Microwave ablation of hepatic tumors with a third generation system: loco­regional efficacy in a prospective cohort study with intermediate term follow-up.

PURPOSE: To evaluate the safety and intermediate-term efficacy of percutaneous microwave ablation (MWA) in primary and secondary liver tumors using a third generation MWA device, under ultrasound guidance. PATIENTS AND METHODS: Sixty-two patients (median age 74 years, 73 % males) with 69 liver tumors were enrolled in this prospective observational study. Forty-seven patients (76 %) had hepatocellular carcinoma (HCC) and 15 (24 %) metastases. Median follow-up was 3.6 years. RESULTS: Median tumor diameter at contrast enhanced computed tomography was 23 mm (I-III quartiles, 18 - 31 mm). All procedures were performed percutaneously using a 2.45 GHz generator. Median ablation time was 10 minutes (I-III quartiles, 10 - 14 minutes). A single percutaneous antenna insertion was performed for 56/69 (81 %) of the tumors. Technical success was obtained in all tumors. Primary efficacy at 24 hours was achieved in 68/69 (99 %) tumors. The overall one-year cumulative local tumor progression rate was 15.1 % (95 % CI, 7.7 - 24.8 %) with no significant difference between HCC and metastases (p = 0.26). There was one procedure-related mortality (1.6 %) and one major bleeding (1.6 %). CONCLUSION: Microwave ablation is a valid option for thermal ablation of HCC and liver metastases with comparable complication rate to other local ablative procedures.

Cox-2 inhibition enhances the activity of sunitinib in human renal cell carcinoma xenografts.

BACKGROUND: Sunitinib (Su), a tyrosine kinase inhibitor of VEGFR, is effective at producing tumour response in clear cell renal cell carcinoma (cRCC), but resistance to therapy is inevitable. As COX-2 is a known mediator of tumour growth, we explored the potential benefit of COX-2 inhibition in combination with VEGFR inhibition in attempts at delaying tumour progression on Su. METHODS: COX-2 expression was compared with areas of hypoxia in tumours that progressed on Su vs untreated tumours. Mice bearing human cRCC xenografts were treated with Su and the COX-2 inhibitor, celecoxib, and the effects on tumour growth were assessed. Sequential vs concurrent regimens were compared. RESULTS: COX-2 expression was increased in cRCC xenografts in areas of tumour hypoxia. The combination of Su and celecoxib achieved longer times to tumour progression compared to treatment with either agent alone or to untreated control animals in four models. This effect was seen with concurrent but not with sequential therapy. CONCLUSION: COX-2 inhibition can extend the effectiveness of VEGFR inhibition. This effect is dependent on the timing of therapy. Clinical trials combining Su and COX-2 inhibitors should be considered as a means delaying time to progression on sunitinib in patients with metastatic cRCC.

Artificial Intelligence in Interventional Radiology: A Literature Review and Future Perspectives.

The term "artificial intelligence" (AI) includes computational algorithms that can perform tasks considered typical of human intelligence, with partial to complete autonomy, to produce new beneficial outputs from specific inputs. The development of AI is largely based on the introduction of artificial neural networks (ANN) that allowed the introduction of the concepts of "computational learning models," machine learning (ML) and deep learning (DL). AI applications appear promising for radiology scenarios potentially improving lesion detection, segmentation, and interpretation with a recent application also for interventional radiology (IR) practice, including the ability of AI to offer prognostic information to both patients and physicians about interventional oncology procedures. This article integrates evidence-reported literature and experience-based perceptions to assist not only residents and fellows who are training in interventional radiology but also practicing colleagues who are approaching to locoregional mini-invasive treatments.

Immuno-oncology and interventional oncology: a winning combination. The latest scientific evidence.

