title: Valid and efficient manual estimates of intracranial volume from magnetic resonance images.
abstract: BACKGROUND
  Manual segmentations of the whole intracranial vault in high-resolution magnetic resonance images are often regarded as very time-consuming. Therefore it is common to only segment a few linearly spaced intracranial areas to estimate the whole volume. The purpose of the present study was to evaluate how the validity of intracranial volume estimates is affected by the chosen interpolation method, orientation of the intracranial areas and the linear spacing between them.
  
  
  METHODS
  Intracranial volumes were manually segmented on 62 participants from the Gothenburg MCI study using 1.5 T, T1-weighted magnetic resonance images. Estimates of the intracranial volumes were then derived using subsamples of linearly spaced coronal, sagittal or transversal intracranial areas from the same volumes. The subsamples of intracranial areas were interpolated into volume estimates by three different interpolation methods. The linear spacing between the intracranial areas ranged from 2 to 50 mm and the validity of the estimates was determined by comparison with the entire intracranial volumes.
  
  
  RESULTS
  A progressive decrease in intra-class correlation and an increase in percentage error could be seen with increased linear spacing between intracranial areas. With small linear spacing (≤15 mm), orientation of the intracranial areas and interpolation method had negligible effects on the validity. With larger linear spacing, the best validity was achieved using cubic spline interpolation with either coronal or sagittal intracranial areas. Even at a linear spacing of 50 mm, cubic spline interpolation on either coronal or sagittal intracranial areas had a mean absolute agreement intra-class correlation with the entire intracranial volumes above 0.97.
  
  
  CONCLUSIONS
  Cubic spline interpolation in combination with linearly spaced sagittal or coronal intracranial areas overall resulted in the most valid and robust estimates of intracranial volume. Using this method, valid ICV estimates could be obtained in less than five minutes per patient.
authors: Institute of Psychiatry and Neurochemistry, Department of Neuroscience and physiology, The Sahlgrenska Academy, University of Gothenburg, Box 430, SE-405 30, Göteborg, Sweden. niklas.klasson@neuro.gu.se.
authors: Niklas
authors: N
authors: Klasson
authors: Institute of Psychiatry and Neurochemistry, Department of Neuroscience and physiology, The Sahlgrenska Academy, University of Gothenburg, Box 430, SE-405 30, Göteborg, Sweden. erik.olsson@neuro.gu.se.
authors: Erik
authors: E
authors: Olsson
authors: Department of Mathematical Sciences, Chalmers University of Technology and University of Gothenburg, SE-412 96, Göteborg, Sweden. rudemo@chalmers.se.
authors: Mats
authors: M
authors: Rudemo
authors: Institute of Psychiatry and Neurochemistry, Department of Neuroscience and physiology, The Sahlgrenska Academy, University of Gothenburg, Box 430, SE-405 30, Göteborg, Sweden. carl.eckerstrom@neuro.gu.se.
authors: Carl
authors: C
authors: Eckerström
authors: Institute of Psychiatry and Neurochemistry, Department of Neuroscience and physiology, The Sahlgrenska Academy, University of Gothenburg, Box 430, SE-405 30, Göteborg, Sweden. helge.malmgren@filosofi.gu.se.|Department of Philosophy, Linguistics and Theory of Science, University of Gothenburg, Box 200, SE-405 30, Göteborg, Sweden. helge.malmgren@filosofi.gu.se.
authors: Helge
authors: H
authors: Malmgren
authors: Institute of Psychiatry and Neurochemistry, Department of Neuroscience and physiology, The Sahlgrenska Academy, University of Gothenburg, Box 430, SE-405 30, Göteborg, Sweden. anders.wallin@neuro.gu.se.
authors: Anders
authors: A
authors: Wallin
mesh_terms: D000368:Aged; D001921:Brain / Q000473:pathology*; D060825:Cognitive Dysfunction / Q000473:pathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D015588:Observer Variation; D009929:Organ Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity