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J J Lagendijk

Publications and source records attributed to J J Lagendijk.

At least 55 records · Page 3Linked to original sources
PubMed1992

Temperature uniformity during hyperthermia: the impact of large vessels.

During hyperthermia the presence of a large vessel entering the heated volume and carrying blood at the systemic temperature can be an important source of temperature non-uniformity and possible underdosage. The minimal tumour temperature near a large vessel is determined by the vessel wall temperature: a number of factors influencing the vessel wall temperature are considered--effective tissue conductivity, flow type, vessel size, entrance effects and counter-current flow. In some specific cases, especially when tissue perfusion is high, the vessel wall temperature may reach therapeutic levels when the mean blood temperature is still low. In general, well perfused tumours have a better chance of being heated uniformly. Regional heating improves temperature uniformity by reducing entrance and equilibration effects as blood is heated before entering the tumour. Raising the core temperature also reduces temperature inhomogeneity. Spatial SAR resolution should preferably be of the order of magnitude of a centimetre or better.

Blood Vessels↗
PubMed1991

Interstitial heating: experiments in artificially perfused bovine tongues.

Isolated perfused bovine tongues were heated with a 2 x 2 hot water tube interstitial hyperthermia system (tube outer diameter 2.0 mm, spacing 16 mm). Tongue blood flow ranged between 0 and 17 ml min-1/100 g. The temperature distribution was mapped with 5 to 8 single thermocouples (diameter 50 microns). Model predictions using both the conventional bioheat transfer equation and the effective conductivity model were compared to the experimental results, with emphasis on the role of blood flow. Results indicate a better qualitative agreement with the k-effective model than with the heat sink model. In this set up a 16 mm spacing proved sufficient for adequate heating between the needles at normal blood flow rates, in the absence of large vessels.

Animals↗
PubMed1991

A fast and simple algorithm for the calculation of convective heat transfer by large vessels in three-dimensional inhomogeneous tissues.

A fast and simple algorithm has been presented for the calculation of time-dependent temperature distributions in inhomogeneous vascularized tissue. Three-dimensional anatomical data of tissues and vessel structures are decomposed into elementary cubic nodes by a special digitizing routine with vessels represented by connected strings of vessel nodes. Vessel cross sections may be irregular shaped and/or tapered. Conductive and convective heat transfer was calculated through use of the heat balance technique on each cubic node resulting in an explicit finite difference computational scheme. Employing a three time level scheme, the Fourier stability criterion is circumvented allowing arbitrary time steps to be defined in the algorithm. Time steps as large as 100 times the Fourier restricted one still result in stable and convergent calculations of the stationary temperature distribution. Vessels with different flows and diameters are incorporated by performing a vessel specific second discretization step in time. Using the new algorithm as a mathematical tool the thermal equilibration length of vessel segments have been established under a broad range of geometrical and flow conditions. Validation followed from comparing transient and stationary temperature distributions derived by the proposed algorithm to those from an accurate cylindrical numerical model. Predicted values for the thermal equilibration lengths are compared to an analytical expression and phantom experiments. The algorithm is incorporated in a thermal model being the main part of our hyperthermia treatment planning system.

Algorithms↗
PubMed1990

31P NMR study of cisplatin- and doxorubicin-induced changes in tumour metabolism in rats with a cisplatin-sensitive or -resistant immunocytoma.

