Non-Invasive Measurement of Temperature Distributions During Hyperthermia Treatments using Ultrasound B-mode Images

Iseki, Yuya; Anan, Daisuke; Saito, Takahiro; Shindo, Yoshitaro; Ikuta, Futoshi; Takahashi, Kenji; Kato, K.

doi:10.3191/thermalmed.32.17

Cited by 16 publications

(10 citation statements)

References 16 publications

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“…Strain‐based US thermal imaging is limited, in that the temperature estimation is only valid for temperatures below 50°C, whereby the speed of sound is a dominant factor and the relationship between the temperature change and the strain is constant . Given that the expected temperature for PVI is 50°C, the strain‐based approach has been a promising method for the monitoring of the tissue temperature during laser ablation for PVI.…”

Section: Discussionmentioning

confidence: 99%

“…Several studies evaluated the coefficient k on liver tissues but did not report on its values for cardiac tissue . Thus, to calculate the k value for cardiac tissue, the temperature measurements from the thermocouple were used as the reference temperatures.…”

Section: Discussionmentioning

confidence: 99%

“…When the tissue temperature is less than 50°C, coefficient k is mainly affected by the change of speed of sound (

β

) than by thermal expansion (

α

) . When the initial values ( T 0 and c 0 ) and the measured temperature ( T ) are known, the coefficient k is the slope of the assumed linear relationship between the measured temperature change ( T − T 0 ) and the strain

(\partial (δ s) / \partial z)

from the change of speed of sound . Owing to the inhomogeneity of tissue, the coefficient k is depth‐dependent, and can be expressed as k ( z ).…”

Section: Methodsmentioning

confidence: 99%

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Application of Ultrasound Thermal Imaging for Monitoring Laser Ablation in Ex Vivo Cardiac Tissue

et al. 2019

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Background and Objective Laser ablation can be used to treat atrial fibrillation by thermally isolating pulmonary veins. In this study, we evaluated the feasibility of high‐resolution (<1 mm) ultrasound thermal imaging to monitor spatial temperature distribution during laser ablation on ex vivo cardiac tissue. Study Design/Materials and Methods Laser ablation (808 nm) was performed on five porcine cardiac tissue samples. A thermocouple was used to measure the interstitial tissue temperature during the laser ablation process. Tissue‐strain‐based ultrasound thermal imaging was conducted to monitor the spatial distribution of the temperature in the cardiac tissue. The tissue temperature was estimated from the time shifts of ultrasound signals owing to the changes in the speed of sound and was compared with the measured temperature. The temperature estimation coefficient k of porcine cardiac tissue was calculated from the estimated thermal strain and the measured temperature. The degree of tissue coagulation (temperatures > 50°C) was derived from the estimated temperature and was compared with that of the tested cardiac tissue. Results The estimated tissue temperature using strain‐based ultrasound thermal imaging at a depth of 1 mm agreed with thermocouple measurements. During the 30‐second period of the laser ablation process, the estimated tissue temperature increased from 25 to 70°C at a depth of 0.1 mm, while the estimated temperature at a depth of 1 mm increased up to 46°C. Owing to the uncertainty of the coefficient k, the k value of the porcine cardiac tissue varied from 160 to 220°C with temperature changes of up to 20°C. The estimated coagulation region in the ultrasound thermal imaging was 20% wider (+0.6 mm) but 9% shallower (−0.1 mm) than the measured region of the ablated porcine cardiac tissue. Conclusions The current study demonstrated the feasibility of temperature monitoring with the use of ultrasound thermal imaging during the laser ablation on ex vivo porcine cardiac tissue. The high‐resolution ultrasound thermal imaging could map the spatial distribution of the tissue temperature. The proposed method can be used to monitor the temperature and thermal coagulation to achieve effective laser ablation for atrial fibrillation. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…When the tissue temperature is less than 50°C, coefficient k is mainly affected by the change of speed of sound (

β

) than by thermal expansion (

α

(\partial (δ s) / \partial z)

from the change of speed of sound . Owing to the inhomogeneity of tissue, the coefficient k is depth‐dependent, and can be expressed as k ( z ).…”

Section: Methodsmentioning

confidence: 99%

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Application of Ultrasound Thermal Imaging for Monitoring Laser Ablation in Ex Vivo Cardiac Tissue

et al. 2019

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“…The coefficient k depends on tissue type and fat content [ 27 ]. According to the previous study, the coefficient k of porcine livers is 207.67°C [ 28 ], which was used as the initial value in the proposed algorithm. Subsequently, three groups of experiments were performed using RFA powers of 10, 15, and 20 W, respectively.…”

Section: Methodsmentioning

confidence: 99%

Adaptive ultrasound temperature imaging for monitoring radiofrequency ablation

Liu

Zhou

et al. 2017

PLoS ONE

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Radiofrequency ablation (RFA) has been widely used as an alternative treatment modality for liver tumors. Monitoring the temperature distribution in the tissue during RFA is required to assess the thermal dosage. Ultrasound temperature imaging based on the detection of echo time shifts has received the most attention in the past decade. The coefficient k, connecting the temperature change and the echo time shift, is a medium-dependent parameter used to describe the confounding effects of changes in the speed of sound and thermal expansion as temperature increases. The current algorithm of temperature estimate based on echo time shift detection typically uses a constant k, resulting in estimation errors when ablation temperatures are higher than 50°C. This study proposes an adaptive-k algorithm that enables the automatic adjustment of the coefficient k during ultrasound temperature monitoring of RFA. To verify the proposed algorithm, RFA experiments on in vitro porcine liver samples (total n = 15) were performed using ablation powers of 10, 15, and 20 W. During RFA, a clinical ultrasound system equipped with a 7.5-MHz linear transducer was used to collect backscattered signals for ultrasound temperature imaging using the constant- and adaptive-k algorithms. Concurrently, an infrared imaging system and thermocouples were used to measure surface temperature distribution of the sample and internal ablation temperatures for comparisons with ultrasound estimates. Experimental results demonstrated that the proposed adaptive-k method improved the performance in visualizing the temperature distribution. In particular, the estimation errors were also reduced even when the temperature of the tissue is higher than 50°C. The proposed adaptive-k ultrasound temperature imaging strategy has potential to serve as a thermal dosage evaluation tool for monitoring high-temperature RFA.

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“…．画像変位量から温度分布を推定する計算式を式 1 および式 2 に示す19,[22][23][24] ． Agar phantom shaped like a human leg. (X-Y plane cut model) に，本研究で開発した超音波プローブ固定用の冶具を示す．電気的絶縁性に優れた素材である Improvement of cavity for OA Y. Shindo et al…”

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Improved Deep Thermal Rehabilitation System with Temperature Measurement Function Using Ultrasound Images

Shindo

Takahashi

Ikuta³

et al. 2017

Thermal Med.

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Non-Invasive Measurement of Temperature Distributions During Hyperthermia Treatments using Ultrasound B-mode Images

Cited by 16 publications

References 16 publications

Application of Ultrasound Thermal Imaging for Monitoring Laser Ablation in Ex Vivo Cardiac Tissue

Application of Ultrasound Thermal Imaging for Monitoring Laser Ablation in Ex Vivo Cardiac Tissue

Adaptive ultrasound temperature imaging for monitoring radiofrequency ablation

Improved Deep Thermal Rehabilitation System with Temperature Measurement Function Using Ultrasound Images

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