Bending of thin catheter by tempo-spatial division of ultrasound emission and evaluation of viscosity effect

Abstract

We have already experimented on the bending of a thin catheter with acoustic radiation force. Considering future in vivo applications, it is necessary to develop a method of bending a catheter in an arbitrary direction to adopt a limited installation position of ultrasound transducers on a body surface. Therefore, using a two-dimensional array transducer (256 elements, 1 MHz), which realizes not only the spatial design but also the dynamic variation of an acoustic field, we realized the bending of a thin catheter by forming multiple focal points. However, since the acoustic energy is dispersed with the multiple focal points, it was difficult to obtain sufficient displacement. Therefore, we attempted to bend the thin catheter with tempo-spatial division emission of a single focal point. Also, we compared the effect of the medium of not only water but also viscous liquid, which has similar viscosity to blood, where the bending performance of the catheter in the viscous liquid was reduced compared with that in water. Then, we derived the appropriate condition to bend the catheter with the transition rate of the focal point of 2.0 mm/s, and the spatial interval between 0.2 and 1.0 mm through various experimental trials. Finally, we succeeded in holding the tip of the catheter with the maximum displacement.

Experimental study of ultrasound retention of bubble-surrounded cells under various conditions of acoustic field and flow velocity

“…We confirmed that BSCs were retained by a single focal point acoustic field under flow condition and a multi-focal acoustic field with tempo-spatial division emission, [21][22][23][27][28][29] which forms the shaping of acoustic field, using a twodimensional array transducer. To apply this technique, we developed a cell delivery system in an internal organ.…”

“…Figure 2 shows the vertical view of the experimental setup including the same fluorescence microscope and digital camera, a two-dimensional array transducer, a water tank, and the artificial blood vessel. The transducer, which has a central frequency of 3 MHz and 128 elements, 28) was installed at the bottom of the water tank and targeted the observation area with a distance of l = 60 mm. The elevation angle θ was set to 60°such that the irradiation area of the acoustic field was included in the observation area.…”

“…To investigate the method of ultrasound emission to retain as many cells as possible, we applied the tempo-spatial division emission, 28) which moves the position of a single focal point electrically by changing the delay time, in the observation area. Figure 3 shows the positions of the focal points, which move repeatedly from f 1 to f n , where the value n indicates the number of focal points.…”

Validation of damage on vascular endothelial cells under ultrasound exposure according to adhered situation of bubbles

“…From the results obtained in this research, we elucidated a measure to protect vascular endothelial cells from ultrasound irradiation by varying adhesion situations of LBs. In our preceding studies, [8][9][10][11][12][13][14][15][16][17][18][19][20][21]22) in which we examined active control of micro objects in an artificial blood vessel, we concentrated to irradiate ultrasound to those objects without considering damage on the blood vessels. For the development of therapeutic system including active control of micro objects in blood vessel, the results obtained in this research should be important.…”

“…[15][16][17][18][19] In an actual situation, a catheter should be used to place the micro objects close to the target area. Once micro objects are released from the tip of the catheter, 20,21,22) they are exposed to a sound pressure of several 100 kPa. When tempo-spatial division emission, 17,19,21,22) which generates multiple focal points by temporally and spatially distributing acoustic energy, is applied, emission duration and duty ratio should be primarily considered for an effective performance.…”