An investigation of statistical power for continuous arterial spin labeling imaging at 1.5 T

Iris Asllani, Ajna Borogovac, Clinton Wright, Ralph Sacco, Truman R. Brown, Eric Zarahn

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Variance estimates can be used in conjunction with scientifically meaningful effect sizes to design experiments with type II error control. Here we present estimates of intra- and inter-subject variances for region of interest (ROI) from resting cerebral blood flow (CBF) maps obtained using whole brain, spin echo echoplanar (SE-EPI) continuous arterial spin labeling (CASL) imaging on 52 elderly subjects (age = 70.5 ± 7.9 years, 29 males). There was substantial intrasubject systematic variability in CBF of gray matter ROIs corresponding to a range of standard deviations = [39-168] (ml/(100 g min)). This variability was mainly due to two factors: (1) an expected inverse relationship between ROI volume and intrasubject variance and (2) an increased effective post-labeling delay for more superior slices acquired later in the sequence. For example, intrasubject variance in Brodmann area 4 (BA 4) was ∼ 8 times larger than in hippocampus, despite their similar gray matter volumes. Estimated ROI-wise power was computed for various numbers of acquired CBF images, numbers of subjects, and CBF effect sizes for two experimental designs: independent sample t-test and paired t-test. The theoretical effects of pulse sequence and field strength on general applicability of these results are discussed.

Original languageEnglish (US)
Pages (from-to)1246-1256
Number of pages11
Issue number3
StatePublished - Feb 1 2008


  • ASL
  • CBF
  • fMRI
  • Intersubject variance
  • Intrasubject variance
  • Statistical power

ASJC Scopus subject areas

  • Cognitive Neuroscience
  • Neurology


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