Axcaliber: A method for measuring axon diameter distribution from diffusion MRI
Open accessAbstract
The diameter of a myelinated nerve axon is directly proportional to its conduction velocity, so the axon diameter distribution helps determine the channel capacity of nervous transmission along fascicles in the central (CNS) and peripheral nervous systems (PNS). Previously, this histological information could only be obtained using invasive tissue biopsies. Here we propose a new NMR-based approach that employs a model of water diffusion within "restricted" cylindrical axons to estimate their diameter distribution within a nerve bundle. This approach can be combined with MRI to furnish an estimate of the axon diameter distribution within each voxel. This method is validated by comparing the diameter distributions measured using the NMR and histological techniques on sciatic and optic nerve tissue specimens. The axon diameter distribution measured in each voxel of porcine spinal cord using MRI and using histological methods were similar. Applications are expected in longitudinal studies designed to follow nerve growth in normal and abnormal development, as well as in diagnosing disorders and diseases affecting specific populations of axons in the CNS and PNS.
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The Standard Model framework underlies, or is closely related to, several influential models and approaches, including CHARMED, AxCaliber, NODDI, WMTI, SMT, and related multi-compartment formulations.
“This framework underlies, or is closely related to, several influential models and approaches, including CHARMED, AxCaliber, NODDI, WMTI, SMT, and related multi-compartment formulations (Assaf & Basser, 2005; Assaf et al., 2008; Zhang et al., 2012).”
From 40 Years of diffusion MRI in the brain: From history to emerging frontiers (2026) · cites this paper as Assaf et al., 2008
CHARMED and AxCaliber were influential early attempts to estimate restricted fractions and axon caliber distributions from diffusion data.
“CHARMED and AxCaliber were influential early attempts to estimate restricted fractions and axon caliber distributions from diffusion data (Assaf & Basser, 2005; Assaf et al., 2008).”
From 40 Years of diffusion MRI in the brain: From history to emerging frontiers (2026) · cites this paper as Assaf et al., 2008
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40 Years of diffusion MRI in the brain: From history to emerging frontiers
Le Bihan, D. (2026) · Imaging Neuroscience · doi:10.1162/imag.a.1365
“This framework underlies, or is closely related to, several influential models and approaches, including CHARMED, AxCaliber, NODDI, WMTI, SMT, and related multi-compartment formulations ( Assaf & Basser, 2005; Assaf et al., 2008; Zhang et al., 2012).”
- Authors
- Assaf, Y., Blumenfeld‐Katzir, T., Yovel, Y., & Basser, P. J.
- Affiliations
- Tel Aviv University (IL)
- National Institutes of Health (US)
- Corresponding author
- Assaf, Yaniv
- Venue
- Magnetic Resonance in Medicine
- Publisher
- Wiley
- Published
- 2008-05-27
- Volume
- 59
- Issue
- 6
- Pages
- 1347-1354
- ISSN
- 0740-3194 (ISSN-L)
- 1522-2594
- PMC
- PMC4667732
- OpenAlex
- W2122662954
- Cited by
- 849
- References
- 2
- Citations by year
- 2026: 21 · 2025: 42 · 2024: 33 · 2023: 32 · 2022: 40 · 2021: 64 · 2020: 70 · 2019: 64 · 2018: 55 · 2017: 66 · 2016: 63 · 2015: 75 · 2014: 51 · 2013: 55 · 2012: 31
- FWCI
- 22.34
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Magnetic Resonance in Medicine (publishedVersion)
- PubMed (publishedVersion)
- Europe PMC (PubMed Central) (acceptedVersion)
- PubMed Central (acceptedVersion)
- ORCA Online Research @Cardiff (Cardiff University) (submittedVersion)
- Funders
- Israel Science Foundation
- Tel Aviv University
- National Institutes of Health
- National Institute of Child Health and Human Development
- Eunice Kennedy Shriver National Institute of Child Health and Human Development (Z01HD000266)
- Topics
- Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Advanced Neuroimaging Techniques and Applications
- Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › NMR spectroscopy and applications
- Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Advanced MRI Techniques and Applications
- Keywords
- axon diameter distribution, diffusion MRI, restricted diffusion, myelinated axons, nerve conduction velocity, sciatic nerve, optic nerve, spinal cord, nerve fascicles, peripheral nervous system, central nervous system
- MeSH terms
- Animals, Axons, Image Processing, Computer-Assisted, Magnetic Resonance Spectroscopy, Optic Nerve, Sciatic Nerve, Spinal Cord, Staining and Labeling, Swine, Diffusion Magnetic Resonance Imaging
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