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Biomedical subjects

J W Hand

Publications and source records attributed to J W Hand.

54 records · Page 3Linked to original sources
PubMed1979

A microwave heating system for improving temperature uniformity in heated tissue.

A microwave heating system, designed to improve temperature uniformity in heated tissue, is described. The system employs parallel-opposed waveguide applicators, operating in the TE10 mode at 2450 MHz with the tissue to be heated (i.e. mouse intestine) immersed in a liquid which is both biologically compatible with and dielectrically similar to the tissue. The liquid improves the microwave coupling and avoids shape and size dependent absorption characteristics of the irregularly shaped tissue. Also, by maintaining this liquid at a suitable temperature with respect to that required in the tissue, the thermal losses and hence temperature gradients in the tissue are reduced compared with heating in hot liquid alone.

Animals↗
PubMed1979

The influence of blood flow on temperature distribution in the exteriorized mouse intestine during treatment by hyperthermia.

The non-uniform effects of hyperthermia observed in mouse intestine when heating is achieved by immersion of an exteriorized loop of jejunum in a hot bath were quantified. Intestinal damage was assayed by crypt destruction and correlated with local temperature and distance from major mesenteric blood vessels. The rate of rise of temperature during heating was much greater in regions far from blood vessels than in those close to vessels. Equilibrium temperatures in regions close to vessels were as much as 2 degrees C below liquid bath temperature. Such temperature differentials agreed well with those predicted from the heterogeneity observed in crypt destruction. Both histological and thermometric data suggest that major blood vessels may influence tissue temperature over a distance of approximately 2 mm and, within this region, temperature gradients of 1 degree C per mm may exist. These findings raise questions concerning the interpretation of previously reported data from water-bath heating of both tumours and normal tissues. They also emphasize the need for consideration of the influence of blood flow on heating patterns during hyperthermal treatment of patients.

Animals↗
PubMedDate not supplied

Pre-clinical evaluation of a two-channel microwave hyperthermia system with adaptive phase control in a large animal.

A pre-clinical assessment of the heating capabilities of a two-channel 915 MHz Microfocus-1000 hyperthermia system, with adaptive phase control, was carried out in a series of experiments using a large animal model. The results of the experimental measurements of specific absorption rate (SAR) and tissue temperature show that when muscle tissue of the hind legs of pigs was compressed to 6.5-7 cm, then a pair of parallel opposed, coherently driven, transverse electromagnetic wave applicators could elevate the temperature in deep tissue to therapeutic levels without overheating superficial tissues when the phase difference between applicators was determined by the adaptive phase control algorithm.

Animals↗
PubMedDate not supplied

Observation by MR imaging of in vivo temperature changes induced by radio frequency hyperthermia.

Volunteers have undergone radio frequency hyperthermia in a magnetic resonance (MR) imaging system to investigate which of several possible MR parameters would be most convenient and sensitive to use to observe in vivo temperature changes. Measurements were made for T1, T2, and perfusion and diffusion variations, although the number of sequences needed at each temperature meant that the number of data points obtainable was limited. However, in the temperature range studied (around 28-42 degrees C), changes in both T1 and the diffusion coefficient were observed that agreed quite well with those predicted theoretically (respectively around 1.3%/degrees C and 2.4/degrees C).

Body Temperature↗
PubMedDate not supplied

An assessment of local hyperthermia in clinical practice.

A total of 116 small superficial tumours have been treated by radiation alone, hyperthermia alone, or radiation and hyperthermia combined in a Phase I/II study. Most tumours were metastases or local recurrences of adenocarcinoma of breast but other histologies were involved including melanoma. Hyperthermia was delivered predominantly by microwaves, but radiofrequency and ultrasound methods were also used. Rigorous thermal dosimetry, based on measurements from invasive multipoint thermocouple arrays, has shown that 58 per cent of hyperthermal treatments reached a minimum dose within tumour equivalent to 20 min at 43 degrees C (minEq43); 24 per cent reached at least 60 minEq43. Minima of 20 minEq43 were achieved successfully on every intended occasion in a quarter of the 75 tumours heated, and on one/two occasions in 39; unfortunately, this minimum threshold was not reached at any point monitored at any hyperthermia session in 17(23 per cent) tumours. Tumours that received radiation and effective hyperthermia were more likely to disappear completely (CR rate 86 per cent) than those that were irradiated but inadequately heated (CR rate 35 per cent) (P less than 0.001) or were treated by the same doses of radiation alone (CR rate 35 per cent) (P less than 0.05). This improvement with hyperthermia became more apparent with suboptimal radiation doses. A small but measurable growth delay was imposed by heat alone with a poor complete response rate (11 per cent). The real-time use of a thermal dose unit in clinical practice facilitates hyperthermal treatment comparisons and provides an important parameter for checking the technical performance of a heat delivery system. The results of this study emphasizes the need for improvements in intratumour temperature distribution, in order to establish minimum threshold temperatures to enhance tumour response rates.

Adenocarcinoma↗
PubMedDate not supplied

Preliminary studies of interstitial hyperthermia using hot water.

