Balanced steady-state free-precession MR imaging for measuring pulsatile motion of cerebellar tonsils during the cardiac cycle: a reliability study

Assessment of the motion of the cerebellar tonsils is of interest in diseases affecting the CSF flow at the foramen magnum. Cardiac-gated balanced steady-state free-precession technique, which has recently been shown to demonstrate the pulsatile motion of neural structures, appears well suited to allow direct measurement of craniocaudal translation of cerebellar tonsils during the cardiac cycle. Our aim was to assess the intra-observer and inter-observer variability in the assessment of tonsillar motion utilizing this technique. We retrospectively identified 44 patients who had undergone MR imaging with cine TrueFISP sequence, as a part of CSF flow study. Two neuroradiologists independently assessed the images. The tonsillar pulsatility was subjectively characterized into none, minimal, and marked categories after review of the images on a cine loop. For patients with identifiable tonsillar motion, the maximal extent of translation of the inferior edge of the cerebellar tonsil was directly measured. Both readers repeated the measurements after a minimum interval of 2 weeks. Intra- and inter-observer variability was characterized by calculating the kappa statistics. The intra-observer agreement for subjective assessment of tonsillar pulsatility was near perfect while the inter-observer agreement was substantial. A good intra- and inter-observer correlation was also seen for the objective measurements of the tonsillar motion. A good correlation was found between the subjective categorization of the tonsillar pulsatility and the objective measurements. Steady-state balanced free-precession MR imaging technique allows for a reproducible subjective and objective assessment of tonsillar pulsatility.