Magnetic Resonance Imaging in Children
The use of Magnetic Resonance Imaging when
Measuring Abnormality in Children
Mila Tellez
DePaul University – Loop Campus
In partial fulfillment of the requirements for PW9 and PW10
Morris Fiddler
March 13, 1998
The Use of Magnetic Resonance Imaging when measuring
Abnormality in children
Our knowledge of normal/abnormal development in children has changed radically in the last decade because of the emergence of the technology of Magnetic Resonance Imaging (MRI). MR imaging is a way of looking inside the body without using surgery, harmful dyes or radiation, to produce remarkable clear pictures of human tissue. The majority of brain research today is conducted with MR imaging especially in the area of the developing brain. MR imaging measures gray/white differentiation in the brains of children that indicate their rate of development. This allows researchers to examine potential correlation’s that could only be previously theorized. In the past, researchers lacked the tools to distinguish the rate of brain development in a child. Obviously, it is very difficult to form predictive measures when the basic data points are lacking. Indeed, most developmental theory came out of the field of psychology with most clinical work targeting individual behavior.
Design
Because of the voluminous amounts of information on the brain, I reduced this research project to a specific area that dealt with tracking normal/abnormal development in the brains of children using MR imaging. I excluded areas such as trauma, inflammation, accident, etc., and focused on studies of non-traumatized children. I narrowed the subject to three categories: children, brain, and magnetic resonance imaging. Although other imaging techniques like X-ray and CAT scan are used in some areas of brain research, for my intent of tracking brain development, MR imaging is the leader in this field.
In gathering research on this topic, I was surprised by the lack of books on this subject. The only book on the subject of MR imaging that I found at a number of local and university libraries was printed in the early fifties. It did not contain extensive information about MR imaging and brain scans. I had to rely on Journals for most of my information. Fortunately, I was able to search these journals through the Internet; specifically Medline powered by Grateful Med search engine, and Paperchase bibliographic database.
This research paper attempts to answer the question: How is MR imaging used in measuring the brain in the development of children, and where is the technology of MR imaging headed? To better frame this question, a history of MR imaging is presented with an explanation of its technology, as well as some recent studies that demonstrate its diagnostic use. I conclude with some information on some of the newest research in MR imaging systems today.
The relevance of this study is that it may help students of human development bridge the gap between a physiological and a psychological understanding of the brain, specifically, as it applies to normal/abnormal brain development in children.
My interest in this subject was originally piqued when I viewed the TV show Nightline on July 22, 1997. The show included a segment called Unlocking the Mysteries of the Brain. They interviewed a number of couples who had adopted Eastern European orphans. These couples were experiencing a multitude of issues with their adopted children that all seemed to revolve around the lack of attachment between the child and the parents. A doctor claimed that the lack of love and attention during the orphan’s first year of life had left "black holes" in their brains. These "black holes" were created while the infants were institutionalized and were the root cause of the attachment issues. It was during that show that I first heard about using MR imaging to research and track brain development. (1)
While MR imaging can be used in extreme situations to track brain development, it also can be used in many circumstances where a parent is questioning whether their child is normal. Ponder the frustration of Margie, a young mother, whose three year-old son Sammy has worn her out. Sammy still rolls around on the floor, cannot hold a spoon, has difficulty making eye contact, and never seems to stop running around. When Margie made an appointment with her pediatrician, she was not certain if this behavior was typical of three year-old kids or if Sammy had a problem. After examining him, her pediatrician recommended that Sammy get an MRI scan on his brain. MR imaging has become a very important diagnostic tool for doctors in helping to determine the normal development of children.
MR imaging is performed in most radiology departments and is used for looking at non-bony parts of the body. It is safe for a majority of patients except those who have devices such as pacemakers, or other metal implants. Because of the magnetism that is used, metal could damage the MRI scanner or harm the patient. Essentially a patient lies on a special table that is moved into the center of a very strong magnet that is housed in a long tube. While the patient is in the tube he will hear hammering noises, and feel vibrations while the scanner takes pictures during the examination. In order to receive clear pictures the patient must stay very still and not move. These pictures are recorded on a computer. (2)
If we take a look at the technology behind how MR imaging works, we are able to understand more fully why doctors use it to determine brain development. Let us start by looking at the atom that is made up of protons and neutrons that live in its nucleus, with electrons orbiting around that nucleus. These particles are magnetic and possess something-called spin. Adding the spin of protons and neutrons together will give you either zero or an odd number. If it has an odd number, the nucleus is said to have net spin, which is the case of the hydrogen nucleus. This is important because hydrogen is a component of water, and water makes up different parts of the brain. MR imaging measures the hydrogen atoms that reside in the different parts of the brain. The net spin of the hydrogen nucleus creates a tiny magnetic field making it act like a tiny compass. If we are measuring water that is put inside of the strong magnetic field of the magnetic resonance imager, the nuclear magnets in the hydrogen atoms will point in the same direction as the magnetic field. Add these nuclear magnets together and you create a large magnetization, which acts like a big compass. The nuclear magnets pointing toward the magnetic field and precessing (wobbling), cause this magnetization. This happens gradually, and creates a steady state called T1. After the T1 State has been reached, we turn on a second magnetic field. When this happens we are exciting the nuclear magnets so that they respond by precessing, and this creates a signal that is recorded. When the signal decays away it is called T2. The size of the signal depends on the amount of water present in the sample, and another factor is at what speed T2 takes place. Both of these are important in terms of creating a nuclear magnetic signal. When we image a slice of the brain, it is divided into a matrix, so that we are able to keep track at what rate T1, and T2, are given off, as well as the amount of water given off. By doing this we are able to view the resulting signal for each area of the brain. If there is a strong signal, there will be a white spot in the image; if no signal appears, there will be a black spot; intermediate signals are gray. In the field of view, the contrast is based on how much T1, T2, is given off and the amount of water given off. (3)
