Original Research Assessment of Corticospinal Tract (CST) Damage in Acute Stroke Patients: Comparison of Tract-Specific Analysis Versus Segmentation of a CST Template Patricia Vargas, MS, 1–3 Marie Gaudron, MD, 1–4 Romain Valabre `gue, PhD, 1,2,5 Eric Bertasi, MS, 1,2,5 Fr  ed  eric Humbert, BS, 1,2,5 St  ephane Leh  ericy, MD, PhD, 1,2,5,6 Yves Samson, MD, 1–3,7 and Charlotte Rosso, MD, PhD 1–3,7 * Purpose: To compare two techniques to assess corticospi- nal tract (CST) damage in stroke patients: tract-specific analysis by probabilistic tractography and segmentation using a CST template. Materials and Methods: We extracted fractional anisot- ropy (FA) values, the FA ratio, and mean diffusivity (MD) in 18 stroke patients and 21 healthy volunteers matched for age and sex. We compared the two methods in order to determine their ability to detect 1) differences between diffusion tensor imaging (DTI) parameters of healthy vol- unteers and stroke patients, 2) the correlation between DTI parameters and clinical scores, and 3) the correlation between DTI parameters and blood oxygen level-depend- ent (BOLD) signals in a fist-closure task. Results: FA values were higher with the tractography approach than with the segmentation method, but differen- ces between the ipsilesional CST and the homologous region in healthy subjects were detected using both meth- ods. In patients, clinical scores were significantly correlated with FA values and FA ratios with both methods. The BOLD signal was positively correlated with FA values for CST with the segmentation but not with the tractography approach. Conclusion: CST damage in stroke patients can be assessed by either probabilistic tractography or segmen- tation of a CST template. Although each method has advantages and limitations, both are sensitive enough to detect differences among stroke patients and identify spe- cific correlations with clinical scores. Key Words: stroke; corticospinal tract; DTI; FA; MD J. Magn. Reson. Imaging 2012;000:000–000. V C 2012 Wiley Periodicals, Inc. UNDERSTANDING DYNAMIC CHANGES in cerebral organization after stroke is important for poststroke recovery (1,2). Recent studies suggest that white mat- ter integrity is an important determinant, particularly in the corticospinal tract (CST), which transmits infor- mation to the spinal cord (3,4). The CST is fundamental to motor control and has been identified as a major structure influencing motor prognosis (5–8). CST damage, assessed by diffusion tensor imaging (DTI), has been associated with clinical outcome in several studies in subacute (9–11) and chronic stroke patients (4–6). Fractional anisotropy (FA), which is computed by DTI, reflects a combina- tion of properties related to diameter, density, myeli- nation, axonal alignment, and integrity of white mat- ter tracts (4), and, in particular, the directionality of the diffusion process (12). FA is the most widely used index for assessing white matter integrity in stroke patients. Other DTI parameters such as mean diffu- sivity (MD) and tract volumes have also been eval- uated using this application (4,13,14). Most DTI studies use a region-of-interest (ROI) approach to evaluate CST damage in particular loca- tions such as the corona radiata, the posterior limb of the internal capsule, or the pons (6,13,15). To study the entire CST, the use of CST-specific tractography has several advantages compared to other methods because it gives information about tract volumes, con- nectivity, and disruption after stroke (5,9,16). How- ever, some tractography algorithms may fail to recon- struct tracts properly due to crossing fibers or the disorganization caused by stroke lesions (15,17). Probabilistic tractography is the most robust method for fiber reconstruction and is a valid technique for 1 UPMC Paris 6, Univ 75006, Paris, France. 2 lnstitut du Cerveau et de la Mo€ elle  epinie `re, Paris, France. 3 COGIMAGE, Centre de Recherche de l’Institut du Cerveau et de la Mo€ elle  epinie `re, UPMC Paris 6, Inserm, U975, CNRS, UMR 7225, Paris, France. 4 Service de Neurologie, CHU Tours, 37000, France. 5 Centre de Neuro-Imagerie de Recherche (CENIR), Centre de Recherche de l’Institut du Cerveau et de la Mo€ elle  epinie `re, UPMC Paris 6, Inserm, U975, CNRS, UMR 7225, Paris, France. 6 APHP, Service de Neuroradiologie, Ho ˆpital Piti e-Salpe ˆtrie `re, Paris, France. 7 APHP, Urgences C er ebro-Vasculaires, Ho ˆpital Piti e-Salpe ˆtrie `re, Paris, France. *Address reprint requests to: C.R., APHP Urgences C er ebro-vasculaires, Ho ˆpital Piti e-Salpe ˆtrie `re, 47-83 Bd de l’Ho ˆpital, 75013 Paris, France. E-mail: charlotte.rosso@gmail.com Received September 6, 2011; Accepted September 7, 2012. DOI 10.1002/jmri.23870 View this article online at wileyonlinelibrary.com. JOURNAL OF MAGNETIC RESONANCE IMAGING 000:000–000 (2012) CME V C 2012 Wiley Periodicals, Inc. 1