OBJECTIVE: Interventional oncology (IO) is an emergent field in interventional radiology that can be considered the fourth pillar of oncology. Interventional oncology has the unique capability to treat malignancy in a loco-regional fashion enabling curative (percutaneous ablation), disease stabilization (intra-arterial chemo/radioembolization), and palliative treatment (such as biliary drainage or nephrostomy). The whole arsenal of IO acts by inducing necrosis and apoptosis, with interactions with the tumour's microenvironment potentially crucial for oncological outcomes. Considering that tumour's microenvironment is a pivotal target for both immuno-oncology and interventional-oncology, the interactions between these two anti-tumour weapons must be investigated to understand their synergy. Interestingly, substantial efforts have been directed to understand which technique combinations are best for specific tumours. This review article summarizes the latest scientific evidence highlighting the future prospective of this winning combination, integrating evidence-reported literature and experience-based perceptions.

The ten commandments of chemoembolization: expert discussion and report from Mediterranean Interventional Oncology (MIOLive) congress 2017.

Transarterial therapies in the setting of primary and secondary liver malignancies are becoming an essential part of the oncology landscape. The mechanism of action of c-TACE is the induction of tumor necrosis due to the high concentration of the chemotherapeutic that is delivered only locally and to the embolic effect that causes ischemia and increased dwell time of the chemotherapeutic in the tumor. Recently, DEB-TACE has emerged as a variation of c-TACE with the potential for the selective delivery of large amounts of drugs to the tumor for a prolonged period, thereby decreasing plasma levels of the chemotherapeutic agent and related systemic effects. There is an increasing consensus that compared with conventional lipiodol-based regimen, DEB-TACE offers standardized methodology, is more reproducible and is associated with improved response and significantly better safety profile. Using an easy to access point by point format, this manuscript summarizes the expert discussion from the Mediterranean Interventional Oncology Live Congress (MIOLive 2017) about the role of TACE in the treatment of liver tumors.

The ten commandments of liver ablation: expert discussion and report from Mediterranean Interventional Oncology (MIOLive) congress 2017.

Percutaneous liver ablation has become a cornerstone of the recently developed subspecialty of radiology - that is, interventional oncology. Thermal ablation technology has evolved rapidly during the past decades, with substantial technical and procedural improvements that can help obtain better clinical outcomes and safety profiles. Due to the widespread use of percutaneous ablation, a comprehensive review of the methodologic and technical considerations seems to be mandatory. This article summarizes the expert discussion and report from Mediterranean Interventional Oncology Live Congress (MIOLive 2017) that was held in Rome, Italy, integrating evidence-reported literature and experience-based perceptions, to assist not only residents and fellows who are training in interventional radiology but also practicing colleagues who are approaching to this locoregional treatment.

The ten commandments of hepatic radioembolization: expert discussion and report from Mediterranean Interventional Oncology (MIOLive) congress 2017.

Microsphere and particle technology represent the next-generation agents that have formed the basis of interventional oncology, an evolving subspecialty of interventional radiology. One of these platforms, yttrium-90 microspheres, is increasingly being used as a treatment modality for primary and secondary liver tumors. Due to the widespread use of radioembolization, a comprehensive review of the methodologic and technical considerations seems to be mandatory. This article summarizes the expert discussion and report from Mediterranean Interventional Oncology Live Congress (MIOLive 2017) that was held in Rome, Italy, integrating evidence-reported literature and experience-based perceptions, to assist not only residents and fellows who are training in interventional radiologists but also practicing colleagues who are approaching to this intra-arterial treatment.

A family study of anticardiolipin antibodies and associated clinical conditions.

