A theoretical comparison of first-pass and gated equilibrium methods in the measurement of systolic left ventricular function.

First-pass and gated equilibrium radionuclide studies of left ventricular function have proven extremely useful in the detection and management of patients with heart disease. Despite this practical experience, however, comparison of these methods generally has been confined to procedural differences that do not reflect the intrinsic properties of the methods. Here, we describe the results of a simple theoretical calculation from first principles that compares the methods based on their relative statistical precision. This analysis assumes that each procedure is carried out with the same tracer dose in the same hypothetical patient under identical conditions and with the same ideal imaging equipment. Results obtained with this model suggest that the imaging time required for a gated equilibrium study to achieve the same statistical precision as a first-pass study is typically less than 2 min in resting subjects and less than 1 min during stress. The analysis also indicates that gated equilibrium studies will tend to possess the greater statistical precision when cardiac output is elevated, such as when the heart is imaged during exercise. On the other hand, this analysis indicates that the first-pass method will tend to possess the greater precision when cardiac output is low and when imaging time is highly constrained.