Ronald R. Pricea)
Vanderbilt University Medical Center, Department of Radiology and Radiological Sciences, Nashville, Tennessee 37232-2675
Medical College of Georgia, Department of Radiology, 1120 15th St., Augusta, Georgia 30912
Richard J. Massoth
Medical X-Ray Center, PC, 1417 S. Minnesota Ave., Sioux Falls, SouthDakota 57015
Geoffrey D. Clarke
University of Texas Health Science Center, Department of Radiology, 7703 Floyd Curl Drive, Room 639F, San Antonio, Texas 78284-7800
Dick J. Drost
St. Joseph’s Health Centre Nuclear Medicine & MRI Department, 268 Grosvenor Street, London, Ontario, N6A 4L6, Canada
Received 23 January 2002; accepted for publication 29 May 2002; published 29 July 2002Functional MR imaging fMRI based upon the Blood Oxygen Level Dependent BOLD effect is currently an important new tool for understanding basic brain function and speciﬁcally allowing the correlation of physiological activity with anatomical location without the use of ionizing radiation. The clinical role of fMRI is still being deﬁned and is the subject of much research activity. In this report we presentthe underlying physical, technical and mathematical principals of BOLD fMRI along with descriptions of typical applications. Our purpose in this report is to provide, in addition to basic principles, an insight into the aspects of BOLD imaging, which may be used by the medical physicist to assist in the implement of fMRI procedures in either a hospital or research environment. © 2002 AmericanAssociation of Physicists in Medicine. DOI: 10.1118/1.1494990 Key words: functional Magnetic Resonance Imaging, BOLD Effect, fMRI
I. THEORETICAL BASIS
Magnetic Resonance Imaging MRI offers the ability to noninvasively image anatomic structures. This ability has been signiﬁcantly enhanced since the ﬁrst description of proton MRI by Paul Lauterbur in 1973.1 The development of MRIas a clinically and scientiﬁcally useful tool has continued with little sign of reduced potential for further application. One of the more recent developments in MRI has been the ability to correlate the functional performance of biological tissues with anatomic location in a living organism. There are several methods by which magnetic resonance can provide functional information on the status ofliving tissue. The function of biological systems is related to the intra and extracellular environment of the cells that make up the system. The phenomenon of magnetic resonance can be used to noninvasively probe the intra and extracellular environment. The use of MRI to detect pH and temperature differentials has been exploited in research applications, but not widely in clinical applications.Proton Magnetic Resonance Spectroscopy MRS is now used in both research and clinical settings to provide information on cellular function, tissue viability, tumor assessment, and differentiation between various pathologies. Contrast enhancement agents have been very effectively used to enhance the visualization of blood– brain barrier disruptions, allowing the assessment of clinical
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pathologies. Contrast enhancement agents are also used in imaging of blood ﬂow Magnetic Resonance contrastenhanced angiography and in imaging tissue perfusion. A critical issue is to deﬁne functional imaging in the context of this report. In this report we will consider functional imaging of the brain by the technique of MRI.
B. What is functional MRI „fMRI…?Functional MRI fMRI could be deﬁned as the use of a variety of techniques to correlate the physiologic activity of a tissue with its anatomic location. Clinical applications employ either endogenous or exogenous contrast agents. In MRI, the effects of contrast agents are detected indirectly through changes in the local signal intensity of speciﬁc pulse sequence protocols. The changes in local signal...