Accurate measurement of brain water content by magnetic resonance

Accurate measurement of total water content (TWC) is valuable for assessing changes in brain water such as edema, which occurs with many neurological diseases, as well as monitoring the effects of treatments. T2 relaxation has been used to measure TWC in brain on 1.5T magnetic resonance imaging (MRI) scanners. This method was modified for 3T in order to ensure accuracy in the presence of increased radiofrequency field inhomogeneities. Phantom validations demonstrated excellent agreement between MRI-measured TWC and known water concentrations of tubes. Simulations indicated a 3% mean error in TWC estimation. Homogeneous TWC maps were produced in the brain of 10 healthy human subjects; TWC values agreed with literature. Two different receiver coil inhomogeneity corrections were compared in the same 10 subjects, as well as 2 multiple sclerosis (MS) patients – one which requires the measurement of a low flip angle image, and the other based on comparison to a homogeneous pseudo TWC map calculated from T1. Both techniques resulted in similar, homogeneous TWC maps in healthy brain, although differences up to 2% were measured in abnormal MS brain tissue. Finally, the TWC method was implemented for two applications. 20 subjects were scanned after consuming 3L of water and again after 9 hours of fasting to determine whether hydration affects brain TWC and volume. No significant changes were measured, indicating that homeostasis mechanisms likely regulated brain TWC during the short term fluid shifts. Some MS drugs have been shown to cause initial accelerated brain volume loss, which is hypothesized to be due to water loss. In the second application, TWC of normal appearing tissue and whole brain and brain volume were measured in 16 MS patients over a 6 month course of treatment with interferon beta. A trend of decreasing brain volume between months 3 and 6 was concurrent with a reduction in whole brain TWC, suggesting that accelerated brain volume loss on interferon beta may be due to reduced inflammation or edema in abnormal appearing tissue. Here we present a useful tool that can be used at 3T to simultaneously assess changes in water and myelin in neurological diseases.Science, Faculty ofPhysics and Astronomy, Department ofGraduat