PURPOSE: To determine the frequency of anticardiolipin antibodies (aCL) and their clinical sequelae in family members of aCL-positive patients. PATIENTS AND METHODS: A prospective serologic and clinical evaluation was performed on 23 patients with elevated aCL titers, 87 blood relatives, 18 spouses, and 37 controls. aCL and antinuclear antibodies (ANA) were measured and clinical histories were assessed for all probands, relatives, spouses, and controls. RESULTS: Fifty of 87 relatives screened (57%) had evidence of autoantibody production (aCL and/or ANA). Twenty-nine (33%) had positive aCL titers. Twenty were positive for aCL-immunoglobulin (Ig) G, 7 had evidence of both aCL-IgG and aCL-IgM, and an additional 2 were positive for aCL-IgM alone. In contrast, only 1 spouse was aCL-IgG positive. Thirty-two relatives and 1 spouse were ANA positive. All controls were negative for aCL and ANA. Significant differences were noted between relatives and spouses for aCL-IgG (P < 0.00001) and aCL-IgM titers (P < 0.0066), and also between relatives and controls (P < 0.00001 for both). Clinically, 4 cases of systemic lupus erythematosus (SLE), 4 SLE-like diseases, and 8 aCL-associated illnesses (2 premature strokes, 3 recurrent fetal losses, 1 recurrent thrombosis, and 2 cases of thrombocytopenia) were documented in the relatives. All cases were associated with aCL and/or ANA production. CONCLUSIONS: ANA, aCL, and clinical events associated with antiphospholipid antibodies occur with increased frequency in relatives, but not spouses of aCL-positive probands. These results suggest that aCL-related illnesses may be familial.

Pleural effusion and ventilation/perfusion scan interpretation for acute pulmonary embolus.

UNLABELLED: This study was conducted to determine if pleural effusion size affects ventilation/perfusion (V/Q) scan interpretation algorithms for acute pulmonary embolus (PE). METHODS: Retrospective analysis identified 163 consecutive patients undergoing angiography for PE with radiographic evidence for pleural effusion. V/Q scanning was performed in 94 (58%) of cases and reported using original Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) criteria. Effusions were classified as small, large and/or bilateral. Radiographic and scintigraphic results were compared with regard to size and location of abnormalities. RESULTS: Of the 163 patients, 57 (35%) had angiographically-proven PE, 77 (47%) had at least one large pleural effusion and 86 (53%) had a small effusion; 33 (43%) with large effusions and 24 (28%) with small effusions had emboli at angiography. Thirty-six of 119 patients (30%) with clear chest radiographs (a control group) had PE. Thus, large effusions were associated with a higher incidence of PE than those with small effusions or clear lungs (p < 0.05). Of those with V/Q scanning, 26 of 94 (28%) had a solitary large effusion, with 12 (46%) positive for emboli. V/Q-matched abnormalities limited to effusion size were found in 16 with a solitary large effusion and 10 with a solitary small effusion. In both groups, 50% were angiographically positive for emboli. Twenty-three (66%) of 35 with bilateral effusions had corresponding V/Q-matched defects at one (n = 11) or both (n = 12) lung bases, and 9 (39%) were positive for emboli. In total, 45% with a V/Q-matched defect of equivalent size to the effusion were angiographically positive for PE. CONCLUSION: Pulmonary emboli are associated with pleural effusions of all sizes. Matched V/Q defects corresponding to radiographically-evident pleural effusions are of intermediate probability for PE. Thus, revision of the traditional lung scan interpretive criteria based upon pleural effusion size is not warranted.

A comparison of iopromide with iopamidol and iohexol for contrast-enhanced computed tomography.

