gms | German Medical Science

Objective: Degeneration of the spine is a very common phenomenon. The occurring morphological changes can be depicted using different imaging techniques. Several grading systems of cervical or lumbar disc and facet joint degeneration are established and validated for current field-strength (1.5 T) MRI. They have proved to have a profound impact on treatment decisions. To evaluate potential and limits in spine imaging at ultra-high-field strength (7 T), we examined a first series of n=10 patients with degenerative disease at different spine levels.

Methods: A custom-built 8-channel transmit/receive phased array RF coil for human spine imaging at 7 T, which had been previously characterized in simulations and bench measurements, was used to acquire high-resolution T2-weighted TSE and T1-weighted VIBE, CISS and DESS sequences in 10 patients. Additional images were acquired at 1.5 Tesla according to clinical routine parameters. Images were evaluated by two radiologists in terms of subjective quality and by quantitative parameters using Contrast-Ratio (CR) measurements in main anatomical structures. A degenerative disease grading was performed according to Pfirrmann et al. and Weishaupt et al.

Results: The 7 T transmit/receive RF coil could be easily integrated into the patient table for examinations of the cervicothoracic and thoracolumbosacral spine. A homogenous excitation over an extensive field-of-view of 40 cm could be obtained. At 7 T, imaging of the soft tissue, especially the ligaments, and the peripheral nerve roots was superior to 1.5 T. Intraspinal contrast at 7 T was variable, depending on muscle/fat volume of the patient, and therefore inferior to 1.5 T imaging. In grading of degenerative disease, results at both field strengths were equivalent, although the grading system as proposed by Pfirrmann et al. had to be adapted for 7 T imaging.

Conclusions: We present the first study on degenerative spine disease at 7 Tesla MRI. Primarily SAR (specific absorption rate) restrictions as yet limit the potential of 7 T spine imaging, affecting especially TSE sequences. With the utilized RF coil, this mainly leads to restricted penetration depth. However, our results indicate the potential of 7 T MRI in better delineation of nerve roots, ligaments and vertebral disc tissue compared to lower field strengths.