http://www.sciencedirect.com/science/article/pii/S0736574816303586
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- Power analysis for imaging-measures of neuroplasticity in cerebral palsy.
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- Details enrolment numbers needed to detect changes in structural and diffusion MRI.
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- A range of assumptions tested, including differences in treatment response.
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- Recommendations made for studies with under 100 participants for improving power.
Abstract
Researchers
in the field of child neurology are increasingly looking to supplement
clinical trials of motor rehabilitation with neuroimaging in order to
better understand the relationship between behavioural training, brain
changes, and clinical improvements. Randomised controlled trials are
typically accompanied by sample size calculations to detect clinical
improvements but, despite the large cost of neuroimaging, not equivalent
calculations for concurrently acquired imaging neuroimaging measures of
changes in response to intervention. To aid in this regard, a power
analysis was conducted for two measures of brain changes that may be
indexed in a trial of rehabilitative therapy for cerebral palsy:
cortical thickness of the impaired primary sensorimotor cortex, and
fractional anisotropy of the impaired, delineated corticospinal tract.
Power for measuring fractional anisotropy was assessed for both
region-of-interest-seeded and fMRI-seeded diffusion tractography. Taking
into account practical limitations, as well as data loss due to
behavioural and image-processing issues, estimated required participant
numbers were 101, 128 and 59 for cortical thickness,
region-of-interest-based tractography, and fMRI-seeded tractography,
respectively. These numbers are not adjusted for study attrition.
Although these participant numbers may be out of reach of many trials,
several options are available to improve statistical power, including
careful preparation of participants for scanning using mock simulators,
careful consideration of image processing options, and enrolment of as
homogeneous a cohort as possible. This work suggests that smaller and
moderate sized studies give genuine consideration to harmonising
scanning protocols between groups to allow the pooling of data.
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