Int J CARS (2009) 4:45–52 DOI 10.1007/s11548-008-0268-8 ORIGINAL ARTICLE Localization and registration accuracy in image guided neurosurgery: a clinical study Reuben R. Shamir · Leo Joskowicz · Sergey Spektor · Yigal Shoshan Received: 9 January 2008 / Accepted: 23 September 2008 / Published online: 28 October 2008 © CARS 2008 Abstract Purpose To measure and compare the clinical localization and registration errors in image-guided neurosurgery, with the purpose of revising current assumptions. Materials and methods Twelve patients who underwent brain surgeries with a navigation system were randomly selected. A neurosurgeon localized and correlated the land- marks on preoperative MRI images and on the intraoperative physical anatomy with a tracked pointer. In the laboratory, we generated 612 scenarios in which one landmark pair was defined as the target and the remaining ones were used to compute the registration transformation. Four errors were measured: (1) fiducial localization error (FLE); (2) target reg- istration error (TRE); (3) fiducial registration error (FRE); (4) Fitzpatrick’s target registration error estimation (F-TRE). We compared the different errors and computed their correlation. Results The image and physical FLE ranges were 0.5–2.0 and 1.6–3.0mm, respectively. The measured TRE, FRE and F-TRE were 4.1 ± 1.6, 3.9 ± 1.2, and 3.7 ± 2.2 mm, respec- tively. Low correlations of 0.19 and 0.37 were observed between the FRE and TRE and between the F-TRE and the TRE, respectively. The differences of the FRE and F-TRE from the TRE were 1.3 ± 1.0 mm (max = 5.5 mm) and 1.3 ± 1.2 mm (max = 7.3mm), respectively. R. R. Shamir (B ) · L. Joskowicz School of Engineering and Computer Science, The Hebrew University of Jerusalem, Givat Ram Campus, 91904 Jerusalem, Israel e-mail: rubke@cs.huji.ac.il; shamir.ruby@gmail.com S. Spektor · Y. Shoshan Department of Neurosurgery, School of Medicine, Hadassah University Hospital, Jerusalem, Israel Conclusion Contrary to common belief, the FLE presents significant variations. Moreover, both the FRE and the F-TRE are poor indicators of the TRE in image-to-patient registra- tion. Keywords Neurosurgery · Image-guided navigation · Localization error · Registration error Introduction Image-guided surgery (IGS) has become one of the meth- ods of choice in a wide variety of neurosurgical procedures, including tumor biopsy, tumor resection, minimal access craniotomies, catheter placement, treatment of hydrocepha- lus, and deep brain stimulation, among many others [1]. IGS provides real-time, visual information of the intraop- erative location of surgical tools with respect to preopera- tive CT/MRI images on which skull entry points and targets inside the brain have been defined. Since the surgeon relies on this information to manipulate the tools and perform surgical gestures, the localization accuracy with respect to the preop- erative images is of utmost importance. Inaccurate localiza- tion can be misleading at best and may result in undesired complications. A key step in IGS is the accurate intraoperative align- ment, commonly termed registration, between preoperative CT/MRI images and the intraoperative physical anatomy. Landmark-based registration consists of correlating fiducials and/or anatomical landmarks present in both the preoper- ative image and intraoperatively on the patient’s anatomy. Patients are preoperatively imaged with a few fiducial mark- ers affixed to their skin or bone, which are then localized in the images together with additional anatomical landmarks. Intraoperatively, the surgeon touches the markers and the anatomical landmarks with a tracked pointer and pairs them 123