A Summary of Heat-Flux Sensor Calibration Data.

This paper presents a statistical evaluation of the responsivity data on a number of heat-flux sensors, calibrated using an electrical substitution radiometer as a transfer standard up to 5 W·cm(-2). The sensors, furnished by the customers, were of circular-foil or thermopile type. Comparison of the NIST and the customer measured responsivity values showed that the measurements agree within 3 % for more than half the number of sensors tested, so far. Considering the variation in the customer calibration techniques and the wide measuring range of the sensors used in the calibration, the agreement is encouraging.

Use of combined systemic hypothermia and local heat treatment to enhance temperature differences between tumor and normal tissues.

The feasibility of combining local heat treatment with whole-body hypothermia in an effort to improve therapeutic gain was assessed. Superficial, nonperfused phantom tumors were fashioned in eight anesthetized mongrel dogs by transplantation of the spleen from the abdomen to a subcutaneous site on the hindlimb. After pretreatment of the animal with the vasodilator hydralazine (0.5 mg/kg, IV) to enhance normal tissue perfusion, the spleen implant was heated with a 2450-MHz microwave diathermy apparatus, first with the animal's core body temperature in the normal range (39 degrees C) and then after the animal had been packed in ice to reduce core temperature to 30 degrees C. Applied power density and temperatures in both the phantom tumor and underlying muscle tissue were recorded during brief interruptions of diathermy until steady-state temperatures had been achieved. Under normothermic conditions with time-averaged applied power of 0.038 W/ml to phantom tumor and 0.014 W/ml to underlying muscle, tumor temperature rose to 45.9 +/- 1.8 degree C, while muscle temperature remained at 40.5 +/- 0.7 degree C. During whole-body hypothermia applied power could be increased to 0.114 W/ml in phantom tumor and to 0.025 W/ml in muscle. Muscle temperature rose only to 33.8 +/- 1.6 degree C, while that of the nonperfused phantom tumor rose to 53.6 +/- 4.3 degrees C with systemic hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)

Theoretical feasibility of vasodilator-enhanced local tumor heating.

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action which can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma and canine transmissible venereal tumor while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, clearly demonstrate improved selective heating for spheroidal tumors over 2 cm in diameter. In the presence of vasodilator drug effect, steady-state center tumor temperatures of 45-50 degrees C can be achieved by increased power input, while surrounding normal tissues remain below 42 degrees C.

The effect of gelled-pad design on the performance of electrosurgical dispersive electrodes.

A two-dimensional model of a simplified configuration of the gelled-pad electrode applied to human tissue was developed. As a consequence of the boundary discontinuity near the edge of the pad, the model predicted high peripheral and low central surface temperature rises. By comparison with base conditions, increased gelled-pad area and gel electrical resistivity and decreased initial pad temperature reduce the temperature rise across the pad surface. Temperature distributions measured on the thighs of human subjects were shown to have similar characteristics to those predicted by the model. Even though three-dimensional and blood flow effects were not considered, the model is satisfactory for evaluating the effect of electrode design changes on thermal performance.

Physical principles of local heat therapy for cancer.

Local hyperthermia therapy for cancer can produce selective heating of solid tumors on the basis of known physical laws. If energy is deposited in the general region of the tumor, temperature tends to develop in the tumor higher than that in surrounding normal tissues. The goal of therapy is to achieve cytotoxic temperature elevations in the tumor for an adequate period of time, without damaging nearby normal tissues. Several modalities exist for local heat treatment, of which radiofrequency and ultrasound offer the most promise for controlled, localized heating at depth. A paucity of blood flow in the tumor compared to that in adjacent normal tissues can enhance selective tumor heating considerably. The tumor types that have reduced flow in their central regions are especially vulnerable to heat therapy, both because they can be heated more efficiently and because hypoxic and acidotic tumor tissues are more susceptible to damage by heat. This effect is more pronounced in larger tumors, which have smaller surface-to-volume ratios and so lose heat less rapidly by thermal diffusion. Selective heat treatment of larger tumor masses with low blood perfusion, therefore, is physically practical and rational therapy. Vigorous research efforts are now underway at many centers to optimize this approach.

Determination of serum bilirubin by skin reflectance: effect of pigmentation.

A noninvasive optical technique by which serum bilrubin can be estimated from skin spectral reflectance measurements has been further investigated. The original work on 30 healthy, full-term white infants and an independent study on 14 white and 30 black infants demonstrate that the method has potential not only for clinical use, but also for the study of the transport of bilrubin to, from and within the skin. The objectives of the present study are to evaluate the method on a larger sample population with special attention to natural skin pigmentation effects and the development of a physical model of the tissue to explain the relationship between serum bilrubin concentration and skin reflectance. Reflectance spectra (380-800 nm) and concurrent serum bilirubin measurements were taken on a sample population of 58 white and 45 full-term black infants (1-3 days of age). Multiple linear regression analysis, comprised of six wavelengths gave a correlation coefficient, r = 0.831 for the white infant group. For the black infant group, a five wavelength analysis provided r = 0.877 with the standard error of estimate being +/- 1.46 mg/100 ml for both groups. The model for establishing a physical basis for the relationship shows that a transformed, normalized Kubelka-Monk function xi (460, 510, 420) is linearly related to serum bilrubin concentration. This function is determined from the spectral reflectance values at three wavelengths, 420, 460, and 510 nm. The wavelength combination is such that effects due to hemoglobin and melanin pigments are minimized. Regression analysis showed that r = 0.778 and r = 0.865 for the white and black infant groups, respectively, with standard error of estimates being +/- 1.4 mg/100 ml for both groups. Routine determinations of total serum bilrubin by laboratory methods have standard errors of estimate ranging from +/- 1 to 1.5 mg/100 ml. Thus, the method herein described shows that the relationship between skin reflectance and serum bilrubin in full-term infants is close to the acceptable limits for clinical use. Furthermore, this work shows that skin pigmentation does not obscure this relationship.

What's new in electrosurgical instrumentation?

A 1976 report of the use of radiofrequency current to devitalize carcinomas in man stimulated this review of the historical background, the presently used techniques, and the problems associated with electrosurgery. Difficulties in electrosurgical techniques requiring further research are identified--i.e., the high heating and variable performance of dry dispersive electrodes, the hazards of tissue stimulation, high-frequency interference, and the potential impact of government regulation.

Evaluation of a high accuracy reflectometer for specular materials.

A high accuracy method for measuring the spectral reflectivity of specular materials over the 0.300-15.0-microm wavelength range is described. The performance of the reflectometer has been evaluated, and results for an evaporated aluminum film are compared with those obtained by the Bennett-Koehler instrument upon which our design is based. For highly reflecting materials, like those of current interest for laser mirror coatings, it is possible to achieve accuracies, based upon evaluated systematic errors, of the order of 1 part in 10(3). Discussion of the effects of sample tilt, detector linearity optical configuration, and bandwidth on the measurements is presented.