Noninvasive Measurement of Local Thermal Diffusivity Using Backscattered Ultrasound and Focused Ultrasound Heating

Abstract

Previously, noninvasive methods of estimating local tissue thermal and acoustic properties using backscattered ultrasound have been proposed in the literature. In this article, a noninvasive method of estimating local thermal diffusivity in situ during focused ultrasound heating using beamformed acoustic backscatter data and applying novel signal processing techniques is developed. A high intensity focused ultrasound (HIFU) transducer operating at subablative intensities is employed to create a brief local temperature rise of no more than 10°C. Beamformed radio-frequency (RF) data are collected during heating and cooling using a clinical ultrasound scanner. Measurements of the time-varying "acoustic strain", that is, spatiotemporal variations in the RF echo shifts induced by the temperature related sound speed changes, are related to a solution of the heat transfer equation to estimate the thermal diffusivity in the heated zone. Numerical simulations and experiments performed in vitro in tissue mimicking phantoms and excised turkey breast muscle tissue demonstrate agreement between the ultrasound derived thermal diffusivity estimates and independent estimates made by a traditional hot-wire technique. The new noninvasive ultrasonic method has potential applications in thermal therapy planning and monitoring, physiological monitoring and as a means of noninvasive tissue characterization.

Volumetric MRI‐guided high‐intensity focused ultrasound for noninvasive, in vivo determination of tissue thermal conductivity: Initial experience in a pig model

“…In three of the five unsuccessful cases, a safety algorithm caused the treatments to be automatically discontinued once the near-field or far-field temperature exceeded the predefined temperature safety limit (16); in the other two cases treatment failure was due to equipment malfunction. The mean standard deviation for the temperature in untreated regions was 1.1 6 0.2 C. The regions of real-time temperature change for all treatment cell sizes (4,8,12, and 16 mm) were roughly ellipsoidal, with the longest axis, as expected, being in the direction of propagation of the HIFU beam (as seen in the sagittal monitoring plane and in a circular cross-section in each of the three coronal treatment planes). Figure 3A-D presents the complete sequence of steps, including imaging on the planning console (Fig.…”

“…Modern techniques such as infrared imaging (11), ultrasonography (12), and magnetic resonance imaging (MRI) (13) have been used to noninvasively measure the thermal conductivity of epidermis on the arm of a Caucasian adult, the breast of a turkey, and the thigh muscle of rabbit, respectively. Infrared imaging, however, is restricted to superficial applications because its penetration depth (which is wavelength-dependent) is only a few millimeters.…”

Influence of Temperature-Dependent Thermal Parameters on Temperature Elevation of Tissue Exposed to High-Intensity Focused Ultrasound: Numerical Simulation

“…The temperaturedependent thermal properties of in vivo tissues during HIFU treatment were monitored using volumetric magnetic resonance thermometry (Oliveira et al 2009). Thermal conductivity and perfusion (Cheng and Plewes 2002) and thermal diffusivity of tissues after focused ultrasound heating (Anand and Kaczkowski 2008) were estimated non-invasively. The changes in physical properties of the target tissues heated by HIFU may effectively modify the temperature distribution, that is, thermal lesion geometry.…”

Uncertainty evaluation from non-invasive estimation of temperature variation using B-mode ultrasonic images from a plastic phantom

“…signals. The most well known methodologies were those based on estimation of temporal echo-shifts [4,6,7] and on the backscattered energy [8], due to changes in speedof-sound, medium expansion/contraction, and scatters density change due to temperature.…”