RATIONALE AND OBJECTIVES: Iopromide is a new monomeric, nonionic contrast agent that exhibits low osmolality and low viscosity in high concentration in aqueous solutions. Double-blind, randomized clinical trials have established the efficacy, safety, and tolerance of iopromide for excretory urography, coronary angiography, routine and digital subtraction angiography, and phlebography. However, iopromide had not previously been evaluated in blinded clinical trials for contrast-enhanced computed tomography (CECT). Thus, a double-blind, prospective randomized trial was performed to compare the efficacy, safety, adverse experience profile, and tolerance of iopromide to that of iopamidol and iohexol in patients requiring CECT of the head or body. METHODS: Of 190 patients entered into the study, 95 received iopromide and 95 received a comparator (iopamidol, n = 55; and iohexol, n = 40) at 300 mg I/mL. Efficacy, adverse experiences (AEs), and tolerance were measured, and a safety profile was obtained that monitored changes at 24 hours in physical examination, vital signs, hematologic profile, and blood chemistries. RESULTS: Efficacy was similar for all drugs with excellent/good visualization in 98.4% of studies. The total number of patients reporting AEs was equivalent (iopromide 13.8%, comparators 12.6%; P > .10). However, although 2.5% of patients in the iopromide and iopamidol groups had possibly related mild AEs, 15% receiving iohexol had related AEs, one of which was severe. Excellent tolerance was noted, with no patients reporting localized pain; there were low rates of mild to moderate warmth on injection (8.5% for iopromide versus 9.5% for comparators; P > .10). Safety profiles were comparable. Postprocedure, there were no significant changes or significant differences between groups, except for a significantly increased incidence of systolic blood pressure decrease by greater than 20 mm Hg at 24 hours in the comparator group. CONCLUSIONS: Iopromide has an efficacy, safety, and tolerance profile comparable to that of iopamidol and iohexol at 300 mg I/mL for head and body CECT. It may have a superior adverse experience profile to iohexol, but is similar to iopamidol. Thus, iopromide is a reasonable choice of nonionic contrast medium for all CECT procedures.

Monitoring of radio frequency tissue ablation in an interventional magnetic resonance environment. Preliminary ex vivo and in vivo results.

RATIONALE AND OBJECTIVES: The authors evaluate the feasibility of monitoring radio frequency (RF) ablation in an interventional, open-configuration, 0.5-tesla magnetic resonance (MR) environment. METHODS: Ex vivo and in vivo RF coagulation necrosis were induced in porcine paraspinal muscle tissue using a 300 kHz monopolar RF generator applying 5 to 20 W over 3 to 9 minutes. Images were acquired simultaneous to RF application, after RF application, and in an intermittent mode (60 seconds of RF followed by 15 seconds of MR imaging). Temperature changes were monitored based on amplitude (ex vivo) and phase alterations (in vivo) of a T1-weighted graded refocused echo (GRE) sequence enabling an update every 2.5 seconds. A standardized color-coded subtraction technique enhanced signal changes. Additionally, T2- and T1-weighted spin echo (SE) images were acquired with and without intravenous contrast. Macroscopic coagulation size was compared with lesion size seen on MR images. RESULTS: Although lesion diameters were related directly to applied RF power, the application mode had no significant impact on coagulation size (P > 0.05). As could be expected, MR imaging during RF ablation resulted in major image distortion. Radio frequency effects were seen on images acquired in the continuous and intermittent modes. Coagulation size seen on GRE images correlated well with macroscopy both ex vivo (r = 0.89) and in vivo (r = 0.92). Poorer correlation was found with postinterventional SE sequences (r = 0.78-0.84). CONCLUSIONS: Magnetic resonance monitoring of RF effects is feasible both ex vivo as well as in vivo using temperature-sensitive sequences in an open-configuration MR environment.

A new assay for quantifying human reticulocytes.

The authors describe a new method for quantitative reticulocyte analysis. The assay uses a conventional clinical blood cell analyzer to size a patient's red blood cell neocyte population, which relates to the reticulocyte fraction in a linear fashion. Blood is layered atop Stractan (arabino-galactan polysaccharide) and centrifuged for 30 minutes at 1,500 X g. This density medium fractionation process enriches the Stractan layer with neocytes by up to 20-fold as determined by G6PD enzyme analysis. The mean corpuscular volume (MCV) of the red blood cells partitioning in the Stractan layer and the starting whole blood is then measured. The ratio of the two MCV measurements is then related to the reticulocyte percentage by a standard curve. In 93 patients, the derived MCV ratio was linearly correlated with manual reticulocyte counts (r = 0.96/slope = 0.99). Agreement of results obtained for single samples was within 0.2%. The assay's within-run and between-run precision is excellent (coefficient of variation less than 1%). The assay provides data on the percentage of reticulocytes in whole blood with an accuracy and precision that is at least 20 times greater than conventional microscopic technics.

