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A new scintigraphic count-based method for measuring absolute left ventricular volumes is presented. It is a fast and simple technique that allows geometrical assumptions to be avoided and is free of radiation attenuation corrections. This method requires the acquisition of an image of the left ventricle in the right anterior oblique projection and the collection of gated blood pool images in the left anterior oblique projection. To assess the accuracy of the method scintigraphic stroke volumes were compared with those derived from thermodilution measurements during cardiac catheterization in 20 subjects, and to assess its precision the technique was applied to phantom data of known radionuclide volumes. Excellent correlations were found between the scintigraphic and both the thermodilution (r = .98) and phantom data (r = .99). The reproducibility (r = .97) of results was investigated by repeating data acquisition and analysis for 15 subjects on two different days, and the interobserver variability (r = .97) of the method was studied by having two computer operators calculate volumes for the same patient data for 20 randomly selected studies. Circulation 70, No. 4, 672-680, 1984. SEVERAL METHODS have been reported for estimating left ventricular volumes with the use of scintigraphic data and all of these come under the general categories of geometric or count-based methods. Geometric methods such as the Dodge-Sandler approximation1' 2 are convenient in that they do not require any information in addition to gated equilibrium data in one view, but have the disadvantage of not taking into account the variety of shapes of the ventricular chamber.3 Also, these geometric techniques are not particularly well suited to the analysis of scintigraphic data since the resolution of the boundaries of the ventricular walls is poorer than for contrast angiocardiographic chambers,9 "0 while others require removal, processing, and counting of blood samples after the gated equilibrium studies.9-Means of correcting for attenuation by placing a source within the patient's esophogus have been implemented,'2 but may not gain wide acceptance because of the inconvenience to the patient. Aside from the additional time and effort on the part of technologists that these methods require, they can yield inaccurate results in children and in obese patients, as evidenced by the wide range of average attenuation coefficients obtained by these methods.'2The

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Radiation exposure to the angiographer was measured using thermoluminescent dosimeters (TLD), commercial film badges, and appropriate ionization survey meters. Data were collected during 47 coronary artery examinations with the lead overleaf. During a single coronary examination, the angiographer receives 0.9 mR to the lens and 2.8 mR to the hand. The calculated yearly exposure to the angiographer performing 10 examinations per week is 450 mR to the lens, 9% of the maximum permissible dose (MPD), and 1400 mR to the hand, 2% of the MPD. Exposure rates for the left anterior oblique (LAD) and right anterior oblique (RAO) projections during cine and fluoroscopy were taken at the position occupied by the angiographer. Scatter radiation is 5-10 times greater in the LAO projection. The second trial was monitored during 18 coronary artery examinations minus the lead overleaf. A significant decrease in radiation exposure was accomplished through the use of the lead overleaf.

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