Talairach atlas
In 1988, Talairach atlas was manually labeled of brain structure based on a 60-year-old French female [19]. This stereotaxic coordinate system manual is based on two landmarks, the anterior commissure (AC) and posterior commissure (PC). AC point is set as the orien-tation of the coordinate system. AC-PC line lie on the mid-saggital plane and also a straight line in horizontal direction. Fig 1.2 shows four slices of verticofrontal sections in Talairach atlas. As mapping to Talairach atlas, researchers also label AC and PC point on the subject image to do the initial alignment with rotation and translation.
Talairach atlas provides the structure coordinate system with relative location of brain structure in early year, but it also with some errors as template space. First, the atlas is biased to an individual elder woman. The image registration may contain large distortion for the variation from different structure of brain. Secondly, the registration to the Talairach atlas apply with manual landmark mapping which may contains the artificial error. On the other hand, the Talairach atlas assumes that the brain structure is symmetric, which seems to be irrational with the understanding of brain structure now.
MNI305
In 1992, Montreal Neurological Institute (MNI) created an average of 305 subject im-ages mapping to the Talairach atlas called MNI305 [7] [15]. Fig. 1.3(a) displays the tem-plate image. This temtem-plate created based on the coordinate system of Talairach atlas. The construction procedure consisted of two stages. At first, 241 brain images were registered to Talairach coordinates and averaged to become the first-pass image. The registration was achieved by aligning several manually-specified landmarks of 241 brain images together by 9-parameter linear transformation. In the second stage, 305 normal MRI scans were linear normalized to the first-pass image using automatic fitting strategy to reduce the artificial error.
1.2 Related Work 5
Figure 1.2: Talairach atlas. Talairach atlas of the human brain was introduced in 1988 by Talairach and Tournoux. They defined a standard coordinate system based on dissection of an 60-year-old French female’s brain. This figure shows four slices of verticofrontal sections in Talairach atlas.
(Graphic source : http://homepages.nyu.edu/∼ef725/amygdala.html)
MNI305 template is obvious in low contrast from Fig. 1.3(a). The local structure could not been verified clearly (from Fig. 1.3(a)). It may attribute to the contrast of subject images or the registration technique did not provide high accuracy.
Colin27
To reduce the blurred condition of local structure from MNI305, a model was con-structed by an individual subject - Colin Holmes, who had scanned 27 times within 3 months in 1998 [10]. The average image of these 27 images which normalized to MNI305
6 Introduction
template shown in Fig. 1.3(b). Even Colin27 provided in high quality of template image, the template image is biased to this individual source object structure.
ICBM152 and ICBM452
In 1993, ICBM (International Consortium for Brain Mapping) was formed with four research sites: University of California, Los Angeles (UCLA), Montreal Neurologic In-stitute (MNI), University of Texas at San Antonio (UTSA), and the InIn-stitute of Medicine, Juelich/Heinrich Heine University - Germany. This ICBM projects is committed to de-velop a probabilistic reference system for the human brain. In 2001, The ICBM is template is wildly accepted as a standard template image which was constructed with 152 T1 normal subject images in higher contrast [14]. Each individual subject image was linearly regis-tered to the MNI305 template and the average template image is constructed and shown in Fig. 1.3(c). The advantage of this template model is that it exhibits better contrast than MNI305 and also do not bias to any specific individual subjects. Followed by the im-provement of techniques in MRI scanning and registration methods, ICBM still working on creating brain template. The registration method with non-linear technique has started to apply since 2002 and the building procedure has included six iteration times of registration which is show in Fig. 1.3(d) called ICBM152.
The ICBM template provides high resolution T1 images from age 19 to 90 in half males and females with high accuracy registration and still working on template construction.
ICBM452 had published and constructed by 452 subjects. Even though, the template was constructed based on western human brain. As Zilles et al. had proved the inter-ethnic dif-ference [23], we should not apply ICBM template as our common space of brain mapping and eliminate the possible of large distortion in image registration.
1.2 Related Work 7
Figure 1.3: Related well-know template. (a) MNI305 : Constructed by Montreal Neuro-logical Institute (MNI) by averaged 305 normal subjects images mapping to Talairach atlas.
(b) Colin27 : Individual subject scanned 27 times within 3 months and averaged these 27 images which had normalized into MNI305. (c) Affine ICBM152 : An averaged image with 152 higher contrast of subject images which were linearly registered to MNI305 by entirely automatic technique. (d) ICBM152 : Improvement of Affine ICBM152 with non-linear registration.
(Graphic source : http://www.bic.mni.mcgill.ca/)
8 Introduction
Chinese Brain Template
In 2007, the group of National Taiwan University (NTU) constructed a Chinese brain template using their developed software by 10 subject images [21]. This study also verify the difference between the western brain template and Chinese brain template. Fig. 1.4 shows their template image. As the number of subject images was not large enough, the template image is obvious blurry. In 2008, the group of National Chiao Tung University (NCTU) constructed the averaged brain template in 191 normal subject images [6]. The construction procedure selected a representative image from the subject group as initial ref-erence template image and used affine and non-rigid registration between refref-erence image and the whole subject images to refine the template image. The results is shown in Fig. 1.4.
Figure 1.4: Chinese brain template. The upper figure shows the template constructed by NTU in 2007. The lower figure shows thetemplate constructed by NCTU in 2008.
(Graphic source : Upper : Wu, E. L et al. 2007. Lower : Chang, Y. Y et al. 2008)