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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

Lesion growth in ex vivo porcine muscle tissue in conventional B-mode images. (A) The duty cycle was 77%, resulting in TAP of 49 W and average focal intensity of 1,068 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 40 s. (B) Axial section of the lesion induced.
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Figure 4: Lesion growth in ex vivo porcine muscle tissue in conventional B-mode images. (A) The duty cycle was 77%, resulting in TAP of 49 W and average focal intensity of 1,068 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 40 s. (B) Axial section of the lesion induced.

Mentions: The visualization of lesion formation was directly correlated with the B-mode images formed from the pulse-echo RF data, shown in Figure 4A. The induced lesion (Figure 4B) was monitored for 13 h. Figure 5 shows the corresponding Δβ images generated using the same RF data, with every frame representing a 2-D map of change in least squares attenuation coefficient slope. As shown in Figure 4A, a bright hyperechoic region appeared at the focal region in the B-mode image at 2.6 s and then enlarged and grew in intensity during HIFU treatment. Corresponding to the hyperechoic region that appeared in the B-mode images, Figure 5 revealed a high-intensity region that appeared in the Δβ images at 2.6 s and then enlarged and grew in intensity during HIFU treatment. After the treatment, the bright hyperechoic region in the focal region of the B-mode image began to gradually fade, and after 10 min, it was hardly visible in the B-mode images. After 13 h, the hyperechoic region was virtually invisible in the B-mode image. Meanwhile, even after 13 h, the high-intensity region in the Δβ image remained visible. However, this high-intensity region decreased in size and intensity after 10 min had passed, and after 13 h, it decreased in size and intensity to a higher extent.


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

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

Lesion growth in ex vivo porcine muscle tissue in conventional B-mode images. (A) The duty cycle was 77%, resulting in TAP of 49 W and average focal intensity of 1,068 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 40 s. (B) Axial section of the lesion induced.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Lesion growth in ex vivo porcine muscle tissue in conventional B-mode images. (A) The duty cycle was 77%, resulting in TAP of 49 W and average focal intensity of 1,068 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 40 s. (B) Axial section of the lesion induced.
Mentions: The visualization of lesion formation was directly correlated with the B-mode images formed from the pulse-echo RF data, shown in Figure 4A. The induced lesion (Figure 4B) was monitored for 13 h. Figure 5 shows the corresponding Δβ images generated using the same RF data, with every frame representing a 2-D map of change in least squares attenuation coefficient slope. As shown in Figure 4A, a bright hyperechoic region appeared at the focal region in the B-mode image at 2.6 s and then enlarged and grew in intensity during HIFU treatment. Corresponding to the hyperechoic region that appeared in the B-mode images, Figure 5 revealed a high-intensity region that appeared in the Δβ images at 2.6 s and then enlarged and grew in intensity during HIFU treatment. After the treatment, the bright hyperechoic region in the focal region of the B-mode image began to gradually fade, and after 10 min, it was hardly visible in the B-mode images. After 13 h, the hyperechoic region was virtually invisible in the B-mode image. Meanwhile, even after 13 h, the high-intensity region in the Δβ image remained visible. However, this high-intensity region decreased in size and intensity after 10 min had passed, and after 13 h, it decreased in size and intensity to a higher extent.

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