatment modality.

METHODS

Twenty-two RFA sessions for 18 tumors were performed in 11 patients with renal tumors. Indications included coexistent morbidity, high surgical or anesthetic risk, solitary kidney, and hereditary predisposition to renal cell carcinoma. Ten patients had CT-guided percutaneous RFA performed on an outpatient basis. One patient had open intraoperative ultrasound-guided RFA. Technical success was defined as elimination of areas that enhanced at imaging within the entire tumor. With the exception of one patient with renal insufficiency who required gadolinium-enhanced MRI, the remaining patients underwent contrast-enhanced CT for post-treatment follow-up assessment. Follow-up was performed after 2-4 weeks and then at 3, 6, 12 months, and every 12 months thereafter.

RESULTS

Fourteen (78%) of 18 tumors were successfully ablated with one session. Three of the remaining four tumors required two sessions for successful ablation. One tumor will require a third session for areas of persistent enhancement. Mean patient age was 72.82 +/- 10.43 years. Mean tumor size was 1.95 +/- 0.79 cm. Mean follow-up time was 10.91 months. All procedures were performed without any major complications.

CONCLUSIONS

Our early experience with percutaneous image-guided radiofrequency ablation demonstrates it to be a feasible, safe, noninvasive, and effective treatment of small peripheral renal tumors.

Intraoperative Radiofrequency Ablation Using a Loop Internally Cooled-Perfusion Electrode: In Vitro and In Vivo Experiments

OBJECTIVE

We sought to validate the efficiency of intraoperative radiofrequency ablation (RFA) using a prototype loop internally cooled-perfusion (LICP) electrode to induce coagulation in the subcapsular portion of the liver.

MATERIALS AND METHODS

In in vitro experiments, 30 ablation regions were created using a 200-W generator and a LICP electrode featured simultaneous intraelectrode cooling and continuous flow of hypertonic saline along the shaft in explanted bovine liver. In the in vivo experiments, 26 ablation zones were created according to one of the five protocols in 10 dogs: group A, RFA using a cooled-tip electrode (n = 6); group B, RFA using a LICP electrode with 2 cm loop tip (n = 6); group C, RFA using a LICP electrode with a 3-cm loop tip (n = 6); group D, RFA using a cooled-tip electrode and Pringle maneuver (n = 4); and group E, RFA using a LICP electrode with 2 cm loop tip and Pringle maneuver (n = 4). The dimensions of the coagulation parameters were compared between the groups.

RESULTS

In the in vitro experiments, RFA using a 2- or 3-cm diameter LICP electrode (3.6 +/- 0.3 cm, 3.4 +/- 0.5 cm, respectively) created deeper dimensions of coagulation than did a 4-cm electrode (2.3 +/- 0.2 cm; P < 0.05). In the in vivo experiments, the RFA using the LICP electrodes in porcine liver with normal perfusion induced wider but superficial ablation regions when compared to standard RFA using an internally cooled electrode (P < 0.05). However, using a Pringle maneuver, RFA with a LICP electrode created a larger volume of ablation area when compared to RFA using an internally cooled electrode with a similar range of axial diameter along the electrode axis: 30.0 +/- 6.1 cm3 (group D) versus 68.5 +/- 14.0 cm3 (group E; P < 0.05)

CONCLUSIONS

Intraoperative RFA using the LICP electrode induced a well-defined semicircular coagulation with a 3.5-cm axial diameter in the subcapsular region of the liver. This device appears to be promising for the treatment of superficial tumors during intraoperative RFA.

Prevention of biliary lesions that may occur during radiofrequency ablation of the liver: study on the pig

OBJECTIVE

To prevent bile duct injury by using a cold 5% glucose isotonic solution cooling in the bile ducts when radiofrequency (RF) is performed in a porcine model.

SUMMARY BACKGROUND DATA

Complications that may arise during liver RF ablation include biliary stenosis and abscesses.

METHODS

The RITA 1500 generator was used for the experiments. Two lesions were performed in the left liver. The pigs were killed 1 or 3 weeks after the procedure. An ex vivo cholangiogram was obtained by direct injection into the main bile duct. Samples of RF lesions, of liver parenchyma near and at a distance from the RF lesions, underwent pathologic studies. Two groups of 20 pigs each were treated: one without perfusion of the bile ducts and the other with perfusion of cold 5% glucose isotonic solution into the bile ducts. The Pringle maneuver was used in 50% of the RF procedures. Radiologic lesions were classified as biliary stenosis, complete interruption of the bile duct, or extravasation of the radiologic contrast liquid.

RESULTS

Histologic lesions of the bile ducts were observed near the ablated RF lesion site and at a distance from the RF lesions when a Pringle maneuver was performed. Radiologic and histologic lesions of the bile ducts were significantly reduced (P < 0.0001) when the bile ducts were cooled.

CONCLUSIONS

Cooling of the bile ducts with a cold 5% glucose isotonic solution significantly protects the intrahepatic bile ducts from damages caused by the heat generated by RF when performed close to the bile ducts.

Multipolar radiofrequency ablation of large hepatic metastases of endocrine tumours

Radiofrequency ablation (RFA) is a reliable method of creating thermally induced coagulation necrosis. Local recurrence after RFA of hepatic metastases is directly dependent on tumour size related to the free margin of ablation. To produce larger coagulation volumes a bipolar radiofrequency device was developed that allows the simultaneous activation of three active needles. This technique was used at laparotomy in a patient with liver metastases of an endocrine tumour. Coagulation size up to 12 cm in diameter could be created. The postoperative recovery of the patient was uncomplicated. No local recurrence was seen after 13 months of follow-up with computed tomography scan. The use of simultaneously operated multiple radiofrequency electrodes in a multipolar mode expands the treatment options for patients with large and unresectable intrahepatic metastases.

