Quantification of left ventricular volume in gated equilibrium radioventriculography

We have developed a simple method for measuring left ventricular volume based on semi-automated analysis of 40° left anterior oblique images obtained with a standard scintillation camera after equilibrium of an intravenous injection of 20 mCi of technetium-99m in vivo labeled red blood cells. The essence of the method is the use of the dimensions and radioactivity within a segment of aorta to convert observed left ventricular count rates to volume. Four assumptions were made: 1) the aortic arch is nearly parallel to the collimator face when a patient is in the proper left anterior oblique position; 2) a segment at the top of the aortic arch, approximately 1 cm wide, is a right cylinder, 3) the edges of the aorta can be delineated as the lines where the second derivative of a cross sectional profile equals zero; 4) left ventricular and aortic arch counts undergo the same attenuation because they are nearly the same distance from the chest wall in the proper left anterior oblique position. By measuring the counts and volumes of two regions of known shape, one in the middle, the other at the edge of the aortic arch, and calculating their differences a background-independent volume count ratio (Δv/ΔC) can be obtained. The left ventricular and diastolic volume (LVEDV) is calculated with the equation: LVEDV=(Δ/ΔC) LVEDC, where LVEDC represents left ventricular end diastolic counts. Twenty-six patients were evaluated by equilibrium radio- and contrast-ventriculography, the latter analyzed by planimetry. The radionuclide method yielded an end diastolic volume that correlated well with contrast ventriculography (r=0.96, Y=0.91 X+21 ml). In addition to its simplicity and objectivity, a major advantage of this method of determining ventricular volume is that it does not require a blood sample.