Paradoxic effect of multiple mild coagulation factor deficiencies on the prothrombin time and activated partial thromboplastin time.

Single coagulation factor deficiencies predictably prolong the prothrombin time (PT) and activated partial thromboplastin time (APTT) at levels below 35% of normal activity. Acquired coagulopathies generally are characterized by multiple coagulation factor deficiencies. The effect was studied of such combined deficiencies on the PT/APTT using plasma from patients congenitally deficient in specific factors and pooled normal plasma. The PT begins to lengthen when individual factor levels fall below 25%. The APTT becomes prolonged when the levels of Factor V fall below 45%; the levels of Factors II and XI fall below 40%; and the levels of Factors I, V, VII, VIII, IX, and XII fall below 25% of normal. When plasma samples containing 50% activity of a single factor and 100% of all other factors were prepared by mixing the congenitally deficient plasma samples with the normal pool, the resulting mixtures had normal PT and APTT values. However, when two of these 50% factor-deficient plasmas were combined so that the mixture contained 75% activity of two coagulation factors and 100% of all other factors, the resulting PT and APTT were prolonged over the clotting times of either 50% factor-deficient plasma. Similar findings were obtained in patients with mild factor reductions caused by warfarin treatment. These data indicate that prolongations of the PT and APTT in disorders of coagulation affecting multiple factors represent less of a reduction in factor levels than is generally appreciated. This may explain the poor clinical correlation between abnormalities in these test results and clinical bleeding in acquired disorders of hemostasis.

Clinical utility of serum tests for iron deficiency in hospitalized patients.

Serum iron and ferritin measurements lack the requisite sensitivity and/or specificity to accurately diagnose iron deficiency. To determine their utility in hospitalized patients, the authors compared the results of these tests with the presence of stainable iron in bone marrow aspirates of 301 patients. Forty (13.3%) had absent marrow iron. The serum diagnosis of iron deficiency was accepted on the basis of the following: iron less than 11 mumol/L, total iron-binding capacity (TIBC) greater than 45 mumol/L, transferrin saturation (%Sat) less than 0.20, and ferritin less than 13 micrograms/L for females and less than 25 micrograms/L for males. Using these criteria, iron deficiency was correctly diagnosed by serum iron in 41%, TIBC in 84%, %Sat in 50%, and ferritin in 90% of the patients. The serum ferritin is clearly the only useful serum test for diagnosing iron deficiency in hospitalized patients but is limited by a low sensitivity. The bone marrow examination is the most sensitive test for diagnosing iron deficiency in hospitalized patients.

Comparison of bolus and constant infusion methods of gadolinium administration in MR angiography.

PURPOSE: To determine whether the method of delivery of gadolinium can alter optimal small-vessel detail in MR angiography. METHODS: Six healthy volunteers were studied with MR angiography using both a constant infusion and a bolus method of contrast administration to a total dose of 0.1 mmol/kg. Both three-dimensional time-of-flight and 3-D phase-contrast techniques were used. RESULTS: Constant infusion did not prove superior to bolus administration of contrast. With both techniques, gadolinium enhancement uniformly improved visualization of small vessels. Delay from the time of contrast administration to scan acquisition decreased vessel enhancement. CONCLUSIONS: Bolus administration of gadolinium is sufficient to improve small vessel visualization with MR angiography. When a series of contrast-enhanced images is to be obtained, MR angiographic sequences should be obtained first.

Comparison of single- and triple-dose contrast material in the MR screening of brain metastases.

