title: A practical guideline for intracranial volume estimation in patients with Alzheimer's disease.
abstract: BACKGROUND
  Intracranial volume (ICV) is an important normalization measure used in morphometric analyses to correct for head size in studies of Alzheimer Disease (AD). Inaccurate ICV estimation could introduce bias in the outcome. The current study provides a decision aid in defining protocols for ICV estimation in patients with Alzheimer disease in terms of sampling frequencies that can be optimally used on the volumetric MRI data, and the type of software most suitable for use in estimating the ICV measure.
  
  
  METHODS
  Two groups of 22 subjects are considered, including adult controls (AC) and patients with Alzheimer Disease (AD). Reference measurements were calculated for each subject by manually tracing intracranial cavity by the means of visual inspection. The reliability of reference measurements were assured through intra- and inter- variation analyses. Three publicly well-known software packages (Freesurfer, FSL, and SPM) were examined in their ability to automatically estimate ICV across the groups.
  
  
  RESULTS
  Analysis of the results supported the significant effect of estimation method, gender, cognitive condition of the subject and the interaction among method and cognitive condition factors in the measured ICV. Results on sub-sampling studies with a 95% confidence showed that in order to keep the accuracy of the interleaved slice sampling protocol above 99%, the sampling period cannot exceed 20 millimeters for AC and 15 millimeters for AD. Freesurfer showed promising estimates for both adult groups. However SPM showed more consistency in its ICV estimation over the different phases of the study.
  
  
  CONCLUSIONS
  This study emphasized the importance in selecting the appropriate protocol, the choice of the sampling period in the manual estimation of ICV and selection of suitable software for the automated estimation of ICV. The current study serves as an initial framework for establishing an appropriate protocol in both manual and automatic ICV estimations with different subject populations.
authors.forename: Saman
authors.initials: S
authors.lastname: Sargolzaei
authors.forename: Arman
authors.initials: A
authors.lastname: Sargolzaei
authors.forename: Mercedes
authors.initials: M
authors.lastname: Cabrerizo
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.forename: Mohammed
authors.initials: M
authors.lastname: Goryawala
authors.forename: Shirin
authors.initials: S
authors.lastname: Noei
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Ranjan
authors.initials: R
authors.lastname: Duara
authors.forename: Warren
authors.initials: W
authors.lastname: Barker
authors.forename: Malek
authors.initials: M
authors.lastname: Adjouadi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000175:diagnosis*; D001921:Brain / Q000473:pathology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000592:standards* / Q000706:statistics & numerical data*; D008297:Male; D009929:Organ Size; D012984:Software