@article{f131dddd-691a-4fa7-a42c-399c8e15c830,
  abstract     = {{<p>BACKGROUND AND PURPOSE: The glymphatic system facilitates perivascular clearance, and its dysfunction has been implicated in neurodegenerative diseases. Diffusion tensor imaging along the perivascular space (DTI-ALPS) has been proposed as an indirect approach to assess glymphatic function, but its reliability is debated. The choice of b-value is an aspect of possible improvement. While a b-value of 1000 seconds/mm² is commonly used, the optimal b-value for DTI-ALPS remains unknown. This study aims to determine the optimal b-value for DTI-ALPS. MATERIALS AND METHODS: Simulations were conducted to examine how the choice of maximum b-value influences bias, precision, and effect size of the ALPS index. DTI-ALPS was applied in a cohort of 194 participants divided into 4 groups: healthy controls (HCs) (n=42), patients with Parkinson disease (n=119), patients with Parkinson disease dementia (PDD) (n=16), and patients with progressive supranuclear palsy (PSP) (n=17). ALPS indices were calculated by manually placing regions of interest on projection and association fibers in each hemisphere. Group differences in ALPS indices across b-values were analyzed using mixed models. RESULTS: In vivo, ALPS indices were higher at a b-value of 500 and 250 seconds/mm² compared with a b-value of 1000 seconds/mm² in both hemispheres. Simulations indicated a bias-variance trade-off: very low b-values reduced sensitivity and compromised precision, while high b-values improved precision but reduced accuracy. The simulated effect size of the ALPS index peaked at intermediate b-values (≈ 700 seconds/mm²). In vivo, ALPS indices were lower in patients with PDD and PSP compared with HCs, though differences varied across b-values. CONCLUSIONS: Both simulations and in vivo results suggest that the commonly used b-value of 1000 seconds/mm² is not optimal for assessing diffusion in the perivascular spaces. Intermediate b-values at approximately 700 seconds/mm² appear more suitable. However, further optimization of acquisition parameters is needed.</p>}},
  author       = {{Vuong, Nelly and Lasic, Samo and Hall, Sara and Spotorno, Nicola and van Westen, Danielle and Hansson, Oskar and Nilsson, Markus and Georgiopoulos, Charalampos}},
  issn         = {{0195-6108}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{7}},
  pages        = {{1920--1926}},
  publisher    = {{American Society of Neuroradiology}},
  series       = {{American Journal of Neuroradiology}},
  title        = {{Balancing Accuracy and Precision : Optimal b-Values for Diffusion Tensor Imaging along the Perivascular Space}},
  url          = {{http://dx.doi.org/10.3174/ajnr.A9199}},
  doi          = {{10.3174/ajnr.A9199}},
  volume       = {{47}},
  year         = {{2026}},
}