The<unk>  is a device that enables guidance of stereotactic surgery or radiosurgery using tomographic images that are obtained via computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET). The<unk>  comprises a diagonal rod that spans two vertical rods to form an N-shape (Figure 1) and permits calculation of the point where a tomographic image plane intersects the diagonal rod. Attaching three<unk> s to a stereotactic instrument allows calculation of three points where a tomographic image plane intersects three diagonal rods (Figure 2). These points determine the spatial orientation of the tomographic image plane relative to the stereotactic frame. The<unk>  is integrated with the Brown-Roberts-Wells (BRW), Kelly-Goerss, Leksell, Cosman-Roberts-Wells (CRW), Micromar-ETM03B, FiMe-BlueFrame, Macom, and Adeor-Zeppelin stereotactic frames and with the Gamma Knife radiosurgery system. An alternative to the<unk>  is the Sturm-Pastyr<unk>  that comprises three rods wherein two diagonal rods form a V-shape and a third, vertical rod is positioned midway between the two diagonal rods (Figure 3). The Sturm-Pastyr<unk>  is integrated with the Riechert-Mundinger and Zamorano-Dujovny stereotactic frames. Compared to the<unk> , the Sturm-Pastyr<unk>  is less accurate and necessitates more elaborate calculations to determine the spatial orientation of the tomographic image plane relative to the stereotactic frame. In contrast to the<unk>  that does not require specification of the pixel size in a tomographic image, the Sturm-Pastyr<unk>  requires precise specification of the pixel size. Research conducted four decades after the introduction of the<unk>  and Sturm-Pastyr<unk>  has revealed computational techniques that improve the accuracy of both<unk> s.
N-localizer
LI-RADS
PI-RADS
BI-RADS
Hunt and Hess scale
Afterimage
Talairach coordinates
SNOMED CT