title: Susceptibility-based time-resolved whole-organ and regional tissue oximetry.
abstract: The magnetism of hemoglobin - being paramagnetic in its deoxy and diamagnetic in its oxy state - offers unique opportunities to probe oxygen metabolism in blood and tissues. The magnetic susceptibility χ of blood scales linearly with blood oxygen saturation, which can be obtained by measuring the magnetic field ΔB of the intravascular MR signal relative to tissue. In contrast to χ, the induced field ΔB is non-local. Therefore, to obtain the intravascular susceptibility Δχ relative to adjoining tissue from the measured ΔB demands solution of an inverse problem. Fortunately, for ellipsoidal structures, to which a straight, cylindrically shaped blood vessel segment conforms, the solution is trivial. The article reviews the principle of MR susceptometry-based blood oximetry. It then discusses applications for quantification of whole-brain oxygen extraction - typically on the basis of a measurement in the superior sagittal sinus - and, in conjunction with total cerebral blood flow, the cerebral metabolic rate of oxygen (CMRO2). By simultaneously measuring flow and venous oxygen saturation (SvO2) a temporal resolution of a few seconds can be achieved, allowing the study of the response to non-steady-state challenges such as volitional apnea. Extensions to regional measurements in smaller cerebral veins are also possible, as well as voxelwise quantification of venous blood saturation in cerebral veins accomplished by quantitative susceptibility mapping (QSM) techniques. Applications of susceptometry-based oximetry to studies of metabolic and degenerative disorders of the brain are reviewed. Lastly, the technique is shown to be applicable to other organ systems such as the extremities using SvO2as a dynamic tracer to monitor the kinetics of the microvascular response to induced ischemia. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
authors.affiliation: Lucas Center for Imaging, Department of Radiology, Stanford University, James H. Clark Center, 318 Campus Drive, Suite S170, Stanford, CA 94305.
authors.forename: Audrey P
authors.initials: AP
authors.lastname: Fan
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania.
authors.forename: Zachary B
authors.initials: ZB
authors.lastname: Rodgers
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania.
authors.forename: Erin K
authors.initials: EK
authors.lastname: Englund
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Langham
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D010100:Oxygen
keywords: Applications, Other functional MRI methods; Endogenous Contrast Methods; Functional MRI (fMRI) Methods; Methods and Engineering, CMRO2; Methods and Engineering, Normal brain; Neurological; Susceptibility weighted imaging