Assessment of Cardiac Function: First-Pass, Equilibrium Blood Pool, and Gated Myocardial SPECT

Radionuclide-based techniques have been used to measure ventricular function for over three decades [1–8]. The methods for measurement of ventricular function can be divided into two basic categories. The first category employs any tracer that can directly label the blood pool itself. One then examines the deformity of the cavitary blood pool as it is moved by the thickening and systolic motion of the myocardial walls. With these methods one can directly image the blood pool in the ventricular cavity throughout the cardiac cycle. The second category of methods for measurement of ventricular function uses tracers that label the myocardial walls (e.g., 99mTc-sestamibi, [18F]-fluorodeoxyglucose). One then examines how those walls thicken and translate, move, or contract throughout the cardiac cycle. With this method one can directly image the myocardium throughout the cardiac cycle. Active movement or contraction of the inner endocardial wall of the ventricular chamber compresses the blood pool and deforms the ventricular cavity and is the conventional marker for systolic ventricular wall motion or function. Only this method permits the evaluation of myocardial wall thickening, a marker of systolic function and viability that can help separate passive systolic wall motion from active myocardial contraction. This method for measuring ventricular mechanical function simultaneously yields a measurement of myocardial perfusion or of metabolism (depending on the tracer used to label the myocardium). However, this advantage is also a source of one of the method’s disadvantages, namely, that if perfusion or metabolism is reduced in a particular segment of the myocardium, then that segment is not easily visualized, hampering visualization of wall motion or thickening in that segment. Temporal and spatial resolution of the related functional image data is not as good as the blood pool method.