Percutaneous splanchnic nerve radiofrequency ablation for chronic abdominal pain

BACKGROUND

Splanchnic nerve block is a useful alternative to coeliac plexus block in the management of patients with chronic upper abdominal pain. The predictable relationship of the splanchnic nerves to other structures allows for accurate needle placement and hence a low risk of iatrogenic damage. Radiofrequency ablation (RFA) uses a high frequency alternating current to heat tissues leading to thermal coagulation. It produces predictable and accurate lesions and hence is useful alternative to more conventional phenol and alcohol neurolytic methods.

METHODS

The present study examined a series of 10 patients undergoing percutaneous RFA splanchnic nerve blockade for chronic pancreatitis. Pain levels, anxiety, quality of life, daily activity, mood and interpersonal relationships were all assessed pre- and postprocedure, using a visual analogue score. Median follow-up was 18 months (range: 12-24 months). Statistical analysis was undertaken using non-parametric Wilcoxon matched pair analysis, statistical significance was set at the 95% confidence intervals.

RESULTS

Splanchnic nerve RFA not only led to a decrease in pain scores, opiate analgesia use and acute admissions for pain; but it also resulted in improvement of other parameters associated with long-term debilitating chronic pain, such as anxiety levels, daily activity, overall mood and general perception of health. There were no major complications. All changes observed were statistically significant.

CONCLUSION

Although preliminary data regarding RFA ablation of splanchnic nerves are encouraging, further trials are also needed comparing percutaneous splanchnic nerve ablation with opioid analgesia and coeliac plexus blockade.

A review of the general aspects of radiofrequency ablation

As an alternative to standard surgical resection for the treatment of malignant tumors, radiofrequency ablation (RFA) has rapidly evolved into the most popular minimally invasive therapy. To help readers gain the relevant background knowledge and to better understand the other reviews in this Feature Section on the clinical applications of RFA in different abdominal organs, the present report covers the general aspects of RFA. After an introduction, we present a simple definition of the energy applied during RFA, a brief historical review of its technical evolution, and an explanation of the mechanism of action of RFA. These basic discussions are substantiated with descriptions of RFA equipment including those commercially available and those under preclinical development. The size and geometry of induced lesions in relation to RFA efficacy and side effects are discussed. The unique pathophysiologic process of thermal tissue damage and the corresponding histomorphologic manifestations after RFA are detailed and cross-referenced with the findings in the current literature. The crucial role of imaging technology during and after RFA is also addressed, including some promising new developments. This report finishes with a summary of the key messages and a perspective on further technologic refinements and identifies some specific priorities.

Semiautomatic parametric model-based 3D lesion segmentation for evaluation of MR-guided radiofrequency ablation therapy

RATIONALE AND OBJECTIVES

Interventional magnetic resonance imaging (iMRI) allows real-time guidance and optimization of radiofrequency ablation of pathologic tissue. For many tissues, resulting lesions have a characteristic two-boundary appearance featuring an inner region and an outer hyper-intense margin in both T2 and contrast-enhanced (CE) T1-weighted MR images. We created a geometric model-based semiautomatic method to aid in real-time lesion segmentation, cross-sectional/three-dimensional visualization, and intra/posttreatment evaluation.

MATERIALS AND METHODS

Our method relies on a 12-parameter, 3-dimensional, globally deformable model with quadric surfaces that describe both lesion boundaries. We present an energy minimization approach to quickly and semiautomatically fit the model to a gray-scale MR image volume. We applied the method to in vivo lesions (n = 10) in a rabbit thigh model, using T2 and CE T1-weighted MR images, and compared the results with manually segmented boundaries.

RESULTS

For all lesions, the median error was < or =1.21 mm for the inner region and < or =1.00 mm for the outer hyper-intense region, values that favorably compare to a voxel width of 0.7 mm and distances between the borders manually segmented by the two operators.

CONCLUSION

Our method provides a precise, semiautomatic approximation of lesion shape for ellipsoidal lesions. Further, the method has clinical applications in lesion visualization, volume estimation, and treatment evaluation.

Radiofrequency Ablation with a New Perfused-Cooled Electrode Using a Single Pump: An Experimental Study in Ex Vivo Bovine Liver

