title: Cerebrovascular autoregulation as a neuroimaging tool.
abstract: Functional transcranial Doppler (fTCD) sonography provides a high temporal resolution measure of blood flow and has over the years proved to be a valuable tool in the clinical evaluation of patients with cerebrovascular disorders. More recently, due to advances in physics and computing, it has become possible to derive indices of cerebrovascular autoregulation (CA) as well as cerebrovascular pressure reactivity (CR), using non-invasive techniques. These indices provide a dynamic representation of the brain's regulatory blood flow mechanisms not only in pathological states but also in health. However, whilst the temporal resolution of these regulatory indices is very good, spatially, the localization of brain regions remains very poor, thus limiting its brain mapping capacity. Functional MRI, on the contrary, is a brain-imaging technique that operates on similar blood flow principles; however, unlike fTCD, it provides high spatial resolution. Because both fTCD and fMRI determine blood flow-dependant imaging parameters, the coupling of fTCD with fMRI may provide greater insight into brain function by virtue of the combined enhanced temporal and spatial resolution that each technique affords. This review summarizes the fTCD technique with particular emphasis on the CA and CR indices and their relationship in traumatic brain injury as well as in health.
authors.affiliation: 1School of Psychiatry, The University of New South Wales, Australia.
authors.forename: Jim
authors.initials: J
authors.lastname: Lagopoulos
authors.affiliation: 1School of Psychiatry, The University of New South Wales, Australia.
authors.forename: Gin S
authors.initials: GS
authors.lastname: Malhi
authors.affiliation: 1School of Psychiatry, The University of New South Wales, Australia.
authors.forename: Belinda
authors.initials: B
authors.lastname: Ivanovski
authors.affiliation: 1School of Psychiatry, The University of New South Wales, Australia.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Cahill
authors.affiliation: 5Department of Neurosurgery, Westmead Hospital, Westmead, Australia.
authors.forename: Erhard W
authors.initials: EW
authors.lastname: Lang
authors.affiliation: 6Intensive Care Unit, Westmead Hospital, Westmead, Australia.
authors.forename: Yugan
authors.initials: Y
authors.lastname: Mudaliar
authors.affiliation: 5Department of Neurosurgery, Westmead Hospital, Westmead, Australia.
authors.forename: Nick
authors.initials: N
authors.lastname: Dorsch
authors.affiliation: 5Department of Neurosurgery, Westmead Hospital, Westmead, Australia.
authors.forename: Alan
authors.initials: A
authors.lastname: Yam
authors.affiliation: 5Department of Neurosurgery, Westmead Hospital, Westmead, Australia.
authors.forename: Jane
authors.initials: J
authors.lastname: Griffith
authors.affiliation: 6Intensive Care Unit, Westmead Hospital, Westmead, Australia.
authors.forename: Jamin
authors.initials: J
authors.lastname: Mulvey