Forward cardiac output measurement with first-pass technique using 99mTc-labeled myocardial perfusion imaging agents

The aim of this study was to develop and validate a new first-pass method for the measurement of forward cardiac output (CO) using Tc-99m-labeled myocardial perfusion imaging agents. Methods: In protocol 1, to test the new method for measuring CO, the conventional method and the new method for CO measurement were performed in 1 d in 57 patients (32 men, 25 women; age 68 +/- 11 y). In the conventional method, radionuclide angiography (1 frame/s) with in vivo Tc-99m labeling (110 MBq) of red blood cells was performed for 2 min in the left anterior oblique projection. Five minutes later, a 1-min equilibrium image was obtained, and a blood sample was taken for calculation of the distribution volume. To obtain data for the new method, further radionuclide angiography (1 frame/sec) with 99mTc labeling (600-740 MBq) of red blood cells was then performed in the anterior projection. CO was calculated using the following equation: CO = C-max x V-LV/integral f(t)dt. where C-max is the background-corrected peak count of the whole thorax during angiography, integral f(t)dt is the area under the gamma variate-fitted left ventricular (LV) time-activity curve after background correction and V-LV is the LV volume obtained by the area length method applied to the radionuclide angiography and myocardial tomography In protocol 2, to evaluate the new method, 24 patients (16 men, 8 women; age 71 +/- 9.2 y) underwent radionuclide angiography with Tc-99m-tetrofosmin (600-740 MBq), and the measured CO was compared with the CO obtained by the conventional method with Tc-99m-labeled red blood cells. Results: In protocol 1, good correlation was observed between the CO by the new method (Y) and the CO by the conventional method (X): Y = 1.0X + 57 mL/min and r = 0.95. There was good agreement between the two methods (mean difference -56 +/- 381 mL/min). Inter- and intraobserver correlation coefficients were 0.96 and 0.98, respectively. In protocol 2, the CO by the new method using 99mTc-tetrofosmin (Y) showed a good correlation with the CO by the conventional method (X): Y = 0.90X + 453 mL/min and r = 0.93. Good agreement between the two methods was observed (mean difference 73 +/- 390 mL/min), Inter- and intraobserver correlation coefficients were 0.95 and 0.98, respectively. Conclusion: This new method permits accu- rate forward CO measurement using the first-pass data with Tc-99m-terofosmin, which is applicable to other Tc-99m-labeled myocardial perfusion imaging agents.