Comparison of frameless stereotactic systems: Accuracy, precision, and applications

OBJECTIVE: Frameless stereotactic systems have become an integral part of n eurosurgical practice. At our center, we recently introduced for clinical u se a small, portable, frameless stereotactic system, namely the Cygnus PFS system (Compass International, Rochester, MN). The purpose of this study wa s to compare the accuracy of the Cygnus PFS system with that of two larger systems that are also currently in use at our institution, i.e., the SMN sy stem (Zeiss, Oberkochen, Germany) and the ISG viewing wand (ISG Technologie s, Toronto, Canada). These systems represent three kinds of frameless stere otactic technologies that are commercially available. Each system uses a di fferent method of spatial localization, i.e., mechanical linkage (ISG syste m), magnetic field digitization (Cygnus system), or optical technology (SMN system). METHODS: Using a stereotactic "phantom," we measured the accuracies of all three systems with identical data sets. The errors in localization in three -dimensional space for nine targets were calculated by using 10 magnetic re sonance imaging data sets. The precision of each system was also calculated . RESULTS: With this experimental protocol, the Cygnus system attained a mean accuracy of 1.90 +/- 0.7 mm, the ISG viewing wand system a mean accuracy o f 1.67 +/- 0.43 mm, and the SMN microscope a mean accuracy of 2.61 +/- 0.99 mm. The precision values were not significantly different among the system s. CONCLUSION: We observed only small differences in accuracy and precision am ong these three systems. We briefly review the advantages and disadvantages of each system and note that other factors, such as portability, ease of u se, and microscope integration, should influence the selection of a framele ss stereotactic system.