A novel ultrasonic-imaging based temperature approach by instantaneous frequency detection (Instantaneous frequency detection for temperature estimation)

Focused ultrasound thermal therapy relies on temperature monitoring for treatment guidance and assurance of targeting and dose control; a potential approach to achieve these is ultrasonic temperature estimation. The approach used currently involves the detection of echo time shifts based on cross-correlation processing from the segmented radio-frequency (RF) data. In this study, we propose a novel 2D ultrasonic temperature measurement approach by detecting changes in instantaneous frequency. We proposed a novel echo time-shift based algorithm to perform fast temperature estimation from ultrasonic imaging. This new algorithm may serve as an alternative for implementing 2D temperature estimation into a clinical ultrasound imager. Focused ultrasound was used as the heating source, and the beamformed RF signals provided from a 2D ultrasound imager were used to verify the proposed algorithm for temperature change estimation. For comparison, a conventional cross-correlation technique was also evaluated. Heating experiments of tissue-mimicking phantoms and ex-vivo porcine muscles were conducted. Our results show that the proposed new algorithm yields up to six times better computational efficiency while its contrast detection ability and precision rival those of cross-correlation-based algorithm. In the ex-vivo tissue experiments, we also presented the irreversibility of the echo time-shift effect in the necrotic region, which is different from that in the tissue-mimicking phantoms. In this study, we propose a new approach for temperature estimation by employing instantaneous frequency detection; it was implemented by using a simple zero-crossing algorithm. Some of the features of this approach are its superior computational efficiency and the possibility of higher spatial resolution for temperature mapping. Further, the experimental results have demonstrated that the proposed algorithm can provide similar temperature detection ability and precision as compared to the cross-correlation algorithm. Tissue irreversibility when approaching the necrotic temperature encounters difficulty in accurate temperature estimation, which has been proposed and discussed as an alternative possibility to detect tissue necrosis rather than temperature. This provides useful information as well as an alternative for the clinical applications of such an ultrasound-based temperature estimation technology.