TER HAAR REPLIES: The comments made by Kirby Vosburgh and Narendra Sanghvi are well taken. In a brief overview, it is impossible to mention all the contributors to this field. A review article can only be a personal judgement regarding the major milestones in a technique’s development. The researchers in Indiana have certainly made significant contributions, but so too, for example, did Padmaker Lele at MIT, John Pond at Guy’s Hospital, London, and, more recently, Dominic Cathignol’s group in Lyon, France. There was simply not the space to detail these contributions, nor those of many other notable researchers.

I did not mean to understate the role of magnetic resonance imaging in acoustic surgery; I recognize and am excited by its considerable potential. The ability to image 1–2°C temperature rises, while useful, must not be overstated, because without good understanding it may lead to mispositioning of the high-power focus. The strength of MRI-guided acoustic surgery lies in its ability to overlay, on an anatomical image, the distribution of thermal dose achieved, thus allowing an essentially real-time assessment of the treatment. Ultrasound techniques do not yet provide such information, but may in the future. Undoubtedly there will be clinical applications—for example, in the brain—for which MRI will be the best way to monitor treatments, but for many others, diagnostic ultrasound will prove to be more appropriate. Certainly, because of the expense of, and limited access to, MR scanners, acoustic surgery that is ultrasound guided will be available to more patients worldwide.

Clinical interest in acoustic surgery is expanding rapidly; concurrently, many commercial enterprises are appearing, some farther down the road to regulatory approval and commercialization than others. The devices mentioned by Vosburgh and Sanghvi are just two of several currently in clinical trial. I considered it beyond the scope of the article to review the information available from these sources.