The purpose of this study was to assess the efficacy of a new perfused-cooled electrode that uses a single pump for creating a large ablation zone in explanted bovine liver. This was done by comparing with the radiofrequency (RF) ablation zones that were created with a monopolar cooled electrode to the RF ablation zones that were created by the new perfused-cooled electrode. We developed a new perfused-cooled electrode that uses a single pump by modifying a 17-gauge cooled electrode (Radionics) with a 2.5-cm outer metallic sheath (15-gauge) in order to allow use of the internal cooling water (5.85 % hypertonic saline) for the infused saline. Thirty ablation zones were created in explanted bovine livers (12-min ablation cycle; pulsed technique; 2000 mA, maximum) with three different regimens: group A, RF ablation with the 17-gauge cooled electrode; group B, RF ablation with the 15-gauge cooled electrode; group C, RF ablation with the perfused-cooled electrode. T2-weighted magnetic resonance (MR) imaging was obtained immediately after RF ablation for calculating volumes of the ablation zone. Following MR imaging, the ablation zones were excised and measured for transverse diameters and vertical diameters. The transverse diameter, vertical diameter, and the calculated volumes of the ablation zones on MR imaging were compared among the groups. Ablation zones created with the perfused-cooled electrode (group C) were significantly larger than those created with the 17-gauge cooled electrode (group A) and the 15-gauge cooled electrode (group B) according to the transverse diameter and vertical diameter on the gross specimens (p < 0.05): 3.6 +/- 0.38 cm and 4.4 +/- 0.20 cm in group A, 3.7 +/- 0.08 cm and 4.6 +/- 0.16 cm in group B, and 5.4 +/- 0.65 cm and 6.0 +/- 0.56 cm in group C, respectively. On the MR imaging, the calculated volumes of the ablation zones in group C were significantly larger than those in groups A and B (p < 0.05): 23.1 +/- 8.7 cm3 in group A, 28.9 +/- 5.7 cm3 in group B, and 80.0 +/- 34 cm3 in group C, respectively. A new perfused-cooled electrode using a single pump could efficiently increase the size of the ablation zone in liver compared with a monopolar cooled electrode, and this was due to its simultaneous use of internal cooling and saline infusion.

Porcine liver: morphologic characteristics and cell viability at experimental radiofrequency ablation with internally cooled electrodes

PURPOSE

To evaluate morphologic characteristics and cell viability of radiofrequency ablation zones in porcine liver.

MATERIALS AND METHODS

Approval of the study protocol was obtained from the Ethics Committee on Use of Live Animals for Teaching and Research at University of Hong Kong. Internally cooled electrodes were used to produce 120 ablated zones ex vivo and 60 ablated zones in vivo with single electrodes (1-, 2-, and 3-cm exposed lengths) or clustered electrodes (1.0-, 2.0-, and 2.5-cm exposed lengths) at 4, 8, 12, and 16 minutes of ablation (ex vivo) and 8 and 12 minutes of ablation (in vivo). Morphologic measurements of each ablated zone were performed. Cell viability in each ablated zone was assessed qualitatively with histochemical staining and quantitatively with measurement of intracellular adenosine 5'-triphosphate (ATP) concentration.

RESULTS

Exposed length of electrode (coefficient = 0.79, standard error = 0.04, P < .001), duration of ablation (coefficient = 0.14, standard error = 0.01, P < .001), and clustered electrode design (coefficient = 1.21, standard error = 0.05, P < .001) were independent factors that affected minimal transverse diameter and volume of ablated zone in ex vivo study. Similar morphologic characteristics existed among ablated zones in in vivo study. Mean distance of ablation beyond the electrode tip remained constant (ex vivo, 1.0 cm +/- 0.08 [standard deviation]; in vivo, 0.5 cm +/- 0.05) regardless of different ablation conditions. Histochemical staining revealed no viable hepatocytes from center to margins of white zone in each ablated area. Mean intracellular ATP concentration in margins of white zone (9.5 x 10(-12) mol/microg DNA +/- 1.43) was lower than that in red zone (4088 x 10(-12) mol/microg DNA +/- 65.97, P < .001) and in adjacent normal liver (4528 x 10(-12) mol/microg DNA +/- 52.74, P < .001).

CONCLUSION

Distance of ablation beyond the tip of the electrode remained constant (ex vivo, 1.0 cm; in vivo, 0.5 cm) with different conditions of ablation. Complete and uniform cellular destruction was achieved in the white zone of ablated area.

Radiofrequency thermoablation of primary non-spinal osteoid osteoma: optimization of the procedure

Osteoid osteoma is a small benign tumor that requires treatment due to the intense pain it causes. Surgical therapy has been the ablative technique of choice after a failure of medical therapy. Recently, numerous less invasive, alternative procedures have been proposed: drill trepanation with or without ethanol injections, cryoablation, and thermoablation with laser or radiofrequency. The aim of this review is to retrospectively assess the effect of radiofrequency (RF) thermoablation in the treatment of primary non-spinal osteoid osteoma. From June 2001 to July 2003, we treated 106 patients affected by osteoid osteoma with RF thermoablation. Five patients with spinal osteoid osteoma and four with a previously treated osteoma were excluded from the study. In this paper, we assess the results obtained in a selected group of 97 primary non-spinal osteoid osteoma. The lesions were predominantly in the metaphysics of the femur. Central nidus calcifications were frequent and there was no prevalence for which side they occurred. Primary success was achieved in 82 patients (85%), while we obtained secondary success in 15 patients (15%). In two patients (2%), pain persisted between the two treatments and failed to be resolved, even after the second treatment; therefore, surgical excision was performed and complete resolution was obtained. No complications were reported. In conclusion, our results confirm that the treatment of choice for non-spinal osteoid osteoma is RF thermoablation, offering several advantages over ablative techniques.

Radiofrequency Neurotomy for Low Back Pain: Evidence-Based Procedural Guidelines

OBJECTIVE

This review was undertaken to outline the procedural limitations of the randomized controlled trials (RCTs) of radiofrequency (RF) neurotomy for low back pain. Second, the literature related to patient selection, diagnostic testing, and the technique of performing lumbar spine RF neurotomy will be critically reviewed and analyzed. Based on these analyses, diagnostic and procedural guidelines will be proposed.

DESIGN

A Medline and EMBASE search identified three RCTs and two systematic reviews of RF neurotomy for low back pain. A similar search identified pertinent literature related to the method of patient selection for a diagnostic block, the medial branch and L5 dorsal ramus comparative block, and the anatomical and technical parameters of lumbar spine RF neurotomy.

