Feasibility of T1rho imaging in lateralization of the epileptogenic zones in patients with mesial temporal lobe epilepsy : comparisons with MR volumetry and T2 relaxometry

Abstract

Underling neuronal loss and subsequent hippocampal sclerosis, as reflected by hippocampal atrophy on structural magnetic resonance (MR) imaging, are the dominant findings in the patient with mesial temporal lobe epilepsy (MTLE). Yet, prolongation of T2 relaxation time has also been reported as an early marker for MTLE, but it is a rather insensitive marker. Typical age-related atrophy often constitutes a significant confounding factor, and atrophy often represents a late sign in hippocampal sclerosis. In this connection, there is an urge for a sensitive independent predictor for the early detection of MTLE. T1rho MR imaging provides a distinct contrast mechanism in tissue characteristics. It is sensitive to physio-chemical processes and has been tested successfully in Alzheimer’s disease, Parkinson’s disease and certain brain tumors. Therefore, it is possible to depict early biochemical change in patients with MTLE by means of measuring the changes in T1rho relaxation time. T1rho relaxation time is not affected by age-related atrophic changes and thus can be used as an independent marker. In this preliminary study, we aimed to assess the feasibility of T2 relaxometry and T1rho MR imaging in identification of the atrophied zones in patients with MTLE. Seven patients with unilateral MTLE and fourteen normal subjects were recruited. Three-dimensional T1-weighted imaging, axial T2 relaxometry and T1rho imaging were performed on a 3T MR scanner. Hippocampal head, hippocampal body, hippocampal tail and amygdala were contoured on the axial T2-weighted images and then co-registered onto T2 relaxometry and T1rho images. A combination of visual and quantitative volumetric assessment was used as the primary end outcome. For T2 relaxometry and T1rho imaging, their respective relaxation times together with the corresponding right-left asymmetric ratios were calculated for subsequent analysis. Abnormal right-left asymmetric ratio is defined as a deviation of 2SD from the mean of the Z-score. In the lateralizing epileptogenic zones, T1rho yielded an overall accuracy of 92.9% (sensitivity 100%, specificity 60%), while T2 relaxometry yielded an overall accuracy of 71.4% (sensitivity 65.2%, specificity 100%) only. T1rho imaging is thus superior to T2 relaxometry (P = 0.036, by chi-square test). To conclude, the present study indicated that T1rho is feasible and potentially useful to serve as a non-invasive imaging tool in the detection of lateralization of the epileptogenic zone in patients with MTLE. It can also facilitate prompt diagnosis and longitudinal disease monitoring. In addition, the generation of associated color-coded parametric map can provide an easy mean for direct visual analysis.