Quantitative magnetization transfer characteristics of the human cervical spinal cord in vivo: Application to Adrenomyeloneuropathy

Magnetization transfer (MT) imaging has assessed myelin integrity in the brain and spinal cord; however, quantitative MT (qMT) has been confined to the brain or excised tissue. We characterized spinal cord tissue with qMT in vivo, and as a first application, qMT-derived metrics were examined in adults with the genetic disorder Adrenomyeloneuropathy (AMN). AMN is a progressive disease marked by demyelination of the white matter tracts of the cervical spinal cord, and a disease in which conventional MRI has been limited. MT data were acquired at 1.5T using 10 radiofrequency offsets at one power in the cervical cord at C2 in 6 healthy volunteers and 9 AMN patients. The data were fit to a two-pool MT model and the macromolecular fraction (Mob), macromolecular transverse relaxation time (T2b) and the rate of MT exchange (R) for lateral and dorsal column white matter and gray matter were calculated. Mob for healthy volunteers was: WM=13.9±2.3%, GM=7.9±1.5%. In AMN, dorsal column Mob was significantly decreased (p<0.03). T2b for volunteers was: 9±2µs and the rate of MT exchange (R) was: WM=56±11Hz, GM=67±12Hz. Neither T2b nor R showed significant differences between healthy and diseased cords. Comparisons are made between qMT, and conventional MT acquisitions.