RESULTS

Substantial procedural shortcomings were identified in all three RCTs. In the systematic reviews, these procedural limitations were not accounted for by the quality assessment of study design which resulted in an inaccurate estimate of clinical effectiveness. Analysis using likelihood ratios showed that screening criteria could increase the probability of zygapophysial joint pain before performing diagnostic blocks. Similar analysis showed that comparative medial branch blocks, rather than single blocks, must be used before RF neurotomy. Anatomical studies demonstrated that the shorter distal compared with the circumferential radius of the RF lesion necessitates placement of the electrode parallel to the course of the nerve along the base of the superior articular process.

CONCLUSIONS

The evidence-based procedural guidelines provide consistent criteria for multisite studies that could enroll a sufficiently large homogenous study cohort.

Hybrid radiofrequency and cryoablation device: preliminary results in an animal model

PURPOSE

To determine whether the simultaneous application of combined bipolar radiofrequency (RF) ablation and cryoablation in a hybrid system produces larger ablation zones than RF or cryoablation alone.

MATERIALS AND METHODS

Multiple 15-minute ablations were performed in ex vivo bovine liver (n = 167) with a hybrid applicator system with RF ablation alone (0.3-0.7 A), cryoablation alone (3,500 psi, two freeze/thaw cycles), and combined RF/cryoablation (0.4-0.7 A, 1,000-3,500 psi) with use of a novel applicator consisting of two 2.5-cm active bipolar RF poles located on the same 18-gauge needle separated by two embedded cryoablation nozzles. Resultant coagulation diameters were compared with use of analysis of variance for more than three groups or Student t tests for two groups. Confirmation of the optimal parameters of combination RF/cryoablation was performed by reassessing a range of argon pressure (1,000-3,500 psi) and RF current (0.4-0.7 A) in in vivo porcine liver (n = 36). Arrays of two to four RF/cryoablation applicators were also assessed in ex vivo (n = 54) and in vivo (n = 12) liver.

RESULTS

In ex vivo liver, simultaneous RF/cryoablation (0.6 A, 3,000 psi) produced 3.6 cm +/- 0.4 of short-axis coagulation. This was significantly larger than that achieved with optimal RF alone or cryoablation alone (1.5 cm +/- 0.3 and 1.6 cm +/- 0.3, respectively; F = 95; P < .01). The coagulation diameter with simultaneous combination RF/cryoablation was related in parabolic fashion to argon pressure and current with a multivariate r(2) of 0.68. For in vivo liver, optimal combination RF/cryoablation achieved 3.3 cm +/- 0.2 of coagulation, which was significantly larger than that achieved with RF alone (1.1 cm +/- 0.1; P < .01) or cryoablation alone (1.1 cm +/- 0.1 and 1.3 cm +/- 0.1; F = 203; P < .01). The greatest contiguous coagulation was achieved with multiple-applicator arrays. For ex vivo liver, short-axis coagulation measured 5.3 cm +/- 0.1, 6.4 cm +/- 0.1, and 7.6 cm +/- 0.1 for two-, three-, and four-applicator arrays, respectively. For in vivo liver, two-, three-, and four-applicator arrays produced 5.1 cm +/- 0.2, 5.8 cm +/- 0.5, and 7.0 cm +/- 0.5 of confluent coagulation, respectively.

CONCLUSION

Simultaneous combination RF and cryoablation with use of a novel applicator design yielded significantly larger zones of coagulation than either modality alone. The large ablation diameters achieved warrant further investigation of the device.

Metastatic Colorectal Carcinoma: Cost-effectiveness of Percutaneous Radiofrequency Ablation versus That of Hepatic Resection

PURPOSE

To evaluate the relative cost-effectiveness of radiofrequency (RF) ablation and hepatic resection in patients with metachronous liver metastases from colorectal carcinoma (CRC) and compare the outcomes, cost, and cost-effectiveness of a variety of treatment and follow-up strategies.

MATERIALS AND METHODS

A state-transition decision model for evaluating the (societal) cost-effectiveness of RF ablation and hepatic resection in patients with CRC liver metastases was developed. The model tracks the presence, number, size, location, growth, detection, and removal of up to 15 individual metastases in each patient. Survival, quality of life, and cost are predicted on the basis of disease extent. Imaging, ablation, and resection affect outcomes through detection and elimination of individual metastases. Several patient care strategies were developed and compared on the basis of cost, effectiveness, and incremental cost-effectiveness (expressed as dollars per quality-adjusted life-year [QALY]). Extensive sensitivity analysis was performed to evaluate the impact of alternative scenarios and assumptions on results.

RESULTS

A strategy permitting ablation of up to five metastases with computed tomographic (CT) follow-up every 4 months resulted in a gain of 0.65 QALYs relative to a no-treat strategy, at an incremental cost of $2400 per QALY. Compared with this ablation strategy, a strategy permitting resection of up to four metastases, one repeat resection, and CT follow-up every 6 months resulted in an additional gain of 0.76 QALYs at an incremental cost of $24 300 per QALY. Across a range of model assumptions, more aggressive treatment strategies (ie, ablation or resection of more metastases, treatment of recurrent metastases, more frequent follow-up imaging) were superior to less aggressive strategies and had incremental cost-effectiveness ratios of less than $35 000 per QALY. Findings were insensitive to changes in most model parameters; however, results were somewhat sensitive to changes in size thresholds for RF ablation, the number of metastases present, and surgery and treatment costs.

