gms | German Medical Science

Objective: Diffusion weighted imaging (DWI) is the basis of fiber tractography (FT) playing an important role in pre-surgical planning. However, DWI suffers from various artifacts during data acquisition and low spatial signal-to-noise-ratio (SNR), which can lead to erroneous results in FT. Various kinds of ways to improve data quality have been reported but less focused on the effect on FT. Thereby, one approach called position orientation adaptive smoothing (POAS) aims to increase spatial SNR while preserving anisotropy (edge-preserving, avoids blurring). In this study, the effect of POAS versus data averaging on FT of corticospinal tract (CST) was evaluated.

Methods: 22 healthy volunteers were included. For each volunteer five repetitive DWI data sets were acquired at a 3T MRI. After preprocessing applying motion and eddy current correction on the one hand, all five data sets were averaged, on the other hand all data sets were processed using the POAS algorithm. FT of the CST was then performed using a standard deterministic among the original data sets (ORG-FT), the averaged (AVG-FT) as well as the smoothed data sets using POAS (POAS-FT). Except for morphological evaluation, a quantitative evaluation regarding the tract profile including tract volume, density, and FA and MD value was performed. Reproducibility among the five original and smoothed data sets was calculated using the Jaccard index.

Results: CST reconstructions using POAS-FT showed more stable and less variable results in comparison to ORG-FT. The tract volumes were significantly larger using POAS-FT compared to ORG-FT in both hemispheres (left: p=0.038, right: p=0.014), whereas no significant difference was found for POAS-FT and AVG-FT. POAS-FT showed significantly smaller tract density in comparison to ORG-FT and AVG-FT within the right hemisphere. FA and MD were decreased for POAS-FT in contrast to ORG-FT and AVG-FT, whereas POAS-FT showed significantly higher tract reproducibility compared to ORG-FT (p<0.001).

Conclusion: Processing DWI data using POAS led to less variable, more stable and reliable tractography results of the CST. Moreover, POAS-FT preserved tract volume, but decreased FA and MD. In this way POAS might correct the overestimation of diffusion metrics typically resulting of low image quality and can supply reliable tractography of the CST which is critical for high-quality imaging in clinical applications.