Long T2 water in multiple sclerosis: what else can we learn from multi-echo T2 relaxation?

Multi-echo T(2) measurements are invaluable in studying brain pathology in multiple sclerosis (MS). In addition to information about myelin water and total water content, the T(2) distribution has the potential to detect additional water reservoirs arising from other sources such as inflammation or edema. The purpose of this study was to better define the T(2) distribution in MS lesions and normal appearing white matter (NAWM) with particular emphasis on the characterisation of longer T(2) components. Magnetisation transfer (MT), T(1) and 48-echo T(2) relaxation data were acquired in 20 MS subjects and regions of interest were drawn in lesions and NAWM. Twenty-seven out of 107 lesions exhibited signal with a markedly prolonged T(2) (200-800 ms). Lesions with a Long-T(2) signal also exhibited a longer geometric mean T(2) (GMT(2)), increased water content (WC), higher T(1), reduced magnetisation transfer ratio (MTR) and decreased myelin water fraction (MWF) than lesions without a Long-T(2) signal. Those subjects with Long-T(2) lesions had a significantly longer disease duration than subjects without this lesion subtype. A strong correlation was observed between T(1) and Long-T(2) fraction, while a slightly weaker relationship was found for GMT(2), MTR and MWF with Long-T(2) fraction. A potential source of the Long-T(2) signal is an increase in extracellular water. This study supports the usefulness of increasing the data acquisition window of the multi-echo T(2) relaxation sequence to better characterise the T(2) decay in MS.