Author response

We thank Drs. Urade and Fukumoto for their comments on our paper. Urade and colleagues described contrast-enhanced intraoperative ultrasonic cholangiography for real-time biliary navigation using perfluorobutane microbubbles in their 2014 study, referenced in our paper. As they mentioned, one limitation of their study was the use of a specific contrast agent and 3D ultrasound probes, which may not be available across all centres, as in our case. We studied the feasibility of using saline, churned with room air as a contrast agent along with a 2D ultrasound probe as an alternative. As mentioned by Drs. Urade and Fukumoto, achieving a specific concentration and stability of saline bubbles was not possible in our study, and this also explains variations in the amount of echogenicity and contrast retention time seen on our ultrasound images. These variations are also mentioned in our results. Constant saline injection in the indwelling catheter obviates the loss of echogenicity due to “unstable contrast.” Also, saline microbubbles may wash out earlier than perfluorobutane microbubbles, thus creating less interference with further imaging. We thank Drs. Urade and Fukumoto for referring to their recent papers, in which they described “pseudostaining” of the liver parenchyma caused by perfluorobutane microbubbles leading to accurate identification of the duct. In our study, use of intrabiliary saline sharply demarcated the segment(s) to which the duct belongs and was clearly visible as parenchymal echogenicity on ultrasound imaging. Primarily, this is how we have identified the duct in our technique and is very similar to “pseudostaining.” The echogenicity caused by saline may be less intense than perflourobutane microbubbles; however, it still sharply demarcates the respective segment(s). Necessity is the mother of invention, and we propose that our technique will be of value to a hepatobiliary surgeon when making intraoperative decisions with minimal resources.