Zonal pattern of blood flow distribution in the Pliss lymphosarcoma microcirculatory bed caused by single exposure of high-intensity focused ultrasound

   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.