Eur Radiol (2012) 22:1797–1802 patients who demonstrate cord narrowing and symptoms without signal change within the cervical cord on conven- tional imaging. Moreover, this technique may be helpful in demonstrating early cord damage, which may be related to acute or reversible changes (transverse change) or to long- term damage (longitudinal change). In clinical situations, one possible role for this type of imaging evaluation would be to assess changes or progression as part of sequential follow-up of patients where the signs and conventional imaging findings are not sufficient to warrant surgery or invasive therapy but are sufficient to warrant follow-up. One potential limitation of this study is the relatively low maximum b value (b 0 2,000 s/mm2) that we used to calcu- late RMSD using q-space analysis. Here, the effective spa- tial resolution was the reciprocal of the maximum q value, i. e. 25.42 μm. This value seemed to be relatively large for the grey and white matter components, and the RMSD values for the spinal cord may have been inaccurate. However, using higher b values (or q values) in the clinical setting leads to fatal image degradation. We therefore decided to evaluate the changes in the RMSD values, rather than the absolute values themselves. Another limitation was the small number of motion prob- ing gradient (MPG) directions. We used 6 directions to reduce the MR data acquisition time. It has been reported that at least 15 different MPG directions are needed to measure mean DK [14]; however, another report has argued that it might be sufficient to measure in only 6 directions to obtain a DK estimate, e.g. in the assessment of multiple sclerosis lesions [30]. We agree with the latter opinion because of the limited MR time available in a busy clinical setting. A third limitation was the heterogeneous age distribution of the patients. The FA and ADC values of the cervical spinal cord may be influenced by age-related changes. In fact, Mamata et al. [6] reported that 46 % of their patients showed no elevation in ADC of the spinal cord at the narrow spinal canal level, and our results showed no significant changes in ADC values, although they tended to increase with compression. Therefore, longitudinal studies and clin- ical correlations with the metrics are needed in the future to avoid the influence of age-related changes. A fourth limitation was that there was no objective as- sessment concluding that neurological damage was present within the patient groups. Neither a gold standard nor con- trol groups were used in our evaluation. Therefore, a future study investigating the relationship between the diffusion metrics and the symptoms, signs and prognosis in a larger number of patients will be needed. 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