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 1.5 Tesla 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 macromo- lecular fraction (M^ob), macromolecular transverse relaxation time (T_2b) 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 M_ob was significantly decreased (P < 0.03). T_2b for volunteers was: 9 ± 2 μs and the rate of MT exchange (R) was: WM = 56 ± 11 Hz, GM = 67 ± 12 Hz. Neither T_2b nor R showed significant differences between healthy and diseased cords. Comparisons are made between qMT, and conventional MT acquisitions.