title: On the contribution of deoxy-hemoglobin to MRI gray-white matter phase contrast at high field.
abstract: High field (> or =7 T) MRI studies based on signal phase have been used to improve visualization of the fine structure of the brain, most notably the major white matter fiber bundles, the gray-white matter subdivision, and the laminar cortical architecture. The observed contrast has been attributed in part to local variations in magnetic susceptibility arising from iron in storage proteins and tissue lipid. Another contribution could come from the paramagnetic blood constituent deoxy-hemoglobin, the tissue concentration of which may vary through local variations in vascular density. To investigate this possibility, we examined phase contrast between gray and white matter in rats after intravenous administration of a superparamagnetic contrast agent at various dosages. At the maximum dosage (3 mg Fe/kg), which resulted in an estimated paramagnetic susceptibility shift 4-8 times larger than deoxy-hemoglobin, we observed a negligible increase in phase contrast between gray and white matter. This result suggests that endogenous deoxy-hemoglobin has no significant contribution to phase contrast between gray and white matter.
authors.affiliation: Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. jonghoyi@mail.nih.gov
authors.forename: Jongho
authors.initials: J
authors.lastname: Lee
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Hirano
authors.forename: Masaki
authors.initials: M
authors.lastname: Fukunaga
authors.forename: Afonso C
authors.initials: AC
authors.lastname: Silva
authors.forename: Jeff H
authors.initials: JH
authors.lastname: Duyn
mesh_terms: D000758:Anesthesia; D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D001923:Brain Chemistry / Q000502:physiology*; D002138:Calibration; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000378:metabolism; D003337:Corpus Callosum / Q000033:anatomy & histology / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D006454:Hemoglobins / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D006454:Hemoglobins; C100003:deoxyhemoglobin