CONCLUSION

RF ablation is a cost-effective treatment option for patients with CRC liver metastases. However, in most scenarios, hepatic resection is more effective (in terms of QALYs gained) than RF ablation and has an incremental cost-effectiveness ratio of less than $35 000 per QALY.

Combined radiofrequency and alcohol injection for percutaneous hepatic tumor ablation

OBJECTIVE

We sought to determine if alcohol potentiates radiofrequency energy by obtaining larger ablative volumes in 30 liver tumors in human patients.

SUBJECTS AND METHODS

We compared two groups of patients: one group treated with radiofrequency ablation alone (radiofrequency-alone group), and a second group treated with radiofrequency ablation and immediate prior injection of alcohol (combined group). The radiofrequency-alone group comprised 20 ablations (mean diameter, 8.4 cm; colorectal cancer metastases [n = 15]; other metastases [n = 5]). The combined group consisted of 30 radiofrequency ablations (mean diameter, 8.8 cm; metastatic colorectal cancer [n = 17]; other metastases [n = 8]; and hepatocellular carcinoma [n = 5]) treated with alcohol injection immediately before radiofrequency ablation. The amount of alcohol injected was determined by the size and location of tumors. Preprocedural laboratory tests (complete blood cell count with differential, liver function tests, and coagulation parameters) were performed in all patients, along with pre- and postprocedural CT, MRI, and PET. Measurements of tissue necrosis were obtained on the postprocedural CT scans and MR images. Volumes of necrosis calculated in each group were corrected for the number of radiofrequency applications and were statistically compared using the Student's t test. In addition, tissue impedances obtained during the radiofrequency ablation procedure were compared between the two groups.

RESULTS

The mean ablation volumes for the radiofrequency-alone group were 32.3 cm(2) (median, 28.6 cm(2); range, 14.4-61.8 cm(2)) and for the combined group, 84.6 cm(2) (median, 78.3 cm(2); range, 34.6-149 cm(2)). The difference in the necrosis volumes was significantly larger (p < 0.0001) in the combined group. Overall, the combined treatment group underwent fewer radiofrequency applications per session. Tissue impedance during radiofrequency ablation was higher in the combined group (mean, 62.7 vs 57.3 Omega in the radiofrequency alone group; p = 0.0005) at comparable times during the ablations. No major complications were seen in either group.

CONCLUSION

Percutaneous radiofrequency ablation appears to be potentiated by immediate prior alcohol injection into the tumor. Consistently larger lesions are obtainable in fewer sessions, without any increase of complications, using the combined method.

Radiofrequency ablation of liver tumours: systematic review

Thermal ablation by use of radiofrequency energy can be used to achieve necrosis of liver tumours, and increased availability of this technique is leading to more widespread use. Much of the impetus for the use of radiofrequency ablation has come from cohort series that have provided an evidence base for this technique. Here, we give an overview of the current status of radiofrequency ablation for liver tumours, including its physical properties, to assess the characteristics that make this technique applicable in clinical practice. We review the technical development of probe design and summarise current indications and outcomes of reported clinical use. We also provide a profile of side-effects and information on the integration of this technique into the general management of patients with liver tumours. Current evidence suggests that radiofrequency ablation can be done with few side effects; however, although this technique seems to ablate tumours effectively, it should form part of multidisciplinary care for liver cancer. Crucially, the role of radiofrequency ablation in lengthening the survival of patients with liver tumours remains to be assessed.

Radiofrequency ablation of primary and metastatic hepatic malignancies

Radiofrequency interstitial tissue ablation is a local ablative therapy in which tumors are destroyed in situ by thermal coagulation and protein denaturation through frictional heating produced by tissue ionic agitation from high-frequency alternating current. This technology can be used to destroy primary and metastatic hepatic lesions generally considered nonresectable or nonoperable, thus providing patients with these tumors, who have few treatment options, a relatively safe and effective alternative with the potential for improved chance of survival. Knowledge of the broad spectrum of potential complications associated with radiofrequency ablation (RFA) is essential for prevention, early detection, and proper management. Combining RFA with other modalities such as surgical resection or hepatic artery infusional chemotherapy is feasible, has increased the pool of operable patients, and may improve treatment efficacy and clinical outcome in properly selected patients. The approach to perform RFA percutaneously, laparoscopically, or during laparatomy should take into consideration tumor characteristics, imaging and technical limitations, and the role of other treatment modalities. Therefore, patients considered for RFA should be evaluated within the context of a multidisciplinary approach to insure proper patient selection and coordination of adjunct therapy.

Fluorescence spectroscopy accurately detects irreversible cell damage during hepatic radiofrequency ablation

BACKGROUND

A current limitation of hepatic radiofrequency ablation (RFA) is an inability to detect ablation margins in real time. Thermal injury from RFA alters the biochemical properties governing tissue fluorescence. We hypothesized that the changes in hepatic fluorescence measured during hepatic RFA could be used to detect irreversible hepatocyte damage accurately and to determine ablation margins in real time.

METHODS

RFA was performed on healthy pig livers and monitored in vivo simultaneously for fluorescence and temperature by a fiberoptic micro-interrogation probe connected to a spectroscopy system. Ablations were stopped based on previously established real-time fluorescence spectral data, not based on temperature or time. To determine where in the ablated tissue cell death occurred, biopsies for transmission electron microscopy were taken from 4 areas of 3 specimens: (1) nonablated liver, (2) hemorrhagic zone/normal liver interface, (3) hemorrhagic zone/coagulated zone interface, and (4) coagulated zone. In vitro fluorescence emission intensity was determined at each biopsy site.

