DYNAMIC ASSESSMENT OF INTRASPINAL NEURAL GRAFT-SURVIVAL USING MAGNETIC-RESONANCE-IMAGING

Although previous work has demonstrated the usefulness of magnetic resonance imaging (MRI) for visualizing intraspinal transplants in vivo the degree to which MRI can differentiate viable fetal neural tissue from evolving spinal cord pathology has not been investigated. Thus, the present study assessed whether MRI performed at earlier postgrafting intervals (0-20 weeks) could document the survival of fetal neural transplants in the injured cat spinal cord. Twelve adult female cats received a hemisection injury at the L(1) level, followed immediately by implantation of either embryonic cat spinal cord or neocortex into the cavity. The spinal cords of three control animals were hemisected but received no transplant. Each animal was subsequently imaged at 4 and 8 weeks postoperative. Selected animals from each group were also studied at additional time points ranging hom immediately postoperative to 20 weeks. Multislice T-2-weighted and intermediate T-1-weighted spin-echo images of the lesion or graft site were obtained. Correlative postmortem histological analyses revealed viable donor tissue in 6 of 12 transplant recipients. Spinal cords from the remaining hosts and the control animals all contained cysts at the surgical site that were devoid of donor neural tissue. The graft sites with viable tissue tended to exhibit a slightly hyperintense signal on both intermediate T-1-weighted (T1WI) and T-2-weighted images (T2WI) throughout the entire experiment. Control cats and cats with failed transplants also were slightly bright on T1WI, but were very hyperintense on T2WI. Comparison of the normalized mean pixel intensity on T1WI at the lesion or transplant epicenter showed no significant differences between viable grafts, failed grafts, and controls at any time point studied. In contrast, viable grafts had significantly less signal than both failed grafts and control lesions on T2WI at 4, 8, and 12 weeks postoperative. We conclude that transplant survival may be observed as early as 2 to 4 weeks postgrafting by the presence of medium signal intensity on T-2-weighted images. In addition, T1WI were not useful for predicting graft survival, but aided in defining the graft or lesion boundaries. (C) 1995 Academic Press, Inc.