PURPOSE: Although studies obtained with triple-dose contrast administration can show more brain metastases than those obtained with single-dose contrast material in patients with multiple metastases, such studies are costly and of limited clinical benefit. Since most patients who undergo screening have negative findings or a single metastasis, this study was performed to compare the clinical utility of single-dose versus triple-dose contrast administration in this large group of patients who could benefit from the possible increased sensitivity in lesion detection. METHODS: Ninety-two consecutive patients with negative or equivocal findings or a solitary metastasis on single-dose contrast-enhanced MR images underwent triple-dose studies. Findings were compared with a standard of reference composed of panel review and long-term follow-up. Further analysis was performed by comparing results with those obtained by two blinded readers. RESULTS: In all 70 negative single-dose studies, the triple-dose studies depicted no additional metastases in terms of the standard of reference. No statistically significant difference was seen between the results of the single- and triple-dose studies. For 10 equivocal single-dose studies, the triple-dose study helped clarify the presence or absence of metastases in 50% of the cases. In 12 patients with a solitary metastasis seen on the single-dose study, the triple-dose study depicted additional metastases in 25% of the cases. In the results of one of the two blinded readers, use of triple-dose contrast led to a statistical difference by decreasing the number of equivocal readings but at the expense of increasing the number of false-positive readings. CONCLUSION: Routine triple-dose contrast administration in all cases of suspected brain metastasis is not helpful. On the basis of our investigation, we conclude that the use of triple-dose contrast material is beneficial in selected cases with equivocal findings or solitary metastasis, although with the disadvantage of increasing the number of false-positive results.

Radiofrequency tissue ablation in the rabbit lung: efficacy and complications.

RATIONALE AND OBJECTIVES: We assessed the feasibility and safety of performing percutaneous radiofrequency ablation of pulmonary tissue in rabbits. METHODS: Using an aseptic technique and computed tomography (CT) guidance, insulated 19-gauge aspiration biopsy needles were inserted into the right lower lobe of eight New Zealand White rabbits. Radiofrequency was applied via a coaxial electrode for 6 min at 90 degrees C. Probe-tip temperature, tissue impedance, and wattage were recorded at baseline and at 60-sec intervals throughout the procedure. CT scanning was used to assess tissue destruction and the presence or absence of pneumothorax immediately after the procedure and at 24 hr, 3 days, 10 days, 21 days, and 28 days. Three rabbits were sacrificed immediately, and the remaining rabbits were euthanized at 24 hr and at 3 days. 10 days, and 28 days (two rabbits). Gross and microscopic pathology were obtained and correlated with CT findings. RESULTS: The mean initial tissue impedance was 509 +/- 197 omega, marked changes in tissue impedance were found during the procedure (240-1380 omega). Rigid temperature control required continuous manual fine-tuning of generator output. Increased respiratory rate was noted in one rabbit during the first 30 sec of radiofrequency application. Homogeneous, ovoid opacities 8.4 +/- 2.4 mm in diameter and 1.4 +/- 0.1 cm in length were found by CT scanning immediately after the procedure. These opacities showed maximal consolidation at 3 days, corresponding to coagulative necrosis and a peripheral acute inflammatory reaction. At 10 days, peripheral hyperattenuation with central hypoattenuation (early fibrosis surrounding degenerating blood products) was seen. Minimal residual fibrosis, pleural scarring, or both were noted by 28 days, suggesting a rapid, near-total recovery from the procedure. Lesion sizes were within 2 mm of gross pathologic findings. Pneumothoraces were noted in three of the eight rabbits (37.5%). CONCLUSION: Radiofrequency tissue ablation was safely performed in pulmonary parenchyma via a percutaneous, transthoracic approach using a coaxial needle technique. Tissue response to thermal injury was predictable and easily monitored by CT scanning with excellent radiologic-pathologic correlation.

Radiofrequency tissue ablation: increased lesion diameter with a perfusion electrode.

