Molecular Imaging Insight - March 2008 - (Page 5) Read more on Siemens SPECT/CT ADDiTioNAL RESouRCES: dial infarction (MI). Studies have shown PET/CT can rule out an MI with greater confidence, often avoiding unnecessary hospital admissions. PET/CT is helpful in identifying jeopardized, but still viable, myocardium that can be salvaged via revascularization. PET/CT further offers a superior option over SPECT for morbidly obese patients over 450 pounds. SPECT/CT, too, is gaining more attention for its superiority in diagnosing women thanks to its attenuation correction and a shorter study time frame than SPECT. Taking a closer look, SPECT/CT reduces the soft-tissue attenuation artifacts that create the false positives in SPECT studies, thus rendering the test more specific. Cardiologists can obtain a calcium score while performing the study, which can provide information about the location and extent of calcified plaque in the coronary arteries. A build up of plaque in the coronary arteries narrows the cardiac arteries over time, constricting blood flow to the heart muscle, which can result in angina as well as heart attack and strokes. Research on and awareness of gender differences in the symptoms, diagnosis and treatment of women with cardiac disease followed the publication of an American Heart Association Scientific Statement in 2005 that discussed the important role of noninvasive testing in evaluating women with suspected coronary artery disease. The statement highlighted the benefits of SPECT, cardiac CT, cardiac MRI and carotid intima-media thickness (IMT) and noted that although much more evidence needed to be gathered, that it was fairly clear that women at risk for coronary artery disease are not referred as often for further testing as men. In the research A number of studies are underway that seek to determine which diagnostic tests are best for women at various stages of risk for coronary artery disease. Heller, who is the past president of the American Society of Nuclear Cardiology, is involved in a study examining the differences in the diagnosis of women with cardiac disease using exercise stress testing and SPECT/CT. “It’s becoming clear that in the diagnostic hierarchy, SPECT/ CT has higher diagnostic accuracy than an exercise stress test and PET/CT has even higher diagnostic accuracy than SPECT/ CT. This is being confirmed by [clinical] studies,” says Heller. A study reported at the fall 2007 meeting of the American Society of Echocardiography reported that stress echocardiography had a better chance of identifying women at high risk for coronary artery disease than traditional stress tests. The WISE Study research published in the Journal of the American College of Cardiology in January 2006 found that as many as three million women who have coronary heart disease don’t experience build-up of cholesterol plaque into a major blockage. Instead, it spreads throughout the artery wall, a condition known as coronary microvascular syndrome that causes reduced blood flow to the heart along with chest pain. Because the syndrome doesn’t block arteries, it can remain undetected. Coronary microvascular syndrome is linked to Syndrome X and is thought to cause it. In a study conducted by the Multi-Ethnic Study of Atherosclerosis (MESA) that was published in the Archives of Internal Medicine in December 2007, investigators noted that women’s risk for cardiovascular disease is understated using traditional Framingham risk scores and recommended that women with symptoms or risk factors undergo imaging of their coronary arteries to define heart attack risk. MESA facilities and researchers continue to work on a variety of studies to assess gender, age and ethnic differences in cardiovascular disease. MolecularImaging.net PET/CT 82Rubidium images and maps from the Siemens Biograph 40 show inferior wall ischemia. Source: Emory University, Atlanta, Ga. Future enhancements Hartford Hospital’s Heller estimates the number of PET/CT studies has increased about 25 percent a year over the past few years. “In the next two to four years, PET/CT will assume a strong role in the diagnosis of coronary disease in women,” he says. One exciting potential development is a PET/CT study done while the patient is exercising, says Berman. “One drawback of PET/CT currently is that you have to induce stress pharmacologically instead of with exercise, and exercise is generally the preferable method of stress testing,” he says. “But you can’t do it because with 82Rubidium there is a 75-second half-life, so there isn’t enough time to take the measurement.” A new isotope that would be used during exercise stress is being tested in an FDA Phase I test. Advances in both PET/CT and SPECT/CT are leading to better detection and treatment of coronary artery disease in both men and women. Di Carli believes that a patient-centered approach, rather than a gender-centered approach, is likely to result in the most accurate diagnosis and best treatment path for patients, keeping gender differences in mind. “We have a variety of important tools available to us and it is important to clinically tailor the type of diagnostic test or tests to the specific needs of the patient,” he says. “You would not do the same diagnostic test necessarily on an obese short woman presenting with symptoms of coronary artery disease as you might on a lean woman.” PET/CT and SPECT/CT offer the opportunity of a comprehensive anatomic and biologic evaluation of the consequences of atherosclerosis in the coronary arteries and myocardium—and perhaps, ultimately, tailoring diagnosis and treatment to the unique needs of women. March 2008 | Molecular Imaging Insight 5 http://www.siemens.com/symbia http://MolecularImaging.net
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