Interactive MRI-guided radiofrequency interstitial thermal ablation of abdominal tumors: clinical trial for evaluation of safety and feasibility

This clinical trial was performed to evaluate the safety and feasibility of interactive MR-guided radiofrequency (RF) interstitial thermal ablation (ITA) performed entirely within the MR imager. RF-ITA was performed on 11 intra-abdominal metastatic tumors during 13 sessions. The RF electrode was placed under MR guidance on a .2-T system using rapid fast imaging with steady state precession (FISP) and true FISP images. A custom 17-gauge electrode was used and was modified in four sessions to allow circulation of iced saline for cooling during ablation. Tissue necrosis monitoring and electrode repositioning were based on rapid T2-weighted and short-inversion-time inversion recovery (STIR) sequences. Morbidity and toxicity were assessed by clinical and imaging criteria. The region of tissue destruction was visible in all 11 tumors treated, as confirmed on subsequent contrast-enhanced images. No significant morbidity was noted, and patient discomfort was minimal. In conclusion, interactive MR-guided RF-ITA is feasible on a clinical .2-T C-arm system with supplemental interventional accessories with only minor patient morbidity. The ability to completely ablate tumors with RF-ITA depends on tumor size and vascularity.

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.

Hepatic metastases: percutaneous radio-frequency ablation with cooled-tip electrodes

PURPOSE

To assess the feasibility and safety of using cooled-tip electrodes to increase the volume of coagulation necrosis obtained or reduce the number of treatment sessions necessary with percutaneous tumor radio-frequency (RF) ablation.

MATERIALS AND METHODS

Twenty-nine patients with 44 hepatic metastases (1.3-5.1 cm diameter) from colorectal (n = 22), gastric (n = 5), pancreatic (n = 1), or breast (n = 1) carcinoma were treated with RF ablation using cooled-tip, 18-gauge electrodes with 2-3 cm tip exposure. Each tumor was treated in one or two treatment sessions.

RESULTS

Technical success, ablation of all visualized tumor, was achieved in 40 (91%) metastases. Findings at computed tomography (CT) and magnetic resonance (MR) imaging performed 3-6 months after treatment confirmed complete necrosis of the entire metastasis in 66%. Disease-free survival was 50% at 12 months and 33% at 18 months, with localized progression of disease in 34% of treated lesions. Overall survival was 100%, 94%, and 89% at 6, 12, and 18 months, respectively. Only one complication, self-limited hemorrhage, was seen.

CONCLUSION

Use of cooled-tip electrodes was a safe and feasible adjunct for tumor RF ablation therapy that produced larger volumes of coagulation necrosis with fewer electrode insertions than is produced with other RF ablation techniques.

Prognostic indicators in acute pancreatitis: CT vs APACHE II

PURPOSE

To investigate the correlation between established contrast-enhanced computed tomography (CECT) criteria of disease severity in acute pancreatitis and the APACHE (Acute Physiology and Chronic Health Evaluation) II score and to assess the utility of each as prognostic indicators in acute pancreatitis.

MATERIALS AND METHODS

Over a 1-year period, prospective, consensus interpretation of the CECTs of 35 consecutive inpatients was performed with determination of the CECT grade, degree of necrosis, and severity index. The APACHE II score was calculated within 24 h of CECT. Multiple clinical endpoints were recorded: local complications (pseudocyst, abscess, or acute fluid collections requiring urgent surgical or radiological intervention), systemic disease (intensive care unit admission), and duration of hospitalization. Statistical analysis was performed to determine correlations.

RESULTS

No statistically significant correlation existed between the APACHE II score and CECT grade, the degree of necrosis, or the CECT severity index. Only the CECT grade and severity index correlated significantly with the occurrence of local complications (P = 0.0035 and 0.0048, respectively). The APACHE II score was superior to the CECT grade as a predictor of the need for ICU admission (P = 0.022 vs P = 0.035), and no other CECT criteria was a significant predictor of ICU admission.

CONCLUSION

The preferred clinical and imaging prognostic measures in acute pancreatitis, the APACHE II score and CECT criteria, do not correlate with one another in the commonly encountered, mixed primary and tertiary care population. The mathematical integration of CECT criteria and the APACHE II score fails to yield a predictor of outcome superior to the use of any one measure alone. CECT criteria best define local anatomic abnormality, and are superior to the APACHE II score as predictors of local complications. The APACHE II score is superior to all CECT criteria as an indicator of systemic disease severity (reflected in the need for ICU admission). The most effective initial triage would be immediate APACHE II calculation. Further use of imaging vs clinical assessment can then be individualized.