RATIONALE AND OBJECTIVES: We sought to induce large zones of coagulation necrosis using radiofrequency (RF) with perfusion electrodes and to define optimal parameters for this system. METHODS: We developed RF electrodes with internal cannulas to enable tip perfusion. Lesions were created with monopolar RF in ex vivo and in vivo liver and muscle tissue with and without perfusion of the electrode tip using 0 degree C saline. In separate experiments, wattage, current, procedure duration, tip exposure, and perfused tip temperatures were studied. RESULTS: In ex vivo liver tissue, a maximum lesion diameter of 3.1 cm without charring occurred with perfusion at 12 min and 50 W. In in vivo liver tissue with perfusion (tip temperature = 25-35 degrees C) and a 3-cm tip exposure, 80 W were deposited in muscle tissue and 65 W in liver tissue for 12 min without inducing charring. Lesion diameters were 4.5 cm and 2.4 cm, respectively. By comparison, without perfusion a maximum of 20 W could be deposited into either tissue type, resulting in 1.8-cm muscle lesions and 1.2-cm liver lesions. Tip temperatures between 45 degrees C and 55 degrees C resulted in charring. Smaller but predictable lesion diameters were created with a lower power, a shorter tip exposure, or both. Of all the parameters, diameter correlated best with the current applied. CONCLUSION: Perfusion of RF electrodes with chilled saline allows for increased power deposition without tissue charring, increasing the volume of coagulation necrosis created with a single electrode insertion. Perfusion electrodes therefore might decrease the number of probe insertions required for percutaneous tumor ablation therapy or allow for the treatment of larger lesions.

Radio-frequency tissue ablation of VX2 tumor nodules in the rabbit lung.

RATIONALE AND OBJECTIVES: The authors investigated whether small pulmonary malignancies could be treated with computed tomography (CT)-guided, percutaneously placed radio-frequency (RF) electrodes. METHODS: Pulmonary tumors were created in 11 New Zealand white rabbits by using CT-guided injection of a VX2 sarcoma cell suspension into the lower portion of the right lung. Tumors were allowed to grow 14-21 days to achieve a diameter of 6-12 mm. Electrodes were placed coaxially into the tumors via insulated 19-gauge Turner needles. Seven tumors were treated with RF for 6 minutes at 90 degrees C. Four tumors served as controls and were not treated. Follow-up CT and histopathologic analysis were performed on days 0-28. Specimens from treated rabbits were examined histopathologically on days 0 and 3 (n = 2 each), and days 1, 5, and 28 (n = 1 each). RESULTS: Immediately following treatment, CT images showed rounded opacities enveloping the tumor. This corresponded histologically to coagulation necrosis of tumor and surrounding alveoli. In all cases, at least 95% of treated tumor nodules were necrotic at histopathologic analysis. Peripheral residual nests of histologically viable tumor were seen in three rabbits (43%). Control rabbits showed growing tumor nodules without necrosis at autopsy (mean survival, 23 days after inoculation). Two RF-treated rabbits (29%) and one control rabbit (25%) had pneumothoraces. CONCLUSION: Percutaneous RF tissue ablation can be used to successfully treat small parenchymal tumor nodules within the lung in an animal model.

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

RATIONALE AND OBJECTIVES: We evaluated the parameters affecting the size and distribution of thermal tissue damage produced by radiofrequency electrodes. METHODS: Thermal lesions were produced by electrodes connected to a radiofrequency generator in specimens of liver (n = 143) and muscle (n = 20). Various combinations of probe tip exposure (0.5-8 cm), gauge (12-24 gauge), duration of treatment (0.5-12 min), and temperature (80-90 degrees C) were studied. The resulting volumes of tissue coagulation were measured and compared. RESULTS: Lesions equal to or less than 1.6 cm in diameter were symmetrically distributed around the electrode. Lesion diameter (but not length) increased with probe gauge and duration of treatment to a maximum of 6 min. However, lesions with mean diameters larger than 1.6 cm could not be produced using a single probe with any technique. Lesion length correlated with probe tip exposure from 1 to 8 cm (r2 = .996). Over the limited range investigated, increased temperature had minimal effects, except for tip exposures greater than 5 cm, in which larger and more uniform lesions resulted. Lesions varied equal to or less than 3 mm in diameter and equal to or less than 5 mm in length for each combination of variables. CONCLUSION: Radiofrequency ablation can accurately and reproducibly cause coagulative tissue necrosis. Necrosed tissue volume increases with length of exposed probe tip, larger probes, and sessions lasting at least 6 min.