RESULTS

Peak hepatic fluorescence intensity occurred at 470 nm and decreased as RFA progressed. Transmission electron microscopy evidence of irreversible hepatocyte damage occurred at the interface of the coagulation zone and the hemorrhagic zone and correlated with a 87.5% +/- 9% decrease in fluorescence emission intensity. Tissue fluorescent changes from thermal injury were unaffected by tissue cooling.

CONCLUSION

Fluorescence spectroscopy accurately detected hepatocellular thermal injury from RFA in real time and can detect irreversible cell damage during tissue thermal therapy.

Hypertrophied anal papillae and fibrous anal polyps, should they be removed during anal fissure surgery?

AIM: Hypertrophied anal papillae and fibrous anal polyps are not given due importance in the proctology practice. They are mostly ignored being considered as normal structures. The present study was aimed to demonstrate that hypertrophied anal papillae and fibrous anal polyps could cause symptoms to the patients and that they should be removed in treatment of patients with chronic fissure in anus.

METHODS: Two groups of patients were studied. A hundred patients were studied in group A in which the associated fibrous polyp or papillae were removed by radio frequency surgical device after a lateral subcutaneous sphincterotomy for relieving the sphincter spasm. Another group of a hundred patients who also had papillae or fibrous polyps, were treated by lateral sphincterotomy alone. They were followed up for one year.

RESULTS: Eighty-nine percent patients from group A expressed their satisfaction with the treatment in comparison to only 64% from group B who underwent sphincterotomy alone with the papillae or anal polyps left untreated. Group A patients showed a marked reduction with regard to pain and irritation during defecation (P = 0.0011), pricking or foreign body sensation in the anus (P = 0.0006) and pruritus or wetness around the anal verge (P = 0.0008).

CONCLUSION: Hypertrophied anal papillae and fibrous anal polyps should be removed during treatment of chronic anal fissure. This would add to effectiveness and completeness of the procedure.

Thermal profile of radiofrequency energy in the inferior glenohumeral ligament

PURPOSE

Currently, two different methods of applying radiofrequency (RF) energy (monopolar and bipolar) are available to the surgeon for thermal shortening of the shoulder capsule. The objective of this study was to investigate the temperature changes and the thermal conduction across the human inferior glenohumeral ligament (IGHL) during radiofrequency energy application.

METHODS

Thermistors were secured onto both the intra-articular and extra-articular surfaces of human IGHL. Monopolar RF energy and bipolar RF energy were delivered to the intra-articular surface at the manufacturer's recommended settings. Pre-treatment and post-treatment ligament lengths, widths, heating times, and temperatures were measured and compared.

RESULTS

For the monopolar devices, temperature spikes to 89 degrees C were recorded for the set temperature of 67 degrees C, averaging 77 degrees C +/- 10 degrees C. Temperatures across the ligament averaged 48 degrees C +/- 3 degrees C. For both devices, the IGHL became thicker with higher RF settings. Recorded temperatures decreased as distance increased from the point of application. Maximum temperatures occurred at least 6 to 7 seconds after cessation of energy application.

CONCLUSIONS

The bipolar and monopolar devices had similar conduction times across the ligament, suggesting that this occurs by simple diffusion of heat. Bipolar and monopolar devices were equally efficacious for capsular shrinkage if the extent of the shortening is tightly defined.

CLINICAL RELEVANCE

The thermal probe should not rest in one position for an extended period of time during RF energy application because, as our study showed, the monitoring of temperature or the visualization of tissue change is not efficacious for determining the end point of thermal shrinkage of the shoulder capsule.

A randomized study between excision and marsupialization and radiofrequency sinus excision in sacro-coccygeal pilonidal disease

BACKGROUND

The surgical approach to pilonidal sinus disease is open to debate. This prospective, randomized study was aimed to compare the outcome of the excision and marsupialization and the sinus excision technique by radiofrequency.

MATERIALS AND METHODS

Thirty patients of chronic pilonidal sinus disease were randomly assigned to radiofrequency sinus excision (n = 15) and excision and marsupialization (n = 15). The parameters measured included intraoperative and postoperative data, wound-related complications, and recurrence. Patient satisfaction score was assessed at 1-year follow-up.

RESULTS

The operation time, postoperative pain, hospital stay, and off work periods were significantly less (p < 0.05) in the technique employing radiofrequency surgery. At 1-year follow-up, there was 1 case of recurrence in each group. The patients from radiofrequency group expressed better satisfaction than the patients operated by marsupialization.

CONCLUSION

Radiofrequency sinus excision technique needs a shorter hospital stay with reduced postoperative pain and early resumption to work in comparison with the sinus excision and marsupialization technique.

Saline-linked surface radiofrequency ablation: factors affecting steam popping and depth of injury in the pig liver

SUMMARY BACKGROUND DATA

Saline-linked surface radiofrequency (RF) ablation is a new technique for applying RF energy to surfaces. The surface is cooled, which prevents charring and results in deeper coagulation. However, subsurface heating may lead to steam formation and a form of tissue disruption called steam popping. We determined parameters that predict steam popping and depth of tissue destruction under nonpopping conditions. A commercially available saline-linked surface RF cautery device (Floating Ball 3.0, TissueLink, Inc.) was used.

METHODS

One hundred eighty circular lesions were created varying in lesion diameter, duration, power, and inflow occlusion. Variables affecting popping were determined. Then factors influencing lesion depth were studied at fixed nonpopping diameter/power combinations (1 cm/10W, 2 cm/15W, 4 cm/60W). Tissue viability was determined in selected samples by staining of tissue NADH.

