Nuclear Cardiology

Chapter 68

Nuclear Cardiology

Nuclear cardiovascular examinations complement anatomic imaging modalities by providing noninvasive methods to assess myocardial perfusion, myocardial viability, myocardial function (including ejection fraction and wall motion), cardiac shunts, and regional pulmonary blood flow in children with congenital and acquired anomalies of the heart and great vessels. Among the different nuclear cardiology techniques, myocardial and pulmonary perfusion imaging are the most commonly used in children.

Myocardial Perfusion

Myocardial perfusion images are obtained by using single photon emission tomography (SPECT) after administration of an intravenous tracer during a time of peak stress and while the patient is at rest. A time of peak stress can be achieved by having the patient exercise in the form of walking on a treadmill or riding a stationary bicycle. For children who are too young to cooperate with exercise testing (usually, children younger than 4 or 5 years), pharmacologic stress testing with use of vasodilators such as dipyridamole and adenosine or inotropic drugs such as dobutamine can be performed safely. Different radiotracers are available for myocardial SPECT in children, including technetium-99m hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI), technetium-99m (99mTc) tetrofosmin, and thallium-201 (201Tl). 99mTc-MIBI and 99mTc-tetrofosmin are both rapidly taken up by the myocardium, reflecting regional perfusion at the time of injection, and show only negligible redistribution compared with 201Tl. The use of technetium-labeled compounds in pediatric nuclear cardiology is favorable compared with 201Tl because of the lower radiation dose, the potentially higher tracer activities for better counting statistics, the advantageous photon energy, and the longer retention in the myocardium, which facilitates acquisition of gated SPECT to assess ventricular wall motion. The 99mTc-labeled compounds (MIBI and tetrofosmin) have largely replaced 201Tl for the evaluation of myocardial perfusion in children.

Myocardial perfusion SPECT is useful for identification of fixed or stress-induced myocardial perfusion abnormalities in patients with a history of Kawasaki disease, transposition of the great arteries after an arterial switch operation, cardiac transplants, cardiomyopathy, chest pain, chest trauma, an anomalous left coronary artery from the right sinus of Valsalva, an anomalous right coronary artery from the left sinus of Valsalva, and a left coronary artery from the pulmonary artery. Other less frequent indications include hyperlipidemia, supravalvular aortic stenosis, syncope, coarctation of the aorta, and pulmonary atresia with an intact ventricular septum. In children with Kawasaki disease and coronary aneurysms (which has surpassed acute rheumatic fever as the leading cause of acquired heart disease in children in the United States), cardiac stress testing for reversible ischemia is indicated to assess the existence and functional consequences of coronary artery abnormalities (Figs. 68-1 and 68-2). It has been shown that myocardial perfusion SPECT is a safe and sensitive diagnostic method for identifying coronary stenosis in these children.

Because 99mTc-MIBI does not show significant redistribution, two injections of the radiopharmaceutical agent are necessary to obtain resting and peak exercise myocardial perfusion images. For a single study (rest or exercise), a dose of 0.25 mCi (9.25 MBq)/kg can be used with a minimum total dose of 2 mCi (74 MBq) and a maximum dose of 10 mCi (370 MBq). If rest and exercise studies are done on separate days (i.e., a 2-day protocol), the same dose of 99m

Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Nuclear Cardiology
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