Liver tumor ablation: real-time monitoring with dynamic CT

RATIONALE AND OBJECTIVES

To determine whether incomplete contact of ethanol with tumor limits the success of percutaneous ethanol injection therapy.

MATERIALS AND METHODS

Percutaneous ethanol injection was performed in seven normal New Zealand white rabbits and 18 rabbits with 1-3-cm liver tumors 10-14 days after percutaneous implantation of suspended tumor cells. A 3-5 mL dose of ethanol was injected at a rate of 0.2 mL/sec either into normal liver remote from large vessels or directly into tumor. During and immediately after injection, axial, 2-mm-thick, contrast material-enhanced computed tomography scans were obtained at reach of three levels every 9 seconds.

RESULTS

In normal animals, virtually all injected ethanol tracked to the hepatic capsule. As ethanol was injected into tumors, peripheral tracking, similar to that seen in normal livers, or extratumoral puddling was observed. Ethanol-tumor contact was incomplete in 16 of 18 animals (89%). Histopathologic analysis showed incomplete tumor necrosis.

CONCLUSION

In this model of hepatic carcinoma metastasis, the tumor failed to hold sufficient ethanol for successful ablation by means of percutaneous ethanol injection therapy.

Transluminal radiofrequency tissue ablation with use of metallic stents

PURPOSE

To determine if transluminal coagulative necrosis can be induced by applying radiofrequency (RF) energy to indwelling metallic stents.

MATERIALS AND METHODS

RF energy was applied to metallic alloy stents (20-68 mm length, 5-16 mm diameter) in tissue phantom (n = 31), ex vivo bovine liver (n = 10), and in vivo porcine hepatic veins (n = 4). For ex vivo and in vivo liver experiments, RF was applied for 5-6 minutes, titrating generator output to produce 85 degrees-95 degrees C temperatures at the stent surface. Local and remote temperature sensing was performed. Imaging and pathologic studies documented the extent of coagulation necrosis.

RESULTS

Phantom studies demonstrated uniform temperature distribution along the entire stent length for all Elgiloy stents powered for 2 minutes with a minimum of 120 watts. Shorter stents required less power or reduced time to achieve uniform temperature. In ex vivo liver, 25-mm stents (n = 5) showed 8-10 mm of uniform circumferential coagulation necrosis along the entire stent length. Fifty-millimeter stents showed less uniform coagulation necrosis. For the in vivo stents (20 mm), 8-10 mm of uniform circumferential coagulation necrosis surrounded the stent along its entire length.

CONCLUSION

Metallic stents can be used to deliver transluminal RF energy from an external source, inducing heat deposition with resultant circumferential tissue coagulation. Clinical applications might include reduction of intimal proliferation in vascular diseases and/or treatment of periluminal tumors compressing the bile ducts, the urethra, or other luminal structures.

Mucinous ductal ectasia of the pancreas

PURPOSE

Pancreatic mucinous ductal ectasia (MDE) is a recently described and poorly understood disorder, with few cases reported in the imaging literature. We undertook this study to describe the spectrum of CT and pancreatographic findings of MDE and to investigate the incidence of associated pancreatic malignancy.

METHOD

The medical records, CT scans, and pancreatograms of 12 consecutive patients with pathologically proven MDE were retrospectively reviewed. There were nine men and three women, ranging in age from 37 to 72 years (mean 59 years).

RESULTS

Focal lesions involved primarily the uncinate (two patients) and head (eight patients) by CT imaging. The entire gland was involved in two patients. CT findings were variable and included focal pancreatic enlargement, a low attenuation or cystic mass, low attenuation of the entire gland, or marked ductal dilatation. Pancreatographic findings were more consistent, showing ductal dilatation with or without intraluminal filling defects, obstruction, or displacement. In all cases, findings at endoscopy were felt to be characteristic, with ductal dilatation, filling defects, or abundant mucus seen upon cannulation of the pancreatic duct. Carcinoma-in-situ was present in six cases, cellular atypia without malignancy in two, and in three cases the lesions were histologically benign. One case demonstrated invasive adenocarcinoma. No finding or group of findings on CT or pancreatography permitted differentiation between benign and malignant lesions.

