Validating Ultrasound-based HIFU Lesion-size Monitoring Technique with MR Thermometry and Histology

Abstract

In order to control and monitor HIFU lesions accurately and cost‐effectively in real‐time, we have developed an ultrasound‐based therapy monitoring technique using acoustic radiation force to track the change in tissue mechanical properties. We validate our method with concurrent MR thermometry and histology. Comparison studies have been completed on in‐vitro bovine liver samples. A single‐element 1.1 MHz focused transducer was used to deliver HIFU and produce acoustic radiation force (ARF). A 5 MHz single‐element transducer was placed co‐axially with the HIFU transducer to acquire the RF data, and track the tissue displacement induced by ARF. During therapy, the monitoring procedure was interleaved with HIFU. MR thermometry (Philips Panorama 1T system) and ultrasound monitoring were performed simultaneously. The tissue temperature and thermal dose (CEM43 = 240 mins) were computed from the MR thermometry data. The tissue displacement induced by the acoustic radiation force was calculated from the ultrasound RF data in real‐time using a cross‐correlation based method. A normalized displacement difference (NDD) parameter was developed and calibrated to estimate the lesion size. The lesion size estimated by the NDD was compared with both MR thermometry prediction and the histology analysis. For lesions smaller than 8mm, the NDD‐based lesion monitoring technique showed very similar performance as MR thermometry. The standard deviation of lesion size error is 0.66 mm, which is comparable to MR thermal dose contour prediction (0.42 mm). A phased array is needed for tracking displacement in 2D and monitoring lesion larger than 8 mm. The study demonstrates the potential of our ultrasound based technique to achieve precise HIFU lesion control through real‐time monitoring. The results compare well with histology and an established technique like MR Thermometry. This approach provides feedback control in real‐time to terminate therapy when a pre‐determined lesion size is achieved, and can be extended to 2D and implemented on commercial ultrasound scanner systems.