We appreciate the comments by Drs Zhou, Wu, Yang, and Tsui regarding our article entitled “Intraoperative ultrasound and tissue elastography measurements do not predict the size of hepatic microwave ablations” .
In their letter, they raise three interesting points of discussion and posit that ultrasound (US) elastography may be useful to monitor hepatic ablations when stress decay, imaging planes, and bubble artifacts are considered. We would like to address these points in the order they were presented.
All ablations in our study (both porcine and human model) were performed in an open fashion at the time of laparotomy. Furthermore, as discussed in our article, a salient difference between the study by Van Vledder and ours is the fact that they obtained cross-sectional images of the ablated livers 3–4 days after treatment . By contrast, median time to imaging was 30 days (interquartile range, 19–67 days) in our series. The difference in the correlation between US and cross-sectional imaging may be explained by ongoing thermal injury. Electrode displacement elastography as reported by Kolokythas et al. is certainly a very interesting technique that may improve the consistency of the pressure release cycle. It perhaps warrants further validation given that the cited study reports the outcome of one patient .
Attempts were made to keep the plane of measurement during intraoperative ultrasound as close to the axial plane as possible; however, there will inevitably be a variable amount of plane shifting, as the probe needs to be in close apposition to the liver surface. The measurement of three-dimensional ablation zone volumes is a reasonable proposition to be considered in future studies.
The use of ultrasound Nakagami imaging as reported by Wang et al. provides an interesting complement to the currently available imaging strategies. The cited article however, although reporting an elegant experimental design, lacks any kind of clinical in vivo correlation or comparison to other imaging modalities. Although the use of Nakagami ultrasound is intriguing, until further clinical comparisons are performed, little can be said about this technique and its usefulness for monitoring liver ablations.
We fully agree with the authors in their contention that elastography has the potential to aid in ablation monitoring, and we share their enthusiasm to elucidate the ideal way to apply this technology to this complex clinical situation. However, in our experience with currently available tools and given the available data, this promise is yet to be fulfilled.
References
1. Correa-Gallego C., Karkar A.M., Monette S., et. al.: Intraoperative ultrasound and tissue elastography measurements do not predict the size of hepatic microwave ablations. Academic radiology 2014; 21: pp. 72-78.
2. Van Vledder M.G., Boctor E.M., Assumpcao L.R., et. al.: Intra-operative ultrasound elasticity imaging for monitoring of hepatic tumour thermal ablation. HPB : the official journal of the International Hepato Pancreato Biliary Association 2010; 12: pp. 717-723.
3. Kolokythas O., Gauthier T., Fernandez A.T., et. al.: Ultrasound-based elastography: a novel approach to assess radio frequency ablation of liver masses performed with expandable ablation probes: a feasibility study. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine 2008; 27: pp. 935-946.
4. Wang C.Y., Geng X., Yeh T.S., et. al.: Monitoring radiofrequency ablation with ultrasound Nakagami imaging. Medical physics 2013; 40: pp. 072901.