CONCLUSION

MDE can present with a variety of appearances on CT, none of which is diagnostic. Pancreatography can be diagnostic if dilatation and intraluminal filling defects are seen. Carcinoma-in-situ, invasive adenocarcinoma, or cellular atypia is present in approximately 75%, but cannot be accurately diagnosed prospectively.

Focal hepatic lesions: effect of three-dimensional wavelet compression on detection at CT

PURPOSE

To evaluate the effect of three-dimensional, wavelet-based compression on the detection of focal hepatic lesions at computed tomography (CT).

MATERIALS AND METHODS

CT images obtained in 69 patients with focal hepatic lesions were studied (35 consecutive cases and 34 cases selected to be difficult on the basis of lesion size or contrast). Image data were compressed by means of a three-dimensional, wavelet-based algorIthm at ratios of 10:1, 15:1, and 20:1. Normal and abnormal sections (on original and compressed images) were reviewed by using an interactive workstation. Four readers rated the presence or absence of a lesion with a five-point scale.

RESULTS

At receiver operating characteristic analysis, no statistically significant difference was detected for all cases considered together. Differences approached but did not reach statistical significance for the diagnostic performance of one reader with compressed images (15:1, P = .054; 20:1, P = .051). For the subset of difficult cases, a significant difference was observed with 20:1 compressed images for one reader (P = .026). Diagnostic performance of readers was less certain in normal than in abnormal cases with both original and compressed images (difference was significant for 15:1 [P = .035] and 20:1 [P < .0001] compressed images).

CONCLUSION

Three-dimensional wavelet compression is satisfactory at ratios of at least 10:1. Additional studies with a larger sample would help confirm findings with higher ratios.

Percutaneous US-guided radio-frequency tissue ablation of liver metastases: treatment and follow-up in 16 patients

PURPOSE

To determine the potential efficacy of radio-frequency (RF) ablation of liver metastases during long-term follow-up.

MATERIALS AND METHODS

Sixteen patients with 31 hepatic metastases were treated with percutaneous, ultrasound-guided RF ablation. RF was applied to monopolar electrodes (2-3-cm tip exposure) either individually or within a multiprobe array (two to four probes) for 6 minutes at 90 degrees C over one to four treatment sessions per metastasis.

RESULTS

In only one of 75 sessions, a moderate complication, self-limited intraperitoneal hemorrhage, was observed. Four patients (four lesions) underwent surgical resection 15-60 days after RF treatment. Residual, viable tumor was seen in all of these patients. The remaining 12 patients were followed up for 9-29 months (mean, 18.1 months). In these patients, 18 of 27 lesions remained stable or decreased in size and showed no enhancement at computed tomography and/or magnetic resonance imaging for at least 9 months. Two patients died of disseminated disease at 13 months and one at 16 months. Disease-free survival was achieved in eight patients.

CONCLUSIONS

RF ablation appears to be a simple, safe, and potentially effective treatment for selected patients with liver metastases and may become a less invasive alternative to surgical therapy.

Saline-enhanced radio-frequency tissue ablation in the treatment of liver metastases

PURPOSE

To assess the effect of intraparenchymal saline injection on the results of radio-frequency (RF) tissue ablation.

MATERIALS AND METHODS

Ex vivo and in vivo animal RF ablation was performed with and without intraparenchymal saline injection. Initially, saline was injected as a bolus (1-20 mL) before RF application. For subsequent in vivo studies, saline was injected as a bolus before RF application or continuously (1 mL/min) during RF application. Finally, 14 patients with liver metastases and one patient with primary cholangiocarcinoma were treated with the continuous infusion technique. A single RF electrode (tip exposure, 1-3 cm) was used with various ablation parameters.

RESULTS

With pretreatment bolus injection of saline, lesions measured 1.4 cm +/- 0.1, 1.6 cm +/- 0.2, and 1.2 cm +/- 0.1 in ex vivo liver, in vivo animal muscle, and in vivo animal liver, respectively. Without saline enhancement, lesion sizes were 1.0 +/- 0.2, 1.2 +/- 0.2, and 0.8 +/- 0.1 cm, respectively. With continuous saline injection in in vivo pig liver, lesion size was 1.8 - 4.1 cm in diameter. In human tumors, necrosis volume was variable, but complete necrosis was seen in 13 of 25 lesions (diameter, 1.2-3.9 cm). Partial necrosis greater than 50% was seen in 12 lesions (diameter, 1.5-4.5 cm).

CONCLUSION

Saline-enhanced RF ablation might permit percutaneous destruction of large liver lesions.

