agar and Fever

To determine the effect of background tissue thermal conductivity on RF ablation heating using ex vivo agar phantoms and computer modelling.. Two-compartment cylindrical agar phantom models (5% agar, 5% NaCl, 3% sucrose) were constructed. These included a standardized inner compartment (2 cm diameter, 4 cm length, 0.25% agar) representing a tumour, surrounded by an outer compartment representing background tissue. The thermal conductivity of the outer compartment was varied from 0.48 W m-1 degrees Celsius (normal liver) to 0.23 W m-1 degrees Celsius (fat) by adding a fat-saturated oil-based solute (10-90%) to the agar. RF ablation was applied at 2000 mA current for 2 min. Temperatures were recorded up to 4 cm from the electrode tip at 1 cm intervals. Subsequently, a 2-D finite element computer model was used to simulate RF ablation of 2-24 min duration for tumours measuring 2-4 cm in diameter surrounded by tissues of different thermal conductivity with the presence or absence of perfusion (0-5 kg m-3 s-1) (n = 44). A comparison of results was performed.. In agar phantoms, the amount of fat in the background tissue correlated with thermal conductivity as a negative exponential function (r2 = 0.98). Significantly increased temperatures were observed at the edge of the inner compartment (1 cm from the electrode tip) as the fat content of the outer compartment increased (p < 0.01). Thus, temperatures at 2 min measured 31.5 +/- 2.2 degrees Celsius vs 45.1 +/- 3.1 degrees Celsius for thermal conductivities of 0.46 W m-1 degrees Celsius (10% fat) and 0.23 W m-1 degrees Celsius (90% fat), respectively. On the other hand, higher levels of fat led to lower temperature increases in the background compartment (0.2 +/- 0.3 degrees Celsius for 90% fat vs. 1.1 +/- 0.05 degrees Celsius for 10% fat, p < 0.05). Phantom thermal heating patterns correlated extremely well with computer modelling (r2 = 0.93), demonstrating that background tissues with low thermal conductivity increase heating within the central tumour, particularly for longer durations of RF ablation and in smaller tumours. Furthermore, computer modelling demonstrated that increases in temperature at the tumour margin for background tissues of lower thermal conductivity persisted in the presence of perfusion, with a clinically relevant 4.5 degrees Celsius difference between background thermal conductivities of fat and soft tissue for a 3 cm tumour with perfusion of 2 kg m-3 s-1, treated for 12 min.. Lower thermal conductivity of background tissues significantly increases temperatures within a defined ablation target. These findings provide insight into the 'oven effect' (i.e. increased heating efficacy for tumours surrounded by cirrhotic liver or fat) and highlight the importance of both the tumour and the surrounding tissue characteristics when contemplating RF ablation efficacy.

Topics: Agar; Catheter Ablation; Computer Simulation; Fever; Hot Temperature; Models, Theoretical; Neoplasms; Phantoms, Imaging; Temperature; Thermal Conductivity; Time Factors

Topics: Agar; Animals; Body Temperature; Cellulose; Chromatography, Ion Exchange; Edetic Acid; Fever; Peptide Biosynthesis; Peptides; Polysaccharides; Pyrogens; Rabbits; Snakes; Swine; Toxins, Biological; Venoms

Topics: Adult; Agar; Antibody Formation; Cell Line; Child; Child, Preschool; Culture Techniques; Diploidy; Exanthema; Female; Fever; Glucose; Humans; Injections, Subcutaneous; Lung; Lymphadenitis; Male; Rubella; Rubella Vaccine; Rubella virus; Switzerland; United States; Urine; Vaccination; Viral Vaccines; Virus Cultivation

Topics: Agar; Alcoholism; Anemia, Hypochromic; Bone Marrow; Bone Marrow Cells; Cardiovascular Diseases; Culture Techniques; Fever; Gastrointestinal Diseases; Humans; Leukemia; Skin Diseases

The specificity in the agar diffusion precipitation test of the reaction between the antigen of hog cholera virus diffusing from infected tissues and its homologous antibody was verified. Alternate freezing and thawing of infected tissues was found to give optimum release of the antigen from fresh tissue frozen for 18 hours. A study of the effect of the size and age of pigs upon the diffusion of the antigen from tissues showed that tissues from pigs of less than 250 lbs. gave good results provided the tissues were from animals showing gross clinical manifestations. Specimens from infected breeding sows and dead animals usually did not give a reaction.

Topics: Agar; Animals; Antigens; Classical Swine Fever; Classical Swine Fever Virus; Clinical Laboratory Techniques; Diagnosis, Differential; Erysipelothrix; Fever; Immunodiffusion; Reproducibility of Results; Serum Globulins; Swine