The response of tumours to treatment with the cytostatic drugs cisplatin (CDDP) or doxorubicin (DXR) was followed in vivo by 31P NMR spectroscopy. A CDDP-sensitive parent line (IgM-I) and a CDDP-resistant subline (IgM/CDDP) of the IgM-immunocytoma grown s.c. on LOU/M WsL rats were used. Animals from both tumour groups (n = 33) were divided into 3 subgroups: CDDP-treated (1 mg/kg), DXR-treated (10 mg/kg) and control. In 3 out of the 4 treated subgroups where the tumours regressed to less than one half of the initial size, 31P NMR spectroscopy revealed alkaline shifts of 0.31-0.41 pH units at day 4, while the ratio of nucleoside triphosphate to Pi in the tumours, increased continuously to 250-435%. Following CDDP treatment, the 31P NMR spectra of the non-responding IgM/CDDP tumours showed a similar pH increase (0.37 units). The ratio of NTP/Pi showed a temporary decrease to 63 +/- 14% SEM at day 1, which was followed by a recovery to 130 +/- 12% at day 2 and 119 +/- 15% at day 4. The control tumours showed no change in pH and a gradual decrease in the ratio of NTP/Pi. In DXR-treated rats the concentrations of DXR in the immunocytoma tumour and its subline were similar, but in the CDDP-treated rats the IgM-I tumours contained significantly higher levels of platinum than the IgM/CDDP tumours, both measured at 3 and 4 days after administration. The continuous increase in NTP/Pi ratio observed in the responding tumours, is a phenomenon characteristic of tumour regression, while the early temporary decrease in tumour NTP/Pi ratio could be associated with resistance to CDDP. Whether the reported response-specific spectral change applies to other tumour types and other treatment regimens remains to be established.

Animals↗
PubMed1990

Experimental verification of bioheat transfer theories: measurement of temperature profiles around large artificial vessels in perfused tissue.

The verification of thermal models for use in hyperthermia treatment planning is essential. We investigated the heat transfer between a single vessel and the surrounding vascularised tissue, comparing the conventional bioheat transfer theory and the recently developed keff model using analytical and numerical methods. A plastic tube inserted into the tissue of an isolated perfused organ served as an artificial vessel. This enabled us to vary the blood flow in the vessel and in the tissue independently. The organ used was a bovine kidney, turned into a perfused tissue phantom using an alcohol fixation technique. The temperature profile within the tissue was mapped with constantan-manganin thermocouple wire sensors with a total diameter of 50 microns. The temperature profile relative to the temperature difference between the vessel and organ was measured; increased perfusion caused a reduction of the vessel wall temperature but did not affect the width of the profile. Studying the transient tissue temperature after a step-wise change of the blood temperature in the vessel revealed a faster diffusion of heat at higher perfusion rates. These facts are in accordance with the keff model, but not with the conventional heat-sink theory.

Animals↗
PubMed1989

Effects of microwave-induced hyperthermia on the anterior segment of healthy rabbit eyes.

Hyperthermia was induced in nine healthy rabbit eyes by means of a microwave 2450 MHz stripline applicator. The anterior segment of each eye was heated to a fixed temperature of between 42 degrees C and 46 degrees C for 30 min. The temperature distribution in the eye was calculated using a thermal model and the actual boundary temperatures and microwave intensity were measured. The effects of treatment were evaluated by daily macroscopic examination, fluorescein angiography and fluorophotometry, as well as by histology. Histological examination of changes induced by this hyperthermic delivery system revealed a sharp transition at 44 degrees-45 degrees C from no permanent damage to the anterior chamber at lower temperatures to serious damage such as local necrosis, pigment disruption and local cataract at high temperatures. A sharp transition in the same temperature range was observed in vivo in the fluorescein leakage of the iris vessels by comparative fluorescein angiography and by anterior segment fluorophotometry.

Animals↗
PubMed1984

A three-dimensional description of heating patterns in vascularised tissues during hyperthermic treatment.

A three-dimensional finite difference computer model has been developed to calculate temperature distributions in vascularised tissues in hyperthermia. Besides offering the possibility of calculating temperature distributions according to the conventional ' bioheat transfer' method, this model allows the introduction of several discrete blood vessels and can describe their influence on the temperature distribution. The model can be used to evaluate all types of heating techniques. First calculations on discrete large vessels show inhomogeneities caused by these vessels in the temperature distribution in tissue in hyperthermia. The theory and model presented can form the basis of a new bioheat transfer theory, with a vessel-temperature related bioheat transfer heat-sink term able to describe the small-scale temperature variation problems in local hyperthermia.

Blood Vessels↗
PubMed1983

A new coaxial TEM radiofrequency/microwave applicator for non-invasive deep-body hyperthermia.