Enhancement of hepatic parenchyma, aorta, and portal vein in helical CT: comparison of iodixanol and iopromide

OBJECTIVE

The purpose of this study was to determine hepatic, aortic, and portal vein enhancement with a new dimeric, nonionic, isotonic contrast medium (iodixanol) in a routinely performed helical CT protocol and compare enhancement characteristics with those of a monomeric, nonionic, low-osmolality contrast medium (iopromide).

SUBJECTS AND METHODS

In 81 patients, we injected 150 ml of iodixanol (320 mg I/ml), iodixanol (300 mg I/ml), or iopromide (300 mg I/ml). Injection rate was 5 ml/sec. A dual-phase helical CT scan was obtained (first helical scan began at 30 sec. second helical scan began at 70 sec), and enhancement characteristics were assessed. Results were analyzed taking into account various intrinsic parameters of patients.

RESULTS

During the second imaging phase, iodixanol at 320 mg I/ml and iodixanol at 300 mg I/ml provided significantly higher enhancement of the liver (75 H, 69 H, 62 H), aorta (144 H, 140 H, 122 H), and portal vein (147 H, 147 H, 118 H) than did iopromide at 300 mg I/ml. No significant differences were observed during the first imaging phase.

CONCLUSION

The combination of higher vascular and parenchymal enhancement levels after injection of the isotonic agent may represent a different quality of tissue enhancement. Such an enhancement would be characterized more by a higher contribution of the blood pool compartment to absolute enhancement levels than by a contribution of the interstitial compartment. Further studies are needed to determine whether the use of isotonic agents effects lesion conspicuity.

Block-copolymer of polyethylene glycol and polylysine as a carrier of organic iodine: design of long-circulating particulate contrast medium for X-ray computed tomography

In order to obtain small, polymer-stabilized particulate carriers for organic iodine to serve as a contrast agent for X-ray computed tomography (CT) an attempt was made to design a carrier based on polymeric micelles. Here we describe the synthesis of an iodine-containing amphiphilic block-copolymer which can micellize in aqueous solutions. The two blocks of the copolymer consisted of methoxypoly(ethyleneglycol) and poly[epsilon,N-(triiodobenzoyl)-L-lysine]. Upon dispersion in water, the block copolymer formed particles with average diameter 80 nm and iodine content up to 44.7%. The particles start to dissociate to the individual polymeric chains in the concentration range of 0.05-0.5 microM in water at 23 degrees C. Upon intravenous injection at 250 mg of iodine/kg (570 mg of the agent/kg) in rabbits the medium demonstrated exceptional 24 hr half-life in the blood substantiating corona/core structure of the particles with PEG chains protecting the iodine-containing core. The possible use of these particulates as contrast medium for X-ray computed tomography is discussed.

Functional CT with an experimental intravascular contrast agent in the assessment of liver vascular physiology

RATIONALE AND OBJECTIVES

We evaluated liver vascular physiology with a functional spiral computed tomography (CT) technique and an intravascular contrast agent.

METHODS

Eleven rabbits were studied by means of continuous 40-second single-section data acquisition after bolus injection of an experimental contrast agent. Sequential images were reconstructed at 200-msec intervals. Aortic, portal and hepatic venous, and liver time-HU curves were obtained. From these, hepatic blood volume and flow, tissue transit times, and arterial and portal contributions to total liver blood supply were assessed.

RESULTS

The following measures were obtained: hepatic blood volume fraction, 0.33 +/- 0.03 (mean +/- standard error); total flow, 241.1 mL/min +/- 33.6 per 100 g of tissue (arterial component, 11.3 mL/min +/- 3.0 per 100 g of tissue; portal component, 226.4 mL/min +/- 30.7 per 100 g of tissue); arterial transit time, 8.7 seconds +/- 1.6; portal transit time, 8.7 seconds +/- 1.3; arterial to portal perfusion ratio, 0.06 +/- 0.01; and calculated arterial and portal perfusion indexes, 0.05 +/- 0.01 and 0.95 +/- 0.01, respectively.

CONCLUSION

Functional CT is a promising, high-resolution tomographic imaging technique for evaluating liver perfusion.

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.

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.

Quantitative high-resolution measurement of cerebrovascular physiology with slip-ring CT

PURPOSE

To implement and validate spiral slip-ring CT for use in cerebrovascular studies.

