Therapeutic significance in the studies of HIFU-induced effects of is attached to the local heating of tissues, but the role of the mechanical component caused by non-stationary cavitation is practically not taken into account. Calculations show that the temperature inside cavitation bubbles can differ significantly from the temperature in the thermal ablation zone, and the developing temperature gradient can change the formation of the thermal field. Collapsing bubbles can cause mechanical destruction of tissues.
Introduction. One of the promising methods of treating oncological diseases is high-frequency focused ultrasound (HIFU). The high-frequency acoustic field generated by the emitters induces mechanothermal effects whose significance has not yet been fully assessed and their study will change the tactics of therapy. To analyze their role, we selected cellular perivascular regulators of local blood flow – mast cells (MCs). Changes in the microcirculation (MCT) allow us to judge the morphofunctional state of the MC. The aim of the study is to assess the state of the rat’s skin periphocal tissue blood flow and MCs morphofunctional properties after HIFU-exposure.Material and methods. Adult male Wistar rats were used. Animals were divided into 3 groups: control, non-contact local heating of the skin and HIFU-induced exposure. For HIFU, an experimental setting was used, consisting of a concave emitter H-148 S / N 010 with a central oscillation frequency of 1.4 MHz. In the averaged interference spot, the radiation intensity was 8.2 kW/cm2. The exposure duration from 150 to 700 ms. Depth of focus is about 1 mm. To assess the MCT, a laser doppler flowmeter was used. Material for the manufacture of film preparations of MCs was taken at the site of exposure and according to the standard method. MCs calculation was carried out using the software «Multimedia Catalog» taking into account their morphofunctional characteristics.Results. HIFU exposure led to a significant increase in blood flow in rat’s skin at an exposure time of 250 ms or more (p<0.01). The maximum increase in perfusion was noted at 400 ms. The highest increase in tissue blood flow with local heating was observed at 45°C (p<0.001). HIFU-exposure led to a significant decrease in the density of MCs in the subcutaneous fat tissue of rat’s skin compared with the control at an exposure time of 250 ms or more (p<0.05) and a significant decrease in the relative number of type I cells, and an increase in type II and III, which indicates degranulation (p<0.05). Similar changes in the amount and morphofunctional characteristics of MCs were observed in a series of experiments with local heating, but the changes were not so significant.Conclusions. With HIFU-induced exposure, increased MCT in the peripheral zones is observed, accompanied by processes of morphofunctional rearrangement of the MCs, which indicates a combined mechanothermal disturbance in the focus zone, which forms the spatiotemporal continuum of the thermal field.
Introduction. Cell damage is not the only important mechanism of high-intensity focused ultrasound (HIFU) for cancer therapy; concomitant microcirculation disorders having alterations patterns not studied enough also have high significance. The aim of the study was to analyze perfusion along the tumor perimeter depending on the HIFU exposure. Materials and methods. We used a stand for HIFU therapy (MTL LLC). Mode: 8.2 kW/cm2 intensity at 0.6 mm focal spot at 1.4 MHz, exposure time: 150, 200, 250 and 500 ms. The object of the study is the vascular bed of Pliss lymphosarcoma. Tumor tissue temperature was monitored by a T-8 thermograph (Russia), blood flow was measured by the BLF21 laser Doppler recorder (USA). Results. After HIFU exposure time from 150–250 ms, perfusion was noted to have decreased to 1.06 perfusion units (pf.u) in the central zone (p<0.01) compared to the control, but by the 30 min perfusion has increased to 1.22 pf.un. No signs of perfusion improvement were found in exposure time of 500 ms. In the peripheral zone, against the background of a decrease in blood flow to 3.6 pf. u. (p < 0.05) by 30 min of the experiment, hyperperfusion was restored to 5.86 pf. u. in all exposure time. In the central zone, a sharp decrease in microcirculation was observed, probably caused by damage of blood vessels; in the periphery of the tumor, perfusion changes had a phasic and reversible pattern. Conclusion. An increase of HIFU exposure correlates with an increase of temperature of Pliss lymphosarcoma tissue near the focus of exposure. Specific perfusion changes are recorded in the central and peripheral zones of the tumor when single exposed to HIFU with different time exposure; the severity of changes depends on ultrasound exposure-time and is characterized by a zonal pattern of blood flow distribution due to the formation of zones of irreversible and reversible damage to microcirculation.
The nature of changes in the structure of the PAG-3 biophantome under the action of HIFU indicates the significance of shock-wave shifts involved in the formation of the heat pattern and the destruction zone. The thermal effect is accompanied by the accumulation of thermal energy, the limitation of the thermal field, which predetermines the therapeutic efficiency of focused ultrasound exposure, however, it is advisable to take into account the role of mechanical effects in focused ultrasound therapy.
New technologies and methods designed to reduce the risk and magnitude of surgical manipulations are being actively introduced into clinical practice, one of which is the method of high-intensity focused ultrasound (HIFU) thermoablation. However, it is quite difficult to assess the spatial distribution of acoustic and thermal fields when selecting a therapy scheme. To simulate the architectonics of the treatment area it is proposed to use a dosimetric phantom. The pattern of changes in the phantom in the heat-affected zone is shown with an ultrasound scanner in real time, which allows to visualize structural changes in the area of thermal destruction and verify the dosimetric plan of ultrasound therapy.
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