Imaging a developing human brain can help researchers determine if abnormalities exist or if the situation is one of delayed development. Growth and myelination characterize brain development in infants. Myelin is a cell membrane devoid of MR imaging signal; it is made up of a white fatty material composed of lipids and lipoproteins that enclose certain axons and nerve fibers, also known as medulla. Researchers use this as a marker for determining abnormalities and delayed development in children. Delayed myelination means delayed development, or that the myelin cell membrane has grown. As this myelination takes place, the MR imaging signal that is recorded on the computer appears black. The MR images obtained at different cycles of myelination are a result of changes in brain tissue water content, the multiplication of glial cells, and from the accumulation of lipid myelin precursors contained in cells. As myelination takes place, it is sequential, and very precise. The myelination process takes place at different times and speeds, in different brain regions, varying in relation to
Time. (4)
MR imaging assessment of myelination in infants and children was developed through a study of 60 one month to three year-old children. The study objective was to examine the normal progression of white matter myelination on MR imaging. Different areas of the brain, which include the cerebral hemisphere and cerebellum, were examined for the degree of myelination. It was found that MR imaging is sensitive to the early changes of white matter myelination, and that these findings correlate with others taken during previous autopsies. These changes were shown by both T1 and T2-weighted images, which showed that the changes during myelination are due to a decrease in the water content of the white matter as myelination progresses. These patterns of myelination are extremely important when evaluating infants and children for delayed development. (5)
MR imaging has emerged as a major diagnostic tool for detecting many different abnormal conditions in children. For 20 years, fetal alcohol syndrome (FAS) has been associated with abnormal brain development. To assess what high doses of alcohol will do during the prenatal period, a study of thirteen children with histories of significant prenatal alcohol exposure, and 12 normal control children were evaluated with MR imaging. It was found that two children of the 13 alcohol-exposed children had agenesis of the callosal areas, and the remaining alcohol exposed children has smaller callosal areas when compared with the control group. The findings suggest a correlation between high levels of prenatal alcohol usage and abnormalities of the corpus callosum. (6) Another area of study with MR imaging has been Sudden Infant Death Syndrome (SIDS).
The study tried to determine if myelin abnormality could be found in the brains of 28 SIDS when compared with 14 control infants. The brains of both groups were fixed in formalin and then scanned with MRI. The amount of myelin in 15 out of 21 scanned revealed no difference; in three, myelination was greater in SIDS, and in the last three, the rate of myelination for age was greater in SIDS. The conclusion of the study of MR imaging scans of older SIDS infants (more than 8 months) showed that white matter development may be slightly advanced in SIDS as compared to the control group. (7) And finally, a recent study in December 1997 suggests that the maldeveloped neural circuitry producing schizophrenic symptoms may include the cerebellum. Anatomic brain scans were taken using MR imaging for 24 patients with onset of schizophrenia by age 12 and compared to 52 healthy children. The results were that the volume of the interior posterior lobe remained significantly smaller in the schizophrenic patients. The findings support other consistent observations of this in adult schizophrenia and provide further evidence for abnormal cerebellar function in childhood and adult-onset schizophrenia. (8)
The history of MR Imaging dates back to more than 50 years ago, much after the X-ray, but well before CAT scan. The first nuclear magnetic resonance (NMR) experiments were independently undertaken by a group at Stanford University in 1946 lead by Block, while another group was doing the same thing at Harvard led by Purcell. The discovery that nuclei resonated at slightly different frequencies let researchers to see NMR as the perfect tool to use for chemical analysis. It was Jasper Jackson that recorded the first NMR signal of a live animal in 1967. Two-dimensional images of a water sample were generated in 1972 by researcher Paul Lauderbur, and during the 1970’s scans were made for the first time of fruit, animals and finally humans. It was around 1981 that the first commercial scanners became available for use in hospitals. At that time they were called nuclear magnetic resonance imaging (NMR), but around 1985, the word nuclear was dropped because people feared there was radioactivity involved with this particular kind of imaging. (9) MR imaging started out as a tomographic imaging technique that produced an image of the NMR signal in a thin slice of the human body. Now MR imaging has gone to dimensional images to present a comprehensive picture.
The most recent developments of MR imaging have been to expand its use into the realm of surgery and other therapeutic procedures. Stanford University Medical Center has designed a new scanner which guides a needle for tissue biopsies and other more complicated procedures. They are trying to replace some types of open surgery with less invasive procedures using magnetic resonance therapy (MRT). The MRT replaces the long tunnel that is used in the MR imaging system with two round coils that look like doughnuts. The patient slides through the two coils allowing space between the coils for physicians and radiologists to stand on both sides of the patient and perform a procedure. Ultimately this would allow doctors to perform procedures in the scanner, once they become familiar with MRT. Dr. Stephen Kee a Stanford researcher said "potentially we could do interventions through catheters within the magnet, which would enable us to, for example, approach a liver cancer from a catheter in the hepatic artery and see the cancer in the liver at the same time." (10)
With the advancement of MR imaging to MR therapy it is possible to envision major changes in medicine that would change the whole field dramatically over the next decade. Certainly as we move into the next century it is possible to imagine surgeons doing highly specialized operations with minimal invasion.
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