{"doi":"10.1002/mrm.29667","title":"Axon fiber orientation as the source of <scp>T<sub>1</sub></scp> relaxation anisotropy in white matter: A study on corpus callosum in vivo and ex vivo","abstract":"Purpose Recent studies indicate that T 1 in white matter (WM) is influenced by fiber orientation in B 0 . The purpose of the study was to investigate the interrelationships between axon fiber orientation in corpus callosum (CC) and T 1 relaxation time in humans in vivo as well as in rat brain ex vivo. Methods Volunteers were scanned for relaxometric and diffusion MRI at 3 T and 7 T. Angular T 1 plots from WM were computed using fractional anisotropy and fiber‐to‐field‐angle maps. T 1 and fiber‐to‐field angle were measured in five sections of CC to estimate the effects of inherently varying fiber orientations on T 1 within the same tracts in vivo. Ex vivo rat‐brain preparation encompassing posterior CC was rotated in B 0 and T 1 , and diffusion MRI images acquired at 9.4 T. T 1 angular plots were determined at several rotation angles in B 0 . Results Angular T 1 plots from global WM provided reference for estimated fiber orientation–linked T 1 changes within CC. In anterior midbody of CC in vivo, where small axons are dominantly present, a shift in axon orientation is accompanied by a change in T 1 , matching that estimated from WM T 1 data. In CC, where large and giant axons are numerous, the measured T 1 change is about 2‐fold greater than the estimated one. Ex vivo rotation of the same midsagittal CC region of interest produced angular T 1 plots at 9.4 T, matching those observed at 7 T in vivo. Conclusion These data causally link axon fiber orientation in B 0 to the T 1 relaxation anisotropy in WM.","journal":"Magnetic Resonance in Medicine","year":2023,"id":338353,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":17,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9563,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2023-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1071241,"name":"Jeromy Thothard","orcid":null,"position":1,"is_corresponding":false},{"id":1070789,"name":"Henri Leskinen","orcid":"0000-0001-5043-3101","position":2,"is_corresponding":false},{"id":256595,"name":"Pramod Kumar Pisharady","orcid":"0000-0002-0756-1199","position":3,"is_corresponding":false},{"id":1053758,"name":"Eppu Manninen","orcid":"0000-0002-9353-6079","position":4,"is_corresponding":false},{"id":1070790,"name":"Mikko I. Kettunen","orcid":"0000-0002-2004-660X","position":5,"is_corresponding":false},{"id":256596,"name":"Christophe Lenglet","orcid":"0000-0003-4646-3185","position":6,"is_corresponding":false},{"id":426005,"name":"Olli Gröhn","orcid":"0000-0003-1372-1651","position":7,"is_corresponding":false},{"id":281629,"name":"Michael Garwood","orcid":"0000-0003-1578-9166","position":8,"is_corresponding":false},{"id":485160,"name":"Mikko J. Nissi","orcid":"0000-0002-5678-0689","position":9,"is_corresponding":false},{"id":901779,"name":"Risto A. Kauppinen","orcid":"0000-0003-3383-6608","position":0,"is_corresponding":true}],"reference_count":50,"raw_metadata":null,"created_at":"2026-07-19T01:10:35.973121Z","pmid":"37145027","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}