In vivo determination of multiexponential T2 relaxation in the brain of patients with multiple sclerosis

Abstract

In vivo measurement of T 2 relaxation times in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) is potentially useful for the evaluation of the disease activity. Seven patients with definite MS were investigated over a period of three years (19 examinations), using a whole-body MRI scanner operating at 0.15 T with a specially designed high-power radio-frequency head coil. A modified CPMG sequence with a 180° pulse interval of TE = 6 msec and 128 echoes was used for the T 2 relaxation measurement of the areas of increased signal (AIS) and white matter (WM). A biexponential T 2 analysis of each pixel of the spin-echo images was computed. The T 2 relaxation processes were found to be a monoexponential function in WM. The T 2 relaxation times of apparently normal white matter in MS patients was significantly longer than in control subjects. The T 2 relaxation curves of the AIS were found in most cases to fit a biexponential function characterized by a short and a long T 2. T 2long relaxation times of AIS were spread out over a wide range (150–560 msec). The study of T 2long histograms shows that some AIS can be divided into two or three parts depending on the T 2long values. Each of these parts may correspond to a pathological process such as edema, demyelination and gliosis. Evolution of T 2 relaxation times over a period of time cannot as yet be correlated with modifications in the clinical state.