Quantitative measurements of the spinal cord and canal by MR imaging and myelography.

There is a large individual variation in human spinal cord and canal size, even in patients of different series studied by the same modality, and no authorized standard method has been established. A comparative study of sagittal diameters of the cervical spinal cord and canal using myelography and MRI is presented. The purposes of this paper are (a) to establish the correction factor (CF) needed for quantitative comparison of the two imaging modalities, and (b) to determine the different factors that may modify the measurement of these diameters. We studied 45 patients with clinical findings compatible with cervical spondilotic myelopathy. In our experience, the CF for accurate correlation of MRI and myelography measurements is 1.32 and depends almost entirely on the radiographic geometry of the myelographic procedure. In addition, there is a variability in the group of MRI results due to imprecision of the pressure-pad measuring/input device of the instrument itself and the sequence performed.