At the moment great efforts are being made to develop non-invasive heating systems which produce controlled local or regional deep-body hyperthermia. Electromagnetic interference techniques (10-80 MHz) with several separated applicators or with multiple applicators can produce deep-body heating. In our institute a coaxial frequency-independent TEM radiofrequency/microwave applicator has been designed. This applicator can produce a theoretically optimal interference maximum in the centre of the body. The applicator is very simple to construct and inexpensive. To test the design with the equipment available, a scaled prototype of the TEM applicator has been developed. The prototype has a diameter of 20 cm and operates at 434 MHz. The applicator has been tested on several phantom materials. The measured absorbed power distributions are in good agreement with the calculated theoretical distributions. The theoretical calculations of the absorbed power distributions of a 10-80 MHz TEM deep-body applicator are very encouraging.

Diathermy↗
PubMed1982

A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment.

A mathematical model based on the finite difference method has been developed to calculate transient and steady state temperature distributions in normal unexposed human and rabbit eyes, and human and rabbit eyes heated by various heating techniques. The normal steady state temperature distributions in human and rabbit eyes are given. The model has been experimentally fitted to data obtained from measurements on rabbit eyes. The heat transfer from the choroid to the body core temperature of the rabbit is described by the heat transfer coefficient hs = 65 W m-2 degrees C-1, and from the cornea to the surrounding air temperature by hc = 20 W m-2 degrees C-1. The thermal conductivity and the specific heat of the lens of the rabbit eye were determined empirically to be 0.40 W m-1 degree C-1 and 3.0 J g-1 degree C-1 respectively. The thermal properties of the vitreous humour were taken to be equal to the thermal properties of water.

Animals↗
PubMed1982

A microwave heating technique for the hyperthermic treatment of tumours in the eye, especially retinoblastoma.

A special microwave stripline applicator (2450 MHz) has been designed for the hyperthermic treatment of eye tumours, especially retinoblastoma. The measured microwave absorbed power distribution was put into a thermal finite difference computer model of the human and rabbit eye to calculate the resulting temperature distributions. The temperature distributions have been experimentally verified on rabbit eyes, and satisfactory temperature distributions can be obtained. The anterior part as well as the posterior part of the eye can be heated uniformly to temperatures in the range of 37-44 degrees C. The complete hyperthermia system is described.

Animals↗
PubMedDate not supplied

Development of a regional hyperthermia treatment planning system.

A flexible and fast regional hyperthermia treatment planning system for the Coaxial TEM System has been devised and is presented. Using Hounsfield Unit based thresholding and manually outlining of the tumour, a 40 cm CT data set (slice thickness 5 mm) is segmented and down scaled to a resolution of 1 cm, requiring only 30 min. The SAR model is based on the finite-difference time-domain (FDTD) method. The number of time steps to achieve numerical stability has been determined and was found to be 7000. Various optimizations of the SAR model have been applied, resulting in a relatively short computation time of 3.7 h (memory requirements 121 MB) on a Pentium III, 450 MHz standard personal computer, running GNU/Linux. The model has been validated using absolute value(Ez) measurements in a standard phantom inserted in the Coaxial TEM Applicator under different conditions and a good agreement was found. Hyperthermia treatment planning in combination with the homemade visualization tools have provided much insight in the regional hyperthermia treatment with the Coaxial TEM Applicator.

Electromagnetic Fields↗
PubMedDate not supplied

The use of absorbing structures during regional hyperthermia treatment.

Local pain is the main factor that limits regional hyperthermia treatment. Using the SAR model of the regional hyperthermia treatment planning system, the capability of absorbing blocks to reduce peripheral hot spots was investigated. The effect of rectangular absorbers of various size and salinity on an elliptical phantom in the Coaxial TEM was evaluated. The computed results were compared with SAR values measured in the phantom. Absorbers of 9 x 9 x 4 cm3 and a salinity of 18 gram l(-1) provide a SAR reduction in the muscle equivalent material, centrally under the absorber of at least 50% at a depth of up to 3 cm. The effect on the central (i.e. tumour) region is less than 20%. Larger absorbers have a more global effect and cause more attenuation in the central region. The attenuating effect depends strongly on the thickness of the fat layer between muscle and absorber. More than 2 cm fat limits the effective use of absorbers. Absorbers can induce a significant increase of SAR in muscle and fat near their edges. This effect also depends on absorber size and salinity and the thickness of the fat layer. The effect of an absorber was also evaluated with a patient anatomy, yielding results in agreement with the phantom experiments.

Humans↗