We demonstrate that within a range of physiologic conditions commonly encountered in routine clinical scans (no pretreatment with hydration, well hydrated before MRI, and overnight fasting), brain TWC and brain volumes are not substantially affected in a healthy control cohort. J. Magn. Reson. Imaging 2016;44:296-304.

Study design: This was a prospective cohort observational study. Objective: To determine the effect of dehydration and rehydration on spinal cord cross-sectional area (CSA) measurement on magnetic resonance imaging (MRI). Setting: MRI Research Centre, University of British Columbia, Canada. Methods: Ten healthy subjects (aged 21-32 years) were scanned on a 3T MRI scanner at four time points: (1) baseline, (2) rescan after 1 h, (3) the next day after fasting for a minimum of 14 h and (4) after rehydration with 1.5 l of water over the course of 1 h. Two independent, established semi-automatic CSA measurement techniques (one based on two-dimensional (2D) edge detection, the other on three-dimensional (3D) surface fitting) were applied to a 3D T1-weighted scan of each subject at each time point, with the operator blinded to scan order. The percentage change in CSA from baseline to each subsequent time point was calculated. One-tailed paired t-tests were used to assess the significance of the changes from baseline. Results: A decrease in CSA following dehydration was detected by both measurement methods, with a mean change of À0.654% INTRODUCTIONMagnetic resonance imaging (MRI) is commonly used to measure spinal cord atrophy in studies of neurodegenerative diseases such as multiple sclerosis (MS). 1,2 Atrophy of the spinal cord, in particular the cervical cord, 3 is believed to contribute to physical disability in MS. 2,4 Significant correlations between the cross-sectional area (CSA) of the cord and physical disability in MS patients have been found in previous cross-sectional and longitudinal studies. 5-7 However, there have been contradictory findings in patients with the relapsing remitting form of MS (RRMS), which typically precedes a more progressive form. A number of studies have found that cord CSA is not reduced in RRMS patients 8,9 and could be used to distinguish progressive MS from RRMS patients, 8 whereas others have shown that cord atrophy is detectable in RRMS patients. 10 The inconsistent findings of cord involvement in RRMS may be because of many reasons. The average CSA of a normal adult cervical cord is B80 mm 2 . Most current MRI studies of the cord use a spatial resolution of B1 mm 2 in each plane, which is B1% of the cord CSA. As atrophy is a slow process, with an annual atrophy rate of about À1.6% observed in secondary progressive MS patients, 11 a resolution of 1 mm 2 can be considered coarse, and a high methodological sensitivity is essential to accurately estimate the true rate of change on current MRI data. A number of reproducible image analysis methods

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