What Is Really Causing the Contrast in Spin-Echo Imaging at 7T?

Robert Trampel¹, Robert Turner¹

Spin-echo and turbo-spin echo images of brain tissue displaying a strong contrast between grey and white matter are usually referred to as T2-weighted. However, since earlier studies show very little difference in T2 relaxation times between grey and white matter, the actual underlying contrast mechanism remains unclear. We therefore investigated the contrast obtained using a common spin-echo sequence at 7T with a range of sequence parameters. The results clearly show that T2 relaxation contributes hardly at all to the contrast obtained in brain tissue. Depending on the sequence parameters, variations in proton density, T1 relaxation, and magnetization transfer are the main sources of image contrast in common spin-echo imaging.