Thermal (temporal) strain imaging (TSI) is being developed to detect the lipid rich core of atherosclerotic plaques and fatty liver disease. However, the effects of ultrasonic clutter on TSI have not been considered. In this study, we evaluated whether pulse inversion harmonic imaging (PIHI) could be used to improve estimates of thermal (temporal) strains. Using mixed castor oil-gelatin phantoms of different concentrations and artificially introduced clutter, we showed that PIHI improved the signal-to-noise ratio of TSI by an average of 213% or 52.1% as compared to 3.3 MHz and 6.6 MHz imaging. In a phantom constructed using human liposuction fat in the presence of clutter, the contrast-to-noise ratio was degraded by 35.1% for PIHI as compared to 62.4% and 43.7% for 3.3 MHz and 6.6 MHz imaging, respectively. These findings were further validated using an ex vivo carotid endarterectomy sample. PIHI can be used to improve estimates of thermal (temporal) strain in the presence of clutter.
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