Functional Magnetic Resonance Imaging and Spectroscopic Imaging of the Brain: Application of Fmri and Fmrs to Reading Disabilities and Education

Todd L. Richards

Department of Radiology, University of Washington, Seattle, WA

Address Correspondence to:

Todd L. Richards, PhD

Department of Radiology, Box 357115

University of Washington

Seattle, WA 98195

Phone: 206-598-6725

Fax: 206-543-3495

Email: toddr@u.washington.edu

Acknowledgement: Grant No. P 50 33812 from the US National Institute of Child Health and Human Development (NICHD) supported preparation of this article.

Abstract

This tutorial/review covers functional brain imaging methods and results used to study language and reading disabilities. Although the main focus of this paper is on functional MRI and functional MR spectroscopy, other imaging techniques are discussed briefly such as positron emission tomography (PET), electroencephalography (EEG) , magnetoencepholography (MEG), and MR diffusion imaging. These functional brain imaging studies have demonstrated that dyslexia is a brain-based disorder and that serial imaging studies can be used to study the effect of treatment on functional brain activity.

Functional Magnetic Resonance Imaging and Spectroscopy of the Brain:

Application of fMRI and fMRS to Reading Disabilities and Education

Functional magnetic resonance imaging (fMRI) and functional magnetic resonance spectroscopy (fMRS) have been used to study adults and children with developmental reading disabilities. These individuals struggled or struggle in learning to read despite normal intelligence and sensory abilities. In contrast, individuals with acquired dyslexia had normal reading function but lost it due to disease or injury. The purposes of this article are to a) provide a brief tutorial on fMRI and fMRS, and b) provide an overview of the most recent findings in the use of these neuroimaging tools to study learning disabilities specific to reading (dyslexia). This information should allow professionals in the fields of education and psychology to be more critical consumers of the growing body of research on functional brain imaging of dyslexia. Recent data from functional neuroimaging of the brain in children with dyslexia has demonstrated that there is a biological basis for developmental dyslexia. However, even though dyslexia is a brain-based disorder, it is treatable, as will be discussed.

Tutorial on Functional MR Imaging and Spectroscopy

Functional MRI (fMRI) and functional MR spectroscopy (fMRS) are techniques that measure different physiological parameters of neural activation (See Table 1). These functional brain imaging techniques are very labor intensive for both acquisition and processing the data and require a multidisciplinary team of scientists such as psychologists, MRI physicist/engineers, neuroscientists, neuroradiologists, and computer scientists. These brain imaging techniques are referred to as functional (rather than structural) because participants perform tasks while they are in the magnet; as a result, analyses of the imaging permit conclusions about activation of the functioning brain rather than neuroanatomy of the resting brain. These techniques are often referred to as in vivo because they can be administered to living people. Both of these techniques are noninvasive and are based on magnetic resonance imaging, which is briefly described here. Noninvasive means in part that the subject is not exposed to ionizing radiation. In contrast, the PET technique, which is also included in Table 1, is invasive and cannot be used to study healthy children.

MRI is a way to look inside the body (brain in this case) without using X-rays. The body contains hydrogen nuclei (protons) that can absorb and give off energy in the presence of a magnetic field. MRI scanners use a magnet, which creates a strong, steady magnetic field. This magnetic field is very homogeneous near the center of the magnet where the head is positioned for a brain scan. This field causes the protons to line up together and spin at a specific frequency, which is dependent on the strength of the magnetic field. A radiofrequency signal is transmitted into the body using a radiofrequency (RF) coil. This RF energy is absorbed by the protons and makes them move out of alignment -- similar to a spinning top when someone hits it. When the RF transmission stops, the protons gradually move back to their aligned position and release energy. There is another RF coil positioned near the body for receiving this signal as energy is released from the protons. It takes some time for the protons to return to their equilibrium state (the state before they were perturbed by the rf transmission). A computer is used to control and orchestrate all of the scanner electronics such as rf transmission, signal reception, pulse timing, and signal delay time. The software written to control these channels is called a pulse sequence. The timing parameters inside the pulse sequence can be adjusted to produce various types of tissue contrast.

Because most of the hydrogen nuclei in the body are part of water molecules, over 90% of the signal comes from water. The signal amplitude that comes from the body is dependent on several biochemical/biophysical properties of the tissue such as protein and lipid content and the presence of paramagnetic substances such as blood deoxyhemoglobin. This sensitivity to blood oxygenation makes this proton signal ideal for functional brain imaging. This proton signal is also influenced by the mobility of tissue water, which dramatically changes in tumors or inflammation (swelling). Thus, clinicians can use this technology to assist in diagnosis of many diseases such as cancer and multiple sclerosis as well as the investigation of developmental processes such as learning to read. However, it is important to keep in mind that MRI does not measure all biological processes in the brain. Figure 1 shows an example of an MR scanner with a child on the table.

Basic concepts in fMRI. Functional magnetic resonance imaging (fMRI) is a relatively new and potentially powerful tool can be used to study the thinking brain (Sanders & Orrison, 1995). fMRI is based on the fact that when part of the brain is used for thinking there are increases in the need for energy, nutrients (supplied from the blood), and oxygen