In vivochange in ultrasonic backscattered energy with temperature in motion-compensated images

Abstract

Ultrasound is an attractive modality for non-invasive imaging to monitor temperature of tumorous regions undergoing hyperthermia therapy. Previously, we predicted monotonic changes in backscattered energy (CBE) of ultrasound with temperature for certain sub-wavelength scatterers. We also measured CBE values similar to our predictions in bovine liver, turkey breast muscle, and pork rib muscle in both 1D and 2D in in vitro studies. To corroborate those results in perfused, living tissue, we measured CBE in both normal tissue and in implanted human tumors (HT29 colon cancer line) in 7 nude mice. Images were formed by a phased-array imager with a 7.5 MHz linear probe during homogeneous heating from 37 degrees to 45 degrees C in 0.5 degrees C steps and from body temperature to 43 degrees C during heterogeneous heating. We used cross-correlation as a similarity measure in RF signals to automatically track feature displacement as a function of temperature. Feature displacement was non-uniform with a maximum value of 1 mm across all specimens during homogeneous heating, and 0.2 mm during heterogeneous heating. Envelopes of image regions, compensated for non-rigid motion, were found with the Hilbert transform then smoothed with a 3 x 3 running average filter before forming the backscattered energy at each pixel. Means of both the positive and negative changes in the BE images were evaluated. CBE was monotonic and accumulated to 4-5 dB during homogeneous heating to 45 degrees C and 3-4 dB during heterogenous heating to 43 degrees C. These results are consistent with our previous in vitro measurements and support the use of CBE for temperature estimation in vivo during hyperthermia.

<italic>In Vivo</italic> Ultrasound Thermography in Presence of Temperature Heterogeneity and Natural Motions

“…Although the derivations in these models include the spatial dependency of the temperature change, the final result is similar to the δ-ESF in time domain and does not account for the temperature gradients. Additionally, methods which are not based on displacement estimation have been proposed in [11], [12] and [13] with varying degrees of development in terms of real-time implementation and spatial and temporal resolution.…”

Classification of breast lesions using segmented quantitative ultrasound maps of homodyned K distribution parameters

“…Homodyned K distribution was used in this study, but similar methods can be applied to Nakagami imaging or other quantitative ultrasound techniques which utilize parametric maps. 27,28,53,54 Our method can be expanded to handle 3D data or a larger set of parametric maps. It would be interesting to connect the segmentation of a particular tumor with its molecular type.…”

Exploring potential mechanisms responsible for observed changes of ultrasonic backscattered energy with temperature variations

“…Conventionally, the CBE is calculated by comparing the intensity of an image acquired from a sample at a particular temperature with a reference image from the same sample at 37 • C. 22,23 In studies where the SOS changed, before performing the frame-to-frame comparison, it was necessary to register the images to account for apparent motion in the imaging plane. The registration was required because of the change in SOS, which effectively moved the location of the scatterers to be closer to the transducer as the SOS increased.…”

“…[11][12][13][14][15][16][17][18] Another method based on ultrasonic signals is to correlate temperature elevation with changes in the backscattered energy (CBE). [19][20][21][22][23] The CBE has been hypothesized to be produced by changes in the local scattering from lipid and aqueous scatterers in the tissues versus temperature. [19][20][21] According to the hypothesis, the temperature changes would produce a decrease in the CBE for regions dominated by aqueous scatterers and an increase in the CBE for regions dominated by lipid scatterers.…”