The feasibility of using thermal strain imaging to regulate energy delivery during intracardiac radio-frequency ablation.

University of California, Davis, Department of Biomedical Engineering, Davis, CA, USA.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control (Impact Factor: 1.8). 07/2011; 58(7):1406-17. DOI: 10.1109/TUFFC.2011.1960
Source: PubMed

ABSTRACT A method is introduced to monitor cardiac ablative therapy by examining slope changes in the thermal strain curve caused by speed of sound variations with temperature. The sound speed of water-bearing tissue such as cardiac muscle increases with temperature. However, at temperatures above about 50°C, there is no further increase in the sound speed and the temperature coefficient may become slightly negative. For ablation therapy, an irreversible injury to tissue and a complete heart block occurs in the range of 48 to 50°C for a short period in accordance with the well-known Arrhenius equation. Using these two properties, we propose a potential tool to detect the moment when tissue damage occurs by using the reduced slope in the thermal strain curve as a function of heating time. We have illustrated the feasibility of this method initially using porcine myocardium in vitro. The method was further demonstrated in vivo, using a specially equipped ablation tip and an 11-MHz microlinear intracardiac echocardiography (ICE) array mounted on the tip of a catheter. The thermal strain curves showed a plateau, strongly suggesting that the temperature reached at least 50°C.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Tissue temperature is critically related to the success or failure of catheter ablation procedures. Temperature imaging using ultrasound techniques is attractive because of the potential to provide real-time information at low cost. The signal-processing methods used here were developed to investigate the feasibility of monitoring ablative therapy by identifying the point at which the slope of the thermal strain curve changes sign caused primarily by speed of sound variations with temperature. Previously, we have demonstrated the feasibility of this method in-vivo using porcine models. In this paper, we present recent results with temperature validation for this method in-vivo using an integrated intracardiac echocardiography (ICE) probe. Also preliminary results on thermal strain imaging using a cMUT array integrated into the ICE probe are presented.
    Ultrasonics Symposium (IUS), 2011 IEEE International; 01/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: Quantitative ultrasound (QUS) imaging is hypothesized to map temperature elevations induced in tissue with high spatial and temporal resolution. To test this hypothesis, QUS techniques were examined to monitor high-intensity focused ultrasound (HIFU) exposure of tissue. In situ experiments were conducted on mammary adenocarcinoma tumors grown in rats and lesions were formed using a HIFU system. A thermocouple was inserted into the tumor to provide estimates of temperature at one location. Backscattered time-domain waveforms from the tissue during exposure were recorded using a clinical ultrasonic imaging system. Backscatter coefficients were estimated using a reference phantom technique. Two parameters were estimated from the backscatter coefficient (effective scatterer diameter (ESD) and effective acoustic concentration (EAC). The changes in the average parameters in the regions corresponding to the HIFU focus over time were correlated to the temperature readings from the thermocouple. The changes in the EAC parameter were consistently correlated to temperature during both heating and cooling of the tumors. The changes in the ESD did not have a consistent trend with temperature. The mean ESD and EAC before exposure were 120 ± 16 μm and 32 ± 3 dB/cm(3), respectively, and changed to 144 ± 9 μm and 51 ± 7 dB/cm(3), respectively, just before the last HIFU pulse was delivered to the tissue. After the tissue cooled down to 37°C, the mean ESD and EAC were 126 ± 8 μm and 35 ± 4 dB/cm(3), respectively. Peak temperature in the range of 50-60°C was recorded by a thermocouple placed just behind the tumor. These results suggest that QUS techniques have the potential to be used for non-invasive monitoring of HIFU exposure.
    Ultrasonic Imaging 06/2014; · 1.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The liver has been hypothesized to have a unique arrangement of microvasculature that presents as an arrangement of quasiperiodic scatterers to an interrogating ultrasound pulse. The mean scatterer spacing (MSS) of these quasiperiodic scatterers has been proposed as a useful quantitative ultrasound biomarker for characterizing liver tissue. Thermal ablation is an increasingly popular method for treating hepatic tumors, and ultrasonic imaging approaches for delineating the extent of thermal ablation are in high demand. In this work, we examine the distribution of estimated MSS in thermally coagulated bovine liver and normal untreated bovine liver ex vivo. We estimate MSS by detecting local maxima in the spectral coherence function of radio frequency echoes from a clinical transducer, the Siemens VFX 9L4 transducer operating on an S2000 scanner. We find that normal untreated bovine liver was characterized by an MSS of approximately 1.3 mm. We examined regions of interest 12 mm wide laterally, and ranging from 12 mm to 18 mm axially, in 2 mm increments. Over these parameters, the mode of the MSS estimates was between 1.25 and 1.37 mm. On the other hand, estimation of MSS in thermally coagulated liver tissue yields a distribution of MSS estimates whose mode varied between 0.45 and 1.0 mm when examining regions of interest over the same sizes. We demonstrate that the estimated MSS in thermally coagulated liver favors small spacings because the randomly positioned scatterers in this tissue are better modeled as aperiodic scatterers. The submillimeter spacings result from the fact that this was the most probable spacing to be estimated if the discretely sampled spectral coherence function was a uniformly random two-dimensional function.
    Ultrasonic Imaging 04/2014; 36(2):79-97. · 1.58 Impact Factor

Full-text (2 Sources)

Available from
Jun 3, 2014