title: Cerebral vascular mean transit time in healthy humans: a comparative study with PET and dynamic susceptibility contrast-enhanced MRI.
abstract: Cerebral vascular mean transit time (MTT), defined as the ratio of cerebral blood volume to cerebral blood flow (CBV/CBF), is a valuable indicator of the cerebral circulation. Positron emission tomography (PET) and dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI) are useful for the quantitative determination of MTT in the clinical setting. The aim of this study was to establish a normal value set of MTT as determined by PET and by DSC-MRI and to identify differences between these methods. Seven healthy volunteers were studied with (15)O-PET (H(2)(15)O and C(15)O) and gradient-echo echo-planar DSC-MRI at 1.5 T. In the DSC-MRI study with bolus injection of contrast agent, deconvolution analysis was performed. Comparison of gray-to-white matter ratios showed fairly good agreement between PET and DSC-MRI for all parameters (relative CBV, relative CBF, and relative MTT), confirming the validity of relative measurements with DSC-MRI. However, quantitative MTT measured by DSC-MRI was significantly shorter than that measured by PET in cerebral cortical regions (2.8 to 3.0 secs for DSC-MRI versus 3.9 to 4.3 secs for PET) and the centrum semiovale (3.5 secs for DSC-MRI versus 4.8 secs for PET). These discrepancies may be because of the differences in the intrinsic sensitivity of each imaging modality to vascular components; whereas PET measurement of CBV is equally sensitive to all vascular components, measurement with DSC-MRI originates from the microvasculature in the vicinity of the brain parenchyma. This underlying difference may influence interpretation of MTT determined by PET or by DSC-MRI for patients with cerebrovascular disease.
authors.affiliation: Department of Radiology and Nuclear Medicine, Akita Research Institute of Brain and Blood Vessels, Akita, Japan. iba@akita-noken.go.jp
authors.forename: Masanobu
authors.initials: M
authors.lastname: Ibaraki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ito
authors.forename: Eku
authors.initials: E
authors.lastname: Shimosegawa
authors.forename: Hideto
authors.initials: H
authors.lastname: Toyoshima
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ishigame
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Takahashi
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
authors.forename: Shuichi
authors.initials: S
authors.lastname: Miura
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003287:Contrast Media; D003627:Data Interpretation, Statistical; D005682:Gadolinium; D006400:Hematocrit; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D012016:Reference Values
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D005682:Gadolinium