title: The pulsatility volume index: an indicator of cerebrovascular compliance based on fast magnetic resonance imaging of cardiac and respiratory pulsatility.
abstract: The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain-heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes. We implemented a fast non-gated two-dimensional MRI pulse sequence based on echo-planar imaging (EPI) with ultra-short repetition time (approx. 30-50 ms), which stepped through slices every approximately 20 s. We constrained the solution of the Bloch equations for spins moving faster than a critical speed to produce an endogenous contrast primarily dependent on spin volume changes, and an approximately sixfold signal gain compared with Ernst angle acquisitions achieved by the use of a 90° flip angle. Using cardiac and respiratory peaks detected on physiological recordings, average cardiac and respiratory MRI pulse waveforms in several brain compartments were obtained at 7 Tesla, and used to derive a compliance indicator, the pulsatility volume index (pVI). The pVI, evaluated in larger cerebral arteries, displayed significant variation within and across vessels. Multi-echo EPI showed the presence of significant pulsatility effects in both S0 and [Formula: see text] signals, compatible with blood volume changes. Lastly, the pVI dynamically varied during breath-holding compared with normal breathing, as expected for a compliance indicator. In summary, we characterized and performed an initial validation of a novel MRI indicator of cerebrovascular compliance, which might prove useful to investigate brain-heart interactions in cerebrovascular disease and other disorders.
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA martab@nmr.mgh.harvard.edu.
authors.forename: Marta
authors.identifier: http://orcid.org/0000-0001-9606-6853
authors.initials: M
authors.lastname: Bianciardi
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA Medical Physics Section, Department of Biomedicine and Prevention, Faculty of Medicine, University of Rome 'Tor Vergata', Via Montpellier 1, 00133 Rome, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Toschi
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Polimeni
authors.affiliation: Department of Psychiatry, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: Karleyton C
authors.initials: KC
authors.lastname: Evans
authors.affiliation: Siemens Healthcare, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Bhat
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA Institute for Medical Physics and Radiation Protection, Life Science Engineering, Mittelhessen University of Applied Science, Wiesenstrasse 14, 35390 Giessen, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Keil
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Rosen
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Boas
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th Street, Charlestown, Boston, MA 02129, USA.
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
mesh_terms: D008279:Magnetic Resonance Imaging / Q000379:methods*
keywords: cardiac pressure wave; cerebrovascular compliance; echo-planar imaging; magnetic resonance imaging indicator; pulsatility volume index; respiratory pressure wave