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Balancing Accuracy and Precision : Optimal b-Values for Diffusion Tensor Imaging along the Perivascular Space

Vuong, Nelly LU ; Lasic, Samo LU ; Hall, Sara LU ; Spotorno, Nicola LU ; van Westen, Danielle LU orcid ; Hansson, Oskar LU orcid ; Nilsson, Markus LU and Georgiopoulos, Charalampos LU orcid (2026) In American Journal of Neuroradiology 47(7). p.1920-1926
Abstract

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... (More)

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.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
American Journal of Neuroradiology
volume
47
issue
7
pages
7 pages
publisher
American Society of Neuroradiology
external identifiers
  • pmid:41663208
  • scopus:105043573507
ISSN
0195-6108
DOI
10.3174/ajnr.A9199
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2026 by American Journal of Neuroradiology
id
f131dddd-691a-4fa7-a42c-399c8e15c830
date added to LUP
2026-09-25 15:27:25
date last changed
2026-09-26 03:31:41
@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}},
}