The value of thallium-201 imaging

Article Abstract:

In coronary artery disease (CAD), the large arteries that bring blood to the heart muscle become partially clogged with deposits of fats such as cholesterol. If a coronary artery becomes completely blocked, a myocardial infarction (MI, heart attack) results. The portion of the heart normally served by the blocked artery may then become scar (dead) tissue. But regions of the heart that receive reduced blood flow may not actually die; instead they may still be viable, or alive, but ischemic, meaning that blood flow is decreased. Physicians need as much information as possible about blood flow within the heart muscle in order to plan the most effective treatment for each CAD patient, and one aspect of this is identifying defects in blood flow and determining whether the defects represent dead, or viable but ischemic, tissue. To evaluate this, patients undergo ''stress tests.'' The radioactive isotope thallium-201 is injected while they exercise on a treadmill, and images are taken of the heart that reveal where and how quickly blood is flowing. Normal heart tissue quickly releases the thallium, but ischemic tissue and scar tissue retain the thallium longer; this is called a defect. The method of the stress test has evolved over the years from giving two injections of thallium to giving only one. But in the July 19, 1990 issue of the New England Journal of Medicine, Dilsizian and colleagues report that injecting thallium a second time in patients with coronary blood flow defects improved the ability to determine whether the defects were scar or viable tissue; half the defects that appeared dead after the first thallium dose were found to be viable after the second dose. If these preliminary results are confirmed by additional studies, the two-injection technique will become the method of choice in thallium stress testing. Other, related heart imaging techniques are discussed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Diagnosis, Testing, Physiological aspects, Coronary heart disease, Heart attack, Heart, Isotopes, Ischemia, Treadmill exercise tests, Thallium, editorial

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Imaging the brain, part 2

Article Abstract:

Techniques for imaging the brain include computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT). CT and MRI are most commonly used to image the brain and can be used for brain tumors, cerebral trauma, strokes, multiple sclerosis, meningitis, encephalitis, cerebral abscesses, neurologic complications of AIDS, dementia and movement disorders.

Analysis, CT imaging, CAT scans, Brain, Magnetic resonance imaging

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New horizons in oncologic imaging

Article Abstract:

Two studies published in 2003 illustrate the use of innovative imaging technologies for monitoring cancer patients. One found that combined use of CT and PET scanning was more effective than either alone in staging non-small-cell lung cancer. The other evaluated a new MRI contrast agent that can detect cancerous lymph nodes in prostate cancer patients that might be missed by conventional MRI scans.

Innovations, Tumor staging, Cancer staging, Diagnostic imaging

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