Dear Bruce, Doug, Nick, and other co-workers,
As authors of the recent paper “The effects of FreeSurfer version, workstation type, and Macintosh operating system version on anatomical volume and cortical thickness measurements” we would like to take the opportunity to respond to the numerous e-mails and reactions written on mailings lists and websites. We have never expected that our paper would have such an adverse impact. We have noticed that several so-called “journalists” have misinterpreted and erroneously extrapolated our conclusions. Even though this is not in our hands, we want to express our disappointment of these events and that we feel very uncomfortable with the created harassment. We want to stress that it has never been our intention to put FreeSurfer in a bad light or to blame its developers, rather we wanted to quantify the effects that you frequently warned the users about. The results of our study confirm your recommendations and increase the awareness of such effects to (novice) users. It is of course unavoidable that modifications to algorithms will produce different results; we, nevertheless, must admit that we were surprised that some effects were rather large. We are using FreeSurfer frequently for our MRI data and we definitely intend to do so in the future. We are impressed by the efforts of your team to improve the algorithms and to extend the capabilities of FreeSurfer. We are most grateful to you and the other developers because these continuing efforts enabled and will enable us to perform our research in a valid and proper manner. Unfortunately, the media attention gave the impression that our conclusions would only be directed to FreeSurfer. We have written in our discussion section that some of the conclusions may apply to other packages in the field of neuroimaging as well. We hope that you can acknowledge our sincere intention to examine and increase awareness of uncontrolled variation in MRI data analyses in general and not to pinpoint Freesurfer. Therefore, we have informed also the users and developers of FSL about possible similar effects.
Ed Gronenschild, Petra Habets, Heidi Jacobs, Ron Mengelers, Nico Rozendaal, Jim van Os, Machteld Marcelis