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Forward Cardiac Output Measurement with First-Pass Technique Using ^99mTc-Labeled Myocardial Perfusion Imaging Agents

Department of Nuclear Medicine, Kanazawa University School of Medicine, Kanazawa
Division of Nuclear Medicine, Department of Radiology, and Division of Cardiology, Department of Internal Medicine, Noto General Hospital, Nanao, Japan

Correspondence: For correspondence or reprints contact: Junichi Taki, MD, Department of Nuclear Medicine, Kanazawa University School of Medicine, 13-1 Takaramachi, Kanazawa 920-8640, Japan.

ABSTRACT

The aim of this study was to develop and validate a new first-pass method for the measurement of forward cardiac output (CO) using ^99mTc-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 ^99mTc 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:
where C_max is the background-corrected peak count of the whole thorax during angiography, 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 ^99mTc-tetrofosmin (600–740 MBq), and the measured CO was compared with the CO obtained by the conventional method with ^99mTc-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 accurate forward CO measurement using the first-pass data with ^99mTc-terofosmin, which is applicable to other ^99mTc-labeled myocardial perfusion imaging agents.

Key Words: forward cardiac output • ^99mTc-labeled myocardial agents • tetrofosmin • radionuclide angiography

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