METHODS

Continuous data were acquired from an experimental, first-pass, iodine contrast, bolus study by unidirectional X-ray tube rotation, and images were reconstructed at 100-millisecond intervals. Functional maps of cerebral blood volume (CBV) and cerebral blood flow (CBF) were constructed with voxel-by-voxel gamma variate fitting. Reproducibility studies, different injection volumes and sites, and CO2 challenge were applied to verify the technique.

RESULTS

Average absolute cortical gray and white matter and basal ganglia results were reproducible within +/- 0.8 ml/100 g for CBV and +/- 20 ml/100 g per minute for CBF, CBV response to changing arterial CO2 tension was significant only in cortical gray matter and basal ganglia; CBF response was significant in gray and white matter, as well as in the basal ganglia.

CONCLUSION

Functional CT and constructed functional maps provide an optimal, high-resolution tool with which to visualize cerebrovascular parameters and their changes.

Evaluation of selected two-dimensional segmentation techniques for computed tomography quantitation of lymph nodes

RATIONALE AND OBJECTIVES

As contrast agents that selectively target normal lymph nodes are undergoing development and evaluation, it has become important to accurately and reproducibly determine nodal boundaries to study the agents and determine such values as lymph node area or mean nodal contrast concentration. This study was performed to evaluate the accuracy of different two-dimensional computer segmentation methods, tested on acrylic phantoms constructed to imitate the appearance of lymph nodes surrounded by fat.

METHODS

Five segmentation techniques (manual tracing, semiautomatic local criteria threshold selection, Sobel/watershed technique, interactive deformable contour algorithm and thresholding) were evaluated using phantoms. Subsequently, the first three methods were applied to the images of enhanced lymph nodes in rabbits.

RESULTS

Minimum errors in phantom area measurement (< 5%) and interoperator variation (< 5%) were seen with the Sobel/watershed technique and the interactive deformable contour algorithm. These two techniques were significantly better than thresholding and semiautomated thresholding based on local properties.

CONCLUSION

Methods based on Sobel edge detection offer more objective tools than thresholding methods for segmenting objects similar to lymph nodes in computed tomography images. Both methods, Sobel/watershed and interactive deformable contour algorithm, are fast and have simple user interfaces.

Radiofrequency tissue ablation: importance of local temperature along the electrode tip exposure in determining lesion shape and size

RATIONALE AND OBJECTIVES

We determined whether heat distribution along a radiofrequency (RF) electrode would be uniform when longer tip exposures are used and whether local temperature effects would influence the shape of induced tissue coagulation.

METHODS

Thermistors were embedded within 18-gauge RF electrodes at both ends and in the middle of the exposed tip. The length of tip exposure varied from 1 to 7 cm. RF was applied in vitro to pig liver for 6 min using a constant tip temperature, which was varied in 10 degrees C increments from 60 degrees C to 110 degrees C. Experiments were performed in triplicate. The 3- and 5-cm probes were used at a 90 degrees C tip temperature to create lesions in live pig liver and muscle using similar parameters. Temperature was measured throughout the procedure. Observable coagulation necrosis was measured at the end of the treatment. Regression analysis was used to evaluate the local temperature-lesion diameter relationship.

RESULTS

Temperatures were not uniform along the tip exposure for any given trial. Temperature variation increased with higher tip temperatures and longer tip exposures. The diameter of local coagulation necrosis was a function of the local mean temperature. For in vitro trials, no coagulation was seen when the local temperature was less than 50 degrees C. Temperatures above this threshold resulted in progressively greater lesion diameter, with a minimum of 1 cm of necrosis occurring at 71 degrees C. Additional increases in lesion diameter (1.4-1.6 cm) were observed at approximately 90 degrees C. Mathematical modeling demonstrated a best-fit curve: lesion diameter (in cm) = ¿1.4 + 0.03 (tip exposure)¿ ¿1 - e [-0.067(local temp - 49.5 degrees C)]¿, r2 = .986, SD = 0.14 cm for each curve. In living tissue, less uniformity in the shape of coagulation necrosis was seen around the electrodes. Local temperature-lesion diameter data fit the same logarithmic relation, but the threshold for coagulation necrosis was 8.5 degrees C higher than for in vitro specimens.

CONCLUSION

Using a single-probe technique for RF-induced tissue necrosis, the diameter of tissue coagulation may be predicted by the local temperature along the exposed electrode. The uniformity of temperature decreases with increased tip exposures. This effect may be partially corrected by creating lesions at higher tip temperatures, where necrosis diameter is increased. Because effects are more pronounced in vivo, uniform volumes of tissue necrosis are limited to tip exposures of 3 cm or less.

