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Estimating dynamic changes of tissue attenuation coefficient during high-intensity focused ultrasound treatment.

Rahimian S, Tavakkoli J - J Ther Ultrasound (2013)

Bottom Line: After the treatment, Δβ and Δα 0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images.At 10 min after the treatment, they reached values in ranges 0.75-1 dB/(MHz.cm) and 1-1.5 dB/cm, respectively, and remained stable within those ranges.This increase was not accompanied with the appearance of bubble clouds in the B-mode images.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada.

ABSTRACT

Background: This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indicators of tissue thermal damage.

Methods: Two-dimensional pulse-echo radio frequency (RF) data were acquired before, during, and after HIFU exposure to estimate changes in least squares attenuation coefficient slope (Δβ) and attenuation coefficient intercept (Δα 0). Using the acquired RF data, Δβ and Δα 0 images, along with conventional B-mode ultrasound images, were constructed. The dynamic changes of Δβ and Δα 0, averaged in the region of interest, were correlated with B-mode images obtained during the HIFU treatment process.

Results: At a HIFU exposure duration of 40 s and various HIFU intensities (737-1,068 W/cm(2)), Δβ and Δα 0 increased rapidly to values in the ranges 1.5-2.5 dB/(MHz.cm) and 4-5 dB/cm, respectively. This rapid increase was accompanied with the appearance of bubble clouds in the B-mode images. Bubble activities appeared as strong hyperechoic regions in the B-mode images and caused fluctuations in the estimated Δβ and Δα 0 values. After the treatment, Δβ and Δα 0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images. At 10 min after the treatment, they reached values in ranges 0.75-1 dB/(MHz.cm) and 1-1.5 dB/cm, respectively, and remained stable within those ranges. At a long HIFU exposure duration of around 10 min and low HIFU intensity (117 W/cm(2)), Δβ and Δα 0 gradually increased to values of 2.2 dB/(MHz.cm) and 2.2 dB/cm, respectively. This increase was not accompanied with the appearance of bubble clouds in the B-mode images. After HIFU treatment, Δβ and Δα 0 gradually decreased to values of 1.8 dB/(MHz.cm) and 1.5 dB/cm, respectively, and remained stable at those values.

Conclusions: Δβ and Δα 0 estimations were both potentially reliable indicators of tissue thermal damage. In addition, Δβ and Δα 0 images both had significantly higher contrast-to-speckle ratios compared to the conventional B-mode images and outperformed the B-mode images in detecting HIFU thermal lesions at all investigated TAPs and exposure durations.

No MeSH data available.


Related in: MedlinePlus

Timing diagram of HIFU exposure and data acquisition.
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Figure 3: Timing diagram of HIFU exposure and data acquisition.

Mentions: For the shorter-duration HIFU exposures (40 s), the duration of interruption was 120 ms (off-time) for every HIFU on-time, allowing the capture of two RF data frames, and the HIFU on-time was 400 ms, resulting in a duty cycle of 77%. The total HIFU treatment time was 40 s for TAP levels of 34, 37, 39, 44, and 49 W. A total of four lesions were created at every TAP value. RF data were acquired 10 min after the completion of HIFU treatment, and in one case, RF data were acquired 13 h after the completion of HIFU treatment as well. Figure 3 illustrates the timing diagram of HIFU exposure and RF data acquisition.


Estimating dynamic changes of tissue attenuation coefficient during high-intensity focused ultrasound treatment.

Rahimian S, Tavakkoli J - J Ther Ultrasound (2013)

Timing diagram of HIFU exposure and data acquisition.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4265947&req=5

Figure 3: Timing diagram of HIFU exposure and data acquisition.
Mentions: For the shorter-duration HIFU exposures (40 s), the duration of interruption was 120 ms (off-time) for every HIFU on-time, allowing the capture of two RF data frames, and the HIFU on-time was 400 ms, resulting in a duty cycle of 77%. The total HIFU treatment time was 40 s for TAP levels of 34, 37, 39, 44, and 49 W. A total of four lesions were created at every TAP value. RF data were acquired 10 min after the completion of HIFU treatment, and in one case, RF data were acquired 13 h after the completion of HIFU treatment as well. Figure 3 illustrates the timing diagram of HIFU exposure and RF data acquisition.

Bottom Line: After the treatment, Δβ and Δα 0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images.At 10 min after the treatment, they reached values in ranges 0.75-1 dB/(MHz.cm) and 1-1.5 dB/cm, respectively, and remained stable within those ranges.This increase was not accompanied with the appearance of bubble clouds in the B-mode images.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada.

ABSTRACT

Background: This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indicators of tissue thermal damage.

Methods: Two-dimensional pulse-echo radio frequency (RF) data were acquired before, during, and after HIFU exposure to estimate changes in least squares attenuation coefficient slope (Δβ) and attenuation coefficient intercept (Δα 0). Using the acquired RF data, Δβ and Δα 0 images, along with conventional B-mode ultrasound images, were constructed. The dynamic changes of Δβ and Δα 0, averaged in the region of interest, were correlated with B-mode images obtained during the HIFU treatment process.

Results: At a HIFU exposure duration of 40 s and various HIFU intensities (737-1,068 W/cm(2)), Δβ and Δα 0 increased rapidly to values in the ranges 1.5-2.5 dB/(MHz.cm) and 4-5 dB/cm, respectively. This rapid increase was accompanied with the appearance of bubble clouds in the B-mode images. Bubble activities appeared as strong hyperechoic regions in the B-mode images and caused fluctuations in the estimated Δβ and Δα 0 values. After the treatment, Δβ and Δα 0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images. At 10 min after the treatment, they reached values in ranges 0.75-1 dB/(MHz.cm) and 1-1.5 dB/cm, respectively, and remained stable within those ranges. At a long HIFU exposure duration of around 10 min and low HIFU intensity (117 W/cm(2)), Δβ and Δα 0 gradually increased to values of 2.2 dB/(MHz.cm) and 2.2 dB/cm, respectively. This increase was not accompanied with the appearance of bubble clouds in the B-mode images. After HIFU treatment, Δβ and Δα 0 gradually decreased to values of 1.8 dB/(MHz.cm) and 1.5 dB/cm, respectively, and remained stable at those values.

Conclusions: Δβ and Δα 0 estimations were both potentially reliable indicators of tissue thermal damage. In addition, Δβ and Δα 0 images both had significantly higher contrast-to-speckle ratios compared to the conventional B-mode images and outperformed the B-mode images in detecting HIFU thermal lesions at all investigated TAPs and exposure durations.

No MeSH data available.


Related in: MedlinePlus