Comparison of thallium scintigraphy and positron emission tomography

Assessment of tissue viability has become an important issue in recent years. Scintigraphic measurements have provided important diagnostic, therapeutic, and prognostic information in patients with myocardial dysfunction, who may improve in left ventricular function after revascularization. For detection of regional myocardial ischemia and viability, thallium 201 (²⁰¹Tl) has been the most widely used tracer in single-photon scintigraphy. However, ²⁰¹Tl scintigraphy may underestimate regional viability, especially after myocardial infarction. Positron emission tomography (PET) provides an advanced imaging technology that permits the accurate definition of regional tracer distribution. In combination with nitrogen (¹³N) ammonia, PET allows for the sensitive and specific detection of coronary artery disease. Several studies indicate the superiority of this approach in comparison with standard ²⁰¹Tl tomographic (SPECT) imaging. In addition, regional blood flow can be accurately measured with ¹³N ammonia PET, and this approach can be employed in conjunction with pharmacologic stress imaging to quantify regional flow reserve. In combination with metabolic markers, such as fluorine 18 (¹⁸F) deoxyglucose, an indicator of glucose uptake, PET is capable of assessing myocardial viability. Furthermore, the PET approach may differentiate between various forms of cardiomyopathy. More studies are needed to define the cost-benefit ratio of both the ²⁰¹Tl reinjection and the PET technique for the management of patients with coronary artery disease or cardiomyopathy.