Purpose Brain myelin plays an important role in normal brain function. Demyelination is involved in many degenerative brain diseases, thus quantitative imaging of myelin has been under active investigation. In previous work, we demonstrated the capability of the method known as Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn) to provide image contrast between white and gray matter in human and rat brains. Here, we provide evidence pointing to myelin being the major source of this contrast. Methods RAFFn relaxation time constant (TRAFFn) was mapped in rat brain ex vivo. TRAFFn was quantified in 12 different brain areas. TRAFFn values were compared with multiple other MRI metrics (T1, T2, continuous wave T1ρ, adiabatic T1ρ and T2ρ, magnetization transfer ratio), and with histologic measurements of cell density, myelin and iron content. Results Highest contrast between white and grey matter was obtained with TRAFFn in the rotating frames of ranks n = 4 and 5. TRAFFn values correlated strongly with myelin content, whereas no associations between TRAFFn and iron content or cell density were found. Conclusion TRAFFn with n = 4 or 5 provides a high sensitivity for selective myelin mapping in the rat brain.
Bibliographical noteFunding Information:
Academy of Finland; Grant sponsor: Sigrid Juselius Foundation; Grant sponsor: National Institutes of Health Biomedical Technology Resource Centers; Grant numbers: P41-EB015894; P30-NS057091; R01- NS061866. We thank Maarit Pulkkinen for technical assistance.
- contrast imaging
- fictitious field
- rotating frame