We read with interest the articles by Renoux et al1 and Facon et al,2 respectively, in the October 2006 and in the June–July 2005 issues of the AJNR.
The authors evaluated the diagnostic accuracy of diffusion tensor imaging (by using the apparent diffusion coefficient and fractional anisotropy) in inflammatory diseases of the spinal cord1 and in spinal cord compression.2 In these 2 articles, diffusion tensor imaging was compared with T2-fast spin-echo (FSE)–weighted sequences. The authors found a higher sensitivity in the detection of spinal cord abnormalities with diffusion tensor imaging than with T2-FSE–weighted sequences in both articles.1,2
We draw the authors’ attention to the previously published reports about the diagnostic accuracy of spinal cord abnormalities with conventional MR imaging sequences. We cite only 2 of them because of the restriction on the number of references. These reports showed that short τ inversion recovery FSE (STIR-FSE) sequences may have a higher sensitivity than T2-FSE–weighted sequences in the detection of spinal cord lesions.3,4 Campi et al3 and Rocca et al4 concluded that STIR-FSE sequences had a higher sensitivity in the detection of demyelinating lesions. Furthermore, Campi et al showed a better demarcation and maybe a better sensitivity in the detection of spinal cord abnormalities in a group of patients with myelopathy of unknown etiology with STIR-FSE sequences.
We hypothesize that the best conventional sequence, with the highest sensitivity in the detection of spinal cord abnormalities, may be the STIR-FSE sequence. We think that future studies evaluating the diagnostic accuracy of diffusion tensor imaging in the detection of spinal cord abnormalities should include STIR-FSE sequences.
Reply:
Short τ inversion recovery (STIR) MR imaging has a better sensitivity to detect spinal cord lesions compared with regular spin-echo (SE) T2-weighted imaging as stated in this letter. The purpose of our work in the 2 cited articles1,2 was mostly based on how diffusion tensor imaging (DTI) and fractional anisotropy (FA) could help locate lesions within the spinal cord and, at the same, how to better understand the pathophysiology of inflammatory myelitis as well as spinal cord compressions. Sensitivity of MR SE T2-weighted imaging sequences was only assessed to hypothesize pathophysiologic patterns of these diseases. Indeed, our observations led us to draw a scheme of FA value changes that may correlate with patient outcome. If conventional MR imaging sequence sensitivity plays an important role in detecting spinal cord lesions, this sensitivity could not be used to assess understanding of the neuronal cluster regeneration that occurs in such diseases, contrary to the use of DTI and FA values. We used SE T2-weighted imaging instead of STIR because we focused more on pathophysiology than on MR imaging accuracy.
The authors of the letter are right: STIR is better than SE T2. However, only DTI, FA, and fiber tracking may help to understand these diseases at the water molecule level.
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