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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

Dynamic changes of Δβ in ex vivo porcine muscle tissue during slow HIFU treatment. Δβ values were estimated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. The duty cycle was 77%, with TAP of 5 W, resulting in an average focal intensity of 117 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 9 min and 39 s.
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Figure 15: Dynamic changes of Δβ in ex vivo porcine muscle tissue during slow HIFU treatment. Δβ values were estimated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. The duty cycle was 77%, with TAP of 5 W, resulting in an average focal intensity of 117 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 9 min and 39 s.

Mentions: Figure 15 shows the dynamic changes of attenuation slope (Δβ) in the region of interest during the slow HIFU exposure. Δβ maps were generated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. As evident in Figure 15, Δβ rose gradually in the first 6 min of treatment from 0 to 1.5 dB/(MHz.cm). From 6 to 7 min, there was a jump in the value of Δβ from 1.5 to 2.1 dB/(MHz.cm). Δβ maintained its value around 2.1 dB/(MHz.cm) with some fluctuations until the end of HIFU treatment at 9 min and 39 s when it reached a maximum value of 2.2 dB/(MHz.cm). After treatment, Δβ gradually decreased to 1.8 dB/(MHz.cm)and remained stable at that value. Once again, the output of the Δβ algorithm at the end of the treatment was used to assess the performance of the algorithm in detecting tissue thermal damage in the absence of boiling bubbles and temperature rise. Table 2 summarizes the resulting Δβ values in the region of interest (ROI), for different TAP values, approximately 10 min after HIFU treatment.


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

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

Dynamic changes of Δβ in ex vivo porcine muscle tissue during slow HIFU treatment. Δβ values were estimated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. The duty cycle was 77%, with TAP of 5 W, resulting in an average focal intensity of 117 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 9 min and 39 s.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 15: Dynamic changes of Δβ in ex vivo porcine muscle tissue during slow HIFU treatment. Δβ values were estimated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. The duty cycle was 77%, with TAP of 5 W, resulting in an average focal intensity of 117 W/cm2 at the HIFU treatment site, for a total HIFU treatment time of 9 min and 39 s.
Mentions: Figure 15 shows the dynamic changes of attenuation slope (Δβ) in the region of interest during the slow HIFU exposure. Δβ maps were generated by spatially averaging the Δβ values axially and laterally in the region of interest (20 mm × 34 mm) centered around the lesion generated by HIFU as shown in Figure 14. As evident in Figure 15, Δβ rose gradually in the first 6 min of treatment from 0 to 1.5 dB/(MHz.cm). From 6 to 7 min, there was a jump in the value of Δβ from 1.5 to 2.1 dB/(MHz.cm). Δβ maintained its value around 2.1 dB/(MHz.cm) with some fluctuations until the end of HIFU treatment at 9 min and 39 s when it reached a maximum value of 2.2 dB/(MHz.cm). After treatment, Δβ gradually decreased to 1.8 dB/(MHz.cm)and remained stable at that value. Once again, the output of the Δβ algorithm at the end of the treatment was used to assess the performance of the algorithm in detecting tissue thermal damage in the absence of boiling bubbles and temperature rise. Table 2 summarizes the resulting Δβ values in the region of interest (ROI), for different TAP values, approximately 10 min after HIFU treatment.

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