RESULTS

The probability of steam popping was directly related to power level and inflow occlusion, and indirectly related to lesion diameter. Depth of injury under safe nonpopping conditions was directly related to power, lesion size, and inflow occlusion. Maximum depth in excess of 20 mm was achieved using a 4 cm diameter at 60W with inflow occlusion. Microscopy of NADH-stained tissues showed a complete cell killing in the macroscopically visible coagulated area.

CONCLUSIONS

Steam popping can be avoided by selecting power level/lesion diameter combinations. Tissue destruction to 20 mm can be safely achieved with short periods of inflow occlusion. The device has promise as a treatment of superficial tumors and close resection margins.

Learning curve for radiofrequency ablation of liver tumors: prospective analysis of initial 100 patients in a tertiary institution

OBJECTIVE

This study aims to evaluate the effect of operator experience on the treatment outcomes of radiofrequency ablation (RFA) for malignant liver tumors.

SUMMARY BACKGROUND DATA

RFA is gaining popularity as the ablative therapy of choice for liver tumors. It is generally considered a simple and safe technique, and little attention has been paid to the importance of operator experience in this treatment. A learning curve in this treatment modality has not been documented before.

PATIENTS AND METHODS

The clinical data and treatment outcomes of the initial 100 patients undergoing RFA for liver tumors (hepatocellular carcinoma, n = 84; metastasis, n = 15; cholangiocarcinoma n = 1) were collected prospectively. All patients were managed by a single team of surgeons and interventional radiologists. The data of the first 50 patients (group I) and the second 50 patients (group II) were compared.

RESULTS

RFA was performed by percutaneous (group I, n = 22; group II, n = 19), open (group I, n = 26; group II, n = 30) or laparoscopic (group I, n = 2; group II, n = 1) approach. In group I, 30 patients (60%) had a solitary tumor and 20 (40%) had multiple tumors; in group II, 35 patients (70%) had a solitary tumor and 15 (30%) had multiple tumors (P = 0.295). The size of the largest tumor was comparable between groups I and II (median, 2.8 cm in both groups; P = 0.508). Group II had significantly shorter hospital stay (median, 4.0 versus 5.5 days; P = 0.048), lower morbidity rate (4% versus 16%; P = 0.046) and higher complete ablation rate (100% versus 85.7%; P = 0.006) than group I. There was 1 hospital death (2%) in group I and 0 in group II. By multivariate analysis, treatment period (group I versus group II) was an independent significant factor affecting the morbidity rate and complete ablation rate.

CONCLUSIONS

A low complication rate and a high complete ablation rate could be achieved with the accumulated experience from the first 50 cases of RFA for liver tumors by a specialized team. This study demonstrates that there is a significant learning curve in RFA for liver tumors.

Adrenal Neoplasms: CT-guided Radiofrequency Ablation—Preliminary Results

PURPOSE

To evaluate initial experience with radiofrequency (RF) ablation of adrenal neoplasms.

MATERIALS AND METHODS

Thirteen adrenal masses in 12 patients (bilateral metastases in one patient) were treated with computed tomography (CT)-guided percutaneous RF ablation. Eleven adrenal lesions were metastases (five from lung cancer, four from renal cell carcinoma, and two from melanoma); one lesion was a pheochromocytoma and one was an aldosteronoma. There were 10 men and two women (average age, 58 years; range, 40-77 years) in the study; average adrenal mass diameter was 3.9 cm (range, 1-8 cm). Average number of RF applications per adrenal mass was 2.7 (range, 1-5 applications); average time per application was 7.8 minutes (range, 4-13 minutes). An internally cooled single electrode was used in five sessions; an internally cooled cluster electrode was used in eight sessions.

RESULTS

Average follow-up was 11.2 months (range, 1-46 months). Eleven of 13 lesions were treated successfully with RF ablation after one session. Successful treatment was defined as lack of enhancement of the treated region on follow-up CT images and resolution of the biochemical abnormality in two patients. In two patients with large adrenal lesions (4 and 8 cm in diameter), enhancement of residual tissue was observed after one treatment session; this finding was indicative of residual tumor. One patient with thrombocytopenia that resulted from chemotherapy had a small hematoma, but no transfusion was required. No patient developed hypertension during the RF application. No patient with metastases had recurrent tumor at the treated site, and this lack of recurrence indicated effective local control; 11 patients had progression of metastatic disease at extraadrenal sites.

CONCLUSION

Preliminary data suggest that CT-guided RF ablation is an effective technique for local control of adrenal neoplasms.

Ultrasound-guided percutaneous thermal ablation of hepatocellular carcinoma using microwave and radiofrequency ablation

AIM

To investigate the therapeutic efficacy of thermal ablation for treatment of hepatocellular carcinoma (HCC) using microwave and radiofrequency (RF) energy application.

MATERIALS AND METHODS

A total of 190 nodules in 97 patients (84 male, 13 female; mean age 53.4 years, range 24-74 years) with HCC were treated with microwave or RF ablation in the last 4 years. The applicators were introduced into the tumours under conscious analgesic sedation by intravenous administration of fentanyl citrate and droperidol and local anaesthesia in both thermal ablation procedures. The patients were then followed up with contrast-enhanced computed tomography (CT) to evaluate treatment response. Survival was analysed using the Kaplan-Meier method.

