In this work a new MRI modality entitled Relaxation Along a Fictitious Field in the rotating frame of rank 4 (RAFF4) was evaluated in its ability to detect lower myelin content in lysophosphatidyl choline (LPC)-induced demyelinating lesions. The lesions were induced in two areas of the rat brain with either uniform or complex fiber orientations, i.e., in the corpus callosum (cc) and dorsal tegmental tract (dtg), respectively. RAFF4 showed excellent ability to detect demyelinated lesions and good correlation with myelin content in both brain areas. In comparison, diffusion tensor imaging metrices, fractional anisotropy, mean diffusivity and axonal and radial diffusivity, and magnetization transfer (MT) metrices, longitudinal relaxation during off-resonance irradiation and MT ratio, either failed to detect demyelination in dtg or showed lower correlation with myelin density quantified from gold chloride stained histological sections. Good specifity of RAFF4 to myelin was confirmed by its low correlation with cell density assesed from Nissl stained sections as well as its lack of sensitivity to pH changes in the physiological range as tested in heat denaturated bovine serum albumin phantoms. The excellent ability of RAFF4 to detect myelin content and its insensitivity to fiber orientation distribution, gliosis and pH, together with low specific absorption rate, demonstrates the promise of rotating frame of rank n (RAFFn) as a valuable MRI technique for non-invasive imaging of demyelinating lesions.
Bibliographical noteFunding Information:
Electron microscopy was performed utilizing Sib-labs infrastructure at the University of Eastern Finland. The work was supported by EU H2020 Marie Sklodowska RISE project #691110 (MICROBRADAM), Academy of Finland grants #275453 and #298007, EU FP7-HEALTH project #602102 (EPITARGET), NIH BTRC grants, P41 EB015894, P30 NS057091. OG was supported by Professor Pool grant from Svenska Kulturfonden, SMi was supported by Fulbright-Saastamoinen Foundation Grant in Health and Environmental Science. LL was supported by MnDRIVE and the Emil Aaltonen Foundation.
© 2017 Lehto, Albors, Sierra, Tolppanen, Eberly, Mangia, Nurmi, Michaeli and Gröhn.
- Lysophosphatidyl choline
- White matter damage