Technical reportPrecentral gyrus discrepancy in electronic versions of the Talairach atlas
Introduction
The atlas of Talairach and Tournoux (1988) is widely regarded as the standard space used to define anatomical regions for imaging studies. This has been popular for the PET literature and more recently for functional MRI. There have been recent efforts made towards digitizing these atlases. A segmented and labeled digital version of the original Talairach and Tournoux (1988) brain atlas is available from Thieme, the publisher of the original printed atlas. The digital Talairach–Tournoux atlas contains fully segmented (color-coded) and labeled Brodmann's areas, gyri, and subcortical structures (137 structures) available publicly at www.cerefy.com (Nowinski and Thirunavuukarasuu, 2001). A software application for using the digital Talairach atlas with functional imaging data has recently been published by Thieme (Nowinski et al., 2000). There is also a web-based application, called the Talairach Daemon Lancaster et al., 1997a, Lancaster et al., 1997b, Lancaster et al., 2000, that returns anatomic and cytoarchitectonic labels for sets of coordinates in Talairach space (http://www.biad73.uthscsa.edu/resources/body.html). In the +35 mm axial section of the original Talairach and Tournoux atlas, there is a large unlabeled gyrus that extends into the prefrontal cortex. The digitized versions of the atlas have labeled this region as precentral gyrus (Fig. 1). In this paper, we carefully evaluate this portion of the atlas using the orthogonal projections from the original printed color plates of Talairach and Tournoux. We demonstrate that the digitized versions of the atlas of Talairach and Tournoux have erroneously identified the unlabeled gyrus in the prefrontal cortex as the precentral gyrus when it is in fact the middle frontal gyrus.
Section snippets
Materials and methods
Three sources of digitized versions of the Talairach atlas were used. These included the Brain Atlas for Functional Imaging (BAFI) (Nowinski et al., 2000), the neuroradiology online atlas available at http://www.cerefy.com (CNA), and the Talairach Daemon database. The former two are “official” versions of the Talairach atlas from Thieme, the publisher of the original version of the atlas. BAFI and CNA provide a software application for interrogating portions of the atlas. Anatomical labels are
BAFI and CNA digital atlases
Using the triplanar display capabilities within BAFI and CNA, the cursor was placed over the anterior extension of the precentral gyrus on the axial slice labeled +35 mm. The software applications automatically identified the region as precentral gyrus and displayed the corresponding coronal and sagittal images with the cross-referenced cursor location marked. The axial and corresponding sagittal and coronal slice levels and positions were copied using a shareware frame grabber (SNAGIT, the
Talairach Daemon
Using the Talairach Daemon online JAVA client software, we interrogated axial slice level +35 mm for the precentral gyrus. This slice was copied using the frame grabber and compared to the BAFI and CNA digital atlases and to the printed Talairach and Tournoux atlas.
Reconstructing gyral labels for the anomalous region
The technique used to reconstruct the appropriate labels for the discrepant region was to cross-reference coordinates along the gyral contours of this area (which are unlabelled in the printed atlas) to the sagittal and coronal printed atlas (in which portions of the area are labeled). Axial slice level +35 mm, sagittal slice levels +29, 33, 37, 41, 43, 47, 51, 55, 59, and coronal slice levels +28, 24, 20, 16, 12, 8, 4, 0, −4, and −8. These are the plates that correspond to the discrepant
Results
Fig. 1 demonstrates axial slice level +35 mm from the three digitized atlases and the original printed version of the atlas. The digitized versions of the atlas have labeled an anterior extension of the precentral gyrus; whereas in the original printed atlas, this gyrus is not labeled. This is better demonstrated in Fig. 2 in which the entire precentral gyrus from the Talairach Daemon for axial slice level 35 is shaded in. Note that the precentral gyrus extends in an anatomically incorrect
Discussion
In this paper we demonstrate that current digital versions of the Talairach atlas have mislabeled a portion of the middle frontal gyrus as precentral gyrus. This creates an anomalous anterior extension of the precentral gyrus far into the frontal lobe that is anatomically incorrect. The discrepant region represents a significant portion of the brain, measuring 30 × 15 × 4 mm on the Talairach atlas. This has the effect of producing what amounts to “horns” on a surface-rendered view of this
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