RESULTS

Complete ablation was obtained in 92.6% (176/190) nodules. The complete ablation rates were 94.6% (106/112) in microwave ablation and 89.7% (70/78) in RF ablation. The complete ablation rates in tumours</=2.0, 2.1-3.9 and >/=4.0 cm were 93.1, 93.8 and 86.4%, respectively. Local recurrence was found in 9.5% nodules and the rates in tumours</=2.0, 2.1-3.9 and >/=4.0 cm in diameter were 3.4, 9.9 and 31.8%, respectively. In the follow-up period, 7.1% nodules ablated by microwave and 12.8% by RF presented local recurrence. The 1, 2 and 3-year distant recurrence-free survivals were 47.2, 34.9 and 31.0%, respectively. Estimated mean survival was 32 months, and 1, 2 and 3-year cumulative survivals were 75.6, 58.5, and 50.0%, respectively. One and 2 years survivals of Child-Pugh class A, B and C patients were 83.8 and 70.4%, 78.2 and 53.2%, 36.3 and 27.3%, respectively.

CONCLUSION

Thermal ablation therapy by means of microwave and RF energy application is an effective and safe therapeutic technique for hepatocellular carcinoma. Large tumours can be completely ablated, but have a significantly higher risk of local recurrence at follow-up.

Radiofrequency ablation of renal cell carcinoma

Small renal cell carcinomas of less than 4 cm diameter have been detected increasingly in asymptomatic patients because of the widespread use of cross-sectional imaging. Radical or partial nephrectomy is generally considered the reference for the treatment of a solitary renal cell carcinoma. However, for those patients who are not candidates for surgery, minimally invasive procedures may be desirable. Although percutaneous radiofrequency ablation for the treatment of renal cell carcinoma is a recent innovation, the results of preliminary clinical series and animal studies are encouraging, and show it to be technically feasible with minimal morbidity. In this article, we review the technique, indications, imaging findings, as well as the results of clinical and animal studies of radiofrequency ablation for the treatment of renal cell carcinoma.

Automatic model-based evaluation of magnetic resonance-guided radio frequency ablation lesions with histological correlation

PURPOSE

To develop a model-based method for automatic evaluation of radio frequency (RF) ablation treatment using magnetic resonance (MR) images.

MATERIALS AND METHODS

RF current lesions were generated in a rabbit thigh model using MR imaging (MRI) guidance. We created a 12-parameter, three-dimensional, globally deformable model with quadric surfaces that delineates lesion boundaries and is automatically fitted to MR grayscale data. We applied this method to in vivo T2- and contrast-enhanced (CE) T1-weighted MR images acquired immediately post-ablation and four days later. We then compared results to manually segmented MR and three-dimensional registered corresponding histological boundaries of cellular damage.

RESULTS

Resulting lesions featured a two-boundary appearance with an inner region and an outer hyperintense margin on MR images. For automated vs. manual MR boundaries, the mean errors over all specimens were 0.19 +/- 0.51 mm and 0.27 +/- 0.52 mm for the inner surface, and -0.29 +/- 0.40 mm and -0.12 +/- 0.17 mm for the outer surface, for T2- and CE T1-weighted images, respectively. For automated vs. histological boundaries, mean errors over all specimens were 0.07 +/- 0.64 mm and 0.33 +/- 0.71 mm for the inner surface, and -0.27 +/- 0.69 mm and 0.02 +/- 0.43 mm for the outer surface, for T2- and CE T1-weighted images, respectively. All boundary errors compared favorably to MR voxel dimensions, which were 0.7 mm in-plane and 3.0 mm thick.

CONCLUSION

The method is accurate both in describing MR-apparent boundaries and in predicting histological response and has applications in lesion visualization, volume estimation, and treatment evaluation.

Radiofrequency Ablation: Modeling the Enhanced Temperature Response to Adjuvant NaCl Pretreatment

PURPOSE

To characterize the effects of volume and concentration of adjuvant NaCl pretreatment on radiofrequency (RF) ablation and to model these results to determine their applicability to in vivo systems.

MATERIALS AND METHODS

Standardized 1-L 5% agar phantoms were constructed with central wells of varying volume that were filled with a protein-based polymer gel of varying NaCl concentration (0%-35%). RF ablation to the maximum system current output (2000 mA) was applied to internally cooled 2-cm electrodes placed in the center of the gel wells. Remote thermometry was performed 20 mm from the electrode. Temperatures generated within the phantom were then used to model the response surface by using regression analysis. The generated model was then applied to previously published in vivo data to determine its applicability to a porcine liver tissue model. Statistical analyses included one-way analysis of variance to compare the temperatures reached with different NaCl concentrations and volumes with those reached without NaCl. In addition, modeled functions were evaluated for goodness of fit and the statistical significance of their coefficients.

RESULTS

NaCl volume and concentration had significant effects on RF-generated heating of the agar phantoms. The mean maximum temperature, 91.4 degree C +/- 0.8 (SD), was reached with 3.5 mL of 10% NaCl gel. This was significantly higher than the mean temperature reached in phantoms containing 0% NaCl gel, 40.3 degree C +/- 4.9 (P <.001). Heat increases to the maximum temperature correlated strongly with the deposited RF energy, with maximum temperatures limited by the current output of the RF generator. The response surface was defined by a generator energy-dependent region and a generator current-limited region, which were best modeled by a modified gamma-variate function and an exponential function, respectively (r2 = 0.92). This model correlated well with previously published in vivo data (r2 = 0.86).

CONCLUSION

Modulation of electrical conductivity has different effects on RF ablation response that are dependent on generator capabilities and the volume and concentration of NaCl pretreatment.