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Chapter 1: For Those Who Have Eyes, Let Them See:What is SPECT? An acronym for single photon emission computerized tomography, it is a sophisticated nuclear medicine study that "looks" directly at cerebral blood flow and indirectly at brain activity (or metabolism). In this study, a radioactive isotope (which, as we will see, is akin to myriad beacons of energy or light) is bound to a substance that is readily taken up by the cells in the brain. A small amount of this compound is injected into the patient's vein, where it runs through the bloodstream and is taken up by certain receptor sites in the brain. The radiation exposure is similar to that of a head CT or an abdominal X ray. The patient then lies on a table for about fifteen minutes while a SPECT "gamma" camera rotates slowly around his head. The camera has special crystals that detect where the compound (signaled by the radioisotope acting like a beacon of light) has gone. A supercomputer then reconstructs off line images of brain activity levels. The elegant brain snapshots that result offer us a sophisticated blood flow/metabolism brain map. With these maps, physicians have been able to identify certain patterns of brain activity that correlate with psychiatric and neurological illnesses. SPECT studies belong to a branch of medicine called nuclear medicine. Nuclear (refers to the nucleus of an unstable or radioactive atom) medicine uses radioactively tagged compounds (radiopharmaceuticals). The unstable atoms emit gamma rays as they decay, with each gamma ray acting like a beacon of light. Scientists can detect those gamma rays with film or special crystals and can record an accumulation of the number of beaconsthat have decayed in each area of the brain. These unstable atoms are essentially tracking devicesthey track which cells are most active and have the most blood flow and those that are least active and have the least blood flow. SPECT studies actually show which parts of the brain are activated when we concentrate, laugh, sing, cry, visualize, or perform other functions.
Nuclear medicine studies measure the physiological functioning of the body, and they can be used to diagnose a multitude of medical conditions: heart disease, certain forms of infection, the spread of cancer, and bone and thyroid disease. My own area of expertise in nuclear medicine, the brain, uses SPECT studies to help in the diagnosis of head trauma, dementia, atypical or unresponsive mood disorders, strokes, seizures, the impact of drug abuse on brain function, and atypical or unresponsive aggressive behavior.
During the late '7os and '8os SPECT studies were replaced in many cases by the sophisticated anatomical CAT and later MRI studies. The resolution of those studies was far superior to SPECT's in delineating tumors, cysts, and blood clots. In fact, they nearly eliminated the use of SPECT studies altogether. Yet despite their clarity, CAT scans and MRIs could offer only images of a static brain and its anatomy; they gave little or no information on the activity in a working brain. It was analogous to looking at the parts of a car's engine without being able to turn it on. In the last decade, it has become increasingly recognized that many neurological and psychiatric disorders are not disorders of the brain's anatomy, but problems in how it functions.
Two technological advancements have encouraged the use, once again, of SPECT studies. Initially, the SPECT cameras were singleheaded, and they took a long time-up to an hour-to scan a person's brain. People had trouble holding still that long, and the images were fuzzy, hard to read (earning nuclear medicine the nickname "unclear medicine"), and did not give much information about the functioning deep within the brain. Then multiheaded cameras were developed that could image the brain much faster and with enhanced resolution. The advancement of computer technology also allowed for improved data acquisition from the multiheaded systems. The higher-resolution SPECT studies of today can see into the deeper areas of the brain with far greater clarity and show what CAT scans and MRIs cannot-how the brain actually functions.
SPECT studies can be displayed in a variety of different ways. Traditionally the brain is examined in three different planes: horizontally (cut from top to bottom), coronally (cut from front to back), and sagittally (cut from side to side). What do physicians see when they look at a SPECT study? We examine it for symmetry and activity levels, indicated by shades of color (in different color scales selected depending on the physician's preference, including gray scales), and compare it to what we know a normal brain looks like. The black-and-white images in this book are mostly two kinds of three-dimensional (3-D) images of the brain. One kind is a 3-D surface image, looking at the blood flow of the brain's cortical surface. These images are helpful for picking up areas of good activity as well as underactive areas. They are helpful when investigating, for instance, strokes, brain trauma, and the effects of drug abuse. A normal 3-D surface scan shows good, full, symmetrical activity across the brain's cortical surface.
The 3-D active brain image compares average brain activity to the hottest 15 percent of activity. These images are helpful for picking up areas of overactivity, as seen, for instance, in active seizures, obsessive-compulsive disorder, anxiety problems, and certain forms of depression. A normal 3-D active scan shows increased activity (seen by the light color) in the back of the brain (the cerebellum and visual or occipital cortex) and average activity everywhere else (shown by the background grid).
Physicians are usually alerted that something is wrong in one of three ways: they see too much activity in a certain area; they see too little activity in a certain area; or they see asymmetrical areas of activity that ought to be symmetrical. In the rest of the book, I will go into greater detail about how this remarkable technology has touched people's lives. For now, however, I will simply offer a sample of five common ways in which SI'ECT studies are utilized in medicine. r. To male early intervention possible. Ellen, sixty-three, was suddenly paralyzed on the right side of her body. Unable even to speak, she was in a panic and her family was extremely concerned. As drastic as these symptoms were, two hours after the event, her CAT scan was still normal. Suspecting a stroke, the emergency room physician ordered a brain SPECT study that showed a hole of activity in her left frontal lobe caused by a clot that had choked off the blood supply to this part of the brain...