Trade-off between angular and spatial resolutions in in vivo fiber tractography

Abstract

Tractography is becoming an increasingly popular method to reconstruct white matter connections in vivo. The diffusion MRI data that tractography is based on requires a high angular resolution to resolve crossing fibers whereas high spatial resolution is required to distinguish kissing from crossing fibers. However, scan time increases with increasing spatial and angular resolutions, which can become infeasible in clinical settings. Here we investigated the trade-off between spatial and angular resolutions to determine which of these factors is most worth investing scan time in. We created a unique diffusion MRI dataset with 1.0 mm isotropic resolution and a high angular resolution (100 directions) using an advanced 3D diffusion-weighted multi-slab EPI acquisition. This dataset was reconstructed to create subsets of lower angular (75, 50, and 25 directions) and lower spatial (1.5, 2.0, and 2.5 mm) resolution. Using all subsets, we investigated the effects of angular and spatial resolutions in three fiber bundles—the corticospinal tract, arcuate fasciculus and corpus callosum—by analyzing the volumetric bundle overlap and anatomical correspondence between tracts. Our results indicate that the subsets of 25 and 50 directions provided inferior tract reconstructions compared with the datasets with 75 and 100 directions. Datasets with spatial resolutions of 1.0, 1.5, and 2.0 mm were comparable, while the lowest resolution (2.5 mm) datasets had discernible inferior quality. In conclusion, we found that angular resolution appeared to be more influential than spatial resolution in improving tractography results. Spatial resolutions higher than 2.0 mm only appear to benefit multi-fiber tractography methods if this is not at the cost of decreased angular resolution.

Whole mouse brain connectomics

“…All require acquisition of a “sufficient” number of angular samples. Many studies have probed the question of what is “sufficient” which is in turn dependent on the algorithm, signal to noise of the data and spatial resolution (Jones, ; Jones & Cercignani, ; Jones, Knösche, & Turner, ; Tournier, Calamante, & Connelly, ; Tuch et al, ; Vos et al, ). Maeir‐Hein et al explored the performance of 96 different approaches in mapping human connectomes (2017).…”

“…The fidelity of the tractography and connectome are intimately tied to the spatial resolution, the signal to noise in the composite images, the strength of the diffusion encoding gradients, and the number of different gradient angles acquired. Numerous authors have explored the topic in the context of clinical scanning where the spatial resolution is >1 mm and scan times must remain clinically realistic (<30 min) (Jones et al, ; Vos et al, ; Zhan et al, ). We have previously explored the question in the macaque brain where a fixed specimen was scanned with a fixed time (60 hr) using protocols with spatial resolution of 130 μm and 12 directions to 600 μm resolution with 257 directions (Calabrese et al, ).…”

Building connectomes using diffusion MRI: why, how and but

“…High spatial resolution is also beneficial for better distinguishing tract termination points. 146 Increasing the resolution by using high field strength improves the estimation of the fiber spreading pattern to the cortex and reduces gyral bias. 147 In another recent study, improving on all the data quality aspects of dMRI data increased agreement of connectomes estimated in humans using three different modalities.…”

Abnormal fronto‐parietal white matter organisation in the superior longitudinal fasciculus branches in autism spectrum disorders

“…Despite its popularity for investigating microstructural characteristics of white matter fibre bundles in vivo, fibre tractography results may still be sensitive to data artefacts (Leemans & Jones, ; Perrone et al ., ; Vos et al ., ), partial volume effects (Alexander et al ., ; Vos et al ., ; Szczepankiewicz et al ., ) and choices in implementation, modelling, acquisition protocol and parameter settings (Veraart et al ., ; Tax et al ., ; Thomas et al ., ; Roine et al ., ; Vos et al ., ). Due to such potential confounding factors, great care should be taken when interpreting the results (Jones & Leemans, ; Tournier et al ., ; Vos et al ., ; Deprez et al ., ).…”