Dynamic Contrast-Enhanced Magnetic Resonance Imaging Suggests Normal Perfusion in Normal-Appearing White Matter in Multiple Sclerosis
Authors: Ingrisch Michael , Sourbron Steven , Herberich Sina , Schneider Moritz Jörg , Kümpfel Tania , Hohlfeld Reinhard , Reiser Maximilian F. , Ertl-Wagner Birgit 
Published: August 2016

Objectives
Multiple sclerosis (MS) is a chronic, inflammatory disease of the central nervous system and has been associated with reduced perfusion in normal-appearing white matter (NAWM). The magnitude of this hypoperfusion is unclear. The present study aims to quantify NAWM perfusion with dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in patients with relapsing-remitting (RR) MS and in a control group.

Materials and Methods
The statistical power of a DCE-MRI acquisition to reveal hypoperfusion in MS was estimated using a Monte Carlo simulation: synthetic tissue curves with a contrast-to-noise ratio of 8 were generated for MS patients and control group using perfusion values reported in previous studies. A compartment-uptake model was fitted to these curves, yielding estimates of cerebral blood flow (CBF), cerebral blood volume (CBV), and permeability-surface area product (PS). This was repeated 1000 times. Mean and standard deviation of the resulting distributions were used to calculate the statistical power of a DCE-MRI study to detect perfusion differences between 16 control subjects and 24 MS subjects.
In an institutional review board–approved study, patients with RR-MS (n = 24; mean age, 36 years; 17 women, mean Enhanced Disability Status Scale score, 3.25) and patients without history or symptoms of neurological disorder (n = 16; mean age, 49 years; 9 women) underwent a DCE-MRI examination with a previously established MRI protocol (3D SPGR sequence; 2.1 seconds temporal resolution; 44 slices; spatial resolution, 1.7 × 1.7 × 3 mm). Regions were defined manually in the middle cerebral artery; in the frontal, periventricular, and occipital NAWM; in the pons; and in the thalamus, and CBF, CBV, and PS were quantified using a compartment-uptake model.
Parameter differences between MS and control groups were evaluated using a mixed linear model with subjects as random effect and controlling for age and sex. A P value of less than 0.05 was considered to indicate statistical significance.

Results
For all but one of previously reported effect sizes, the simulation study estimated a statistical power of 80% to 100% to detect reduced CBF in MS. In the patient study, mean (standard deviation) CBF in NAWM was 11.0 (15.1) and 10.4 (8.2) mL/100 mL per minute in the MS and control groups, respectively. Mean CBV in NAWM was 0.50 (0.45) mL/100 mL in the MS group and 0.48 (0.28) mL/100 mL in the control group. Mean values of PS in NAWM were 0.002 mL (0.027)/100 mL per minute in the control group and −0.001 (0.015) mL/100 mL per minute in the MS patients. Differences between patient groups were not statistically significant for CBF, CBV, mean transit time, and PS (P = 0.44, P = 0.20, P = 0.78, P = 0.66, respectively). In both groups, the influence of age on any parameter was nonsignificant. Cerebral blood flow and CBV in the thalamus and pons were significantly higher than in NAWM regions (P < 1e-4); mean transit time was significantly shorter than in NAWM (P < 1e-4). Permeability-surface area product was not significantly different from zero (P > 0.25) in all evaluated regions.

Conclusions
Despite high statistical power, we could not confirm previous reports of NAWM hypoperfusion in MS. This indicates that, at least in our patient cohort, potential hypoperfusion is much less pronounced than reported in previous studies.