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Variations of bubble cavitation and temperature elevation during lesion formation by high-intensity focused ultrasound
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10.1121/1.4812895
/content/asa/journal/jasa/134/2/10.1121/1.4812895
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/2/10.1121/1.4812895

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Schematic diagram of experimental setup that was used to monitor the HIFU-induced lesions and cavitation in transparent polyacrylamide gel phantom and tissue.

Image of FIG. 2.
FIG. 2.

(Color online) (a) Representative PCD signals and (b) the corresponding spectrogram produced by the 50th HIFU burst with the pulse duration of 30 ms and a pulse repetition frequency of 1 Hz. Production of more and stronger harmonics is due to the stable cavitation meanwhile white noise in the spectrogram is associated with inertial cavitation. Temporal-average frequency-average spectrogram within the dashed (7.5–9 MHz) and dotted (13.1–13.3 MHz) regions are used to present the inertial and stable cavitation dose, respectively.

Image of FIG. 3.
FIG. 3.

(Color online) (a) Comparison of temperature measured by a thermocouple (solid line), simulated by a theoretical model (middle dashed line), viscous heating artifact fitted with an effective Gaussian radius (dashed-dotted line), and simulation result including the viscous heating artifact (short dashed line) in the focal region of a HIFU transducer with the pulse duration of 20 ms and a pulse repetition frequency of 1 Hz. A good agreement is found between the measurement and simulation results. The viscous heating artifact decays quickly after the termination of HIFU exposure and then its influence is minimized from the thermocouple measurement. (b) Envelopes of the temperature profile at  = −2.5, 0, and 2.5 mm, respectively, during 200-burst HIFU exposure after artifact correction. Upper and lower lines of each plot are the peak and ambient temperature for each HIFU pulse exposure, respectively.

Image of FIG. 4.
FIG. 4.

(Color online) Progressive lesion production by a HIFU burst (  = 3.3 MHz,  = 46.8 MPa,  = −15.7 MPa) in a transparent 7% BSA gel phantom with the pulse duration of (a) 5 ms, (b) 10 ms, (c) 20 ms, and (d) 30 ms and a pulse repetition frequency of 1 Hz. The values at the top of the frames are the number of bursts delivered. Production of large boiling bubbles with a jet in the HIFU propagation direction is illustrated at  = 10 in Fig. 4(d) . Dark area in the pre-focal region presents the opaque thermal lesion due to BSA denaturation while more transparent one is generated by the mechanical erosion. Arrows show bubbles in the distal end of the lesion, which has a long lifetime after the bubble coalescence and may be emitted by the jet from the focal region and pushed forward by the acoustic radiation force of HIFU burst. Many small bubbles are also found surrounding the lesion shown as the arrowhead. With the increase of pulse duration, the lesion shape will change from “squid” to “dumbbell” and then to “tadpole” with thermal effect dominating in the prefocal region. Ultrasound propagates from the bottom to the top. The scale is 2 mm.

Image of FIG. 5.
FIG. 5.

(Color online) (a) Representative peak-to-peak PCD signals with the progress of HIFU exposure in the gel phantom, and (b) comparison of the maximum and average peak-to-peak PCD signals in gel phantom (solid line) and porcine kidney (dashed line) during the 200-burst exposure with varied pulse duration up to 30 ms and a pulse repetition frequency of 1 Hz. Similar characteristics of PCD signals are found between the gel phantom and studies. ANOVA is used to determine the statistical difference ( < 0.05,  > 5).

Image of FIG. 6.
FIG. 6.

(Color online) (a) Stable and (b) inertial bubble cavitation dose with the progress of HIFU exposure in the gel phantom with varied pulse duration from 5 to 30 ms and a pulse repetition frequency of 1 Hz. Stable cavitation dose is usually higher than that of inertial cavitation.

Image of FIG. 7.
FIG. 7.

(Color online) (a) The maximum temperatures and (b) the box plot of temperature elevations of each burst at  = −2.5, 0, and 2.5 mm, respectively, by 200-burst HIFU exposure with varied pulse duration from 5 ms to 30 ms and a pulse repetition frequency of 1 Hz in the gel phantom ( > 5). Whiskers are 1.5 interquartil ranges. The lower and upper outliner shows the 5th and 95th percentile of the data, respectively. Great variations are indicated as the significant difference between high and low measurements.

Image of FIG. 8.
FIG. 8.

(Color online) Progressive lesion production by a HIFU burst in a transparent 7% BSA gel phantom with the pulse duration of 20 ms and a pulse repetition frequency of (a) 0.2 Hz, (b)0.5 Hz, (c) 2 Hz, and (d) 5 Hz. The values at the top of the frames are thenumber of bursts delivered. Characteristics of lesions are similar to those produced by changing the pulse duration in Fig. 4 that with the increase of PRF thermal effect will play an important role in the prefocal region and change the lesion to “tadpole” shape. Arrow and arrowhead present the bubbles in the distal end of the lesion and scattered bubbles around the lesion, respectively. Ultrasound propagates from the bottom to the top. The scale is 2 mm.

Image of FIG. 9.
FIG. 9.

(Color online) (a) Representative peak-to-peak PCD signals with the progress of HIFU exposure in the gel phantom, and (b) comparison of the maximum and average peak-to-peak PCD signals in the gel phantom (solid line) and porcine kidney (dashed line) during the 200-burst exposure with the pulse duration of 20 ms and pulse repetition frequency from 0.2 Hz to 5 Hz. The similarities are found for the maximum and average PCD signals between in the gel phantom and studies.

Image of FIG. 10.
FIG. 10.

(Color online) (a) Stable and (b) inertial bubble cavitation dose with the progress of HIFU exposure in the gel phantom with the pulse duration of 20 ms and varied pulse repetition frequency from 0.2 to 5 Hz.

Image of FIG. 11.
FIG. 11.

(Color online) (a) The maximum temperature and (b) the box plot of temperature elevation of each burst at  = −2.5, 0, and 2.5 mm, respectively, by 200-burst HIFU exposure with the pulse duration of 20 ms and varied pulse repetition frequency from 0.2 Hz to 5 Hz in the gel phantom ( > 5). Whiskers are 1.5 interquartil ranges. The lower and upper outliner shows the 5th and 95th percentile of the data, respectively.

Image of FIG. 12.
FIG. 12.

Representative B-mode ultrasound images during the HIFU treatment in porcine kidney with the pulse duration of 20 ms and a pulse repetition frequency of 1 Hz. The values at the top of the frames are the number of bursts delivered. White arrow shows the HIFU focus. Beam propagates from the left to the right. A significant hypoecho shown as arrow head may be the mechanical erosion while the surrounding region with lower gray levels shown as right arrow may be the thermal lesion produced by the HIFU pulses. Ultrasound propagates from the left to the right. The scale is 1 cm.

Image of FIG. 13.
FIG. 13.

(Color online) (a) Representative lesions produced by HIFU burst with pulse duration of 20 ms and PRF of 1 Hz, (b) 3D reconstruction of mechanical (inner mesh) and thermal (outside mesh) lesion (the scale is 5 mm), and (c) comparison of the volumes of HIFU-induced mechanical and thermal lesions in porcine kidney with varied pulse duration from 10 to 30 ms and pulse repetition frequency from 0.2 to 5 Hz.

Tables

Generic image for table
TABLE I.

Summary of sonication parameters used in the experiments.

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/content/asa/journal/jasa/134/2/10.1121/1.4812895
2013-08-01
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Variations of bubble cavitation and temperature elevation during lesion formation by high-intensity focused ultrasound
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/2/10.1121/1.4812895
10.1121/1.4812895
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