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The purpose of the study was the experimental assessment of the interaction coefficient characterising the influence of pressure on the conductivity of electrolyte solutions. Pressure pulses were applied to samples of 9 gl-1 sodium chloride contained in cuboid measurement cells of identical cross-sectional dimensions but different thickness along the acoustic beam axis. The magnitude of the changes induced in cell resistance was recorded for three values of applied pressure increment (delta P = 0.94, 1.39 and 1.78 MPa) and three values of cell thickness (e = 0.58, 1.13 and 1.62 mm). A thick, focused transducer generated short (0.1 microsecond), unipolar pressure pulses. A model accounting for the characteristics of the pressure pulse and the geometry of the measurement cell was developed to predict the ultrasound-dependent changes in the measured electrical resistance. Despite some discrepancy between theoretical and experimental results, discussed in the paper, the results validated the order of magnitude of the interaction coefficient (10(-9) Pa-1). The predictions varied from about 50% (e = 1.62 mm, delta P = 0.94 MPa) to 77% (e = 0.58 mm, delta P = 1.78 MPa) of the experimental values.

Although interstitial techniques are invasive, they are still the first-line therapeutic modalities for certain types of tumour. They are mainly relevant to tumours that are either inoperable or located so deep that access is complicated. Of the various types of radiation that can be delivered by the interstitial route, ultrasound is the most suitable for deep heating. The study compares the efficacy of two types of applicator with respect to their ability to induce cylindrical zones of coagulation necrosis. The transducer of the first applicator is tubular, whereas the second is plane and can rotate around its axis. Both have an external diameter of 4 mm, are fitted with surface cooling systems and operate at 10.7 MHz and 14 W.cm-2. Comparison involves mathematical modelling of ablated tissue in the targeted area by resolving the bioheat transfer equation (BHTE) using an algorithm based on finite differences. The BHTE gives a temperature value from which the thermal dose can be determined. It is shown that tissue ablation by tubular transducers is slow, and, in consequence, perfusion disturbs the heating pattern: in vivo, irradiation with a tubular transducer lasting 1081 s would be required to ablate a tissue mass with a radius of 8 mm. The corresponding period using a rotating plane transducer with 20 firing angles is only 618 s. The mean exposure time of each shot lasts 31 +/- 7 s. Therefore perfusion would have much less impact in the case of therapy administered using a plane transducer than that using a tubular one.

Les auteurs decrivent en detail la realisation d'un velocimetre pulse a 20 MHz. Ce choix de la frequence d'emission des ultrasons permet une resolution longitudinale et transversale de plus ou moins 0·15 mm. Diverses applicationsin vitro, puis chez l'animal et chez l'homme justifient le developpement de ce type d'appareil, tant en microchirurgie que pour des etudes hemodynamiques precises.

For several years, we have been using the properties of transthoracic impedance modification as a means for studying simultaneously lung ventilation and perfusion. We have been able to show during this period, both in transplanted dog lung (150 dogs) and in man (50) characteristic modifications of form and amplitude. To carry out a more precise study of the recorded curves, we have built a special apparatus—a patient-computer interface. This device displays immediately all of the important parameters of the right and left ventilation curves; e.g. amplitude, period, expiration and inspiration time, shift between the extension of the rib cage and the ventilation curves. Furthermore, we calculate the mean perfusion curve by an accumulated method. This allows us to obtain perfusion and ventilation curves without artefacts.