A model of focal cancer in rabbit lymph nodes

RATIONALE AND OBJECTIVES

We sought to develop a model of focal cancer in the rabbit lymph node.

METHODS

Under computed tomography (CT) guidance, 4-5 million VX2 cells were directly injected into the popliteal nodes of 14 anesthetized New Zealand White rabbits. Fifteen to 18 days later, percutaneous lymphography was performed with CT scanning using radiopaque nanoparticulates and massage. Histologic correlation also was obtained.

RESULTS

In 12 of the 14 animals, focal lesions were successfully created within (n = 6) and adjacent (n = 6) to the node, and all animals appeared to be healthy when euthanized. Within 15 min after massage, CT lymphography showed homogeneous enhancement of normal node regions and no enhancement of cancer. There was good agreement between histology and lymphography.

CONCLUSION

This method is suitable as a model to test for diagnostic and therapeutic interventions.

The CT small bowel faeces sign: description and clinical significance

OBJECTIVE

To describe a new CT sign of the GI tract: the small bowel faeces sign, and discuss its significance.

METHODS

The small bowel faeces sign consists of gas bubbles mixed with particulate matter in dilated segments of small bowel. This was a retrospective study of 22 patients demonstrating this sign from 1989 to 1993. Final diagnosis was established by surgical, medical or laboratory findings. To determine the prevalence of the sign, the CT examination of 120 consecutive separate control patients were evaluated.

RESULTS

All 22 of the patients demonstrating this sign required hospitalization with surgical or medical intervention. Eighteen of 22 had mechanical small bowel obstruction. The remaining four patients had other abnormalities of small bowel to account for the finding on CT. Twelve of the 22 patients were treated with surgery and the remaining 10 patients were treated with nasogastric tubes (n = 6) or other medical therapy (n = 4). None of the 120 control patients demonstrated the sign.

CONCLUSION

The presence of gas and particulate material resembling faeces in a dilated segment of small bowel on CT is abnormal. Most (18/22; 82%) patients with this sign had small bowel obstruction.

Cytopathologic touch preparations (imprints) from core needle biopsies: accuracy compared with that of fine-needle aspirates

OBJECTIVE

The aim of this study was to evaluate the touch preparation (imprint) cytology method for obtaining rapid interpretations from core material obtained during abdominal percutaneous biopsy.

SUBJECTS AND METHODS

For 28 patients undergoing biopsy of abdominal masses, paired slides were prepared for rapid staining by use of smears of standard fine-needle aspirates and by use of a touch preparation of the core material obtained with a semiautomated biopsy gun. The slides were scored in comparison with the final cytopathologic and histopathologic diagnosis.

RESULTS

Touch preparation slides were equivalent in diagnostic yield to fine-needle aspirate smears, demonstrating similar cellular features. Touch preparation slides revealed features of tumor architecture not present on smears.

CONCLUSION

Touch preparation cytology offers rapid diagnosis from a single core biopsy sample. Carefully performed, the touch preparation method preserves the core material for subsequent permanent fixation and sectioning.

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.

Hepatic imaging with iodinated nanoparticles: a comparison with iohexol in rabbits

RATIONALE AND OBJECTIVES

We evaluated the efficacy of a particulate computed tomography (CT) contrast agent in an animal model of focal liver disease.

METHODS

Ethyl ester of diatrizoic acid (EEDA) is an iodinated (89 mg I/ml) nanoparticulate (200 nm) contrast agent intended for intravenous use that is currently undergoing preclinical testing in our laboratory. Focal liver abscesses were created in 11 New Zealand White rabbits. Iohexol and EEDA were administered to each animal on different days. CT scanning was performed at intervals following contrast agent administration. Liver and abscess enhancement were measured and compared. Dynamic imaging experiments in normal animals were also performed using both agents.

RESULTS

EEDA resulted in significantly greater enhancement of the liver and liver-to-abscess contrast than did iohexol at all time points beyond 5 min at approximately 25% of the total iodine load. During dynamic imaging, liver and aortic enhancement were greater with EEDA than with iohexol, except during a 20- to 40-sec period immediately following contrast agent administration.

CONCLUSION

EEDA is superior to iohexol for imaging liver abscesses. Our results suggest that liver-directed agents such as EEDA may prove to be more efficacious than currently available extracellular agents designed for liver CT scanning.