[Usefulness and limitations of myocardial scintigraphy at present]

There are three major techniques of myocardial imaging in the field of nuclear medicine at present: (1) myocardial perfusion imaging, (2) myocardial infarct-avid imaging, and (3) myocardial metabolism imaging. Although myocardial infarct-avid imaging with Tc-99 m pyrophosphate is useful for diagnosing myocardial infarction when other laboratory evidence is not obvious, it is of limited diagnostic value because of the delayed appearance of the positive images after infarction and occasional false positive cases. Indium-111-labeled antimyosin may be substituted by Tc-99 m pyrophosphate in the near future. Myocardial perfusion imaging with Tl-201 is the most widely accepted procedure in nuclear cardiology. Exercise Tl scintigraphy is superior to the electrocardiographic exercise test for detecting myocardial ischemia. Better results may be obtained by the quantitative analysis of the Tl-201 washout rates. However, the physical characteristics of Tl-201 are not ideal for myocardial imaging because of low energy photopeaks and its relatively long half-life. Therefore, the usefulness of Tc-99 m isonitriles, N-13 ammonia and Rb-82 as substitute radiopharmaceuticals is now being widely investigated. Myocardial metabolism imaging is a promising new technique for estimating myocardial viability. Application of this technique to fields other than myocardial ischemia is also anticipated. Unfortunately, its clinical usefulness is limited by the expensive instrumentation at present.