Claudia Testa1,2, Stefania Evangelisti1,2, Mariagrazia Popeo3,4, Stefano Zanigni1,2, Laura Ludovica Gramegna1,2, Paola Fantazzini5,6, Caterina Tonon1,2, David Neil Manners1,2, Raffaele Lodi7,8. 1. Functional MR Unit, Policlinico S. Orsola - Malpighi, Via Massarenti 9, Bologna, Italy. 2. Department of Biomedical and Neuromotor Sciences, University of Bologna, Via Foscolo 7, Bologna, Italy. 3. Istituto Italiano di Tecnologia, Center for Neuroscience and Cognitive Systems@Unitn, Corso Bettini 31, Rovereto, Trento, Italy. 4. Center for Mind and Brain Sciences, University of Trento, Corso Bettini 31, Rovereto, Trento, Italy. 5. Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna, Italy. 6. Centro Enrico Fermi, Roma, Piazza del Viminale 1, Rome, Italy. 7. Functional MR Unit, Policlinico S. Orsola - Malpighi, Via Massarenti 9, Bologna, Italy. raffaele.lodi@unibo.it. 8. Department of Biomedical and Neuromotor Sciences, University of Bologna, Via Foscolo 7, Bologna, Italy. raffaele.lodi@unibo.it.
Abstract
OBJECTIVES: We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs). MATERIALS AND METHODS: The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD. RESULTS: FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD. CONCLUSIONS: Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.
OBJECTIVES: We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs). MATERIALS AND METHODS: The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD. RESULTS: FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD. CONCLUSIONS: Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.
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