A hot water interstitial hyperthermia unit was used to heat normal tissue in the thighs of rabbits and pigs. A 4 x 4 array of metal needles or plastic tubes spaced at 10 or 14 mm was implanted. Temperature measurements were made using five-sensor thermocouple probes inserted parallel to the implanted needles or tubes. With a water temperature of 48 degrees C, tissue temperature within the implant exceeded 42.5 degrees C when tube spacing was 14 mm and reached 47 degrees C when the spacing was 10 mm. However, at the lower water temperature of 45.5 degrees C inter-tube spacing was more critical, since the tissue temperature was above 43.5 degrees C for a spacing of 10 mm but below 42.5 degrees C for a spacing of 14 mm. Temperatures observed in vivo tended to be higher than those predicted by computer simulations, in which blood flow was assumed to be greater than that of resting muscle i.e. approximately greater than 0.45 kg m-3 s-1. The results show that an interstitial system using hot water can be a simple and efficient method of inducing hyperthermia.

Animals↗
PubMedDate not supplied

Treatment of menorrhagia by radiofrequency heating.

A new technique is described for the treatment of menorrhagia by heating the whole of the endometrial cavity of the uterus. A capacitively coupled probe at 27.12 MHz is inserted into the uterine cavity, which causes the basilis layer to be raised to approximately 50-55 degrees C whilst the rest of the pelvic contents remain at approximately normal (body) temperature. A major advantage of the method is that no special hysteroscopic skills are required, unlike the two other techniques currently used for endometrial ablation: the Nd-Yag laser or the hysteroresectoscopic loop. Also no toxic flushing/distension fluids are necessary, as are required for all hysteroscopic surgery. The method, however, does require the application of a large amount of RF power to the probe and so care must be taken to position the probe correctly in order to prevent any serious complications. Of 32 patients given a single treatment at a power level of 550 W for 20 min, the 'success rate' was 84% with 31% becoming amenhorrhoiec and 53% showing significant reduction in menstrual bleeding. However, retreatment is possible and by this means, combined with improved treatment techniques, an even higher success rate could be achieved. In two of the earlier patients treated at 550 W a fistula was produced at the anterior vaginal wall which had to be surgically repaired. The probe was subsequently modified, since when this problem has not recurred. This new treatment approach offers an alternative to hysterectomy in the treatment of menorrhagia and may offer a number of significant advantages over methods currently used for endometrial ablation.

Adult↗
PubMedDate not supplied

Current sheet applicator arrays for superficial hyperthermia of chestwall lesions.

The current sheet applicator is an electromagnetic heating device whose size may be chosen virtually independent of frequency even though practical limitations may restrict it to VHF and UHF bands. In this paper we investigate absorbed power distributions in muscle tissue from current sheet applicators when used as elements of a planar array intended for superficial hyperthermic treatment of tumours. Advantages offered by current sheet applicators for tissue heating include compact size, a linear polarization of the induced electric field and relatively large heating area. It is shown that the effective field produced by a pair of these elements is continuous regardless of whether the common edges of the elements are perpendicular or parallel to the direction of impressed current. The feasibility of customizing the shape and size of the field is also illustrated. The absorbed power distribution patterns due to a coherently driven array operating around 434 MHz is relatively insensitive to phase variations of about 20 degrees but is sensitive to relative power level variations as low as 10%. Mutual coupling between array elements may be reduced to acceptable levels by incorporating suitable spacing between them. It is also demonstrated that there is good agreement between measurements of absorbed power distributions and predictions using the Gaussian beam model.

Biomedical Engineering↗
PubMedDate not supplied

Early experience of a commercial scanned focused ultrasound hyperthermia system.

Preliminary experiences of the Sonotherm 6500 scanned focused ultrasound (SFUS) system in the hyperthermic treatment of bulky tumours in breast, superficial sites and within the pelvis in 22 patients are reported. Tumour volumes ranged from 235 to 603 cm3 (breast), 105 to 209 cm3 (superficial sites) and 24 to 905 cm3 (pelvis). Temperature distributions in 58 evaluable treatments were analysed in terms of temporal peak and time-averaged temperatures (highest and lowest temperatures, percentage of sensors exceeding index temperatures, etc.) achieved within scanned volumes. Mean number of sensors implanted into tumour was 14 in breast and superficial tumours and approximately 11 in pelvic tumours. Mean time-averaged maximum and minimum temperatures for the best treatments (i.e. for each patient, that with the highest percentage of sensors recording time averaged temperatures greater than or equal to 42 degrees C) administered to patients with tumours in the breast and superficial sites were 44.6 +/- 1.7 degrees C and 39.7 +/- 1.1 degrees C, respectively and the mean number of sensors exceeding 42 degrees C was 58 +/- 19%. In the case of pelvic tumours these figures were 41.6 +/- 0.9 degrees C, 40.0 +/- 0.6 degrees C and 8 +/- 12%, respectively. Patient tolerance to treatments was, in general, good. Areas where technical improvement of the system is appropriate and further research and development are required are identified; these should lead to a better realization of the potential of the SFUS technique, particularly for pelvic tumours.

