Volumes, spatial extents and a probabilistic atlas of the human basal ganglia and thalamus
Introduction
The basal ganglia play an important role in movement control and higher cognitive functioning (Albin et al., 1989). Pathology of basal ganglia structures has been implicated in many movement disorders such as Parkinson's, Wilson's and Huntington's diseases (Cornford et al., 1995, Mitchell et al., 1999), and the spinocerebellar ataxias 2 and 3, and also neurodevelopmental disorders (Nieoullon, 2002).
Modern functional imaging techniques allow visualization of changes in regional cerebral blood flow and localization of drug and ligand binding to receptors, so providing an insight into the functioning of the brain in both health and disease. The exact localization of such changes requires an accurate anatomical description of the brain that can be applied to the original mode of imaging, or the application of an atlas. Most atlases are based on the examination of a single or a few brains and thus are not representative of the population as a whole (see Hammers et al., 2003) and do not take the normal variation in structures into account (Good et al., 2001, Hutsler et al., 1998, Watkins et al., 2001). Attempts have been made to standardize basal forebrain structures in stereotaxic space for example with the use of anchor points and thin-plate spline warping (Buchsbaum et al., 1998). However, this method has a number of limitations which render it less suitable for certain applications, for instance with respect to volumetric estimation of structures.
In the present study we determined in vivo the normal spatial variability of the basal ganglia (nucleus caudatus and accumbens; putamen, pallidum, substantia nigra) and thalamus in healthy young adults. We also provide detailed delineation protocols in a format which should be easily understood by beginners. We used these to produce a probabilistic atlas of the human basal ganglia and thalamus. The reliability of algorithms for the delineation of 6 subcortical structures was formally evaluated with inter-rater reliability tests, and normative data on the volumes and extents of these structures in a cohort of 30 normal subjects are presented.
Section snippets
Subjects
Data sets from thirty healthy volunteers from the database at the National Society for Epilepsy MRI Unit, Chalfont St. Peter, Buckinghamshire, UK, were available as part of a larger project on probabilistic atlases (Hammers et al., 2002, Hammers et al., 2003). Details of the subjects have been described before (Hammers et al., 2006). The cohort included 15 women (median age, 31 years; range 20–54) and all but 5 of the 30 subjects were strongly right handed as determined by routine prescanning
Inter-rater reliability
The inter-rater reliability results for all 6 structures are shown in Table 1, Table 2. The inter-rater reliability data demonstrates that the second rater systematically delineated structures in a more conservative fashion, yielding smaller total volumes than the first rater. The only exception to this was the nucleus accumbens, for which the second rater's delineations produced larger total volumes than those of the first rater. The similarity index values (SIs, Table 2), compared with the
Discussion
In this paper we present a comprehensive assessment of in vivo volumetric and extent data, and the first probabilistic data, for the basal ganglia and thalamus. The reliability of the algorithms was demonstrated under realistic conditions by the inter-rater reliability results. Normative data were generated from the 30 data sets, giving data on structure volumes and extents in both native and MNI stereotaxic space.
Conclusion
The present study demonstrates the relative invariability of basal ganglia and thalamus and provides some data on the hemispheric differences between structural volumes, and to a lesser extent differences found between genders and handedness groups. The volumetric and extent data from this study, and in particular the probabilistic atlases provided, will be useful in the analysis of imaging studies as well as for stereotactic surgery. The probabilistic maps will be made available for academic
Acknowledgments
We are grateful to our colleagues in the Cyclotron Building for help and discussions, to our colleagues at the National Society for Epilepsy for acquisition, preparation and neuroradiological evaluation of the MRI data sets, and to all our volunteers for their participation. AH is funded by an MRC Clinician Scientist Fellowship (G108/585).
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