Breast Neoplasms↗
PubMedDate not supplied

Dose uniformity in scanned focused ultrasound hyperthermia.

Scanned focused ultrasound (SFUS) is unique amongst noninvasive methods of inducing hyperthermia in that the absorbed power (SAR) distribution may be controlled at a scale of 0.5 cm or better. This high degree of spatial control of SAR implies that differences in local tissue cooling due to heterogeneity in perfusion, variations in the density of discrete thermally significant vessels and even local cooling around single large vessels may be compensated during SFUS treatments. In this paper we calculate thermal dose distributions arising from three different SFUS techniques: (1) the high-temperature short-duration (HTSD) ultrasound technique; (2) conventional systems employing a fixed scan and fixed SAR simulated by a uniform SAR; and (3) we optimize the SAR distribution using information from angiography and thermal models. These techniques are tested in the same anatomy having discrete vessels, a non-uniform vessel density and with little, if any, preheating of the incoming blood (i.e. the worst-case situation). The application of a uniform SAR to this volume resulted in a highly non-uniform thermal dose distribution. The situation is clearly improved in HTSD hyperthermia; however, the desired accuracy of positioning within the tumour is high, and to minimize background heating the focus must be stepped slowly and preferably in a semi-random pattern through the target volume. The third technique which employs spatial control over SAR resulted in the greatest uniformity in thermal dose. However, the use of this technique requires the input of the complete three-dimensional discrete vessel network and the availability of a tested three-dimensional discrete vessel thermal model.

Biophysical Phenomena↗
PubMedDate not supplied

Production and manipulation of elevated temperatures in pig abdomen with a three-electrode capacitive heating device.

The ability of a three-electrode capacitive heating device operating at 13.56 MHz to produce and effect spatial redistribution of hyperthermic temperatures is demonstrated through abdominal heating studies conducted with 80 kg female and 65 kg male pigs. Temperature-time profiles over the respective heating periods were obtained in anterior and posterior superficial tissue and in selected abdominal organs. At selected times during heating, spatial redistribution of elevated temperatures was effected through adjustment of power settings for one or more of the three electrodes, i.e. through manipulation of the specific absorption rate (SAR) in-vivo.

Abdominal Muscles↗
PubMedDate not supplied

Analysis of thermal parameters obtained during phase III trials of hyperthermia as an adjunct to radiotherapy in the treatment of breast carcinoma.

An analysis of 351 HT treatment sessions administered to 101 patients receiving radiotherapy and hyperthermia (RT + HT) who were entered into Phase III concurrent randomized trials for recurrent (BrR) and intact (BrI) breast tumours is presented. A complete response (CR) was recorded in 50 of 84 (59.5%) fields in the case of recurrent breast patients and in 10 of 17 (59%) fields in the case of the intact breast patients. In comparison, 15 of 60 (25%) patients entered into BrR who received RT alone and 8 of 12 (66.7%) patients receiving RT alone entered into BrI trial achieved CR. A set of thermal parameters is defined and evaluated on a treatment by treatment basis. Patient and tumour characteristics influential on CR are identified and thermal parameters which have additional prognostic value are investigated. Multivariate logistic analysis of the non-thermal data showed that maximum depth of tumour, presence or history of disease outside the treated area and RT regimen were most influential on CR. Tumour volume (cm3) (OR = 0.996, 95% CI = 0.993-1.004, p = 0.08) was not a strong prognostic covariate; tumour area and linear dimensions were even less significant (p = 0.41). The cumulative minimum thermal isoeffect dose (equivalent minutes at 43 degrees C) accrued over the 1st, 1st and 2nd, and 1st, 2nd and 3rd treatment sessions was the only thermal parameter to exhibit an association with CR consistently, Other thermal parameters found to contribute to the predictive models were MINTIME > 42 degrees C calculated for the first treatment session and %sensors > 43 degrees C (peak) calculated for the 2nd treatment session.

Aged↗
PubMedDate not supplied

Effectiveness of the Gaussian beam model in predicting SAR distributions from the lucite cone applicator.

The Gaussian beam model (GBM) has been shown to be a successful tool in the development of the current sheet applicator. As a result, the effectiveness of the GBM is investigated in single and dual array applications of the lucite cone applicator (LCA). The LCA is a modified water-filled waveguide applicator with an improved effective field size (EFS > 64 cm2, aperture 10 cm x 10 cm). The GB-source parameters were calculated from the emanating E-field of a single LCA. The SAR distribution from a single LCA was measured by E-field scanning and thermographic (TG) imaging, and compared with the GB-predicted SAR distribution. Deviations in the principal planes were found to be less than 5%. TG-measured and GB-predicted SAR distributions from three different dual LCA configurations were compared and evaluated. When water was used as intermedium between LCAs and phantom, a maximum SAR difference of 27% was calculated. In the absence of water as intermedium, this difference increased to 44%. These large deviations were only found in areas where the measured SAR distribution was disturbed due to antenna interactions. The average SAR differences with and without water as intermedium were 7% respectively 11%, indicating that the GBM can provide good qualitative information about the SAR distribution of dual LCA-arrays.

Electromagnetic Fields↗